Five Essentials for Good Foundation Walls
The foundation walls of your home comprise a critical component of the structural support system, which carries loads from the floors and walls above to the footings below. Foundations are overwhelmingly made from concrete, but can also be constructed with masonry, specially treated wood, and other materials. In addition to transferring weight, a properly engineered foundation also serves to keep moisture away from the home.
Before beginning construction of the foundation walls, rough grading on the site should already be complete. Any excavation (if required) should also be complete. Lastly, footings (if not simply pouring a slab on grade) should have been previously poured and sealed. With that set in order, here are the five essentials for constructing good foundation walls.
1) Account for Site Conditions
Have your soil tested to understand the properties and soil conditions on your site. Foundations for sites with highly compacted soil are engineered differently than those with better drainage. Be familiar with the depth as well as the ebb and flow of the underlying water tables. Don’t forget to consider the importance of the backfill materials if your foundation requires excavation. Pay attention to the climate, which impacts the design of your foundation system. Areas where freezing is not a concern have different requirements than those where the depth of the frost line is an important factor in construction.
2) Select the Right Style
Many foundation types are determined by the site conditions, but can also reflect regional preferences as well. Three varieties of foundations are commonly used: full basements (more common in the north), crawl spaces (seen in transitionary areas or central regions), and slabs on grade (more typical in warm weather climates or areas with high water tables).
Each option should be weighed against the prevailing trends in the area which impact resell value—if yours is the only home in the neighborhood that doesn’t have a basement your home’s value will be discounted. The economics of your project are also important. The cheapest and quickest foundation style is a slab on grade. On the other hand, the cheapest per square foot living space is the basement area below grade. Safety factors such as durability in extreme storms like tornadoes and hurricanes may influence your decision as well. Maintenance considerations also come into play as repairs to infrastructure like plumbing under a slab are much more expensive than with a crawl space.
Nontraditional foundations include pier foundations, which use strategically located points to focus the load of the home over a few specific areas. Beams are used to transfer the load to the highly concentrated piers. This type of foundation is used in wetlands, coastal areas, on steep grades, or other complex building sites.
3) Plan for Moisture Control
Keeping subsurface water away from the homes foundation walls will help prolong the life of the home; prevent settling; mitigate flooding; and control mold, mildew, and dampness. The first line of defense is proper grading—with installation of a subsurface drainage system if called for based on your site’s conditions. Once the foundation walls are poured and cured, applying a waterproofing sealant (looks like tar) to all surfaces below grade helps keep water from coming through the walls. The third component to moisture control is accomplished with the backfill materials. Use a porous backfill to allow for drainage away from the building. As an added benefit, a good backfill also provides additional stability to the home’s foundation.
4) Know the Pitfalls
Understand the cracks. Small vertical cracks are seldom problematic unless the width is not consistent from top to bottom as this could indicate uneven settling of the underlying footings. A horizontal crack is bad news and is indicative of complete failure of the foundation wall’s structural integrity.
Look for honeycombing. Concrete is made of cement (the powder-like substance), aggregate (i.e. gravel), and water. These are mixed together creating a mud which cures as it dries into a strong cohesive concrete surface. When the mud is poured into the forms for the foundation wall, vibration is often induced to form a slurry along the edges. This creates a smooth surface when cured, but also ensures the aggregate is well-binded with the cement. A sign that this has not taken place is the honeycombing appearance when you can see the aggregate in the finished concrete surface. The biggest problem with this is the potential to break down more quickly than a smooth, uniform surface. It could also mean the structural properties of the aggregate are being utilized within the finished concrete in a suboptimal manner.
The foundation walls should be square, plumb, and level. Any deviation from exactness creates difficulties for the framers and most other subcontractors to follow. Don’t settle for shoddy workmanship on the foundation. The quality of the rest of your house literally rests upon it.
5) Follow these Tips
º Consider insulating under the slab – reduces condensation and makes the basement not feel or smell like a basement
º Ensure proper base materials are used as specified and that they are compacted properly prior to pouring the footings for the foundation walls and any slabs (slab on grade or basement slab).
º To save costs use a more square foundation type instead of following every jog in the home’s footprint; use cantilevered construction techniques above grade for jogs like bay windows
º Pour the foundation in one continuous pour to bind the entire structure together
º Allow the concrete to cure properly
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