# Help with finishing basement walls



## Bob Mariani (Dec 1, 2008)

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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## callmevo4short (Nov 18, 2009)

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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## Bob Mariani (Dec 1, 2008)

no, this is not enough R-Value to avoid condensation (depending on where you are of course)


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## callmevo4short (Nov 18, 2009)

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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## stadry (Jun 20, 2009)

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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## callmevo4short (Nov 18, 2009)

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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## Bob Mariani (Dec 1, 2008)

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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## ctkeebler (Nov 8, 2009)

Bob Mariani said:


> 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?

Thanks


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## callmevo4short (Nov 18, 2009)

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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## Piedmont (Nov 1, 2007)

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.


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## ClemS (Dec 13, 2009)

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 :thumbsup:


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## Bob Mariani (Dec 1, 2008)

ClemS said:


> 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 :thumbsup:


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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## stadry (Jun 20, 2009)

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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## ClemS (Dec 13, 2009)

Bob Mariani said:


> 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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## Kevin M. (Nov 26, 2009)

ClemS said:


> 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,
> 
> ...


Hey Clem,

Back in the 70's we would fur basement walls with 1x2's and add 3/4" ridgid foam put up a poly vapor barrier and sheetrock. In the 80's we would fur out the walls with 2x2's and add 1 1/2 ridgid foam put up a poly vapor barrier and sheet rock. In the 90's we would remove 90 percent of the work we did in the 70's and 80's because the poly vapor barrier would trap the condensate and create mold city.

In recent times, we eliminate the furring strips, poly vapor barrier, install 2" ridgid foam and build a traditional stud wall and insulate accordingly. 

Go figure! Times they are a changing. 

KK

Good Building to you!


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## ClemS (Dec 13, 2009)

Kevin M. said:


> Hey Clem,
> 
> Back in the 70's we would fur basement walls with 1x2's and add 3/4" ridgid foam put up a poly vapor barrier and sheetrock. In the 80's we would fur out the walls with 2x2's and add 1 1/2 ridgid foam put up a poly vapor barrier and sheet rock. In the 90's we would remove 90 percent of the work we did in the 70's and 80's because the poly vapor barrier would trap the condensate and create mold city.
> 
> ...


I'm not saying that there's anything wrong with that. It just isn't the way it's done around here. To *me* it's a waste of money, time, and space simply because there's nothing wrong with doing it without the foam, *at least around here.* :thumbsup:


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## Kevin M. (Nov 26, 2009)

ClemS said:


> I'm not saying that there's anything wrong with that. It just isn't the way it's done around here. To *me* it's a waste of money, time, and space simply because there's nothing wrong with doing it without the foam, at least around here. :thumbsup:


OK, 

Staten island has been around since 1670. I'm going to have to do some historic research to determine if the British may have ran off with all the ridgid foam. That would explain why you have not seen much of it in your area. :yes:

I'll be in touch when my studies are concluded. :jester:


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## ClemS (Dec 13, 2009)

Kevin M. said:


> OK,
> 
> Staten island has been around since 1670. I'm going to have to do some historic research to determine if the British may have ran off with all the ridgid foam. That would explain why you have not seen much of it in your area. :yes:
> 
> I'll be in touch when my studies are concluded. :jester:


I build new houses for a living, Kevin. I don't mean to come off as a jerk, I'm simply telling you how it's done down (or up) here. I've seen plenty of rigid foam insulation, although not in the application that was described. 

This is the typical detail for new construction around here:
8"-10" foundation wall keyed into a footing.
foundation wall is water-proofed to grade.
4" poured slab over 6 mil vapor barrier over crushed stone.
2x4 perimeter framing with r13 insulation.

this is pretty consistent with all architects in the area.


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## Kevin M. (Nov 26, 2009)

ClemS said:


> I build new houses for a living, Kevin.* I don't mean to come off as a jerk,* I'm simply telling you how it's done down (or up) here. I've seen plenty of rigid foam insulation, although not in the application that was described.
> 
> This is the typical detail for new construction around here:
> 8"-10" foundation wall keyed into a footing.
> ...


Hey Clem,

I was not insinuating you were a jerk, sorry if it came off that way. I'm sure you have learned much in your 13 years of hands on experience. The British thing was just my attempt to add a bit of humor to the situation. If I offended you, I apologize. 

Best regards,

Kevin


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## II Weeks (Jan 6, 2009)

Ive done a few basements and like someone mentioned, they started out with 1X2 furring strips, so on and so on.

What we do now is different. The outside walls we frame out with 2X3 metal studs. When all the plumbing and electric is complete, we call in a spray foam company and have the spray 2 feet into the floor/ceiling joists and one foot lower than the frost line. Being that we dont go all the way from floor to ceiling, the cost isnt that much more than regular R 13 and spray foam is as close to perfect as you can get.


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## firehawkmph (Dec 12, 2009)

Hey Clem,
I'm with you. I went to the building science site and read the article. I don't know what they do in other parts of the country, but here in northeast Ohio, I have never seen anyone do a basement wall like they show in their diagram. Here we build 2 x 4 walls, leave 1/2-3/4" space between it and the block walls, insulate with fiberglass bats, drywall and finish. This is common practice around here, and I have been doing them like that for 30 years and haven't had a moisture problem with them. 
Mike Hawkins


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