Engineering and Construction

Foundations for light framing, originally made of stone or brick, are  now made in most cases of sitecast  concrete or concrete block masonry  (Figures 5.5-5.11). These materials  are highly conductive of heat and  usually must be insulated to meet  code requirements for energy con- servation (Figures 5.8, 5.9, 5.12, and  5.13). Where concrete and masonry  construction methods are not practical, such as in extremely cold regions, foundations may be constructed entirely of preservative-treated wood  (Figures 5.14 and 5.15). Such  permanent wood foundations can be con- structed in any weather by the same crew of carpenters that will frame the building; they are readily insulated in the same manner as the frame  of the house they support; and they easily accommodate the installation of electrical wiring, plumbing, and interior finish materials.

Figure 5.5 Step One in the construction of a simple platform frame building: establishing the position, shape, and size of the building on the site. After the corners of the foundation have been staked, batter boards are erected safely beyond the limits of the excavation area. String lines crossing over the corner stakes are stretched from the batter boards, and their positions on the boards are preserved with notches or nails in the boards. Later, after excavation, the strings are stretched again, and the foundation corners can be relocated at the bottom of the excavation. This drawing begins a series of isometric drawings that will follow the erection of a wood light frame building step by step throughout the course of this chapter.

Figure 5.6 Typical details for a sitecast concrete foundation and basement for a platform frame building. Details A, B, and C are keyed to the circled portions of the drawing in Figure 5.7.

Figure 5.7 Step Two in the construction of a typical platform frame building: excavation and foundations. The letters A, B, and C indicate portions of the foundation that are detailed in Figure 5.6.

Figure 5.8 Most building codes require thermal insulation of the foundation. These are three different ways of adding insulation to a  cast-in-place concrete or concrete masonry basement and one way of insulating a crawlspace foundation. The crawlspace may  alternatively be insulated on the outside with panels of plastic foam. The interior batt insulation shown in B is commonly used but  raises questions about how to avoid possible problems arising from moisture accumulating between the insulation and the wall.

Figure 5.9 Some typical concrete slab-on-grade details with thermal insulation. In areas where termites are common, there must be a metal fl ashing (termite shield) similar to that shown in Figure 5.18 C or other interruption that passes through the foam insulation above ground level to prevent termites from tunneling undetected through the insulation to reach the wood structure. This applies to the foam-insulated basement details in Figure 5.8 as well.

Insulating  concrete formwork (ICF) foundation  systems using permanent insulating  forms are easy to construct, eliminate the need for formwork removal, and provide integral insulation  (Figure 14.12).  Proprietary  precast  concrete foundation systems relying on factory-fabricated reinforced  concrete panels are rapidly erected  on site and can be used to construct  basement structures of consistent  strength and quality. They may be  manufactured with insulation integral to the precast panel or designed  to readily accept insulation added in  the field.

All basements also need to be carefully dampproofed and drained  to avoid flooding with groundwater
and to prevent the buildup of water pressure in the surrounding soil  that could cause the walls to cave in  (Figures 5.6, 5.7, and 5.11).

Figure 5.10 Erecting formwork for a sitecast concrete foundation wall. The footing has already been cast and its formwork removed. It is visible in front of the worker at the left.

Figure 5.11 Masons construct a foundation of concrete masonry. The fi rst coat of parging, which is portland cement plaster applied to help dampproof the foundation, has already been applied to the outside of the wall, and the drainage layer of crushed stone has been backfi lled in place. The projecting pilaster in the center of the wall will support a beam under the center of the main fl oor. After a second coat of parging, the outside of the foundation will be coated with an asphaltic dampproofi ng compound. (Reprinted with permission of the Portland Cement Association from Design and Control of Concrete Mixtures, 12th edition; Photos: Portland Cement Association, Skokie, IL)

Figure 5.12 A concrete masonry foundation with polystyrene foam insulation applied to its outer surface.

Figure 5.13 Following completion of the exterior siding, a worker staples a glass fi  ber reinforcing mesh to the foam insulation on the exposed portions of the basement wall. Next, he will trowel onto the mesh two thin coats of a cementitious, stucco- like material that will form a durable fi nish coating over the foam.

Figure 5.14 Erecting a permanent wood foundation. One worker applies a bead of sealant to the edge of a panel of preservative- treated wood components as another prepares to push the next panel into position against the sealant. The panels rest on a horizontal preservative-treated plank, which, in turn, rests on a drainage layer of crushed stone. Wood founda- tions can be constructed in any weather and can be insulated in the same way as the superstructure of the building.

Figure 5.15 The difference in color makes it clear where the preservative-treated wood foundation leaves off and the untreated superstructure of the building begins.