Roxul Batts in basement wall?

[TechBoyJK]

I know fiberglass insulation in a basement wall is a big no no, but I'm curious if I could get away with using roxul in a limited area where I'd like the insulation there for acoustic reasons. I just need it in a 15ft wide area.

Could I get away with it? Or is it just as risky as using fiberglass?

 

[NetWareHead]

Is this a foundation wall or an interior wall located in the basement?

re: insulating with batts on interior basement wall
"Can I insulate on the interior with fiberglass batts, mineral wool batts, or cellulose?

No. Fiberglass batts, mineral wool batts, and cellulose are air-permeable. When this type of insulation is installed in contact with concrete, the moisture in the interior air condenses against the cold concrete surface, leading to mold and rot. That’s why I advise builders that fiberglass batts, mineral wool insulation, and cellulose should never be installed against a basement wall.​

The risk of moisture problems is reduced if the concrete is first covered with a continuous layer of rigid foam or closed-cell spray foam. If that is done, some builders then install a 2x4 wall on the interior side of the foam insulation and fill the stud bays with fiberglass batts. This approach is less risky than installing fiberglass directly against the concrete. However, I don’t think that fiberglass batts belong in a basement. My advice: if you want a higher R-value, just install thicker rigid foam, and leave the stud bays empty.​

from: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-insulate-basement-wall

 

[Exterous]

I know fiberglass insulation in a basement wall is a big no no, but I'm curious if I could get away with using roxul in a limited area where I'd like the insulation there for acoustic reasons. I just need it in a 15ft wide area.

Could I get away with it? Or is it just as risky as using fiberglass?

Technically you can use fiberglass (or mineral wool for that matter) in basement walls, just not when it comes into contact with concrete.

What is your goal for 'acoustical reasons'? If its for loud noise control you may be disappointed as lower frequency sound waves easily travel through most insulation along with studs, electrical outlets, lights and air vents. The best defense against this is mass and decoupling. Get clips like the IB-3 to decouple your studs from the floor above and add two layers of drywall with an acoustic glue between them.

Failing that things like roxul safe'n'sound or thermafiber aren't that much better at sound dampening that your standard pink fluffy.

 

[TechBoyJK]

1) It would be in contact with a concrete wall.

2) We're using framing that was in the home before we moved in. It's mostly ok, and it would have busted our budget and calendar to tear it all out and rebuid. Otherwise, I would have just put up foam boards first, then framing. In fact, one side of the basement already has the foam insulation. Just not the part I'm looking at.

3) Simply wanted the insulation in the walls for sound absorption and to normalize the acoustics.

4) Yep, I was curious if Roxul batts alleviated the concerns that fiberglass has with being in contact with concrete and moisture.

I'm reading it might be more practical to just get some really dense, heavy wood and fill in the studs with it. It would have added benefit of reinforcing the walls.

 

[Rvenger]

I used fiberglass batts in my basement walls but painted the concrete with a sealer and put a heavy gauge plastic sheeting all the way to the floor. I cut off the insulation at 6 inches above the bottom sill plate. I also run a dehumidifier year round and used purple board.

 

[TechBoyJK]

I used fiberglass batts in my basement walls but painted the concrete with a sealer and put a heavy gauge plastic sheeting all the way to the floor. I cut off the insulation at 6 inches above the bottom sill plate. I also run a dehumidifier year round and used purple board.

did you stop at 6" so that if there was any water that pooled up at the bottom it wouldn't hit the insulation?

 

[Exterous]

1) It would be in contact with a concrete wall.

You don't want either to come into contact with the concrete.

3) Simply wanted the insulation in the walls for sound absorption and to normalize the acoustics.

It will prevent some noise and any additional vibration from an otherwise open air cavity but there'll still be noise pollution. Not saying don't do it (it will certainly be better than nothing) just be aware when setting expectations

I'm reading it might be more practical to just get some really dense, heavy wood and fill in the studs with it. It would have added benefit of reinforcing the walls.

Wood really shouldn't come into contact with concrete either. Local building codes vary but, esp for colder climates, many are now putting rigid insulation against the conrete walls and tuck taping the seams to create the vapor barrier. Then place unfaced batts in the wall cavities before drywalling

Some older codes that may still be effect call for a double vapor barrier which essentially traps moisture in the wall cavity causing mold issues. Not sure if they are still around but WI had this in their energy code as of 2010 or so. Just something to be aware of if you're pulling permits

 

[TechBoyJK]

You don't want either to come into contact with the concrete.



It will prevent some noise and any additional vibration from an otherwise open air cavity but there'll still be noise pollution. Not saying don't do it (it will certainly be better than nothing) just be aware when setting expectations



Wood really shouldn't come into contact with concrete either. Local building codes vary but, esp for colder climates, many are now putting rigid insulation against the conrete walls and tuck taping the seams to create the vapor barrier. Then place unfaced batts in the wall cavities before drywalling

Some older codes that may still be effect call for a double vapor barrier which essentially traps moisture in the wall cavity causing mold issues. Not sure if they are still around but WI had this in their energy code as of 2010 or so. Just something to be aware of if you're pulling permits

The framing was already up when we bought it and the inspector said we were ok to put in electric and hang drywall. but if we tear down the framing and redo it, we have to pull a permit.

 

[NetWareHead]

4) Yep, I was curious if Roxul batts alleviated the concerns that fiberglass has with being in contact with concrete and moisture.

Roxul is mold resistant being made of melted rock etc... so it doesnt get infested like fiberglass insulation. However, if it gets wet, Im sure the R-value diminishes. In any event, its mold resistance is not something I would like to put to the test in my own home by installling it next to an exterior concrete wall. Install it correctly for peace of mind.

You have to be careful about putting batts in the framing next to the concrete walls. The roxul might not rot, but the moisture the batts trap between them and the wall will mold and rot the wood framing.

Can you carefuly pry the nails out of the framing and reuse it after properly insulating the wall first?

 

[TechBoyJK]

Roxul is mold resistant being made of melted rock etc... so it doesnt get infested like fiberglass insulation. However, if it gets wet, Im sure the R-value diminishes. In any event, its mold resistance is not something I would like to put to the test in my own home by installling it next to an exterior concrete wall. Install it correctly for peace of mind.

You have to be careful about putting batts in the framing next to the concrete walls. The roxul might not rot, but the moisture the batts trap between them and the wall will mold and rot the wood framing.

Can you carefuly pry the nails out of the framing and reuse it after properly insulating the wall first?

There's too much tied into the existing framing to tear it down. Cliffs: costs too much.

Right now the plan is no insulation at all. Our only legit option at this point is to spray it in, and that's $1000+ to have it done right. At this point, I'm just looking for ways to minimize sound bouncing off the concrete.

 

[NetWareHead]

There's too much tied into the existing framing to tear it down. Cliffs: costs too much.

Right now the plan is no insulation at all. Our only legit option at this point is to spray it in, and that's $1000+ to have it done right. At this point, I'm just looking for ways to minimize sound bouncing off the concrete.

Thats not a legit option either IMO. You run into the same issue where the wood will mold after you entomb it under sprayed insulation against the concrete.

You might want to install carpet or some sort or furniture. That has an added effect of reducing echo. Or put in a drop ceiling.

 

[TechBoyJK]

Thats not a legit option either IMO. You run into the same issue where the wood will mold after you entomb it under sprayed insulation against the concrete.

You might want to install carpet or some sort or furniture. That has an added effect of reducing echo. Or put in a drop ceiling.

Well, I read quite a bit of stuff that said the spray foam was the way to go for old construction, because its the only thing that will get between the studs and concrete. Everything else, even batts, will leave gaps. Even various insulation sites and a few reddit posts suggested it.. but also said 'better if you tear it out' in the same conversation.

 

[MustISO]

I always wondered about this. When our house was built in the early 2000's they used fiberglass insulation in all the basements. It has the paper backing and the silver front but it's right up against the basement walls which is poured concrete.

Basement is finished at this point so not a lot I can do about it but we do have one unfinished area we use for storage and the insulation looks like it's either fading or yellowing.

 

[NetWareHead]

Well, I read quite a bit of stuff that said the spray foam was the way to go for old construction, because its the only thing that will get between the studs and concrete. Everything else, even batts, will leave gaps. Even various insulation sites and a few reddit posts suggested it.. but also said 'better if you tear it out' in the same conversation.

Would make me nervous. How big is the gap between the concrete and the stud? Can spray foam in the thicknesss of the gaps properly stop moisture infiltration? There is a reason why "better if you tear it out" was suggested. Its the only way to guarantee a proper install.

 

[Exterous]

The framing was already up when we bought it and the inspector said we were ok to put in electric and hang drywall. but if we tear down the framing and redo it, we have to pull a permit.

If you're putting in electrical I'm not sure thats true. Usually new electrical work requires a permit. That said I know many people don't bother. For my area one reason is that they won't pass an electrical inspection if it doesn't meet non-electrical requirements like egress. Their supposed idea is that it will cut down on non-livable space basement renovations. In reality it just seems to mean no one bothers to pull permits

Well, I read quite a bit of stuff that said the spray foam was the way to go for old construction, because its the only thing that will get between the studs and concrete. Everything else, even batts, will leave gaps. Even various insulation sites and a few reddit posts suggested it.. but also said 'better if you tear it out' in the same conversation.

Not an expert on spray foam but I know that some are only vapor barriers if it reaches a certain thickness. So if its only a tiny space between the concrete and the studs then it may not function as vapor barrier

I always wondered about this. When our house was built in the early 2000's they used fiberglass insulation in all the basements. It has the paper backing and the silver front but it's right up against the basement walls which is poured concrete.

Basement is finished at this point so not a lot I can do about it but we do have one unfinished area we use for storage and the insulation looks like it's either fading or yellowing.

Recommendations and some codes for this have changed quite a bit in the last 2 decades. How much it matters depends on your climate (colder tends to be worse) and how damp your concrete is. If you have a low voltage outlet (coax, ethernet etc) then its possible they may not have used a fully enclosed box for it allowing you to see the condition of the insulation behind the wall and evaluate the situation.

 

[TechBoyJK]

Just to be clear; we did have to pull a permit for the electric that was installed. What we didn't need was a 'construction/building' permit for finishing the walls because the framing was already there.

If we tore out the existing framing and installed new framing, we'd need a permit for that, plus a permit for electrical.

We needed a permit for electrical either way.

 

[Humpy]

I always wondered about this. When our house was built in the early 2000's they used fiberglass insulation in all the basements. It has the paper backing and the silver front but it's right up against the basement walls which is poured concrete.

Basement is finished at this point so not a lot I can do about it but we do have one unfinished area we use for storage and the insulation looks like it's either fading or yellowing.

There are two separate issues that are not being differentiated in this thread.

Your concrete walls are almost 100% likely to have been waterproofed from the outside so there is very little chance of water infiltration.

Your concern is warm, moist air condensing on the colder surface of the concrete and wetting the insulation. Depending on a few specifics there shouldn't be much moisture to contend with and what little there is should be able to dry to the inside of the house without causing much of an issue.

 

[MustISO]

There are two separate issues that are not being differentiated in this thread.

Your concrete walls are almost 100% likely to have been waterproofed from the outside so there is very little chance of water infiltration.

Your concern is warm, moist air condensing on the colder surface of the concrete and wetting the insulation. Depending on a few specifics there shouldn't be much moisture to contend with and what little there is should be able to dry to the inside of the house without causing much of an issue.

The concrete was definitely sprayed with some type of waterproofing. If I recall correctly they did two coats on the outside and one inside. The insulation also had some type of heavy plastic against the concrete. After watching some videos on youtube I'll definitely go for the solid foam if/when we purchase a new house.

 

[paperfist]

Foam board?

 

[Humpy]

The concrete was definitely sprayed with some type of waterproofing. If I recall correctly they did two coats on the outside and one inside. The insulation also had some type of heavy plastic against the concrete. After watching some videos on youtube I'll definitely go for the solid foam if/when we purchase a new house.

You shouldn't have any issues with your basement. 🙂

Exterior insulated and waterproofed basements solve most all of the issues with moisture and allow more freedom in using the interior space. I wouldn't want a new house built any other way.

 

[TechBoyJK]

Foam board?

New construction pretty much always insulates the basement wall with solid foam board around the entire perimeter, then you frame up walls after that. Has to do with the solid foam not having any nooks and crannies for air to slip through.

 

[Rvenger]

did you stop at 6" so that if there was any water that pooled up at the bottom it wouldn't hit the insulation?

Exactly. I doubt it would happen but you never know if the drains were to ever fail I guess.

 

[paperfist]

New construction pretty much always insulates the basement wall with solid foam board around the entire perimeter, then you frame up walls after that. Has to do with the solid foam not having any nooks and crannies for air to slip through.

I might not understand, but it sounded like you were asking if the Roxul could go against concrete. If it already has foam board against the concrete then I don't see where there's a problem with going over the foam with Roxul.