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lovallo t1_j5wb8m4 wrote

Knowing if you are in a heating or cooling dominated climate is helpful here.

You want your thermal barrier and air barrier at the same boundary.

If you insulate the floor the space below will certainly get colder. Would the pipes be in the spray foam? that might be safe enough in terms of freezing. Do you have a sense for how cold it gets down there currently in the winter?

If you insulate the crawl space walls then you will want to seal up the vents to the crawl space.
Moisture is a concern, dehumidification can get expensive. An exhaust fan on a humidistat might accomplish what you need at a lower operating expense.

Since you have pipes and ducts down there I would seal the crawlspace and put in mechanical ventilation and or other moisture control.

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ThinkSharp OP t1_j5wckvw wrote

Thank you. I think I’m ASHRE zone 4. Central WV (not the mountains). Winters are not typically severe but can be single digits a few times and we recently had negatives (dry bulb) during this bomb cyclone.

So you recommend if I insulate, do it at the walls mainly because of the moisture issue?

I realize I didn’t answer your whole question. Typical temps in the crawl space during winter are probably 55-60. Long t shirt feels perfect, short sleeve if working. Humidity is typically high. We had to install a vapor barrier and sump pumps. It gets foundation run in from one side. Correcting the swale outside is on my list for things this summer but part of the issue is a cement slab that needs raised. May not be able to handle that. In other words I expect it to always have some water coming in when rainy/snowy. I plan to NOT cover over the boards in that area to let them keep breathing and I intend to place a dehumidifier in that area of highest humidity/source.

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Traveling_Carpenter t1_j5wngkr wrote

You have a couple prescriptive options available in the model code if you go the path of insulating the walls, which is a good choice. Look at R408.3 in the International Residential Code - it spells it out pretty clearly. For a more plain-language perspective explanation, I’d check out the Fine Homebuilding article “crawlspaces that work.” Code available here: https://codes.iccsafe.org/content/IRC2021P1/chapter-4-foundations

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ThinkSharp OP t1_j5yc4jq wrote

Thank you, I’ll read each. That’s helpful because I don’t know where this stuff is already studied and prescribed so this is super helpful. No sense recreating the wheel

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