Basement wall - vapor barrier

[Covenant Clone]

Does the type of foundation play into this equation at all? Most of the conversation has focused on concrete, as in poured. My 1965 built dwelling has HCB foundation walls. I can't imagine it'll make any difference, but thought I'd ask while the topic was "hot"! TIA

Yeah, I would look at every situation differently. Have you ever had water in your basement? Have you ever noticed at water seeping through the foundation? If you have a dry basement and haven't had any issues you are fine to proceed. If you have, then you need to address that problem first because drylok isn't going to solve that problem. Like I said, I am certainly not saying I am 100% right or that there isn't a better way to do things but that is just the method I have chosen to use.

 

[Wesley]

What type of drywall would you use below grade?

 

[ceeboe]

I would agree with your assessment but this isn't a new construction house. That is why I asked how old the house was. I can guarantee there isn't any waterproofing on the outside of the house. You then have to seal up the concrete (waterproof) from the inside unless you want to dig up your yard and apply it to the exterior. The sealant that you put on the interior isn't going to stop all the water vapor that comes through the foundation. The foundation walls will breathe from interior to exterior and since you put a vapor barrier on the backside of the drywall your drywall will stay dry and the cavity will dry out. I am not saying there isn't other ways of doing things but we have done it this way for a while and have never had a callback. If I was finishing a newer home where waterproofing was applied to the exterior I would look at doing things a little differently. JMHO

And my way might not be the right way but we had to go with something when we started finishing basements and this was the method we decided on. But who knows.

My only concern here is the possibility of mold growth due to a trap with the plastic covering behind the drywall and teh vapor barrior on the foundation wall.

Actually, by my understanding, that condensation wants to dry exterior to interior, not interior to exterior. That would only make sense considering it wants to dry to the warmer side, and since the interior is warmer it would want to dry to the warm side. This is why I believe it's suggested to not have any barrior if at all possible because you're just setting yourself up for possible mold and condensation problems.

I had a whole thing typed up, but then I saw another detail mentioned in my book, Builders Guide to Cold Climate.

It uses a foil faced rigid insulation with taped and sealed joints right next to the foundation wall. What this does is keeps the conc. wall cold and the foil does not allow the wall to dry to the interior. Because of this the only possible drying scenerio for the wall is up through the exposed part above grade. The only exception for this is that you need to allow the conc. foundation wall to dry out and equilibriate otherwise mold is possible. Being that this application is existing and has had plenty of time to dry, I think this approach of a foil based rigid foam on the wall would be best. Here you can then apply a gypsum board directly to your thermal barrier or build out a cavity wall to hold conduents and runs while also insulated with some kind of expanding foam, not a batt insulation.

Does this all make sense?

The best solution to everything is to spray Icynene insulation into your wall cavity. Breathable from the inside and waterproof. But that tends to be a big budget buster. :smile:

As explained above, I completely agree with this as well. It's also a better R-value than any batt insulation and will serve you better in energy conservation. For the same thickness of insulation, you get a 30+ addition to your R-value using the expand foam of sorts.

What type of drywall would you use below grade?

The same as you would use above grade. It's more important on the paint that you use. You want a semi-permeable (latex) paint on your wall to allow your gyp and wall to breathe as much as possible.

Well this has actually been kind of fun. Obviously there are different approaches, but finding the one that actually is good for the home is key. I honestly now think that the Foil based rigid foam might be the best approach in this situation. You want to force the wall to stay cold and to dry to the exterior.

 

[ceeboe]

What type of drywall would you use below grade?

Oh also, there is a new product out there called American Clay. This is a clay based wall covering application that is an alternate to latex paint. It can come in different sorts of textures and pigments to match to your liking. The key is it's a natural product that is naturally breathable. It allows the flow of moisture out of your wall, but not into your wall. It's a really great product with a fine quality finish.

 

[clones_jer]

I think Wesley was asking about "greenboard" for use in basements. pros / cons etc.

 

[Covenant Clone]

Let us know what you find out from the building inspector tomorrow clones_jer, it will be interesting to hear his take on it. This has be a fun discussion.

 

[clones_jer]

Let us know what you find out from the building inspector tomorrow clones_jer, it will be interesting to hear his take on it. This has be a fun discussion.

Ok talked to the building inspector.

First off I talked to the receptionist until the inspector got off the phone and she said that if I asked one guy verses the other I'll get two different answers to the vapor barrier question not a good start.

Anyway finally get the guy on the phone and he indicated that all basement wall vapor barriers should be on the INSIDE, between the drywall and stud wall. I went on to ask him if the foam board acted like a vapor barrier and he said "probably". So then I continued that I should probably not create a cavity by going foam board/fiberglass/plastic and he said that wouldn't be a problem anyway because the plastic keeps the condensation out of the cavity.

So basically he is backing up the practices bhoodjer is recommending, although I was less than impressed by the fact that he didn't really sound like it mattered one way or another. I told him I didn't want to break any city code and he said all I needed was R10 total value of insulation and vapor barrier on the inside of the drywall and I was good to go.

I hate to say it, but I may try to call in some other time and talk to the other inspector just to get another opinion. and I think I'm going to stick to all foam board insulation. 1" in back of the studs and fitted 1 1/2" between which should give me R 12.5 overall.

Thanks for all the comments, and keep 'em coming if you have any other recommendations on basement remodels. :smile:

 

[dmclone]

What are you going to do with the basement? Home theater?

 

[clones_jer]

What are you going to do with the basement? Home theater?

Last summer I found out I had "orangeberg" sewer tile when it collapsed. To make matters worse the underground tile around my house flowed into my sewer line (this is illegal now). so when we had all that rain my tile plugged and my sewer line plugged, water started coming in one wall. It was about 4" deep and holding (with continous pumping out) before the sewer guy was finally able to punch a hole big enough to relieve the pressure.

I added a sump pit & pump, some shallow buried tile, new sewer tile and diverted my underground tile along with adding some dirt to one side of the house.

Long story short its all better now.

The basement was semi-finished with some drywall, no insulation and a ton of paneling and office carpet on about half of the square footage. We pulled all of that out - and now are getting around to rebuilding it. Thankfully we (read:she) like the floor plan, but now its a matter of doing things the way we want them done, and being somewhat proper about the way we do them.

Who knew a sheet of plastic would lead to all this trouble :biggrin:

EDIT: Oh and to answer your question, the main room we're working on will be a half bar / tv room / big aquarium / and hopefully either an air hockey table or something (but don't tell my wife about that last part :wink So whatever you call that sort of room. The rest of the basement is a laundry room, work shop, future kids play room, and a ton of shelving.

 

[clone4life82]

I see that the conversation is pretty much wrapped up but for any consolation, moisture flows from high vapor pressure to low vapor pressure. I believe in a typical basement that would mean that the moisture is entering from the outside to in. So whatever that leaves us at.

 

[clone92]

Ok, think about a pop can, when it is cold, it will attract moisture. Your cold concrete walls in the basement is the pop can. To keep the moisture from getting to the pop can (concrete wall) you need to have the vapor barrier. If you put the vapor barrier directly on the concrete, the moisture will build up on everything up to that point. So if you had studs, fiberglass, etc, the moisture will build up in that material (and probably stay there). If you place the vapor barrier just under your drywall, the moisture can not get to the studs and insulation material, plus the insulation will 'insulate' the cold wall from the vapor barrier eliminating most of the moisture problem.

So, to answer your question, put the vapor barrier as close to the living area as possible (under the drywall).

 

[clones_jer]

Ok, think about a pop can, when it is cold, it will attract moisture. Your cold concrete walls in the basement is the pop can. To keep the moisture from getting to the pop can (concrete wall) you need to have the vapor barrier. If you put the vapor barrier directly on the concrete, the moisture will build up on everything up to that point. So if you had studs, fiberglass, etc, the moisture will build up in that material (and probably stay there). If you place the vapor barrier just under your drywall, the moisture can not get to the studs and insulation material, plus the insulation will 'insulate' the cold wall from the vapor barrier eliminating most of the moisture problem.

So, to answer your question, put the vapor barrier as close to the living area as possible (under the drywall).

I like that answer ... if it were on the concrete wall it would effectively be the same temperature and thus not be doing anything right?

Welcome to the conversation.

 

[cychhosis]

Sorry I missed all this, I was in my basement doing pretty much the same thing. Here's my story: I got free 3" polystyrene (prom decorations) and friction fitted into my basement last spring. The concrete walls were previously painted (Cyclone Gold) with latex and there is a a layer of
'Black jack" on the exterior, but no external insulation. I used nichrome wire and my battery charger to cut grooves for my furring strips in the foam. I'm placing my sheetrock directly on the foam. I have tiled around the basement, have a sump pump, gutters on the house and a grade of 1-2% around the foundation to move surface water away. I am not installing any plastic, and do have a humidifier in the room which drains into the sump. Hope it works!