Owner Builder: Crawlspace Foundation

We have discussed the concrete slab-on-grade foundation and monolithic slabs. The crawlspace foundation is another popular foundation option. The crawlspace foundation is similar to a slab foundation in that concrete footing provide the basis for the foundation.


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Crawlspace Foundation Video



Footings

Just as with a standard slab on grade, the owner builder will need to excavate and pour footings. These footings will carry the weight of the entire house. Footing depth, width and required reinforcement will vary based on the size of the home and soil conditions.

Stem Walls

Stem walls can be poured in place or of reinforced block. Reinforced block is typically used when the foundation is hillside. Hillside foundations sometimes require a stepped foundation. Using block allows for easier stepping of the foundation stem walls.

Termite Treatment

Be certain to schedule in a termite treatment for your foundation, whether it is a crawlspace, slab or basement. Even if it is not a requirement in your municipality, it is important for resale value to be able to say it has been treated.

Piers

Concrete or block piers are set inside of the crawlspace area. Their purpose is to support beams or girders, which, in turn, support the floor joists. Part of each pier is the interior pier footing. Again, the size of pier footings will vary based on the load supported. Blueprint specifications should indicate what is the necessary footing size.

Beams and Girders

Crawlspace foundations that have a wide span will require beams or girders to support the floor joists. A home built with a small foot print may not use piers and beams because floor joists can span from stem wall to stem wall. The larger the footprint of the home, the more likely it is that beams run across piers will be incorporated into the flooring system.

Floor Joists

Floor joists are set on the crawlspace foundation stem wall. If double spans are required, they will also rest on beams, girders or piers. The framing contractor will come in to begin the flooring system after the stem wall is complete. Normally that will include building a short pony wall to raise the flooring. This is always the case if the stem walls are stepped. It is then necessary to frame up the wall to a level elevation to set floor joists.

Running Plumbing and HVAC

After framing is complete, the Plumbing and HVAC Contractors will move into the crawlspace foundation and run their pipes and ductwork underneath the floor. It is important that any cutting of floor joists are approved. Just like roof trusses, floor joists are engineered to perform based on their original specifications. It is a good idea and often a requirement to insulate indivual water lines. Remember, unless sealed, the crawlspace is the exterior of the house and so is subject to winter freezing.

You can insulate the stemwalls of the crawlspace foundation by using insulated concrete forms (ICF's)and by blowing in or using fiberglass batts in the pony wall. Because the crawlspace is vented, you still have exterior cold and hot air moving freely into the space, but insulation can regulate crawlspace temperature to a degree.

Insulating Crawlspace for House

Because the crawlspace is the exterior of the house, all floor joists should be insulated. Discuss with your insulation contractor what your options are. The simplest and most commom form of insulation used in flooring joists is fiberglass batt insulation. There are a couple of reasons for this. First, it is difficult to blow in insulation in the flooring area. Second, because there are so many water lines and mechanical run through the floor joists that any maintenance would be an absolute nightmare if loose cellulose were used. It is critical to hold your insulation contractor to a high standard when installing batts in the crawlspace.

Venting and Access

Venting is required in any standard crawlspace foundation. This is especially true because there is plumbing, gas and HVAC run in the crawlspace. Venting helps prevent moisture which can lead to mold growth and the deterioration of wood. There are calculations for how many square feet of venting is required per cubic foot of vented area. It is important that the owner builder has that information for the framer so they can install the proper number of vents.

Access to the crawlspace is necessary to allow maintenance. If that access is from the house, it must be insulated.

The crawlspace foundation is completed by the framing contractor when they build the flooring system.

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