Chlanny

I am using regular R-20 bat insulation in between my studs in my concrete basement. I am using 2 X 4 studs but they will be roughly 6" away from the wall so there will be a gap between each stud and concrete wall. I am doing this b/c my walls are not straight and I don't what my studs touching the wall. I want to cut strips of the Polystyrene Rigid insulation to tuck in behind the studs. I will try to make each strip snug but I assume I should still fasten/attach them to the stud. Can I use regular wood screws to attach these stips to the studs? Or should I use tape? Or is this just a bad idea?

thanks

c

Hube

Chlanny; Are you saying the FACE of the studs are going to be 6" away from the wall which would make the rear of the stud approx 2 1/2" from the concrete wall? I would hope that it 's not 6" from the REAR of the stud, because that can cut down quite a bit on the overall room size. Anyways, If you are using R 20 insulation, that is good when installed snuggly between the studs, and that alone should be quite efficient . Any insulation placed behind the studs (imo) would be "overkill" and just a waste of time and money.
Normally, unless the concrete wall is drastically not straight, a gap of approx 1" is all that is needed.
Ps; depending on the part of Canada you live in, don't forget to install the vapor barrier in the right position.Myself, I live in central Ontario,Canada, and my basement walls have the vapor barrier on the heated side of the wall, just next to the drywall.

Chlanny

Hi Hube

thanks for the info. I live in Saskatoon so I'll definitely be putting up a vapour barrier. I should have been clearer on my initial post - the rear of the studs will only be 1.5" - 2" away from the wall.

I have another question you might be able to help me with. The joist area is already insulated but imo the contractor did a poor job of it. The vapour barrier is either torn or coming away from the accoustical sealant already in many sections. In addition, all the pipes are "sealed" with tuck tape so I'm not convinced this is doing the trick. I'm thinking about ripping it all out and having the spray foam insulation blown into just my joist space but using the normal batt insulation for my walls. However, I'm not sure if this will work b/c I'll be using 2 methods. Have you heard of anyone doing this?

thanks

c

GBR

http://www.buildingscience.com/documents/reports/RR-0906_Field_Monitoring_Hygrothermal_Modeling_Baseme nt_Insulation.pdf

Oikos: Green Building Library - Insulating with Fiberglass Batts

BSD-012: Moisture Control for New Residential Buildings —

Be safe, Gary

Hube

[QUOTE=Chlanny;40325]Hi Hube
The joist area is already insulated but imo the contractor did a poor job of it. The vapour barrier is either torn or coming away from the accoustical sealant already in many sections. In addition, all the pipes are "sealed" with tuck tape so I'm not convinced this is doing the trick. I'm thinking about ripping it all out and having the spray foam insulation blown into just my joist space but using the normal batt insulation for my walls. However, I'm not sure if this will work b/c I'll be using 2 methods. Have you heard of anyone doing this?
************************************************** *****
Chlanny; I would think you have 2 choices
1 is to repair the existing insulation and vapor barrier,sealing and or taping all vb joints.

2 is to remove this existing "bad" work and either foam this joist area or simply do the same job (insulation and Vb)as you are doing on the walls.
You decide, either way will be good.
Personally, if it were me I would remove the existing joist area junk and 'foam' this joist area. And by using the foam no vapor barrier will be required in this joist area.

Chlanny

Thanks Hube

I discovered more issues with the current insulation work in the joists so I think I'm going to go with the spray foam in this area. However, I still want to use batt insulation and a vapour barrier for my walls. This is where I'm not sure if I can use spray foam in the joists and batt in the walls. You'll have to bear with me. My joists sit on a 4" thick beam that in turn sits on my concrete walls. My framed walls will not touch the bottom of the joists - the top plate will be about 1/2" shorter. This is recommended here b/c of heaving with our drastic temperature changes. My plan is to run a bead of accoustical sealant along the top of the 4" beam, staple the vapour barrier to that and run the vapour barrier over the top plate and then all way down the wall. do you think that would work?

thanks

mc

Hube

Chlanny; Seems to me it's a good plan.
Go for it.