Insulating a unfiinshed basement - DIY Chatroom

govikes · 03-20-2007, 12:30 PM

I am starting to finished my basement but before I start putting studs on the wall I like to make sure I have an understanding of how insulation and vapor barriors works. I have concrete walls on half of my walkout basement as the other half of the walls that face an exterior are already studed and insulated with a vapor barrior.

I was thinking of putting on the concrete walls a water tite sealer to prevent moisture and water damage. Its basically a white paint primer that you paint on the cement walls.

Then I was going to buy the "Owens" pink polystrene foam and glue that on the the concrete walls. Then put the studs against the foam walls.

After the studs are up I would put in the insulation between the studs and then staple a plastic vapor barrior on the face of the studs.

Does this seem like the right way of doing it or am I overkilling with the sealer and the polystrene foam?

Brik · 03-20-2007, 12:48 PM

Sealer is fine for what it is. Best, if you have moisture, is to address it on the OUTSIDE. Grading is first place to start.

There is a lot of debate as to what is best. Range goes from no insulation or vapor barrier to mac daddy super tight. Search here its been discussed before.

You say you are already partially insulated. if this was done by a builder or contractor who knows you area, climate, etc I would just model what was done already.

Its my opinion, and many others share the same, that you DO NOT want a double vapor barrier. Moisture needs to dissipate to either the interior or exterior. EPS (Expanded Polystyrene) is a vapor barrier. If you use that behind your stud walls then no other vapor barrier should be used. If you did add the plastic then you have a situation where moisture could be trapped in the walls leading to moisture issues. So, paint the masonry if you want, add the EPS and build your stud walls, insulate with UNFACED pink stuff and then sheetrock and you are done. If you skip the EPS then build your wall an inch or two away from the masonry and use kraft faced insulation and skip the plastic. The kraft faced insulation is your vapor barrier. the plastic will prevent you from using adhesive when attaching the drywall. You want adhesive.

here is one article http://www.pathnet.org/sp.asp?id=18574

KUIPORNG · 03-20-2007, 01:53 PM

What was half way finished is probably done by the builder for minimum code requirement in order to close the sale of the new home... you should rid them all out and start with a bare concrete wall... treat them all the same upper/lower wall....

If you paint the concrete... I think you don't need another foam layer... but like Brik said, there are about 2 thousands opinion on this one... but I wouldn't waste space by moving wall away from concrete... unless you have too big a space not to waste....

concretemasonry · 03-20-2007, 02:17 PM

Don't go crazy with insulation. It is easy to waste a ton of $$$s if you get lost in nit-picking details and do not look at the big picture.

An example - A basement with a portion finished and a portion unfinished.
Why spend an excess of money on pulling the "exterior" finished walls away from the concrete for an air space and then heavily insulating those walls? You have the same air conditions for the finished interior walls that separate the finished space from the "semi-conditioned" space in the rest of the basement. - A real nit-picker would just insulate the interior walls and install weather tight interior doors to separate the spaces (LOL).

Also, you have about the same floor area (uninsulated) as the walls that are the same temperature at the bottom almost all year.

Your floor and much of the foundation walls provide a big assist in cooling in the summer if you have a reasonably modern HVAC system. If you over insulate, you lose this benefit.

Look at the big picture and don't micro-manage.

govikes · 03-20-2007, 03:15 PM

I just want to make sure when the basement is finished that the temperture is not considerably cooler then my main and upper levels. Currently, its about 20 degrees colder especially in the winter here in MN.

Thanks Brik for your suggestions, what's the difference between kraft face insulation and unface pink insulation? If I did the 2 inch spacing between the concrete walls and studs and use the unface pink insulation,then would need a plastic vapor barrior?

Brik · 03-20-2007, 03:33 PM

Yes but its easier to just use the Kraft faced. Kraft faced has built in vapor barrier, no need for the plastic if you use that. Additionally, if you use Kraft faced you have the studs clear to glue and screw drywall to if you are finishing. If you use the poly vapor barrier you can only screw the drywall. This is the approach I took when finishing my basement (almost done, YEA!) Leaving a small air space is critical, so I understand, with this approach. Its good practice regardless because your masonry walls may not be perfectly plumb and straight anyway. This approach is also somewhat "standard" in SE PA, its easy to do and doesn't cost an arm and a leg.

So, the difference is one has a vapor barrier and one doesn't. My understanding is you never want two vapor barriers. Also, 2" space may be a lot unless your masonry walls are really out of whack. I did 1.5" but needed the space due to a channel for a french drain. As long as you have a continuous uninterrupted air space, my understanding is that's what you want.

Again I'll say, key thing with ANY basement finishing is to do your moisture remediation first, and best from the outside when at all possible.

For example - my basement exterior wall has a sprayed on bituminous waterproofing membrane with a footing drain (french drain) which collects any water along the outside of the foundation plus all the roof water via downspouts and directs it into a 12' deep dry-well, the dry-well has an overflow to daylight below the level of the basement. On the inside I have a second french drain which directs any water to a sump pit/pump. The sump pump dumps its water into the exterior dry-well as well. Also, all of the grading outside is sloped away from the house. My basement is bone dry. Sump only runs once or twice a year. I think the water in the sump is from the AC condensate pump that dumps its water into that pit as well.

Also, remember my advice is free, take it for what its worth.

ksypal · 03-26-2007, 03:39 PM

I'm in the same boat, GoVikes, in terms of researching how to insulate a basement I'm about to finish. As otherse have mentioned, there seem to be a lot of opinions on this topic. One more you might want to consider if you have found it already is that of Building Science. They have an excellent paper on this ins and outs of basement insulation: http://www.eere.energy.gov/buildings...s/db/35017.pdf. I found their site to be extremely helpful and very authoritative. Good luck!

**AtlanticWBConst.** · 03-26-2007, 06:55 PM

Quote:

Originally Posted by ksypal

I'm in the same boat, GoVikes, in terms of researching how to insulate a basement I'm about to finish. As otherse have mentioned, there seem to be a lot of opinions on this topic. One more you might want to consider if you have found it already is that of Building Science. They have an excellent paper on this ins and outs of basement insulation: http://www.eere.energy.gov/buildings...s/db/35017.pdf. I found their site to be extremely helpful and very authoritative. Good luck!

Yes, that is a very good article. Very informative. Just be aware that the article addresses the method of building basement framed walls directly against concrete. It also looks at installing insulation directly against concrete.
Under those contexts, I feel all the information is 'dead on' and worthy of consideration...