Confused about framing old basement... please help.

drunken0monkey

Hi everyone,

I apologize if this has been asked before. I've been researching how to finish the basement of my house and have become somewhat confused about how to frame and insulate in order to achieve best moisture control (actual energy efficiency is NOT the main goal).

This is my situation:

• the house is from the 1960's, concrete block foundation with concrete floors in the basement
• I removed the old 'finish' which was wood strapping nailed to the concrete blocks with thin wood panelling nailed to the strapping
• there was no insulation
• I'd like to frame the basement with 2 x 4 studs, use batt insulation and drywall to finish

My confusion lies in the fact that I'm not entirely sure how (or rather exactly where) to place the framing and how to install the batt insulation while leaving a gap (say 1") between the framing and the concrete block walls so air can circulate and allow any petential moisture to evaporate. My impression is that if I put the framing 1" or so away from the concrete block walls and then put the batt insulation between the studs, the batt insluation will eliminate my 1" gap and stop air from circulating (it would also come in contact with the concrete blocks).

First of all, is the approach I described the correct one in my situation? If so, how do I make sure I've got a gap between the concrete block wall and my framing/insulation? If the approach described above is incorrect, why and what are my alternatives.

It should be noted that I have not detected any mold anywhere during the demolition and there was wood in contact with the walls and floor. I do however have a bit of efflourescence here and there which leads me to believe that the concrete block are (or were at some point) transferring at least some moisture from the soil and I'm assuming I won't be able to stop this completely.

Thanks a lot.

Termite

A gap of an inch or two is a good idea for the reasons you mentioned. Of course, be sure that your foundation wall isn't wicking moisture. If so, a couple coats of DryLock might be in order first.

Your batt insulation will be the depth of your 2x4 studs, so it won't rest against your foundation when all is said and done, provided you leave that gap between the framing and the wall.

The other benefit of the gap is that if your wall heaves, moves, bulges or cracks as foundations do you won't necessarily get damage to your sheetrock wall.

One major consideration of framing a basement wall such as this is the potential for fire or air to feed a fire to travel behind the wall laterally and vertically into the floor framing above. Fireblocking is an absolute necessity, and your building inspector should require it. Check out my thread about how to fireblock framed walls such as yours in the how-to guides section.
How to fireblock framing

drunken0monkey

Thanks a lot for a quick reply.

I will definitely look at the fire information as this is not something I've thought about but what you say does make sense.

A couple of follow up questions:

• Will the batt stay in place by itself if it's not up against the foundation wall? Should I be attaching this to the wood framing somehow to make sure it does not move around? (I'm not sure that makes sense or if I'm explaining it right)
• Will the air in the gap between the insulation and foundation wall be able to circulate once I install a vapor barrier (I'm in Toronto so a cold winter climate)? Should I be leaving a break in the bottom part of the vapor barrier (this is what I've heard mentioned by a few people)? Can/should I NOT install a vapor barrier to allow more circulation and breating into the house and hope that any moisture will evaporate into the air in the gap?
• Though not ideal, is a tiny bit of wicking OK since the moisture will be able to evaporate? This part confuses me also, since in all the old houses I've been in, the basements aren't 100% dry and have a bit of dampness but no mold or musty smells. This leads me to think that it's a matter of degrees from 100% dry which is ideal to actual water which is unacceptable but there may also be an area in between where there is a bit of wicking but with proper air circulation and materials the moisture can be managed and will not lead to mold or big problems, just a slightly damper feel than upstairs. Is this thinking completely wrong?

Again thanks for the help and I do apologize if what I'm asking is stupid or does not make sense.

Martin

Termite

Your questions aren't stupid at all. Stupid would be doing this without asking the questions you don't have answers for!

• The batt will stay in place if you use kraft-faced batts. The kraft paper face has tabs that you staple to the side of the stud right behind the front face of the stud.
• Will air circulate? If done properly, not really. A properly fireblocked framed wall is expressly designed not to circulate air more than 10' horizontally in its concealed spaces.
• The vapor barrier topic is one of much debate. The kraft paper on the insulation serves as an effective vapor barrier (air/drafts). Although a vapor barrier is important, what you're probably actually wanting is a moisture barrier. Putting plastic sheeting back there will cause more harm than good in my opinion, and it is less than effective due to the potential for condensation and the inability to perfectly seal seams and edges. Your best bet is to use an applied waterproofer to the face of the foundation wall. As mentioned, a couple coats of DryLock will do the trick nicely and should put your moisture-wicking concerns at ease (it doesn't sound like you have actual water problems, just the typical humidity down there).
• A properly moisture-proofed basement shouldn't be musty. When done correctly it should have similar humidity levels to the rest of the house. Otherwise it will facilitate mold growth, smells and such.

drunken0monkey

Well, that's part of my confussion. I don't think I've got a real water problem but I'm not sure. I definitely have some wicking through certain concrete blocks and I do see some efflourescence here and there but definitely no actual water or mold. I'm starting to think that this isn't too big of a deal as long as I paint the wall with some kind of waterproofing product. Is this correct?

Also, say overtime the wicking action 'wears' through the waterproofing product... will the air space I'm leaving between the framing and foundation walls help this moisture evaporate?

Martin

Termite

The small space behind the wall won't really provide "new" air for evaporation. A few HVAC return-air-type grilles in the wall might ease your concerns by providing some minimal air circulation into the living space.

I'd really suggest drylock. Not paint, not Kilz...DryLock. It would take the foundation actually cracking for water to get past it, and it will eliminate the wicking of moisture into the living space. It is easy, relatively cheap, and will take care of the little moisture you do get. Of course the best fix is a good waterproofer on the exterior side of the foundation but that probably isn't a good option for most folks with older homes that lack it in the first place!