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Old 10-05-2015, 05:02 PM   #1
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insulating a non-vented crawlspace floor


Hi - I could not find any previous question similar to mine ... my daughter has a house built in 1890 in Denver. While it has been updated over the years, the crawlspace is half-dug out with concrete floor for the mechanicals and h/w heater. The rest is just dirt with little clearance to the floor joist - but enough to crawl on your back and there are a number of trenches previously dug in that area. I believe it is an unvented, although as there are pipes and hvac tubes (which make it even trickier to get to things).

Bottom line is I doubt I could get to the walls sufficiently to do an adequate job insulating them so I want to put insulation between the floor joist and then lay a vapor barrier over the ground (and trench work) ... is there something inherently wrong with this approach (besides the fact it will cost much more? Her wood floors above get very cold in the winter and I fully suspect this is the cause.

thanks for any input.

Jim
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Old 10-05-2015, 05:06 PM   #2
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There wasn't in 1972. I have a similar situation, only CB foundation and that is how they built for electric heat. I may have other options but I don't see where you do. Just make sure to keep the water pipes in the envelope or insulate them really well.

BTW, I only have 3.5" under the floor. If I were you, I would go with at least 6" (r-19) unfaced or the face to the warm side.
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Old 10-05-2015, 05:09 PM   #3
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Its probably be treated, as a result of duct leakage and other communication with the mechanical, as a conditioned crawlspace. If you can get out far enough to put a vapor barrier on the soil, you might as well just spray foam the outside stem wall and do it as a conditioned space.
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Old 10-05-2015, 07:53 PM   #4
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Be vary careful in closing the crawlspace due to radon, the main reason we don't use them here in WA, pp. 3; http://www.kenergy.us/pdf/Regional%2...pace_final.pdf

You also have high levels of radon;http://www.radon.com/maps/ You may need a vent pipe through the roof.

With your winter temps a little warmer than Flagstaff; http://www.usclimatedata.com/climate...tates/usaz0068 ---------------- http://www.usclimatedata.com/climate...tates/usaz0068 It works out better by insulating the floor as you stated, in this study; http://www.google.com/url?sa=t&rct=j...c39J_w&cad=rja

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Old 10-07-2015, 08:07 AM   #5
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thanks Gary, Colby and Windows on Washington for your input. I don't plan to change anything about the ventilation (there are just two smaller vents) as the crawl space is very dry currently and don't want to upset that apple cart ... in fact I am someewhat re-thinking the plastic over the dirt scenario as well since there is no moisture problem on the joist or bottom of the floor now ... and adding the isulation would seemingly only change where the heat/cold barrier is (ie not the floor but the bottom of the insulation) ... so it all ought to remain as is (or so thinks my addled brain).
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Old 10-07-2015, 08:10 AM   #6
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Adding insulation will make the bottom of the joists colder as you will be reducing the heat flow into the crawlspace.

Be aware, while unlike in dry Colorado, you can create a condensation issue where one did not exist previously.
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Old 10-07-2015, 01:25 PM   #7
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Adding fibrous cavity insulation will not change the vapor quantity of the subfloor, it is very vapor open. If a plywood flooring above, the exterior glue is your vapor barrier. You could add Kraft-faced batt for a safe vapor retarder. Your floors would be warmer then.

If you closed-off the two areas from each other, IMO, you would then "be upsetting the apple cart". You would lose the benefit of the HVAC unit circulating drying air to both areas. At the very least, add a vapor barrier to the dirt to reduce the drying load of any moisture possibly coming through, or moisture going right up to the attic (feeding the stack effect)- especially in older balloon-framed houses; check for line-of-sight up the exterior walls, or extra dirt particles caught in your furnace filter requiring more frequent changing; http://dirt-crawl-spaces.com/crawlspace-dirt.html

Doors/windows sticking, moisture condensing on interior side of windows, paint blistering from siding, mildew on attic framing, etc....did you plug all holes in the floor from crawlspace, wiring/plumbing?

Gary
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Last edited by Gary in WA; 10-07-2015 at 01:27 PM. Reason: sp
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Old 10-08-2015, 10:52 AM   #8
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Gary ... I am a little confused by your post ... the top of the floor is hardwood which i presume is on a subfloor but the very bottom - exposed to the crawlspace is more plank type rather than plywood ... but you talk about closing off the two areas - did you mean the area with the mechanicals that is dugout (and by the way has insulation in the joist cavities) from the rest of the crawlspace? or did you mean that insulation in the joist cavities would close the floor off from the crawlspace?
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