A crawlspace can be insulated two ways. The walls of the crawlspace can be insulated on the inside or the outside of the home, creating a conditioned space; or the floor above the crawlspace can be insulated, creating an unconditioned space.
As a general rule, you should treat a crawlspace like a short basement and so insulating the crawlspace walls is recommended for the following reasons:
- Heating ducts and water pipes in the crawlspace will not have to be insulated and will not freeze. Any heat loss from the ducts will not be wasted.
- Reduces the likelihood of moisture/condensation forming on the underside of the floor joists
- It is usually easier to do a thorough insulating job on the walls. Especially when the crawlspace is shallow or the joist spaces are uneven or oddly shaped, it can be challenging to get into the space to insulate the floor above the crawlspace.
A crawlspace with insulated walls needs to be closed (i.e. any vents opened to outside need to be closed and insulated) since it would be treated as a conditioned space. Add a moisture barrier to the crawlspace floor if there is not already one present. This is to prevent moisture from entering the crawlspace from the ground and moving through your home.
Before starting any work in the crawlspace, ensure that any damage and issues (e.g. cracks in the foundation wall, water leaks from pipes or infiltration from outside, etc.) are addressed first.
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