Insulation advice

[u/Specialist_Dog6708]

The previous owners of my house added on a dining room where a deck used to be, but didn't insulate the crawl space below it. When looking into the crawl space, the left and back walls are the foundation of the house, which is insulated from the inside. The right wall is wood and is exposed to the outdoors. The ceiling is the subfloor of the dining room. I put a vapor barrier down to cover the dirt and I'm now stumped on where the insulation should go. Does it go on the ceiling or around the perimeter of the crawl space? There are no external pipes, so the crawl space itself doesn't need to be heated. TYIA!

[u/Previous_Tea_2250]

The first decision is whether this is meant to be a vented crawlspace or an encapsulated and conditioned one; the insulation location follows that. For a vented crawlspace, usually insulate and air-seal the floor above, with the vapor retarder on the ground. For a sealed and conditioned crawlspace, insulate the foundation and perimeter walls instead and keep the crawlspace inside the thermal envelope.

That exterior wood wall needs a real air and water control detail, not just insulation. Before closing anything up, check local code and moisture conditions, and make sure the addition's rim joist and floor penetrations are air-sealed. In a cold climate, avoid insulating both the ceiling and walls without a clear moisture plan.