Foundation insulation can sometimes be overlooked, but it does a lot. An uninsulated basement can account for up to 50% of a homes total heat loss! With that in mind, we figured we would go through how insulation and heat loss pertain to each of the foundation types, and what that means for you.
Full Basements
Basements can be insulated from the exterior or interior with equal efficacy.
- For interior insulation, there are a few forms: Framing with Batt, Wet-Spray Insulation, Rigid Foam, and Extruded Polystyrene or Polyisocyanurate. It is important for each of these to be properly covered, usually with drywall.
- Exterior insulation utilizes extruded/expanded polystyrene directly on the exterior of the basement walls. The main thing to keep in mind for this method is that any insulation exposed above-ground must be covered, protecting it from physical abuse and sun damage. Typically, these coverings are things like roll-metal stock, cementous board, or applied stucco-like finishes
When using exterior insulation foams, there are a few things to make sure during installation and maintenance. A continuous metal termite shield between the top of the foundation and the sill plate aids in preventing wood destroying insect infestations. If waterproofing, be sure to use waterproofing products that are compatible with the foam insulation.
Crawlspaces
In many ways, crawlspaces are essentially short basement walls. The insulation of these therefore is often similar to in basements. However, interior crawlspace insulation tends to use foam board or draped insulation, rather than foam. If foam is used, it extends from the top of the foundation to the top of the footing, and requires that the cavity formed by the rim joist be filled with fiberglass batts or a foam-in-place-product. Some jurisdictions require a crawlspace be ventilated in order to help control moisture. Vent requirements are drastically reduces if the floor of the crawlspace is covered with plastic sheeting, overlapped and taped to reduce moisture. You can also insulate the floor over the crawlspace, which raises the thermal envelope from the crawlspace walls to the insulated floor. This method has insulation benefits, but if you choose to use it, make sure to also freeze-proof piping and insulate heating and cooling ducts.
Slab-on-Grade
Heat loss in a slab-on-grade home is greatest at or near the exterior grade. Insulation is critical in reducing heating costs and avoiding uncomfortable cold floors. Similar to basement insulation, exterior foam insulation works well for these foundations. You want insulation to extend from top of the slab to the top of the footing. It is also common to have foam insulation inside the footing. With this approach, you will want to have a thermal break to prevent thermal wicking from the slab to the outside. A pressure-treated nailer or beveled slab edge can provide that thermal break, without losing floor-covering attachment.
Frequently Asked Questions
If a basement is unfinished, does the foundation still need insulation?
Yes, unless the floor above is insulated. Even if the basement is unfinished and used only for storage or heating and cooling equipment, it still is a part of your house as a thermal environment.
Does foundation insulation increase the risk of termite entry?
No, foundation insulation does not increase risk for termite entry at all. If exterior foam is used, there exists the potential for it to obscure termite infestation, or hamper treatment access, but it itself does not make said infestations more likely.
Does exterior insulation last as long as interior insulation?
Yes! If properly installed, the longevity of foundation insulation is about as long as any other insulation installed in the building.
Will foundation insulation increase my risk for radon problems?
The opposite! Radon enters homes through cracks or other openings below grade. As foundation insulation minimizes thermal stresses and cracking, it reduces your chances of radon entry.
Taking time to plan the best insulation for your home can save energy, and increase comfort. We hope this has been a useful resource for your foundation insulation questions!
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