DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   Insulation (
-   -   Insulating Basement (

mabrown6 03-15-2013 10:11 AM

Insulating Basement
I hope I can explain my question thoroughly. I am in the process of finishing 1,200 sq. ft of my poured concrete basement. I have had the envelope of the house sprayed with 2" of closed cell foam including the 400 sq. foot crawl space. They also completely foamed the walls except for each side of the wall between the space I am finishing and the crawl space. I was told this was because it brought the crawl space into the envelope. There is an 2x4 foot opening between the two. Crawl space is under the 400 sq. foot addition of the master bedroom and bath. The crawl space is 4' with a dirt floor. This leaves 5 feet of the poured wall on the finished side bellow grade without foam as well as the 4 feet above grade on the crawl space side. I am framing the wall and wondering if I need a vapor barrier here. I was not going to use insulation because this is not really an outside wall but am concerned about condensation. I did use DensArmour Plus drywall on the bottom half and Green board on top of Dricore floor. I tend to overkill for just in case situations. Basement is dry but do not like to take chances.:thumbsup: I have looked at many sights and read the building science info but I do not see this issue addressed anywhere. Any info or experiences will be greatly appreciated.

jklingel 03-16-2013 02:03 AM

pics help. i kind of lost you; maybe it's just me. no vapor barriers on walls below grade, but absolutely on the ground and gooed to the walls for several inches up.

ryanh 03-16-2013 02:10 AM

Confused... If the crawlspace is not completely sealed off from the rest of the basement then it would be considered a 'warm zone' still and not require a vapour.. Might be a good idea to poly the dirt floor with some small gravel on top for radon gas prevention

rckkrgrd 03-16-2013 01:57 PM

If I understand correctly your only moisture problem should be from the dirt floor in the crawl space. You might want to cover it with a layer of 6 mil poly. Tape or otherwise seal it to the outside walls but do not seal the laps so than any water that might leak into the area can escape. Try to make as smooth an application as possible.

asinsulation 03-16-2013 02:17 PM

Foam was a great choice, and the application seems good based on your description, but why was the vapor barrier not included to begin with? For full effectiveness, this vapor should have been laid down and run up the wall to about a foot above exterior grade level.

This will stop any moisture and air intrusion through the dirt, protect the integrity of the foam as you are not spraying directly onto damp foundation blocks, and prevent any intrusion from pests.

Get the vapor down, but in my opinion, seal up any seams with a strong double sided adhesive tape. you would be amazed how much airflow moves through the dirt(it actually carries the moisture that you are trying to prevent with the vapor barrier).

Gary in WA 03-16-2013 10:49 PM

The wall between both conditioned spaces does not need insulation nor a vapor barrier, (unless it requires separation from the basement due to conditioning). Cover the dirt with plastic, as said and if you have radon, you will need more; an exhaust vent through roof, perimeter taped to walls, etc.;

If in a termite zone, hope they left the top 2" of wall foam-open for visual inspection, annually;

PS no more multiple identical threads, please, I merged others, we get around, lol.

asinsulation 03-17-2013 04:03 PM

the termite zone is a valid point, but you are essentially killing the purpose of the product to exclude 2" around the perimeter of the home.

gregzoll 03-17-2013 05:26 PM

The closed cell spray foam creates your vapor barrier, so there is really nothing more to do. Personally, it would have been better to wait until you framed the walls, pulled electric, etc., before applying the foam. Depending on the depth that it is, you could have lost anywhere from 4 to 8 inches per wall.

That is a lot of square footage you no longer have now.

mabrown6 03-17-2013 06:16 PM

Insulating Basement
Thank you all for your responses. I did follow the building science suggestions. Yes the poly was put down prior to the foaming and was run up the walls. Yes the walls were framed in the main basement that I am finishing an inch and a half from the wall and electric and plumbing roughed in. My concern is the wall between the crawl space and finished part below grade could build up moisture after the drywall is installed on that wall. I am only concerned about that wall because no foam was applied here and there is no place for the moisture to wick out of the poured foundation from below ground to escape except into the crawl space. With the poly in place in crawl space and no vapor barrier in finished space again just on this one wall, where does this condensation go. Or even just the natural moisture in poured concrete. House built in 60's. Perhaps once the drywall is in and the paint in place this will prevent this wall from the warmth which could create condensation. Just want to make sure I've covered all my bases.

mabrown6 03-17-2013 06:17 PM

Insulating Basement
Oh also in Maine so termites not an issue.

Gary in WA 03-17-2013 11:39 PM

That is good. Termites burrow through (hidden) the foam constructing their tunnels to the wood. Years later you may open the back door and look down at your refrigerator now in the basement...
With the interior bearing concrete wall under the center, not perimeter of the house, rising footing/wall water is not a big concern, IMO, unless you have an underground spring below. The moisture drive is controlled/non-existent because both sides of the wall are conditioned. You don't have a pressure/temperature drive OR near a water source like exterior (perimeter wall) sub-soil that can be saturated with water from rain or downspouts (hopefully not in a new house...). There the capillary action and hydraulic pressures try to force water into the exterior concrete walls. The exterior drainage control system should stop/collect/remove any water present. Page 3;
Page 6, bottom, the soil temps under your slab (6' below-grade) are about 10*F warmer than the surface temps, with about a 1-2 month time-lag: 38-47*F;

Plus 10 = 48-57*F slab temp., IMO, you may want to insulate the slab unless already done (piece of mind/warm bare feet), pp.4;

Center of house slab surface water is minimal the greater distance from the perimeters;


Gary in WA 03-18-2013 12:01 AM

Most 2#SPF has a perm rating of 1.5 or so, per inch, at 2" it is 1/2 that = 0.75 to 0.55, not a Class 1 vapor barrier;

What is your closest city (below the map), Zone 6, or 7? Figure your safe basement RH...


mabrown6 03-18-2013 08:51 AM

Insulating Basement
Thank you so much Gary. Feeling much better. Zone 6 in Maine. I was rather lucky in getting an over exuberant contractor and it actually came out to 3" on the wall. :thumbup:

All times are GMT -5. The time now is 10:20 AM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

Search Engine Friendly URLs by vBSEO 3.6.1