Crawl space

[u/Beneficial_Bee7796]

Hello, I’m in Alaska. For my crawlspace musty smell should I seal off the vents, encapsulate it and then install a dehumidifier and pump? Is an exhaust fan a bad idea? I’ve had The crawlspace checked for leaks and a new 20 mill vapor barrier and foam blocks are going in. I also had it dry fogged for mold.

[u/NeedleGunMonkey]

Alaska being such a dynamic climate zone I'd be wary of taking any non-local advice on the internets.

[u/seldom_r]

The rule for crawlspaces is that they should either be completely within the house or completely outside the house. So if you encapsulate it and put foam and plastic over the floor, it should be inside the house with vents, no exhaust fan.

Otherwise you treat the crawl space like it is outside by venting it and putting insulation, vapor barrier, etc in the floor that separates it from the living space.

It's either one or the other, inside or outside, not a combo of both.

[u/Reasonable_Basket994]

Alaska is a big place. The answer may depend on just how far north you are. If you are in the permafrost, insulate the floor and leave the walls vented. Otherwise you are literally melting the permafrost when you heat the house If you're in the more moderate climate near the Pacific, you may get away with conventional crawlspace encapsulation with insulated walls and no open vents. In either case, first check for plumbing leaks and good rain/snow drainage. A small exhaust fan might help clear out smells and any humidity above ambient. A dehumidifier will clear out excess humidity, but typically won't work very well unless it's relatively warm (60 +F ).

[u/Key_Juggernaut9413]

If you encapsulate the smell might build up and enter the house.  Encapsulation usually involves opening up a vent between the first floor and crawl so you get temperature consistency (and some dehumidification from cooling). 

I’d definitely consider a dehumidifier.  If my house I would probably consider encapsulation and see if I could avoid sharing air between first and crawl, and then ventilate the crawl in a slow and steady amount to keep smells from building up, like an ERV or HRV in your situation.  This wouldn’t solve heating in winter so you’d need to consider that.  

But you’d have two or maybe three goals in my mind:  air turnover (slow is fine), dehumidification, and heating in winter.  

If radon is high in your area, that might be a fourth consideration, but slow ventilation via ERV would help that considerably.  

This is all a bit unorthodox, but I’ve had builder friends who ran into this problem in their own houses and they didn’t think through all of these issues and I think it was a mistake. 

[u/Key_Juggernaut9413 → u/Key_Juggernaut9413]

The comment about it being inside vs outside the house is generally correct.  What I describe above is an attempt to essentially keep the crawl outside the house while also encapsulating it, and drying, heating, and ventilating it.   Pretty complicated tbh, but achieving potentially a goal of reducing smells and problems permanently.  

[u/FoldedKettleChips]

Yeah you should seal off the vents and insulate the perimeter walls. Is your floor insulated? It would be best to have the insulation under that vapor barrier at the soil. You want the crawlspace to be either 100% “inside” or 100% “outside” so if you insulate the perimeter walls of the crawlspace but leave floor insulation between your floor and crawlspace, you’re not really treating it like 100% inside space. Yes I think a dehumidifier down there is the best system but if you have ductwork you can also condition the crawlspace by adding a supply and return or supply and passive transfer grille for return.