Subfloor boards should be face-nailed solidly at every bearing with two 10-penny nails. All butt joints must rest on bearings. Where it is necessary to use subfloor boards wider than 6 inches, extra nailing must be employed at every bearing. Thus, for 1 by 8 inch boards, use three 10-penny nails at all bearings, and for 1 by 10 inch boards four nails.

In buildings where hardwood strip flooring is to be installed over a concrete floor, as for example in a schoolhouse, it is recommended that wooden sleepers be securely "tied" to the concrete, preferably by means of steel clips placed when the mortar is poured. The sleepers should be spaced not more than 16 inches for most uses, on which the usual diagonal wood subfloor will be nailed. The hardwood flooring is then laid in the usual manner.

Kraft building paper, waterproofed with asphalt, should always be laid between the wood subfloor and the hardwood top floor as a protection against moisture absorption by the top floor. It also prevents seepage of minute dust particles through the floor seams, a desirable feature for rooms directly over the basement. For rooms directly over heating plants, use double-weight building paper (30pound asphalt felt) or standard insulating materials of a noncombustible type may be applied on under side of floor joists. (Local building code should be consulted.) This will provide insulation against excessive heat that otherwise might cause the floor to open up from excessive shrinkage. Insulation material can be applied on the

Exception: Building paper between subfloor and top floor is not recommended for basements or other "below grade" installations; instead, place building paper directly over concrete, underneath the sleepers.

basement ceiling or set in between the floor joists, in either new or old buildings.

Where basements are not provided, adequate provision must be made for the free movement of cross currents of air beneath the buildings. This may be provided by vents and other openings in the foundation walls. These openings should be at least 12 percent of the first floor area, or more if possible.

In the few instances where hardwood floors may be laid on sleepers over concrete without subfloors (such as in recreation rooms) it is recommended that a suitable building paper as described above be laid directly over the concrete, under the sleepers.

The top flooring should not be laid until plastering and cement work are thoroughly dry and woodwork and trim are installed. In fact, the laying and finishing of the hardwood floors should be the last operation in connection with the construction of the building. As a final precaution, it is strongly recommended that whether it be summer or winter the heat should be on at least 10 days before flooring is laid.

After the trim is in place, the first course of strips is lined up flush with the face of the baseboard. (Baseboard must not extend below the surface of the top floor.) The first course is surface-nailed directly through that portion to be covered with quarter round or base shoe. Under no circumstances should flooring be laid tight against studding or walls. An expansion space of not less than one-half inch must be left on all sides next to the wall. This will be covered by the base-shoe quarter round, door threshold or saddle.

Do not try to hammer each individual strip of flooring into position as soon as it is nailed, but after laying three or four pieces of the flooring, place a short piece of straight edge hardwood against the tongue of the outside strip and drive up snugly, but not excessively tight.

The type of nail recommended for 1316-inch or 25%2-inch tongued and grooved hardwood flooring is the flat-cut steel nail which is manufactured primarily for this purpose. However, in instances where cut nails are not available a spiral nail is next best, while a third alternative would be the wire finishing nail of the nonsplitting type (without a sharp point).

Nails should be driven through the tongue at an angle of about 45° to 55°, with nails usually spaced so as to hit the floor joist or sleeper whenever possible.

The first nail driven should be nearest to the end of the next piece which is already laid and should be "toenailed" toward the preceding piece so as to make a tight joint. It is always desirable to "break" joints in laying so that no two are very close together. A heavy hammer is favored by floor layers and each nail should be "set" with a nail-set. The following nail sizes are recommended by hardwood flooring manufacturers:

For 3-inch flooring.-4-penny cut steel flooring nails, driven 8 or 10 inches apart. (If these cannot be obtained, 3-penny finishing nails may be substituted.) For 2-inch flooring use 6-penny nails.

For 2532-inch flooring.-Use 6- to 8-penny cut steel flooring nails, or spiral nails, driven not more than 16 inches apart, preferably spaced about 10 inches. For 332-inch flooring.-Use 6- to 8-penny cut steel flooring nails, or spiral nails, driven not more than 16 inches apart, preferably about 10 or 12 inches.

Figure 13.-Foot warmth is essential to the health of school children. Hardwood floors afford excellent insulation against heat or cold. the attractive parquetry designs of this block floor.

Notice

STRIP FLOORING (SQUARE-EDGED)

The same general instructions should be followed as for tongued and grooved strip flooring. However, square-edged flooring_must obviously be surface nailed. The barbed-wire flooring brad No. 16 is recommended for 1316-inch or 516-inch flooring, with two nails every 7 inches, preferably staggered.

Flooring strips should be laid the longest way of the room when possible, and strips should run continuously through doorways into adjoining room, thus eliminating thresholds and giving the advantage and better appearance of a flush floor throughout.

PLANK FLOORS

Plank floors are installed by nailing over wood subfloors of the type used for strip flooring. In addition to being blind-nailed each plank should be face-nailed about every 30 inches and fastened to the subfloor with screws through the face at the ends. The screw heads are countersunk and concealed by glued wooden plugs. The same type of nails and sizes of nails should be used as suggested for strip flooring.

PATTERNED FLOORS

Either the individual parquetry pieces or the prefabricated assembled parquetry blocks are easily nailed over wood subfloors or old wood floors. Detailed nailing instructions are available from the Maple or Oak Flooring Associations or the individual manufacturer. Patterned floors are often laid directly over concrete-in which case a suitable flooring mastic is used. Parquetry floor manufacturers recommend the following procedure:

Diligence should be exercised in inspecting the concrete to make sure there are no loose, moist, or wet spots, uneven places or protuberances, which might cause imperfect bedding of flooring. No finish flooring should be laid until such conditions have been rectified. When floors are to be laid on "ground or below-grade concrete slabs" or over unventilated places where there is danger of dampness, apply, over the concrete subfloor, a two-ply membrane waterproofing of coaltar pitch and tarred felt. If asphalt or asphalt felt is used for membrane, concrete shall first be primed with asphalt primer to assure bond. Application, however, should be the same as with pitch and felt.

Old or dusty concrete surfaces should be carefully brushed with a hair brush and a coat of asphalt primer applied evenly and well brushed in to assure bond. This should be allowed to dry thoroughly before mastic is applied. The usual application of mastic is with a notched spreader to a minimum average thickness of three thirtyseconds of an inch. Choice of brand and type of mastics (hot or cold) is best left to your architect, dealer, or more usually the manufacturer of the blocks, whose instructions for application should be closely followed.

In the laying of hardwood parquetry floors it is important to allow ample expansion joints along walls, around columns, etc.

The planks should not be driven tightly together. Some manufacturers recommend leaving a slight crack the thickness of a putty knife.

METHOD OF ESTIMATING QUANTITY OF STRIP FLOORING NEEDED*

To ascertain the number of board feet of strip flooring required to cover a given area, find the number of square feet of floor space to be covered and add thereto the following percentages:

The above figures are based on laying flooring straight across the room. Where there are bay windows or other projections, allowance should be made for additional flooring. It is always well to order 5 percent additional flooring to take care of floor layer's cutting and possible handling damage.

Thick flooring is made (and so measured) from 14-inch, 12-inch, and 2-inch lumber. Therefore, for flooring thicker than 1316 inch or 2532 inch, first determine the number of board feet of 25/32 inch thickness required under the above method and then add: 25 percent for 3332 inch thickness; 50 percent for 42 inch thickness; 100 percent for 532 inch thickness. For necessary waste in cutting and fitting, add 3 to 5 percent.

It will be found more advantageous to specify and use the standard run of lengths in the different grades instead of special long lengths, because lengths selected, for example, 4 feet or 6 feet and longer are much more expensive without compensating benefits.

PRECAUTIONS IN HANDLING HARDWOOD FLOORING

Following is a series of precautions or "don'ts" which should be carefully followed in order that full satisfaction may be realized in the finished hardwood floor.

The care in manufacture, kiln drying, and handling by the flooring manufacturer may be of relatively little consequence if carelessness exists on the part of retailer and contractor. The most perfectly manufactured flooring may easily become ruined.

For retail building-material dealers:

Don't unload in rain, fog or even excessively humid conditions. Don't store flooring in leaking enclosures.

The first

Don't pile on storage floors that are less than 18 inches from the ground and that have not good air circulation underneath. rule of preserving a good flooring pile is to keep its feet dry. Don't use storage space near the end of the building, even though storage bins are protected by doors. Doors are frequently left opento the detriment of flooring in rainy weather.

9 Patterned flooring is sold on actual face measure, and no allowances are necessary except for usual waste in laying.