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Old 01-18-2020, 01:35 PM   #1
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Quick crawl space question....


1970's house in Colorado trying to help a customer of mine....
Everything Im reading online says to insulate the concrete walls & floor barrier over dirt. It has all of that already but her kitchen floor above is still cold. I will get in there & look for any obvious gaps etc from outside but wondering will adding unfaced insulation between joists help at all or is that complete waste of time & her money?
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Old 01-18-2020, 01:44 PM   #2
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Re: Quick crawl space question....


The crawl space become conditioned space when it is sealed. The floor will always be the temp of the ground which is mid 50s unless you are heating the space below. Floors are hard to heat from above at best so even with insulation you may gain 5* at the floor upstairs.

Just my opinion. It would be nice to hear from some one that has tried it.
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Old 01-18-2020, 01:56 PM   #3
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Re: Quick crawl space question....


Unfaced fiberglass insulation does not do a lot to block air flow.

How much insulation on the concrete walls? And does it also cover the top?

If these are traditional cavities then a piece of 2" rigid foam and fill in front of that (crawlspace side) with mineral wool batts.

Also, I've done many infrared inspections and where the house rests on the foundation always has some major leakage. Before you fill those cavities do a lot of air sealing.

Note, cold weather air leakage forces cold air into the lower portions of the house and then up through the house where it finds an exit. An average home will replace all inside air with that cold outside air every 3 hours. Building codes require that for air quality. When a house is tighter they add air exchange systems or just run exhaust fans.

If the insulation on the concrete is thick enough and the rim cavities well insulated and sealed it can be acceptable to introduce some heat down there. Then she would have warm floors everywhere.

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Old 01-18-2020, 06:56 PM   #4
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Re: Quick crawl space question....


I suffered with a cold crawl space, and cold wood floors above it, for many years. Then I read a Building Science article about crawl spaces:
https://www.buildingscience.com/docu...ace-insulation
Once I closed off the two vents to the outside and installed rigid foam insulation to the rim joists and sealed the edges with caulk, the crawl space now stays at about 63 degrees all year round. Before, it would get down to the upper 30's. I have a remote temperature sensor down there and it shows 63.5 degrees right now, even though it is 16 degrees outside. Some of the heat ducts run through it but are sealed and have no ducts feeding into it.
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Old 01-21-2020, 05:08 PM   #5
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Re: Quick crawl space question....


Thanks for all the help with this... I'm attempting to attach a few pics of the area. There's one wall that doesn't have anything on it, the rest has that foil-faced insukation nailed to it. There are a bunch of nails in the concrete that would make gluing foam board a little tricky maybe? The dirt floor is totally covered and goes up a good 8" around perimeter. The rim joist all have fiberglass insulation in there pretty good & I couldn't see any big gaps under there anywhere, unless they were behind some of the insulation?



So are we saying that the fiberglass insulation that's already down there is basically useless & should all be removed with foam board glued on, really?! Also adding to the challenge is the opening of the crawl space (into the rest of the finished basement) is only about 2-2.5' square meaning all foam would have to be cut down smaller pieces...?!



Typically I would walk away from this, not really my area of expertise but would hate for my customer to waste any money on this if not done properly.


Thanks guys
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Old 01-21-2020, 05:13 PM   #6
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Re: Quick crawl space question....


forgot the pics...
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Old 01-21-2020, 05:35 PM   #7
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Re: Quick crawl space question....


When you insulate the crawl space you are treating it more like a basement.

Most codes and procedures are about new houses figuring out what to do with older houses is really tricky.

This explanation is about the best I have found.

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Old 01-21-2020, 05:51 PM   #8
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Re: Quick crawl space question....


This may be the best solution as from the outside you can also block air leaks below the rim and concrete and between the floor and the wall above. With flexible flashing. Even if the foam does not go all that deep in the ground.

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Old 01-21-2020, 07:27 PM   #9
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Re: Quick crawl space question....


That crawlspace is so clean! I thought it was new construction. Colorado is dry, I guess. Come down southeast and see how vented crawls work here! You could win a science fair.
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