Crawl space insulation recommendation in Northern California
I plan to have the crawl space vented due to the additional cost to seal the crawl space. Home is at
Northern California – 5 months of heating season – wet cold weather, no snow, rarely go below freezing, low typically in 50s. Dry summer and I don’t plan to have AC. There will be plumbing pipes and electrical wires in the crawlspace. Most new homes use fiberglass in the floor joist cavity in my area.
I read through the existing threads and most relevant information I found is from Robert’s suggestion: “use 2″ foil-faced polyisocyanurate insulation board (Thermax, High-R, etc) under the floor joists, well sealed at all joints and edges. The foil is a perfect vapor barrier, an excellent barrier to radiant flow between the floor and the ground below, and high-R insulation.”
Questions:
1) Does the same solution apply to my weather with plumbing and electrical wires in the crawl space? I want material that has least negative impact to IAQ.
– If I want to add additional insulation in the floor joist cavity, what materials do you recommend? Martin recommended against cellulose in crawl space.
– If the moisture (plumbing leak) gets into the floor joist cavity, Will it dry upward into living space?
– Is http://products.construction.com/swts_content_files/2414/290659.pdf the right product? The web site mentions wall and ceiling, not floor.
– Just want to be sure – I assume the 2″ insulation board is glued/nailed to the floor joists and with large air gap between the insulation board and ground dirt, right?
2) Where does the plumbing and electrical wire go?
– between the insulation board and ground dirt?
– between the floor and insulation board? This will reduce the crawl space clearance but may be OK.
3) Since the crawl space is vented, Do I still need to insulate the crawl space foundation walls or cover the ground with plastic sheets? My understanding is that it costs thousands to seal the ground, but it may be better than nothing to just loosely cover the ground?
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Replies
Amy,
If you will have plumbing in the crawlspace and the temperature ever drops below freezing, then you should have a sealed, at least semi-conditioned crawl.
It costs very little to put a vapor barrier on the dirt. Standard 6 mil poly will work but it's better to use a more tear-resistant variety like Tu-Tuf. Seams and penetrations should be taped and the edges caulked to the walls.
Then glue Thermax to the walls and the floor joists can remain uninsulated for easy access to mechanicals. Be sure to place blocks of foam board on the band joists and over the sills and spray foam the edges and joints.
Amy,
If you have a plumbing leak in an insulated floor, there is no insulation on the planet that will "handle" the plumbing leak and allow the moisture to dry harmlessly.
If you have a crawlspace with plumbing, it is false economy to try to save money by omitting insulation on your crawl space walls. I strongly advise you to protect your plumbing pipes by omitting vents -- a savings, by the way, compared to installing vents in your foundation -- and by insulating your crawl space walls to retain your home's heat.
Amy,
I should add that there is typically far less surface area to insulate on the crawlspace walls than there is in the floor above (unless it's a small addition).
Another, but more costly, method of sealing and insulating the crawlspace is to spray closed-cell foam on the walls, sills and rim joists. This is one of the few places where I would suggest using spray foam. This also helps seal the ground VB to the walls.
Make sure than any access door is also insulated and weathersealed.
I also have a home in the CA Bay Area with same weather as Amy described. I know this is an old thread, but thought it worth mentioning that most of the older homes in my area have vented crawl spaces. If I seal off my vents and other air gaps and encapsulate the space, I'll also add a vent from the return duct of my furnace system. It never gets too humid so I'm not concerned about adding a de-humidifier.