Crawl space insulation vs encapsulation
Hoping for some ideas for lowering energy bills and warming the floors of my 1970 ranch house. Northern California, marine zone 3.
The vented crawl space (1700 sq ft) has never been insulated. Pier and beam foundation with a perimeter footing/stem wall. 4×6 floor joists on 48” centers, 1-1/8 ply decking. We’re on a steep hill and the uphill side has historically gotten damp in the winter but never any standing water and should be even dryer now with a recently installed exterior french drain.
I almost pulled the trigger on a full spray foam of the floor, leaving the vents open. Now I’m reading about encapsulation which is more attractive on paper due to less foam, removing the vents for fire danger as well leaving the floor more serviceable/maintainable. But I can’t find any guidelines for my climate zone and foundation/floor construction. I don’t think encapsulation is as common here as in other parts of the country. How much perimeter insulation? Do piers every 6’ make this too labor expensive? Do I need ventilation? Dehumidifier?
Any guidance/experience appreciated, and sorry if this has been asked/answered before.
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Replies
Timfred,
GBA hs dozens of articles on un-vented crawlspaces you can access through the search function.
Here is one you may want to start with: https://www.greenbuildingadvisor.com/article/building-an-unvented-crawl-space
I can't speak to the details for your needs, but I just had mine done, very similar constructed house (including the wet hill on one side). It's absolutely glorious. I had fiberglass batts under the floor that were better for housing the mouse population than keeping my house warm. Now it's clean, shiny, and temperate down there. I just want to hang out in the crawl for fun!
I do just about everything myself, but splurged for the pros on this one. They laid down a thinly insulated (R2ish), heavy plastic sheet on the floor. I don't have as many piers as you, but they just barely jacked up each one and slid the sheeting right under. Walls have 2" foam board, spray foam sealing.
Best money I've ever spent.
If you seal the vents I think it is important to add enough supply and or return registers to fully condition the air in the crawlspace to more or less the same temp and humidity as the rest of your home to avoid mold and rot.
If you can’t being yourself to call it a conditioned crawlspace don’t seal the vents.
Given the wet history of your crawlspace, your mild climate and the fact that venting had worked well for the last 50 years. I think insulating the floor would be a good option. I hate spray foam but it may well be the best option given the number of piers pipes and wires coming in and out of your floor.
Walta