Precast Concrete Foundation Walls
DEAR TIM: A builder in my town has suggested that I use precast concrete foundation walls for my new home. I am a little skeptical of this new process. He says the walls do not require concrete footers. They use compacted crushed stone. Do you feel the precast walls are a good choice? Are there any other benefits? Are they code approved? Maria B., Paris KY
DEAR MARIA: If the precast concrete foundation walls this builder is promoting are like the ones I have seen, they may be ideal for your new home. Precast concrete technology has been around for years in the commercial construction industry and only recently has it started to supplant traditional residential foundation construction methods. There are huge advantages in building with precast foundation components.
I have a traditional poured concrete foundation in my own home, but I also was fortunate and had the absolute best foundation company in my town install it. You might not be so lucky. Here are a few things that can go wrong with traditional block or poured concrete foundation system. A block foundation hod carrier may mix the mortar too weak. An inexperienced block layer may add water to stiff mortar and weaken it. The block foundation may not have any inexpensive reinforcing steel in it.
Poured foundation walls can have cold seams where one batch of concrete gets hard while the next concrete truck is mired in mud in the middle of the job site. The top of a poured in place foundation wall can be out of level. If the forms are not checked and braced before the pour, the foundation can be out of plumb and out of square. Many poured concrete walls have no vertical steel in them. Excessively cold or hot weather can harm concrete or block walls as they are built in the field. Rainfall can stop the traditional foundation construction process in its tracks.
The precast foundation systems solve all of these problems and more. The fact that they do not require a concrete footer does not surprise me. Virtually every roadway around the word uses crushed stone as a base. Railroad tracks are laid on crushed rock as well. Both of these support far more concentrated loads than the foundation of your home. If the soil beneath the foundation is weak, the builder can increase the depth and width of the crushed stone. Frank Lloyd Wright used this method to support foundations on some of his works of art.
The precast systems appeal to me for many reasons. They are poured in controlled conditions in a factory. They use 5,000 pound per square inch (PSI) strength concrete. Most traditional poured walls use 3,500 PSI concrete. The precast walls are cured in the factory so they are guaranteed to achieve the intended design strength. The precast concrete walls are poured square. Once assembled your foundation will be plumb, level and square. The precast systems have 1 inch foam insulation built into the walls. This minimizes cold conduction problems in northern climates. Treated lumber nailers are incorporated in the walls as well. There is no need to build an additional wood interior wall if you desire to finish your basement.
Perhaps the best feature of a precast system is that it can be erected in most cases in less than a day. Once the crushed gravel base is in place, a crane and experienced crew sets the panels like a giant erector set. The wall panels come in heights from 4 feet to 10 feet. Any shape or size foundation can be built. You can have window or door openings included as well. The panels are bolted together and waterproofed with special high performance urethane caulks. If you follow the manufacturers' backfill recommendations, you will not have a drop of water enter these foundation walls.
The precast concrete foundations should sail through your building department approval process. The precast system is recognized and accepted by many of the national model building codes. If your building inspector has a problem or has not worked with them before, the manufacturer will assist you in educating the building department in your town.
Photo Credit: Superior Walls