Cassells' Carpentry and Joinery/Floors

FLOORS.

General Considerations.—The remarks in this paragraph will be found applicable to all sorts of floors. The joists should be laid across the narrowest part of the room, and girders and binders should be so arranged as to take a bearing on a solid pier or wall,

Fig. 313.—Method of Supporting Joists round Brickwork Fender in Basement.

and not over door or window openings. In cases where a long distance has to be traversed by a joist, which is supported by one or more girders in the length, it should be made as long as possible. By this means the strength of the joist is greatly increased, as also is its usefulness as a tie to the walls. Flooring-boards should be cut and prepared, and stacked in the open air, with free ventilation all round, with proper protection from wet, for as long a period as possible before they are required for use. Where such an arrangement is possible it is well to have the boards laid face downwards for some months in the position they are to occupy before they are finally nailed.

Basement or Ground Floors.

The floor in a basement storey, or on the ground level where there is no basement, is formed of joists laid on wooden sleepers, themselves bedded on dwarf walls (Figs. 313 and 314). The walls and sleepers are usually 4 ft. or 5 ft. apart, and the joists 4 in. to 6 in. deep. Occasionally the walls and sleepers are further apart, and then joists 6 in. or even 8 in. deep are used. Fig. 313 is a conventional view, and Fig. 314 a section through a floor of this description, clearly showing how the joists are supported by the brick fender round the fireplace. Oak is considered best for sleepers, and to ensure of its being thoroughly seasoned,

Fig. 314.—Section through Basement or Ground Floor.

Fig. 315.—Plan of Single Floor showing Trimming to Fireplaces, Well-hole, etc.

ship oak is sometimes specified. Formerly it was the practice, more so than at present, to notch or cog the joists to the sleepers. When the joists are deep enough, rows of herringbone strutting are introduced, as indicated at b (Fig. 314), cut and fixed as shown later by Fig. 317.

Single Floors.

The simplest floor consists of a row of beams or joists, varying in thickness and depth with the width or bearing between the walls on which they are supported. To the upper sides of these joists is nailed the floor-boarding, and to the under side the laths which carry the ceiling. These joists should not be placed at a greater distance than 15 in. from centre to centre. An ordinary example of a single floor is shown at Fig. 315, this figure being the plan of the timber of a floor of two rooms, and well-hole for staircase for a dwelling-house, 34 ft. from front to back, and 20 ft. wide in the clear; it shows also the trimming for two 6-ft. chimney-breasts in flank-wall, and for well-hole at opposite flank next the back wall. The well-hole is 7 ft. wide and 12 ft. long. The floor is constructed to carry two framed partitions, one 18 ft. from, and parallel to, the front wall, and the other extending from this partition to the back wall along the well-hole. The middle bearing is required to be under the

Fig. 316.—View of Tusk Tenon and Keyed Joint to Trimmers and Joists.

Fig. 317.—Herringbone Strutting.

Fig. 318.

Fig. 319.

Figs. 318 and 319.—Alternative Methods of Halving Joists on Partition Head.

first-mentioned partition. The trimming joist is 11 in. by 3½ in., and is placed 18 in. from the chimney-breast. The short trimmers are 11 in. by 3 in. and represented not as resting in the party wall, but as being supported on iron corbels built in the wall. Fig. 316 shows, to the left, an isometric view of the tusked and keyed joint to the trimming round chimney-breast; to the right, it shows a sectional isometric view through joint of trimmer and tailing joist. It also represents the kind of joint that

Fig. 320.—Plan of Trimming round Fireplace.

Fig. 321—Cross Section through Coach Head Arch, Trimmer, Hearth, etc.

Fig. 322.—View showing Under Side of Arch, Trimming, and the Tie Bolt.

Fig. 323.

Fig. 324.

Figs. 323 and 324.—Alternative Methods of Housing Joists to Trimmers.

would be used to connect the staircase trimmer and joists shown in well. Fig. 317 (p. 70) gives a view of the herringbone strutting (2 in. by 1½ in.), four rows of which are indicated on the plan. The joists going from back to front are required to be

Fig. 325.—Plan of Binder or Double Floor.

34 ft. 9 in. long; therefore all, or the greater part, would have to be formed of two lengths and halved on the middle bearing; alternative methods of doing this are shown by Figs. 318 and 319.

Fig. 326.—Section through Joists, showing Side of Binder supported by Wall.

Trimming Round Openings.

In projections where fireplaces and flues (usually known as chimney breasts) occur in walls it is necessary to trim round them, so that the nearest timber in front shall be at least 18 in. distant, whilst that at the sides may be only an inch or so. In the plan (Fig. 315) the trimming joist runs parallel with the chimney-breast, and the trimmers which carry the joists are against the sides of the breasts. Fig. 320 is a reverse case, there being only one trimmer, which is parallel to the breast, but two trimming joists, these being at right angles to

Fig. 327.—Section through Binder showing Bridging Joists Cogged, and Alternative Methods of Connection with Ceiling Joists.

it. Fig. 321 is a section through the trimmer, hearth, coach head brick arch, etc., shown in plan at Fig. 320. s (Fig. 321) is a feathered-edge piece of board (a springing piece) nailed to the trimmer for the arch to butt against; f is a fillet nailed to the trimming joists so as to support the piece of scantling to which the laths are nailed. This construction is clearly shown at b (Fig. 322). When a trimmer has to support an arch, to prevent any likelihood of the arch forcing it back, one or two iron bolts are inserted, one end being bedded and hooked into the brickwork, the other having a screw or nut, as indicated at a (Fig. 322). Figs. 323 and 324 show alternative simple methods of housing short joists into trimmers. These are generally adopted in positions where there is not sufficient space to allow of their being inserted with the usual tusk tenon. Trimmers and joists to

Fig. 328.—Binder Chased-mortised for Ceiling Joists.

Fig. 329.—Ceiling Joists connected to Binder by Fillet.

Fig. 330.—Under Side of Floor with Wrought Binder.

Fig. 331.—Section through Double Floor taken across Iron Binder.

which they are connected should always be thicker than the ordinary joists. A common rule is to make the trimmers and trimming joists ⅛ in. thicker for each joist carried. Single floors may span as great a distance as 18 ft. by using 11-in. by 3-in. joists stiffened with two or three rows of herring-bone or solid strutting.

Double Floors.

When the distance between the supporting walls exceeds 14 ft. or 15 ft., it is usual to place binders or girders of wood or iron at intervals of from 6 ft. to 10 ft., and on these to support the bridging joists. Floors so constructed are known as double floors, having two sets of joists, the lower set (ceiling joists) being smaller, and used solely to support the ceiling. Thus the ceiling, being supported independently of the floor joists above, is not liable to be jarred by

Fig. 332.—Section across Bridging Joists showing Method of Fixing Ceiling Joists.

the traffic overhead, and the connection between the ceiling and floor being broken by the space between the two sets of joists, sound from above is not so audible below as when the floor is single.

Wooden Binders.—The outline plan of a double floor is given at Fig. 325, and Fig. 326 is a section through the joists, flooring, and ceiling, showing the side of the binder and also the method of supporting it. Fig. 327 is a section through the binder showing alternative ways of connecting the ceiling joists with the binder by mortise and tenon joints. Ceiling joists which have to be got into position after the binders are built in have their tenons inserted at one end into an ordinary mortise, whereas the tenon at the other end has to slide into a chase mortise as indicated at Fig. 328. To avoid weakening the binder, sometimes a fillet is nailed on so as to support the ceiling joists, which are notched to it as shown at Fig. 329. Fig. 330 illustrates the case where ceiling joists are not used. The binder is wrought and stopped chamfered; the laths for the ceiling would be nailed to the under edges of the bridging joists. The transmission of sound would be lessened by sound boarding and pugging as shown.

Iron Binders.—Two sections through a double floor are presented by Figs. 331 and

Fig. 333.—Conventional View of Double Floor.

Fig. 334.—View of Part of Under Side of Floor adjacent to Chimney Breast.

Fig. 335.—Method of Fitting Oak Border to Floor Boards.

Fig. 336.—Section taken Parallel to Steel Binder in Double Floor.

Fig. 337.—Section taken at Right Angles to Section—Fig. 336.

Fig. 338.—View of Under Side of Floor showing Cased Steel Binder projecting its Whole Depth below Joists.

332. Just above the lath-and-plaster ceiling are the ceiling joists, and running parallel with these is a 10-in. by 5-in. rolled-iron

Fig. 339.—Steel Binder Projecting Part of its Depth below Joists.

Fig. 340.—Section showing Arrangement to avoid Binder Showing.

joist (the binder). Fig. 333 shows the general construction of this floor, the special feature of which is that the ceiling joists are notched to and supported by every fourth bridging joist, which are stouter and deeper, as shown at a and b (Fig. 334). Fig. 335 shows a method of mitreing and fitting an oak border to the floor-boards ready to receive the hearth. Figs. 336 and 337 are sections through a somewhat similar floor, but of a more ordinary character, the ceiling joists being fixed to each bridging

Fig. 341.—Plan of a Framed Floor, showing Girders, Binders, Joists, Trimming, etc.

joist. The binders are of rolled-iron or steel 11 in. deep and 4½ in. wide in the flanges and 10 ft. apart. Fig. 338

Fig. 342.—Section through Girder and Joists.

illustrates a case where the bridging joist rests direct on the iron binder, solid strutting being inserted between the joists to keep them vertical. The ceiling is formed of either lath and plaster or match-boarding fixed direct to the joists, the binder being cased round as shown. Fig. 339 illustrates an arrangement of casing the under side of a girder or binder when it is deeper than the joists. If constructed as shown at Fig. 340 a flat ceiling can be obtained under the binder; but this construction cannot be adopted when the iron member has to serve as a girder for floors having heavy loads to carry, as a single binder would not be deep enough.

Framed Floors.

The plan of a framed floor, 45 ft. by 26 ft., is shown at Fig. 341. Three girders, supported at their centres by iron columns, carry the binders as shown. The sizes of the various members are: Girders, 14 in. by 10 in. sawn, reversed, and bolted with a ¾-in. rolled flitch in the centre; binders,

Fig. 343.—Conventional View of Girders, Binders, Joists, and Head of Column.

Fig. 344.—General View of Part of Framed Floor.

9 in. by 6 in.; bridging joists, 6 in. by 2½ in.; ceiling joists, 3 in. by 2 in. Figs, 342 and 343 will make the construction clear. Figs. 344 to 346 are details of a double floor for a smaller span. Figs. 345 and 346 are views taken at right angles to each

Fig. 345.—Section taken through Girder and Joists.

Fig. 346.—Section taken at Right Angles to Fig. 345.

Fig. 347.—View of Under Side of Framed Floor, with Wood Ceiling and Beams Wrought and Moulded.

other. Fig. 347 is a conventional view showing girder, 12 in. by 10 in.; binders, 8 in. by 6 in.; bridging joists, 8 in. by 2¼ in.; and matchboard ceiling. There

Fig. 348.—Binders supported on Girders by Malleable Iron Stirrup.

Fig. 349.—Another Form of Stirrup.

Fig. 350.—Wrought-iron Stirrup.

Fig. 351.—Method of Hanging Ceiling Joists from Bridging Joists.

being no ceiling joists, the girders and binders have their under-edges moulded. To intercept sound, the floor may be pugged as shown. The strength of wooden girders often being weakened to the extent of one-eighth by being mortised and housed to receive the binders, various forms of stirrup irons have been introduced to carry the ends of the binders, and thus they are well supported without the girder being weakened. Two different forms of malleable iron stirrups are illustrated by Figs. 348 and 349, and one of wrought iron by Fig. 350. A system of supporting ceiling joists by connecting them to the bridging joists by nailing them to strips of wood is shown at Fig. 351, but it has become obsolete.

Fig. 352.	Fig. 353.
Figs. 352 and 353.—Beam Trussed with One Tension Rod.

Floors with Trussed Beams.

In warehouses and factories where there are heavy loads and vibration the girders are sometimes strengthened by trussing. Various methods are adopted. Two ways of trussing by wrought-iron rods are shown by Figs. 352 to 358. In the case of Fig. 352 the beam is sawn down the middle, ends reversed, and bolted together with blocks

Fig. 354.—Enlarged View of End A (Fig. 352).

between, so as to allow of the iron rod passing through the iron heel plate at each end (Fig. 354), so that it can be tightened. Figs. 356, 357, and 358 illustrate a very strong form of trussing by using a solid beam and a tension rod on each side.

Fig. 356.	Fig. 357.
Figs. 356 and 357.—Beam trussed with Two Tension Rods.

Strutting.

Herringbone Strutting.—Cross-pieces of wood, about 2 in. by 1½ in., or 2 in. by 2 in., are frequently fixed between joists, as already shown by Figs. 315, 317, and 332, with

Fig. 358.—Enlarged View of Cast-iron Shoe C (Fig. 356).

the view of strengthening and increasing the rigidity of the whole floor. To prevent splitting at the ends by boring, it is usual to make a saw kerf at each end of the struts (see Fig. 317) for the insertion of the nails. A great advantage in this form of strutting is that, although the joists may shrink in thickness and depth, the strutting remains firm owing to the greatest shrinkage taking place in depth. This will be made clear by Fig. 359. Let a, b, c, d represent the original position of the strutting; then upon shrinkage taking place, the struts move about

Fig. 355.—View of Cast-iron Strut B (Fig. 352).

their centre O, and tend to the positions indicated by the dotted lines a′ b′ and c′ d′, the greatest movement being produced by the depth shrinkage; thus the greater this is the more the compression on the struts, which would produce greater distances between the joists, were it not for the floor boards being nailed to the joists.

Solid Strutting.—When pieces of board are cut and simply driven in tightly between the joists and nailed, they often become loose some months after the floor is completed, owing to the shrinkage of the joists

Fig. 359.—Movement of Herringbone Strutting produced by Shrinkage of Joists.

in thickness, and thus they are of very little use for the purpose for which they were intended. Solid strutting is a most valuable form for stiffening and strengthening floors of warehouses, etc., if a wrought-iron bar or tube is passed through each joist a little above its centre. The bar must have a thread and nut at each end working against an iron plate, so that the struts and joists may be tightened perfectly close to each other. A view of this arrangement is given at Fig. 360.

Supporting Joists by Walls.

Joists are now often supported direct by the brickwork or masonry, or they may take their bearing on a tar and sanded or galvanised iron bar. Figs. 361 to 364 show four general methods of bedding plates for joists in or upon the walls. Fig. 364 shows the plate supported by iron corbels built in the walls. So that the plate may not project below the ceiling, sometimes the joists are notched down to bring their lower edges level with the under side of the plate; but, of course, this weakens the joists.

Fig. 360.—View of Solid Strutting and Bolt.

Determining Sizes of Joists.

Common joists are spaced 12 in. apart, with herringbone strutting every 4 ft. Dimensions for common joists are as follow:

Span or Length of Bearing in Feet		Depth in Inches.
		1½ in. thick.		2 in. thick.		2½ in. thick.		3 in. thick.
6		6		5	¾	5	⅜	5
8		7	½	7		6	½	6	¼
10		8	½	8		7	½	7
12		9	¾	9	½	8	½	8
14		10	½	10		9	½	9
16		11	½	11		10	½	10

The nearest available size should be used, and 2-in. ceiling joists should be ½ in. deep per foot span. The trimming joist is made ⅛ in. thicker for every common joist carried by the trimmer. A rough rule used some years ago was to fix the depth of the joists at one-sixteenth of the clear span, or ¾ in. to each foot between the bearings. The Ecclesiastical Commissioners prescribe the size of joists to be 9 in. by 2¼ in. for 12-ft. spans and 12 in. by 3 in. for 18-ft. spans. A metropolitan authority has fixed upon 8½ in. by 2½ in., and 11½ in. by 2½ in. for the

Fig. 361.—Joists supported by Wall Plate built in Wall.

same respective bearings. By the rough rule of one-sixteenth the distance between the bearings, the depth for an 18-ft. span should be:—

${\frac {18\times 12}{16}}=13{\tfrac {1}{2}}{\text{in.}}$

If, however, the thickness of the joist is taken to be 3 in., the strength of the joist will allow for

${\frac {13.5^{2}\times 3\times 2.5}{18}}=76{\text{cwt.}}$

central breaking load, or

${\frac {76}{6}}=12{\tfrac {1}{2}}{\text{cwt.}}$

central safe load, which is considerably more than is required (see the calculation given below).

Weight on Joists.

The weight on ordinary joists of, say, 18-ft. span, 12 in. deep, and 3 in. thick, and 1 ft. 3 in. centres, may be taken to be as follows:—The superficial space carried on the joist is 18 ft. by 1 ft. 3 in. = 22.5 sq. ft., and this covered with people at, say, 84 lb. per square foot amounts to 22.5 ft. by 84 lb. = 1,890 lb.

The sound-boarding and pugging may be taken at 100 lb. per yd. super., and the lath, plaster, etc., at 80 lb., giving a total weight of 180 lb. per yd., or per ft. super. 180/9 = 20 lb. This multiplied into the area gives 22.5 x 20 lb. ( = 450)

The floorboards will be 18 ft. by 15 in. by 1½ in. = 2•81 ft. cube the joists 18 ft. by 1 ft. by 3 in. = 4.50 /7.31 ft. cube

and the total weight of timber will be 7•30 ft. by 35 lb. ( = 257)

Thus the total distributed weight is 2,597

This is equal to 2597/2 = 1,299 lb. central load, or 11•6 cwt. The strength of the joists under this load will be, by the formula already given, 12² × 3 × 2•5/18 = 60 cwt. breaking load, or 60/6 = 10 cwt. safe load.

Estimating Load on Floors.

Floors should be estimated for according to the nature of the building and the probable load. A crowd of persons is variously estimated to weigh from 41 lb. to 147•4 lb. per square foot of the surface covered. Probably a safe average would be 1 cwt. per ft. super, considered as a live load. Dwelling houses are usually designed for a dead load of 1¼ cwt. per ft. super., churches and public buildings 1½ cwt., and warehouses 2½ cwt. The weight of the structure must be allowed for in addition to the above loads, and this is most important to bear in mind in connection with fireproof floors. For dwelling houses the 1⅓cwt. is usually made to include the weight of the floor itself.

Fig. 362.—Joists supported by Wall Plate bedded on Set-off.

Fig. 363.—Wall Corbelled Out to carry Wall Plate.

Fig. 364.—Plate carried by Wrought-iron Corbels built in Wall.

Bridging Joist for 18-ft. Span, Load 1 cwt. per ft. super.

Let it be required to determine the size of a bridging joist suitable for a span of 18 ft. and capable of carrying a load of 1 cwt. per ft. super., the joists fixed 12 in. centre to center. The preliminary calculation will be as follows: (1) The total weight on one joist is equal to the load on the half space on either side of the joist—that is, 6 in. on each side. Then the total load = 18 × 1 ft. × 1 cwt. = 18 cwt. (2) The load that may be safely carried on the joist is a certain fraction of the breaking weight — that is, of the load that would break the joist. This fraction varies, for the different purposes for which the scantling is to be used, from one-fifth to one-tenth. In the case of floor timbers, where the joist has to sustain a live load, it should not exceed one- seventh or one-eighth the breaking weight. In the example given above, the joist has to carry a load of 18 cwt. Hence the breaking weight is equal to 18 x 8 = 114 cwt. (3) The breadth or thickness of the joist must bear a certain proportion to the depth so as to be satisfactory as regards strength and economy. Let this proportion for a bridging joist be decided by the formula b = '3 d, where b = the breadth and D the depth — all in inches. It is evident that the joist in such a case must be considered as strutted. The preliminary calculations as regards the joist having been made, a formula applicable to every case for calculating the strength of timber, no matter where or for what purpose the scantling may be required, must be decided on. A piece of wood of the same kind as that used for the joist, and 1 ft. long by 1 in. square, loaded at the centre till it breaks, will be the constant for all purposes of calculation when dealing with the same material. It will be found that the strength varies directly as the breadth, directly as the square of the depth, and inversely as the length ; this may be proved by increasing the breadth, length, and depth, and carefully noting the difference in the loads required to break the beam in each case. Briefly, the formula may be stated thus : BW = cbd/L that is, for a central load. But a floor- joist carries a distributed load, and this load will be found to be equal to twice the load it will carry when centrally loaded. Then the formula will be : — BW = 2cbd^2/L

114 = (2 x 4 x 3d x d^2 )/18 and d^3 = 144 x 18 )/2 x 4 x .3 = 1080.

d = 3V1080 = 10 in. nearly, and b = .3 x d = .3 x 10 = 3 in.

Let c be the constant = 4 cwt. ; b the breadth in inches ; d the depth in inches ; L the length in feet ; B.W. the breaking weight = 114 cwt. Therefore a joist 10 in. by 3 in. would be suitable for a span of 18 ft., and would carry a load of 1 cwt. per ft. super. The following rule is given by Tredgold for fir joist : — D = 3VL^2/B x 2-2 In this case a breadth must be assumed, which is, in most cases, a difficult and very uncertain proceeding ; however, assuming for the present example the breadth to be 3 in., Then -7». .0 b = ;/**i! x o.o. D = / 08 o.o -5 x 2-2 = 9 9 in. The result is very much the same as in the previous example, but the advantage of the first method will be obvious when dealing with further calculations, as it is applicable to other beams than floor timber. Determining Size of Binder. Say it is required to determine the size of a binder 10 ft. long and fixed 6 ft. apart, capable of carrying a floor weighing 1 cwt. pecxr ft. super. Make, as before, the necessary preliminary calculation. (1) Total load carried by the binder =10 x 6 = 60 cwt. (2) Breaking weight (say) seven times safe load = 60 x 7 = 420 cwt, (3) Let the ratio of the breadth and the depth be as 6 is to 10, that is *6 d, which is a very suitable ratio for all purposes where stiffness is required. (4) Let c the constant = 4 cwt. Then, using the same formula as before, breaking weight = 2cbd^2 / L

=- 

x 4 x -§d x d 2 10

x 4 x ?3 

.

x 10 

d° — ~ ~ A a = 8 ?5

x 4 x "o

${\begin{aligned}\therefore \ &d={\sqrt[{3}]{875}}=9.5\ {\text{nearly,}}\\{\text{and}}\ &b=.6d=.6\times 9.5=5.7\ {\text{in.}}\end{aligned}}$

Therefore, a binder 9·5 in. x 5·7 in. would carry a floor weighing 1 cwt. per ft. super, over a span of 10 ft. The following rule is given by Tredgold:—

$D={\sqrt[{3}]{\frac {L^{2}}{B}}}\times 3.42.$

In this case, again, the breadth must assumed. Let this be taken as 5·5 in.,

${\begin{aligned}{\text{then}}\ D&={\sqrt[{3}]{\frac {10\times 10}{5.5}}}\times 3.42\\\therefore \ d&={\sqrt[{3}]{18}}\times 3.42\\\therefore \ d&=2.7\times 3.42\\&=9.2\ {\text{nearly,}}\end{aligned}}$

which corresponds very nearly with the first case.

Determining Size of Girder for Supporting Floor.

Girders 10 ft. apart from centre to centre carry a floor weighing 11/4 cwt. per ft. super. Required, the breadth and depth for strength; span 20 ft. (1) The total load carried by the girder is 20 x 10 x 1.25 = 250 cwt.—that is, the length multiplied by half the bay on either side multiplied by the load per ft. super. (2) Let B.W. = 7 times the safe load = 250 x 7 = 1,750 cwt. (3) Let breadth be .6 d. (4) Let c the constant be 4 cwt.

Then

${\begin{aligned}{\text{B.W.}}&={\frac {2cbd^{2}}{L}}\\1750&={\frac {2\times 4\times .6d\times d^{2}}{20}}\\\therefore \ d^{3}&={\frac {1750\times 20}{2\times 4\times .6}}=7262.5\\\therefore \ d&={\sqrt[{3}]{7262.5}}=19.25\ {\text{in. nearly,}}\\\therefore \ b&=.6d=.6\times 19.25=11.550\ {\text{in.}}\end{aligned}}$

Therefore, the breadth and depth of a suitable girder for the required purpose must be 11.5 in. wide and 19.25 in. deep. It is needless to remark that a wooden girder 20 in. deep is impracticable, and a wrought-iron girder would be substituted for it; but as the above is merely an illustrative example, the construction of the girder need not be discussed. Tredgold's rule for fir girder is:

$D={\sqrt[{3}]{\frac {L^{2}}{B}}}\times 4.2$

Let the breadth (which must be assumed) be 12 in. Then:—

${\begin{aligned}D&={\sqrt[{3}]{\frac {20\times 20}{12}}}\times 4.2\\&={\sqrt[{3}]{\frac {400}{12}}}\times 4.2\\&={\sqrt[{3}]{33.3}}\times 4.2\\&=3.2\times 4.2\\&=14\ {\text{in. nearly.}}\end{aligned}}$

It is evident from this that a girder 20 in. deep is by far too large, or that a girder of 14 in. is much too small. If the formulæ in each case are examined it will be found that the first is based on the strength of a small beam determined by trial, while the second is doubtful. It is certain, however, that a girder, 12 in. by 14 in., and 20 ft. long, is not capable of carrying a load of 250 cwt., as determined by the recognized formulæ. It may be mentioned further that the loads are considered as distributed loads, while in reality they are loads placed at certain fixed points, namely, the points where the binders are connected to the girder; consequently the dimensions obtained by the formulæ are slightly less than they ought to be.

Thus

${\begin{aligned}B.W.&={\frac {2cbd^{2}}{L}}\\&={\frac {2\times 4\times 11.5\times 19.25\times 19.25}{20}}\\&=1704.58\ {\text{cwt.}}\end{aligned}}$

which is less than the actual breaking weight calculated for, namely, 1,750 cwt. The strongest floor, for the quantity of timber used, is given in the first case, while the apparent strength shown in the second and third cases results in actual weakness. But single floors should not be used for spans exceeding 16 ft.; and though they are sometimes used for spans up to 24 ft., in such cases deflection is considerable, resulting in cracked ceilings, etc. It may, nevertheless, be stated that each floor has its advantages and its disadvantages. The above Page:Cassells' Carpentry and Joinery.djvu/104 for flooring are 6 in. by 2 in., 6 in. by 2½ in., 6½ in. by 2½ in., 7 in. by 2½ in., and 7 in. by 3 in. When 3-in. by ⅞-in. flooring is being cut and wrought, the most suitable sized batten is 7 in. by 3 in., which gives six pieces, three saw cuts being sufficient—namely, two deep and one flat. This is when wrought single with the flooring machine. When run double with the machine two saw cuts through the depth are sufficient. The flat cutting in this instance is done with the flooring machine. The double working of flooring and lining with machinery, though much the quicker way, is not so satisfactory as the single method, for each alternate board has to be reversed, besides the further disadvantage, if the battens are waney, of the groove being always on the waney edge. Similar sized flooring (⅞ in.) can also be cut from 7-in. by 2½-in. battens. Two boards may be cut ⅞- in. in thickness and one ½ in., thereby utilising the whole batten; 5½ in. by ⅞-in. boards are taken from 6-in. by 2-in. material; 3-in. by 1⅛-in. from 7-in. by 2⅛-in., 3-in. by 1⅛-in. from 7-in. by 3-in.

Fig. 365.—Ordinary Direction of Grain in Floor-Boards.

Operation of Floor-Board Planing Machine.—The fixed cutters or face irons of a flooring machine produce the best and smoothest work. These tools operate on the under side of the boards; therefore the freshly sawn side should be placed downwards to receive the finishing, which the face irons accomplish. The revolving top scutching-block is not so much used for dressing as for bringing the boards to an exact thickness. So long as one side of the board is well dressed and of accurate thickness, it is not important to have the other side so well done. Some machines have fixed planers on the upper side, but such cannot bring the stuff to an accurate thickness like the revolving scutch-block. It is heavy work for fixed cutters to reduce boards 1/18 in.; the scutching-block, however, can easily take ¼ in. off. With evenly sawn wood heavy cutting has seldom to be resorted to. The leading advantage of the scutching-block compared with fixed cutters is that the block makes an irregular surface parallel, whereas fixed cutters follow the uneven nature of the board, and do not alter any irregularity which it may have. There are many cutter heads for the formation of the tongue and groove. The face-iron side of the groove and tongue should project a little more than the scutched side; by this means the faced side of the flooring, when driven home and placed in position, has a better joint than it otherwise would have. The "Shimer" patent heads make the finest work; with a feed speed of 60 ft. or 80 ft. per minute undue chipping is very rare with the "Shimer" patent. A good machine can run from 9,000 to 11,000 sup. ft. of 6-in. or 6½-in. by 1⅛-in. flooring per day, or 4,000 sup. ft. of narrow flooring. All 1⅛-in. material is taken from 2½-in. battens, whether broad or narrow. Flooring above 1½ in. thick is sometimes run with two grooves instead of one, and slip feathers are employed in place of the solid formed tongue. This plan saves ½ in. on the breadth of each board.

Fig. 366.—Direction of Grain for Least Shrinkage of Floor-Boards.

Stacking Floor-Boards.—Finished flooring, no matter how well it may be stacked and pinned, is always liable to become twisted whilst being seasoned. To obviate this, the material should be sawn, pinned, and stacked in the rough. Let it season for six or eight weeks; then finish it with machinery. Work done in this way can be stored in bulk under cover without being pinned or ventilated. Flooring wrought on this principle does not twist, cast, or shrink like material finished and stacked at one operation; it is, moreover, much more easily laid. This rule applies also to lining. Red deal flooring is not so generally wrought for stock as white, for the reason that red deal battens are, as a rule, kept under cover; orders can be executed and despatched without the necessary seasoning that white deal requires. Red deal is more easily manufactured than white. It is to a certain degree softer and not so tough in the reed as spruce.

Fig. 367.

Fig. 367.

Fig. 368.

Fig. 368.

Figs. 367 and 368.—Laying Folded Floors.

Fig. 369.—Cramping Floor-Boards with Dog and Folding Wedges.

Direction of Grain in Floor-Boards.—If a specification does not insist on any particular position of the grain of the wood, it will be complied with by either of the examples shown in Figs. 365 and 366. If the grain is intended to show "annual rings parallel with the edges," words to that effect should be inserted in the specification, or it should be stated that "all boards are to be cut radially from the tree." No doubt the plank shown in Fig. 366 would be less liable to warp than that shown in Fig. 365; but to obtain all like this would mean picking over a very large parcel of boards in order to get the quantity required, and it may be looked upon as impracticable.

Fig. 370.—Floor with Joints broken at 3-ft. Intervals.

Fig. 371.—Ordinary Pattern Floor Cramp.

Laying Floor-Boards.

Folded Floor.—"Floors to be laid folding with the joints broken" means that the heading joints of the boards are not to be in line when laid, but are to be crossed in as long lengths as possible from joist to joist. The system of laying the boards with a succession of joints in line causes unevenness when the boards shrink, and weakens the floor. The term "laid folding" is an old one, and was applied when mechanical means were not available for bringing the joints tightly together. In the absence of a floor cramp the boards may be laid with fairly tight joints by jumping them in, as shown in Fig. 367. The first board next the wall is laid and nailed in its place; then other boards (say five), to make a width of about 3 ft., are laid down. The final position of the fifths board having been ascertained, the fifth board is nailed down ¼ in. inside the line it takes when only hand tight. The four other boards are then jumped in and nailed. A board placed over the loose boards, as seen in Fig. 368, will be found of assistance in getting the floor-boards down to the joists, but there will still be some difficulty unless the four boards are kept loose—that is, none of the intermediate boards between the first and sixth must be nailed until all of them are tight home. Another simple method of cramping is shown in Fig. 369. An iron timber dog (Fig. 47, p. 11) is driven into the top edge of the joist, allowing about 3 in. from the edge of the floor-board. A piece of rough timber 2 in. thick is then laid next the board, and a pair of hardwood folding wedges is driven between the timber and the dog until the joints of the board are close; then the boards are nailed, the dog is removed, and more boards laid in the same manner. Both the methods above mentioned are usually adopted for the commoner kinds of work only.

Fig. 372.—Improved Form of Floor Cramp.

Fig. 374.—Floor brad.

Fig. 373.—Another Improved Floor Cramp.

Fig. 375.—Butt and Splayed Heading Joints.

Laying Floor-Boards with Aid of Cramp.—Floors laid with the heading joints crossed, as in Fig. 370, need a special cramp to bring up the joints; three kinds of cramps are shown by Figs. 371 to 373, but a variety is available. For instance, batten-width tongued and grooved common Baltic flooring would be laid in the following manner. The joists would be tried over and brought to a level. A batten, or line of battens, would be laid down next the wall to line true at the outer edge, and then be nailed to the joists. The remaining rows are laid two or three at the time with the tongues inserted, then cramped into place, nailed, and the next lot of battens applied. If the battens are already tongued, they can be laid either way, as the block, or saving piece, between the cramp and batten can be grooved to clear the tongue. Figs. 371 and 372 show the modes of using floor cramps. When the floor has been finished so far that there is not sufficient room for the cramp, the remaining battens can be wedged in from the wall, or forced together by using a piece of quartering as a lever.

Floor Brads.

Nails used in flooring are called floor brads (Fig. 374), and they are driven through the floor-boards into the joists, two at each passing, about 1 in. from the edge.

Fig. 376.—Straight Floor Joint.

Fig. 377.—Rebated Floor Joint.

Fig. 378.—Rebated and Filleted Joint.

Fig. 379.—Rebated, Grooved and Tongued Joint for Secret Nailing.

Fig. 380.—Iron Tongue Joint.

Fig. 381.—Dowelled Floor Joint.

Joints for Floor-Boards.

Heading Joints.—The points of contact between the ends of two floor-boards are called heading joints (Fig. 375). A (Fig. 375) shows the section of a butt heading joint, but slightly less simple than the splayed heading joint shown in section by B (Fig. 375). These joints should always be arranged to occur over a joist, and in floors laid with the aid of a cramp, contiguous boards should have their heading joints on different joists—that is, should break joint. The actual joint is made in different ways. In common floors the boards simply butt up against each other A (Fig. 375); in better work the heading joints are splayed b (Fig. 375). Even with plain headings it is usual slightly to undercut the ends so as to present as close a surface joint as possible. Sometimes the heading joints are grooved and tongued in a similar fashion to the longitudinal joints described below. In very expensive work the ends of the boards are cut into a series of sharp, salient and re-entering notches, whose ridges are parallel to the surface of the floor. These notches fit one another, and form a tight joint. Such joints are sometimes used in oak floors; they are extremely troublesome and expensive to make, and the point nearest the surface of the floor is very liable to break away even in hard wood.

Edge Joints.—The ordinary straight joint for the longitudinal edges of floor-boards is shown in section by Fig. 376; the rebated joint (Fig. 377) is another common method, a joint requiring more work being the rebated and filleted (Fig. 378). The rebated, grooved, and tongued joint (Fig. 379) is useful for secret nailing. The joint shown in Fig. 380 has an iron tongue, and Fig. 381 shows the dowelled joint. The ploughed and cross-tongued joint with slip feather (Fig. 260, p. 62) is also used. In all floors which are ceiled underneath, means should be taken to prevent dust or particles of any kind from falling between the boards. Any accumulation of organic matter on the upper surfaces of the plaster is certain to decompose. The ceiling being, moreover, always more or less porous, these particles gradually work their way to the under surface, and produce a stained appearance, which no amount of whitewashing or scraping will remove. The usual method of preventing this is to form a ploughed and tongued floor. Each board is grooved on each edge, and thin slips, or tongues, either of wood or of galvanised iron, are then inserted (see Figs. 260 and 380). If of iron, the tongue should be galvanised. The tongue should be fixed nearer to the lower edge of the board than to the upper, so that as much wear as possible can be had out of the floor before the tongue is exposed. Another method of attaining the same object is known as rebating and filleting (see Fig. 378); a rebate is cut on the lower edge of each board, and a fillet of oak or some other hard wood fixed in the space thus formed. For superior work, a dowelled floor (Fig. 381) has the advantage of showing no nails on the surface; the boards are pinned together between the joists with oak dowels, and nailed obliquely on one edge only. Dowelled boards should not be more than 3 in. wide, and not less than 1¼ in. thick when finished. The "Pavodilos" joint is as shown by Fig. 382, a slightly modified form being that shown by Fig. 383, which, although the second key is lost, may possibly be preferred on account of the danger, when nailing down the flooring jointed as in Fig. 382, of damaging the feather-edge of the board that is being fixed.

Double-boarded Floor.

An upper layer of thin oak boards is sometimes fixed over a rough deal floor for the sake of appearance, and also in some cases to obtain an almost impervious surface. A floor of this kind, wax-polished and well laid, is much to be commended for the ease with which it can be cleaned, and for its non-absorbent nature.

Fig. 382.

Fig. 383.

Figs. 382 and 383.—"Pavodilos" Joint in Flooring.

Sound-proof Floors.

One method of preventing the sound from one room being audible in another room immediately below is to nail fillets to the joists, and on these nail a layer of rough boards, and to fill in on the top of these boards a stratum of lime-and-hair mortar. Slag felt, a preparation of slag wool, which is a material produced by blowing off waste steam into the slag of iron furnaces, is also used for this purpose. In the case of the slag felt the process is as follows: On the under side of the joists, fillets are nailed to wooden blocks 1 in. thick, and to these fillets the lathing for the plaster ceiling is affixed. The slag wool (known as "pugging") is then laid on the upper surface of the laths, and is felted by a patent process, this process of felting removing entirely the property which the slag wool possesses of emitting sulphuretted hydrogen, and also reducing the weight of the material. Slag material, being fireproof, is to be preferred to sawdust and other combustible materials sometimes used. Fig. 384 shows the section of part of a common floor, showing 9-in. by 3-in. joists, and 1½-in. boarding with a rebated heading joint. In addition, "pugging" and a lath-and-plaster ceiling are shown. The object of the pugging is to reduce the transmission of sound. The fillets for supporting the pugging need not be of the shape indicated in Fig. 384. Another means of attaining the desired end is to nail strips of felt on the upper edges of the joists, under the floor-boards. By this means the connection between the joists and boarding is broken. This arrangement creates some difficulty in fixing the boards, which can be overcome by nailing a lath along the top of the felt.

Fig. 384.—Section of Sound-proof Floor with Pugging.

Fireproof Wooden Floors.

Protected Wooden Floors.—One of the simplest and most economical methods of constructing a fire-resisting floor is to protect an ordinary wooden floor with slabs of asbestic plaster or of slag wool (silicate cotton), both of which can be obtained commercially in slabs, as cloth, or in the form of loose fibre or wool. The loose wool is useful for filling up the spaces between the joists as a pugging to deaden sound (as already described), as well as affording protection against fire. A convenient method of attaching the slabs is shown in Fig. 385. The slabs are formed by enclosing silicate cotton between sheets of galvanised wire netting, and are made of thicknesses varying from 1 in. to 3 in. They are secured to the under side of the joists, as shown at A, by wooden fillets B B nailed underneath, the nails passing through the slabs. To these fillets are secured the laths, when a lath-and-plaster ceiling C is desired. Additional security can be obtained by placing other slabs between the joists, resting on triangular fillets as shown in Fig. 386. Owing to the comparative cheapness of these methods of construction, and the measure of security they afford, they are worthy of more general adoption in dwelling-houses and office buildings.

Fig. 385.—Asbestos Slabs under Wooden Floor.

Fig. 386.—Asbestos Slabs between Joists.

Solid Wooded Floors.—Woodwork, when used in solid masses, is an excellent material for fireproof construction. It is extremely difficult to destroy timber in bulk by fire, and in America, partly on this account, and also on account of the cheapness of timber, floors and walls are constructed of planks nailed together side by side. The walls of many of the large grain elevators and station buildings are constructed in this way. The system of forming floors by close timbering instead of the ordinary use of joists and flooring boards, was introduced into England by Messrs. Evans and Swain between 1870 and 1880. The joists, instead of being placed at some distance from each other, were laid close together, so that air could not penetrate between them, the planks being then spiked as shown in Fig. 387. As an alternative method, the spikes could be driven in diagonally, and, if thought necessary, the under side of the planks could be protected with a plaster ceiling keyed into grooves formed in the planks. As a test of the capability of this system, a building was erected 14 ft. square inside of 14-in. brick walls, and measuring 7 ft. from the ground to the ceiling. The flooring was laid as described above, of deal battens 7 in. deep by 2½ in. thick, spiked together side by side. One-third of the under side was plastered, the joists being grooved for this purpose; one-third was plastered on nails partly driven into the planks, and the remaining third was left unprotected. The chamber underneath was packed almost full of timber, which was then lighted, and it was not until after five hours' continuous exposure to the flames that the unprotected portion of the floor gave way. The system was afterwards adopted in large warehouses for the East and West India Docks, London, and in other buildings.

Fig. 387.—Floors of Solid Wood.

Other Systems.—A modification of the system just described has been patented by Messrs. Hinton and Day, and is illustrated in Fig. 388. The joists are spaced apart in the ordinary way, but the spaces are filled in with solid blocks, having the grain placed vertically, tongued and grooved together in such a manner that the passage of air between them is prevented. The blocks are carried by fillets nailed to the sides of the joist. A test of this system of flooring was made at Westminster. Four walls of 9-in. brickwork were erected, and the under side of the floor to be tested was 9 ft. 6 in. from the ground. The lower part of the building was filled three parts full with inflammable material (no petroleum or grease, however), and a fierce fire maintained for more than two hours, after which it was extinguished, and the under side of the floor was found to be charred to a depth of ¾ in. In American factory and workshop buildings a layer of mortar D is often introduced between two thicknesses of flooring, as shown in Fig. 389. Here 8-in. by 4-in. wooden joists E support the flooring planks, which are 3 in. thick, on which a layer of mortar, ¾ in. thick, is spread. Floor-boards 1½ in. thick, laid on the top of this, form the working surface of the floor. Sometimes the floor-boards are laid in two thicknesses, crossing each other diagonally, as shown in Fig. 390, in which F indicates the layer of mortar. The beams carrying the floors have air spaces round each end, and to avoid the danger of the wall being pulled down by a falling beam in case the latter should be burnt through, the upper end of the beam is cut away at both ends so that it can fall freely.

Fig. 388.—Solid Blocking carried on Fillets.

Wood-Block Floors.

Solid wood-block floors are now much used in the basements of dwelling-houses, on the ground floors of public buildings, and for covering certain forms of fireproof constructions in the upper floors of warehouses, etc. The advantages they possess over the ordinary boarded floor are: damp-proofness, freedom from dry rot, greater lasting properties, and freedom from vibration, and they do not transmit sound nor harbour vermin; they are more sanitary, through the absence of shrinkage, and consequent open joints of the older system; and the absence of nails is also a great advantage, as the holes made by these are always unsightly, and when the boards wear down the heads project, to the discomfort of the users.

Fig. 389.

Fig. 390.

Figs. 389 and 390.—American Systems of Wooden Floors.

The Wood Blocks.—Wood blocks are generally made from 9 in. to 18 in. long by 3 in. wide, and from 1½ in. to 3 in. thick, of yellow deal, pitchpine, oak, birch, maple, or beech. They should be prepared from thoroughly seasoned and sound stuff. The firms who make a speciality of this work usually dry the blocks in hot-air chambers after working, and afterwards store them in a dry building. Precautions should therefore be taken, when receiving a consignment from the factory, to store them under cover until they are required; and it is wise not to order them until the place is ready, because their storage for any length of time in a damp building will defeat the object of the previous drying, and for this the purchaser has to pay. The smaller sized blocks are sometimes made with square joints, and are held in place by the cement or mastic with which the foundation is covered, but in superior work the blocks are also connected by grooves and tongues or dowels. Several patented systems are on the market, some of the best of which are here illustrated; these combine an interlocking of the blocks with the substance of the bed, by means of dovetailed grooves or inserted keys, and a connection with each other by means of pins or tongues.

Preparing Basement for Wood-Block Floor.—In preparing a basement to receive a Page:Cassells' Carpentry and Joinery.djvu/112 Page:Cassells' Carpentry and Joinery.djvu/113 used for this purpose, fixing down the margins, and cutting and fitting in a bay as shown by the dotted line A (Fig. 391). Once the spread of a bay is known, it is easy to space out the quantity for a room and

Fig. 396.—Section of Herringbone Patterns shown in Fig. 391.

ascertain how many of each length and shape are required. It is best to lay down all recesses like the one shown, and cut in all the blocks, specially marking them. To obtain the size of the recess, lay down the margin blocks tight between the walls, or frame a rough template to the opening. The herringbone pattern must always be laid square—that is, cut ends must be a mitre of forty-five degrees.

Designs of Wood-Block Floors.—Design Fig. 392 is laid similarly, beginning with the blocks No. 1 and following on with 2 and 3, etc. Fig. 393 is an easy design to lay when once the corner is passed; the numbers indicate the order of laying the blocks. Care must be taken to keep the sides of each tile in a straight line, and they should be tested occasionally with a straightedge. Fig. 394 is an easy design to lay, and looks very well in pitchpine. Fig. 395 is more elaborate, but very effective in two coloured woods, the darker one for the frames and the lighter for

Fig. 397.—Turpin's Patent Block Floor.

the panels. All of these designs are based on the right-angled triangle, and, given the size of the block, they can be readily set out to fit any room; each pattern being a repeat, one bay multiplied by the length and width of the room will show the quantity required. It may be mentioned that these blocks are usually sold by the hundred.

Jointing and Fixing Wood Blocks.—Fig. 396 shows the section of a wood-block base-

Fig. 398.—Duffy's Patent Block Floor.

ment floor with grooved and tongued joints. Fig. 397 represents a section of Turpin's patent interlocking system; here a tapering tongue with an undercut shoulder on the lower side is stuck on the solid all round one block, and a corresponding groove in the other, and when the two come together they form a dovetail groove into which the mastic is pressed when laying, thus forming a solid key with the bed. Duffy's patent is shown in Fig. 398, and consists in the connection of the blocks by means of dowels; these are supplied with the blocks and driven in as the blocks are laid. The holes are bored by machinery and are at exactly the same

Fig. 399.—Geary's Patent Block Floor.

distance apart, whether on the end or side, and therefore the blocks can be laid in several combinations. In Geary's patent (Fig. 399) each block is fixed to the mastic by means of two metal keys driven into the

BOXING SHUTTERS TO SASH WINDOW

ends of the block; these project from the bottom, and are buried in the bed material. The key is drawn to enlarged scale in Fig. 400; it is easily knocked out when a block has to be cut, and is re-inserted in a small mortise. A half dovetail groove is also worked on the side of each piece, which forms an additional key to the block. In Fawcett's system, shown in plan at B (Fig. 391, p. 94), and in isometric projection by Fig. 401, the ends of the blocks have a ⅛-in. groove cut across them at an angle of forty-five degrees, and these, when the blocks are laid in herringbone pattern, lie in a continuous straight line. Into these grooves a ¾-in. by 1/18-in. steel tongue is inserted as shown in Fig. 401, the succeeding row of blocks fitting over and completing the groove. This system is very effectual in preventing the rising of individual blocks, and is much used on fire-resisting concrete floors. The letter references in Figs. 391 to 399 not mentioned in the text are: C groove, D mastic, E cement, F concrete, G ground.

Fig. 400.—View of Metal Key.

Fig. 401.—Fawcett's Patent Block Floor.

Parquet Floors.

Parquetry is a method of covering a floor with hard and richly coloured woods, arranged in various fanciful and geometric patterns, the effect of the design being brought out by the various colours, and by the direction of the grain in the component pieces, which are selected chiefly for their differences in this respect. Usually, for the larger portions of the patterns, the natural colours of the wood afford sufficient contrast, but for bands in the borders, and for edgings for the geometric figures, more vivid colours are sometimes desirable, and these are obtained by dyeing some light-coloured wood, such as ash or sycamore, to the required tint. The three forms of parquetry in ordinary use are known respectively as thin, medium, and solid. The two former, which are respectively out of ¼-in. and ½-in. stuff, are glued to ½-in. or ¾-in. deal backings in squares or panels from 10 in. to 18 in. square, and these panels are grooved and tongued all round, or sometimes dowelled, and are attached to the counter-floor either with screws, which are afterwards pelleted, or by gluing down. The former method is employed when it is intended to remove the parquet at some future time; and the latter, when the parquet is to be permanent. The solid parquet is about 1 in. thick, and the various pieces are usually glued direct to the counter-floor and to each other in one operation, the design being formed as the work proceeds. In this method, all pieces more than 1½ in. wide are dowelled, or, in a cheaper class of work, are nailed to each other with wire nails. Borders are fixed first, and, as far as possible, these are made wide enough to bring all small recesses and projections into line, so as to cause no interruption in the pattern; but large openings must have the borders broken and returned around them.