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Old 11-18-2009, 04:50 PM   #1
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Help with finishing basement walls


I'm looking to finish my basement walls but I have an issue. The issue is I have a french drain around the perimeter of the basement. What are my options for building the walls. Here is a picture of what I'm up against, the gap is between 1 and 2 inches.



Thanks in advance,
Keith

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Old 11-18-2009, 05:05 PM   #2
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Help with finishing basement walls


This will not be a problem. Read existing posts (many of them here) by searching basement walls on this forum. 2" foam goes against the wall. Then a 1" air space before you build the walls. So you are past this drain area.

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Old 11-20-2009, 12:33 PM   #3
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Ok well I read up on some of the threads here but I have one question, would it be ok to do 1" insulation board on the wall then 1" of space then the wall with insulation stapled on but away from the insulation board?
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Old 11-20-2009, 01:12 PM   #4
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Help with finishing basement walls


no, this is not enough R-Value to avoid condensation (depending on where you are of course)
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Old 12-13-2009, 10:28 PM   #5
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Help with finishing basement walls




ok if I do the above and put more insulation between the frame studs but leave that gap at the bottom for the holes in the cinderblock would this be ok or since the gap is at the bottom there would be moisture buildup?
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Old 12-14-2009, 05:27 AM   #6
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Help with finishing basement walls


1st off, what leads you to believe that slot is a french drain since you didn't mention any piping under the floor nor a sump/pump/discharge system.

its difficult to ascertain if the walls have paint OR drylock on them,,, if drylock, there's a moisture problem,,, if paint, probably not.
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Old 12-14-2009, 07:34 AM   #7
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Help with finishing basement walls


they are french drains that lead to a sump pump in the back corner of the house. since I've moved into this house there has been no water in the basement even during a 4 inch rain storm we had just over 2 weeks ago here in northern new jersey.
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Old 12-14-2009, 07:53 AM   #8
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Help with finishing basement walls


no need to the weep holes and you do not want the gap at the bottom. All seams on the insulation against the wall must be taped and sealed. Foam or caulk the bottom. You must make a complete capillary break against the concrete block wall.
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Old 12-14-2009, 12:04 PM   #9
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Originally Posted by Bob Mariani View Post
no need to the weep holes and you do not want the gap at the bottom. All seams on the insulation against the wall must be taped and sealed. Foam or caulk the bottom. You must make a complete capillary break against the concrete block wall.
Bob, just use a silicone caulk where the foam meets the cement floor?

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Old 12-14-2009, 12:14 PM   #10
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ok so covering the holes will not cause any problem? and just use basic silicone caulk or is there a special one we should be looking for?
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Old 12-14-2009, 03:23 PM   #11
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Help with finishing basement walls


2" of foam on the walls are only recommended for zone 5 or colder. True going thinner on the foam, the more important dehumidification but you can use 1" if you want. I wouldn't go any thinner because 1" foam has a perm rating of 1, any thinner foam and you have to use a barrier you might as well just get 1"+ instead might be the same price. It is important to first use XPS foam against the walls, be aware the thinner you go the more you have to dehumidify. Your drywall & latex paint (do not use oil based or wallpaper) will dry much faster than the XPS will allow to pass. Do not use any vapor barriers in or on these studwalls bumped away from your foundation you have to allow drying to the interior. Basement walls are buried they can't dry to the exterior. Make sure all seams in the foam are caulked (with silicone) and taped (with aluminum tape in USA, tuck tape in Canada). A pinhole can leak up to a cup of water/season and I find honestly caulking is more effective than taping (I gotta get me some tuck tape from Canada, the aluminum tape is okay but it's a general purpose thing and doesn't grab to insulation as much as I'd like).

FYI you have to seal the walls vertically and horizontally every 10' for fire or draft stopping reasons. That makes these types of assemblies pretty difficult because they're bumped out. Although people say foam is very flammable, it isn't actually. Take a scrap piece and try to light it on fire trust me you won't be able to (I've tried XPS, Polyurethane, and Polyiso). It melts, there is a flame while you hold your flame to it but the moment you pull away it goes out and stays out. I recommend firecode drywall for sealing the tops & verticals of these walls because it can be shaped easier and doesn't break/crumble easily when notched out for each stud. Then caulk with fireblocking caulk or use fireblocking expanding foam (expensive) for the bigger gaps caulk won't work. Your goal is to make chambers in these walls where potentially any fires that start will suffocate or be slowed breaking through to other chambers so you and possibly the fire department has time to react. I was thinking just spray the firecode foam between a few studs and the 1" gap at the top plate until I went to buy the firecode foam and saw it was about $9-$10 a can.

I prefer all firecode drywall in these types of walls in the basement because it is really hard to seal them being bumped out to a decent level. The inside walls are typically drywalled both sides so by their nature are fire/draft sealed but you have to seal wire/pipe penetrations.

Last edited by Piedmont; 12-14-2009 at 04:10 PM.
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Old 12-14-2009, 03:32 PM   #12
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Help with finishing basement walls


OP, I'm not too far from you in you're in northern NJ. We don't really foam are foundation walls around here ever - these other posters may be in a much cooler climate.

frame your walls an inch or so away from the block, insulate them, and be happy
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Old 12-14-2009, 04:51 PM   #13
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OP, I'm not too far from you in you're in northern NJ. We don't really foam are foundation walls around here ever - these other posters may be in a much cooler climate.

frame your walls an inch or so away from the block, insulate them, and be happy
Doing it your way will not be correct. The foam on the wall directly warms the wall enough to prevent condensation on the colder wall. Read more on the science of the correct ways before giving wrong information. I live in CT and we do or do not do it with foam. If you know what you are doing you insulate the wall. if you do not know you do it your way. You just have not torn your wall down yet and therefore have not learned that you are doing it wrong. Read the articles on this at www.buildingscience.com
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Old 12-14-2009, 05:04 PM   #14
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Help with finishing basement walls


do NOT seal the holes as they're for draining the wall's infiltrating water,,, we made a good living in nj for years waterproofing bsmts,,, if there's a sump as you post, the dirt in the slot'll eventually cause whatever drains into it to pool on the floor,,, not IF but WHEN in my experience - ESPECIALLY w/block walls which rot due to the combination of wtr & soil acid.
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Old 12-14-2009, 05:04 PM   #15
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Help with finishing basement walls


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Originally Posted by Bob Mariani View Post
Doing it your way will not be correct. The foam on the wall directly warms the wall enough to prevent condensation on the colder wall. Read more on the science of the correct ways before giving wrong information. I live in CT and we do or do not do it with foam. If you know what you are doing you insulate the wall. if you do not know you do it your way. You just have not torn your wall down yet and therefore have not learned that you are doing it wrong. Read the articles on this at www.buildingscience.com
don't believe everything you read or see on tv.

building to me is not a science, it's my job. in my 13 years of framing new and renovating old houses, i have yet to see a single basement done with foam on the inside. (i have seen foam on the outside of the foundation on some small percentage of new construction.)

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