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Discussion Starter · #1 · (Edited)
Maine to be exact. I'm finishing off a room and will be adding heat via another zone on my boiler. My basement is dry and has zero moisture issues and the walls are protected by dry lock. I framed the exterior walls with 2X4's, 2 inches away from the exterior walls to allow enough space to use R-19 but is it R-19 really necessary? Year round the temps hold right at 60 degrees. I'm going with the standard insulation with the paper backing and would prefer to use R13 to keep costs down.
 

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We build our 2x4 wall 1" away from concrete and use R13. You can get colder out there.

The floor and the lower wall is a pretty standard temperature around 55 degrees.
The top of the wall can get colder down to frost depth so maybe you could split the difference, 13 for 4 ft and 19 for the top.

Fire stopping and air stopping the top of the wall is important. Fire stopping for code and air stopping so air doesn't mingle with air in the floor system.

Close attention to fit and finish of insulation to keep a good separation between warm and cold and you definitely need to block air leaks into the wall.

If you are just doing one room, you want to seal the ends to the concrete to maintain an air seal to behind the wall.

I prefer air barrier poly but you can seal the edges of the wall board and use exterior wall boxes that have a gasket to seal to the drywall.

https://www.shdelectric.ca/archives/1240




 

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Maine has adopted a uniform building code but local authorities can always add to it. You should verify what version of the building codes you are under and if any additions have been made.

For disclosure, I hate basements and usually have issues with some of Neal's advice collected from old habits in Vancouver. End rant.

From your description (unfortunately) you are off to a questionable start.
1. The gap behind the wall is not good.
2. Vapor barriers obstruct the ability of moisture to dry to the inside.
3. Your basement apparently does not have a water problem, but ALL basements have moisture vapor issues and Drylok is vapor permeable. Not bad at slowing liquid water but does not stop moisture vapor as their name implies.
4. And fiberglass (or other fuzzy insulation) should not come on contact with a cold foundation wall.

Note on the gap. The lower portion of the foundation is warmer than the above grade (freezing here in Maine). The resulting convection carries moisture from below up to the cold surface where condensation can form and even a layer of ice. The better approach is a layer of rigid foam insulation (blur or pink) attached directly to the foundation which ensures the inside surface will be warm enough to avoid any condensation.

Pictures always help.

Bud
 

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retired framer
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Bud, you would like basements better if you saw one 20 years old that was done properly. If you don't think your advice works, why are you giving it. End of my rant.
 

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. If you don't think your advice works, why are you giving it. End of my rant.
I didn't say that and you know it. The advice I give is heavily related to what the top in energy science recommends and I have seen it and it works.

Bud
 

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I didn't say that and you know it. The advice I give is heavily related to what the top in energy science recommends and I have seen it and it works.

Bud
I don't know that, you have discouraged people in the several threads.
 

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Discussion Starter · #7 ·
I'm not so sure I'm off to a questionable start with my project. I finished an entire 1300 sqft basement in a previous home and pulled all required permits. This was a little further south but winters were still on the cold side, just not as cold as here in Maine. In that state R-13 was up to code and my research here says I should use R-19 which is probably the route I'll go even though I think it's overkill. I have read and have been told conflicting things on whether dry lock can be used as an effective vapor barrier. The inspector in our previous home said it was more than adequate and was happy to sign off on it. The gap between my studs in the wall will ensure that the fiberglass insulation isn't contacting the dry locked poured concrete walls. It wouldn't be difficult for me to get foam board insulation behind the studded walls but I'm not convinced it's necessary. Appreciate the input.
 

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I'm not so sure I'm off to a questionable start with my project. I finished an entire 1300 sqft basement in a previous home and pulled all required permits. This was a little further south but winters were still on the cold side, just not as cold as here in Maine. In that state R-13 was up to code and my research here says I should use R-19 which is probably the route I'll go even though I think it's overkill. I have read and have been told conflicting things on whether dry lock can be used as an effective vapor barrier. The inspector in our previous home said it was more than adequate and was happy to sign off on it. The gap between my studs in the wall will ensure that the fiberglass insulation isn't contacting the dry locked poured concrete walls. It wouldn't be difficult for me to get foam board insulation behind the studded walls but I'm not convinced it's necessary. Appreciate the input.
Drylok will not stop a leak and if you have a leak it is evident when you have Dryloc so what you have is proof of no leaks which is a good thing.

Anyone that says Dryloc is great where they used it, just never had a problem to start with. Water proofing or more often damp proofing is done on the outside.

I do not disagree with Bud about the foam against the wall being a good thing.
 

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Discussion Starter · #9 ·
My previous basement had some water issues and dry lock took care of that issue.

I'll add foam insulation behind the studs
 

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My previous basement had some water issues and dry lock took care of that issue.

I'll add foam insulation behind the studs
Your water issue was likely wicking up from the ground, not really pressure like a leak. Water will always find a path.


 

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It was coming through a cracks in the wall. 2 coats of drylock took care of it.
How low below ground level was it leaking. I would not trust it. How long has it been since you treated it?

This is extreme the block wall is full of water.

 

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Discussion Starter · #13 ·
The wall was seeping through small cracks just below ground level but it's all moot now. We sold that house years ago.

Our new home was built in 2007 and has a day light walk out basement. The house sits on a hill and this is the driest basement I have ever been in. There is zero mildew or mustiness and it's just begging to be finished. I'm convinced that just using R-19 between the studs is adequate but I'll be taking the extra step of adding and sealing the foam board insulation to the inside walls before insulating. My next question is should I use the paper back or just the batting and add a plastic vapor barrier between the insulation and the dry wall?
 

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Hi Lb, all I can do is give you my recommendations and by the way I'm a retired energy auditor, so not just a visitor with hometown advice.
1. I prefer Roxul over fiberglass. A quick search will describe how it is well suited for below grade applications and provides a bit more r-value.
2. Wall assemblies need at least one direction to dry and in a basement that would be to the inside for areas below grade, so no kraft backing and definitely no plastic VB.
3. Adding a layer of rigid insulation between framing (and insulation) and the foundation is good.
4. Technical note in regards to concrete (or blocks). Concrete acts like a sponge and passes moisture through it easily. Even the damp proofing on the outside or any paint product on the inside will never stop 100% of the moisture vapor. it is beautifully dry right now because any vapor coming through is passing directly to the air. The good news is the amount of vapor is tint and presents no problem in the basement. it only becomes a problem when it is blocked by something like a layer of plastic so it can accumulate and feed any mold spores.

I actually doubt your basement will have any problems but I would still avoid the VB.
Also note, be sure your rigid insulation is not covered with a layer of plastic. 1" pink or blue has a permeability that permits some drying to the inside.

If you are in southern Maine there is an active group down there building some interesting energy efficient homes, Portland area.

Bud
 

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One problem with batts alone in a basement is that they allow for air movement.

When you have air movement, you can get condensation forming on the cold surfaces.

Building materials don't make a very good seal, but platic vapor barrier traps the moisture in the wall assembly.

So as far as I'm concerned, the only good way to use batts below grade is to have a thermal break with rigid insulation against the foundation.

Now for 100% above grade basement walls (sometimes a factor), you can use batts and a well done vapor barrier.
 

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Discussion Starter · #16 ·
Hi Lb, all I can do is give you my recommendations and by the way I'm a retired energy auditor, so not just a visitor with hometown advice.
1. I prefer Roxul over fiberglass. A quick search will describe how it is well suited for below grade applications and provides a bit more r-value.
2. Wall assemblies need at least one direction to dry and in a basement that would be to the inside for areas below grade, so no kraft backing and definitely no plastic VB.
3. Adding a layer of rigid insulation between framing (and insulation) and the foundation is good.
4. Technical note in regards to concrete (or blocks). Concrete acts like a sponge and passes moisture through it easily. Even the damp proofing on the outside or any paint product on the inside will never stop 100% of the moisture vapor. it is beautifully dry right now because any vapor coming through is passing directly to the air. The good news is the amount of vapor is tint and presents no problem in the basement. it only becomes a problem when it is blocked by something like a layer of plastic so it can accumulate and feed any mold spores.

I actually doubt your basement will have any problems but I would still avoid the VB.
Also note, be sure your rigid insulation is not covered with a layer of plastic. 1" pink or blue has a permeability that permits some drying to the inside.

If you are in southern Maine there is an active group down there building some interesting energy efficient homes, Portland area.

Bud
Sounds like sage advice and I am actually in Southern Maine.

Based on your advice this will be my path forward. Please respond and let me know if I'm missing anything.

I'm going to use the foam insulation board against the concrete. Is liquid nails the best way to attach it? Will 1/2 inch board be sufficient or do I need to go with 1 inch? I have read that I should also caulk around the edges of the foam board as well. I'm assuming a silicone caulking will do the trick.

Once the poured concrete is taken care of it sounds like I can just go ahead and add the batting between the studs and dry wall as normal. I've seen Roxul and I believe Deering Lumber carries it so I'll price it and go from there. Appreciate the advice and the assistance. If I've missed anything let me know.
 

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Sorry, fell asleep early last night. At my age you take sleep when you can. But then awake at 2 am so finally got up at 4.

" Is liquid nails the best way to attach it?" It works but is slow to cure and hold. If you can wedge it in place once secured it will stay.

" Will 1/2 inch board be sufficient or do I need to go with 1 inch?" The objective is to ensure the inside surface of the foam board remains above the dew point. The irony is, that means more rigid or less fluffy stuff. Too much fluffy makes that surface colder. Safer to go with 1" especially where any of the foundation is above grade.

Technical note, any foundation area more than 2' below grade suffers very little heat loss. All of the soil acts as insulation.

" I have read that I should also caulk around the edges of the foam board as well. I'm assuming a silicone caulking will do the trick." Yes, see note

Be sure to air seal and detail the rim joist cavity and add fire blocking to the top of your wall.

Bud

Note: I use Loctite Premium 3X in the large tubes. Large tubes cost less per volume and I find the construction adhesive is easy to cap and holds well for months. I cap the end with foil tape.
 
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