Farm Building Construction

New Zealand Journal of Agriculture, Volume 95, Issue 1, 15 July 1957, Page 65

Farm Building Construction

By

H. W. T. EGGERS,

Engineer, Department of Agriculture, Wellington

LAST month's article in this series described various roofing materials. This article L. j. ,1 ~j l il- xl l* l • 1 . . .1 xdiscusses the outside sheathing of a building, which is complementary to the roofing in providing total protection from the elements, and also deals with different types of flooring.

TO fulfil their function as a protection from the elements, materials used for sheathing must not only be waterproof in themselves, but they must lend themselves to fixing in a manner that will prevent penetration of moisture at joints to the timber framing. Any such penetration would quickly set up conditions favourable to fungus growth and decay, which consequently would cause rapid deterioration of the load-carrying part of the structure. Sheathing materials should also have good insulating properties. Timber frame buildings must be covered on the outside with approved weather-resisting materials. These may be metallic materials, timber, asbestos cement materials, cement plaster or stucco, or brick or concrete veneer. Timber Sheathing Timber is the most widely used sheathing material. The hitherto abundant supply of indigenous species particularly suitable for weatherboarding made its almost universal adoption inevitable. Time has established the practice of weatherboard construction securely, but with the

decreasing supplies and rising costs of native timbers alternative sheathings, particularly those using cement and concrete in some form, are being more widely used. The suitable indigenous timbers are not now so readily available and any prejudice against alternative materials must be submerged. This is all to the good, as most alternative materials available have a much greater degree of permanence. The recommendations of the “New Zealand Standard Code of Building By-laws” concerning timber sheathing are as follows: “Weatherboarding shall be either sawn to not less than gin. finished thickness or run from material not less than lin. thick, and in the latter case shall have a minimum thickness on any. reduced edge of fin., or two boards may be skew cut from l|in. thick timber and rebated so as to be in continuous contact with 1 the stud throughout. Boarding of smaller dimensions may be used provided that the outside face of the studs is first closely sheathed with boards of not less than fin. thickness.

"Horizontal joints in external boarding shall be either rebated to a depth of lin. or lapped not less than IJin. “If external boarding is placed vertically, the individual boards shall be placed not further apart than jin They shall be weather grooved within 2in. of each edge and the whole joint covered with a double-grooved 3in. by lin. batten or alternatively some other approved method of weathering to the satisfaction of the Engineer shall be adopted”. Early forms of weatherboard were rebated' on the opposite sides of each edge to give a close-fitting overlap. The rebate on the top edge was finished in a radius to ensure moisture run-off. This method, known as rusticating, can be seen on older buildings. The newer method is to bevel one side of the board only for approximately half its width. The corner of the opposite edge is also chamfered to help moisture run-off. This method is shown in the diagram on page 67. The reason for the chamfer on the outside edge of the concrete foundation illustrated in Fig. 4 of the first article in this series is also shown in the diagram. The first weatherboard is fixed with its bottom edge below the top of the concrete foundation. The damp course material may or may not be bent over to come under the weatherboard.

If the foundations have been carefully finished and the weatherboard is a snug fit to the foundation, this method of construction prevents water running off the walls, under the plate, and down the inside of the foundations. Any cement fillet provided as a sealer between the foundation and the bottom weatherboard is not satisfactory, as the cement shrinks away from the wood, leaving an opening through which the water can penetrate.

All weatherboarding should be primed all over with a good timber priming paint before erection.

Corner Finishing

There are two methods of finishing external corners with weatherboard construction: The boards at the corners may be left square and the corners finished with cover and “scribing” boards or the boards may be joined flush by mitring. Professional builders join by mitring quite satisfactorily, but this is not an easy job for the amateur. When cover and scribing boards are used the cover boards are placed first and a 2Jin. or 3in. by Jin. batten is scribed to the profile of the weatherboard and after being cut out is securely nailed to the edge of the cover board, thereby entirely enclosing the corner.

For finishing internal corners the boards on one side may be finished square and carried beyond the corner to the depth of the weatherboarding. The boards of the mating wall must be cut on an angle to be a close fit to the corresponding boards with which they mate. Alternatively internal corners may also be mitred. To ensure watertightness on internal corners exposed to driving rain it is a good plan to flash behind the corner with metal flashing carried down to below the lower edge of the bottom board. ■ . Weatherboarding should be carried up near enough to the top plate to be well inside any soffit provided under the eaves or,, in gable ends, to be a close fit under the roof overhang. Alternatively gable ends can be finished with a cover board under the roof overhang/and in a tiled roof it can be finished with a scribing board to the profile of the tiles. Asbestos Cement Materials Asbestos cement sheathing is available in two typesflat sheet and “sidings”. - Flat Sheet • ? j Until recently . flat sheet was available in relatively thin sections only . and possessed no structural strength. This necessitated construction of the framing so that no stresses were placed on the sheathing, any movement of the framing being countered by close spacing of studs, bracing, and adequate dwanging. With the availability of thicker sheets- and their ability to resist some stressing, close spacing of studs is no longer necessary and the thicker sheets

can be supported with much less dwanging, as they constitute “structural panels”; that is, each sheet has some inherent strength which can be considered as a contribution to the strength of the building as a whole. Because of its relative thinness flat sheet asbestos cement should not come into direct contact with the woodwork to which it is fastened, a layer of asphalt-saturated fabric being interposed. All joints must be made over a framing member, and horizontal joints must be sealed either with a horizontal cover mould of the same material or metal flashing. All joints should be covered with cover battens made from the same material; wooden battens are not satisfactory, because decay can start from the inside through the penetration of moisture. It is good practice to seal all joints with a suitable sealing compound before cover battens are placed. Asbestos cement sheet is very convenient for using as flat soffit under eaves and is available in strips specially cut for this purpose. Internal and external angle mouldings are also available for finishing and providing weather seal at corners. Flat sheet and all accessories can be fixed by nailing. Flat-head galvanised nails should be used and if nails are placed near the edges of sheets, it is preferable to drill the sheet to accommodate the nail. Battens or mouldings should always be drilled to accommodate the nails.

Sidings

Sidings are virtually asbestos cement shingles Ift. wide by 2ft. long. They are manufactured with a cedar-grained surface and have a wavy lower edge; they are a natural white as at present manufactured, but coloured sidings should shortly be available. As a sheathing they are pleasing in appearance and very adaptable for renovating over existing timber, sheathing being fixed either direct or with furring strips according to the type of weatherboarding. On new construction sidings are fixed to battens nailed to the studs, a layer of asphalt-saturated fabric being placed between the sidings and the battens. Where sidings are liable to damage near the ground a middle batten is placed between the supporting battens for the first few rows as a safeguard against breakages. There are two methods of fixing sidings each regulated by the width of the waterproof fabric underlay. If a narrow underlay is used, each layer overlaps not. only the lower layer of underlay, but also underlaps the row of sidings immediately below. If a wide underlay is used,, backing strips of the same waterproof fabric are placed under each joint. Either method constitutes a first-class sheathing. Cover mouldings, flashings, and all accessories are available to ensure that the finished sheathing will contain no moisture traps, which provide lodgment or entry of moisture to the timber framing. The illustrations on page 69 show a farm building before and after being sheathed with sidings. Cement Plaster or Stucco Cement plaster must be done by a skilled plasterer if it is to be effective. Because of shrinkage while curing improperly prepared or worked plaster is likely to develop hair cracks which form moisture traps. Plaster requires a backing which may be either rigid or non-rigid, depending on the method of construction. The backing must be attached to the studs with galvanised nails or clouts and must be either waterproof or covered with impregnated building paper. Rigid backing may be cement wallboard made for the purpose not less than f-in. thick, asbestos cement sheet, or close boarding with timber not less than -2-in. thick or more than Bin. wide. Non-rigid backing must be waterproof building paper or felt of approved type. Stucco with non-rigid backing must be reinforced with metal lath or galvanised wire mesh not greater, than 2in. mesh or less than 16 S.W.G. or with galvanised wire netting not

greater than fin. mesh or less than 19 S.W.G. Reinforcing should be stretched tight and fixed not less than jin. or more than fin. clear of the backing material by the use of special furring nails. Alternatively self-furring lath may be used. Joints in reinforcing should be lapped at least one mesh and should not be made at angles, where the reinforcing should be doubled for at least 121 n. each side of the angle. Diagonal reinforcing at least 12in. by 18in. should be fixed on all corners of openings. Nail spacings should be not more than 6in. along studs and dwangs, and joints should be lashed with 20 S.W.G. galvanised binding wire. All openings should be adequately flashed with metal flashing. Sand-cement ratio for plaster should not be less than 3: 1 by volume and a suitable waterproofing material should be added. The addition of a little lime, not more than 1/10 part by volume,

helps to produce a “fat” workable plaster.

The thickness of stucco, which must be applied in two coats or more, should, on non-rigid backing, be not less than lin. or more than Hin. On rigid backing these thicknesses can be reduced to fin. and lin. respectively. Brick or Concrete Veneer Wall veneer applied as sheathing to a framed structure consists of a brick or concrete wall, not less than 4in. thick if unreinforced or 3in. if reinforced, resting directly on the foundation. A space of at least l|in. must be provided between the timber frame and the veneer, the veneer walls being attached securely to the frame by non-corrodible ties, two to each square yard of wall. With veneer sheathing the walls should be braced at intervals of not more than 16ft. by adequately braced cross, partitions or alternatively the roof should be so braced as to provide strength equivalent to that given by such cross partitions.

Non-corrodible flashing should be built into the veneer where necessary to prevent moisture from penetrating and the veneer walls should not be more than 12ft. high above the top of the foundations. Standard Code Recommendations The Standard Code concerning wall sheathing recommends: — “All exterior walls shall be covered on the outside with approved weatherresisting materials. “Under all external timber wall coverings in buildings intended for human habitation building paper or other approved waterproof material shall be fixed to the outer faces of the external studs or to the sheathing. At horizontal joints the paper shall be lapped at least 2in. and at perpendicular joints at least 6in. and the waterproof material shall be lapped over

and under all flashings to the extent necessary to exclude moisture”. As the function of the roof and sheathing of a building is to provide adequate protection from all weather, the area covered by the building must be so enclosed and protected that no moisture can penetrate through or round the outside coverings. Joints must be provided with adequate lap or sealing, and window and door openings must be adequately flashed or otherwise protected so that the whole exterior sheathing effects a quick run-off for moisture without pockets or unprotected areas through which moisture can penetrate. A case was experienced by the author in which an outside door facing the prevailing wind, though in itself adequately sealed and protected from driving rain, permitted a large quantity of water to be driven through

the latch keyhole, the protection of which had been overlooked. A simple shield provided a solution to this problem. Though the roof and sheathing in themselves provide protection for the enclosed area the accessories, such as guttering and downpipes, also play an important part in ensuring quick runoff of moisture. With adequate guttering run-off from the roof is kept away from the wall sheathing, thereby saving it from an extreme condition of service which would virtually amount to total submersion. Sheathing, like any other material, if not subject to extreme conditions has a much longer life, and it is therefore in a building owner’s interest to ensure that adequate means of roof water channelling is provided and maintained. Joints in weatherboarding, which is subject to working due to temperature and humidity changes, are not very satisfactory, particularly at corners, if sealed with ordinary putty. Mitred corners may be sealed with sheet metal “soakers”, but butt joints are unsightly if sealed with a cover plate. As ordinary putty dries hard and cracks with the working of the timber, a nonhardening sealing agent is much more satisfactory. It remains elastic and fluid enough to allow for any working of the timber without cracking. Proprietary lines of this type of sealing agent are available from most hardware stores. Of the four ways of sheathing mentioned above, the first two can readily be used by the amateur, as no trades skill is required for sheathing either, in timber or asbestos cement products. Sidings can be easily fixed if instructions available from the suppliers are followed. The last two methods, plaster and veneer, require trade skill to apply satisfactorily and are beyond the scope of the amateur builder. Joinery in External Walls As joinery (windows and doors) used in building construction requires machinery for its manufacture, all joinery is best supplied to requirements by a joinery manufacturer. Joinery is essentially a factory product and arrives on the building site marked and ready for installation. Windows and doors are supplied complete with frames and (if hung) hinges; the frames are temporarily battened to keep them square and all glazing is usually complete. All that is required is the fixing of the frames in the openings left in the sheathing to accommodate them and, after flashing and weatherproofing have been completed, the fixing of the appropriate movable sections in accordance with the marking. The battens holding frames square should not be removed until it is certain that the fixing is sufficient to prevent distortion; additional fixing may be done after removal of the battens provided the frames are

packed between the supporting vertical and horizontal framing members so that distortion is prevented. The steps of external door frames and the sills of windows are usually left unchecked at the ends where they overlap the outside sheathing. This checking must be done on the site for each door or window, as the protrusion of the step or sill beyond the sheathing may be different in each case. This is particularly so with weatherboarding, where the checking must be angular to suit the . slope of the weatherboard. This checking presents no difficulty and can be done accurately by measurement. Door frames must be flashed above and window frames both above and below. The under side of sills and steps can be sealed with quarter-round beading. Outside cover boards, if they are part of the frames supplied, must be sealed to the contour of the sheathing with scribing boards, as described for corner finishing for timber sheathing. FLOORING Floors of farm buildings may be of earth, concrete, or wood. As an earth floor does not depend on foundations for its support, it can carry any superimposed weight within the load-carrying capacity of the soil. Its great disadvantage is dust and, unless it is sealed, it would be unsuitable for general buildings. Earth floors can be sealed satisfactorily with emulsified bitumen and so treated form very good floors for implement or general storage sheds. A concrete floor may be either cast on the ground and finished against the foundation wall of the building or form a monolithic structure with the building foundations and its own supporting columns and beams with reinforcing bonded throughout. For normal service a concrete floor of 4in. thickness or more cast on the ground does not require reinforcing and will carry any load per unit area within the load-carrying capacity for the same area of the soil beneath it, which must include both dead and live loads. If, however, it is subject to concentrated loading higher than the loadcarrying capacity of the soil, reinforcing will bring the load per unit area within safe limits. Where a concrete floor is built continuously with the foundation and its own supporting columns and beams special design is required, consideration having to be given to loading and the conditions of service. Wood is still the principal material used for supported floors and is used almost universally in farm buildings. Though the floor-boards carry the superimposed load, their strength or load carrying is not taken into account when the floor joists and floor supports are being considered. The floor sup-

ports and foundations must be adequately proportioned for the floor loading. For example, the floor of the fertiliser store illustrated in the second article in this series is supported on 6in. by 2in. joists resting on 6in. by 4in. sleeper plates which are supported on close-spaced, adequately proportioned piles. This floor is much stronger than would be required for say a dwelling, as it is proportioned to carry 60 tons of fertiliser, which would impose a distributed load of 5001 b. per square foot, whereas a distributed load of 601 b. per square foot is permissible in dwellings. The floor timber for both these loadings can be standard tongue and groove floor-boards of 3-in. thickness. When timber flooring is being laid it is advisable to start on one side of the building with a full width board, clamping the boards tight with floor clamps before they are nailed. If this is done for every room on the same side of the building, and clamping is carried out evenly, boards will mate satisfactorily where the flooring passes through doorways at right angles to the direction of the boarding. This condition applies only to the same mill run of flooring, as different runs may have slight variations in board widths; to avoid these variations all flooring for any building should be ordered at one time. In buildings with a central passage it is a good practice to start laying' the flooring from the centre and to work out to both sides, as clamping or timber discrepancies will not be multiplied to the same extent where the flooring passes through doorways. Nails should be punched as nailing proceeds, because some nails can be easily missed if punching is left until the whole floor is laid. Floor Coverings Basic flooring as described above will require covering suitable to specified uses of buildings. In a woodshed, where protection from the elements is the main requirement, an earth floor is quite satisfactory. In a garage, store, or implement shed, where dust and dirt must be avoided, the earth floor can be sealed or paved with either bitumen or concrete. If the building is a store in which floor dryness is essential, a concrete floor can be sealed either during laying with a sandwich waterproof membrane or after laying with a bituminous covering. Alternatively an above-ground timber floor can be used, sub-floor air circulation ensuring dryness. ; For dwellings or buildings where good insulation as well as dryness is

Farm Building Construction

necessary a concrete floor should be laid on hard rock fill in preference to soil. The air spaces contained in the hard fill provide insulation and if the floor is a concrete one, it can also be waterproofed. Floor coverings suited to particular conditions include cork materials, linoleum, bituminous materials, terrazzo, rubber materials, wood block or parquet, plastic materials, carpets, and ceramic tiles. With the exception of terrazzo and parquet these materials are available for laying in either small units such as tiles or mats or as a roll covering for laying in strips. Some are particularly suited to hard wear and subjec-

tion to moisture and others have better sound and heat insulating properties. For example, rubber or cork composition floorings are best suited to kitchen use, terrazzo to bathrooms or shower closets, wood block and parquet to halls, and carpet to living rooms. Some floor coverings are suitable for concrete floors only, others for wood floors, and some for both. All are available in a range of colours or combination of colours to suit any colour scheme. Where resilience and sound insulation are required some floor coverings need an underlay of some material that has these , properties to a greater degree than the covering itself; for example, linoleum laid on a concrete floor may deaden sound to some extent, but is just as hard on the feet as concrete itself unless it is pro-

vided with an underlay of some resilient material. Carpets if laid on a wooden floor without underfelt give no softness to the tread and quick!}’ wear out, whereas the inclusion of underfelt provides softness as well as much improved heat insulation. Choice of Flooring The same principle of relation of first costs to life and maintenance applies to choice of floor coverings as to roofing material. It may be unwise to choose either the basic floor or the floor covering that can be provided for least cost, as shortened economic life and increased maintenance may be more expensive over a period and may outweigh any saving in first cost.