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Rock Wool and Vapor Barriers
- Thread starter Samh
- Start date
I did a lot of research and my conclusion was, it depends where you live. I'm in southern PA so I decided no vapor barrier on the inside but Tyvek over the osb sheathing on the exterior. The tyvek will be very carefully installed per duponts specific procedure with tape and disk nails. I'm also doing rock wool.
I believe they say tyvek is an air and water barrier but will let vapor through from inside to outside.
I believe they say tyvek is an air and water barrier but will let vapor through from inside to outside.
The key with any building is air sealing -- when you reduce the movement of air you reduce the amount of water vapor transfer. Air carries water into wall assemblies where it gets trapped. This is why there were so many problems with houses back when plastic was widely used. Small leaks in the plastic allowed water to get into the wall cavity and this water could not get out.
Heat is power -- Warm air can hold more water ..warm air will create a stack effect --pushing that warm air out of the building. Or into a wall cavity
Sealed attics and crawl spaces aid in air sealing
As you move into colder climates the need for a VB increases ... remember plastic is not a recommended VB. It's a 1 and should only be used in very cold climates (AK)--and then done very carefully .. other products are recommended over it anyway. VB is really a vapor retarder.
A properly conditioned building with few people will be different vs one with more people ..
Modern barriers come in rolls now .... I would make sure to use one with the ZIP type exteriors. Tyvek and house wraps are really rain screens .. glorified felt paper. They need to be done correctly especially with vinyl siding as it leaks so much. Installation determines how much of an air barrier they are ..
A proper perm VB on the inside is never going to hurt if done correctly .. rockwool is a better air sealer vs fiberglass. You have to air seal with fiberglass
Heat is power -- Warm air can hold more water ..warm air will create a stack effect --pushing that warm air out of the building. Or into a wall cavity
Sealed attics and crawl spaces aid in air sealing
As you move into colder climates the need for a VB increases ... remember plastic is not a recommended VB. It's a 1 and should only be used in very cold climates (AK)--and then done very carefully .. other products are recommended over it anyway. VB is really a vapor retarder.
A properly conditioned building with few people will be different vs one with more people ..
Modern barriers come in rolls now .... I would make sure to use one with the ZIP type exteriors. Tyvek and house wraps are really rain screens .. glorified felt paper. They need to be done correctly especially with vinyl siding as it leaks so much. Installation determines how much of an air barrier they are ..
A proper perm VB on the inside is never going to hurt if done correctly .. rockwool is a better air sealer vs fiberglass. You have to air seal with fiberglass
theoldwizard1
Well-known member
Rock/mineral wool only has a few benefits of fiberglass.
• Reduced fire risk (not that your insurance company would give you a discount)
• Better noise insulation.
Got any proof ?
A 1"-2" layer of spray foam, even if it is just along the joints, is even better.
• Reduced fire risk (not that your insurance company would give you a discount)
• Better noise insulation.
A proper perm VB on the inside is never going to hurt if done correctly .. rockwool is a better air sealer vs fiberglass.
Got any proof ?
A 1"-2" layer of spray foam, even if it is just along the joints, is even better.
rustyjames
Well-known member
There's no question that rockwool is much more denser than fiberglass. I like it because it's much easier to cut and fit into cavities without any type of fasteners.
ace10
Well-known member
On our detached garage:
No vapor barrier on the inside. 2x6 construction. Roxul batts. Exterior is wrapped in Pro Clima Solitex, under brick veneer and hardieplank.
No vapor barrier on the inside. 2x6 construction. Roxul batts. Exterior is wrapped in Pro Clima Solitex, under brick veneer and hardieplank.
Last edited:
James-W
Well-known member
In my opinion you would be better off with spray foam. The "up front" cost is quite a bit more money, but long term I think you will find the savings in heating/cooling will more than make up for the higher initial cost.
To clarify, I already have the rock wool. I should have put more info in the initial post. I am in climate zone 3 according to the DOE climate map. Walls are 2x6. Tyvek housewrap with taped seams. Cement fiberboard siding. Am doing plywood for internal wall coverings.
Rock/mineral wool only has a few benefits of fiberglass.
• Reduced fire risk (not that your insurance company would give you a discount)
• Better noise insulation.
Got any proof ?
A 1"-2" layer of spray foam, even if it is just along the joints, is even better.
What ... that a perm will not cause a problem ? or Rockwool is denser and better at reducing air movement ? both are true
In my opinion you would be better off with spray foam. The "up front" cost is quite a bit more money, but long term I think you will find the savings in heating/cooling will more than make up for the higher initial cost.
IMO -- spray is always the best --- That's what I use ... but, the OP is talking about Rockwool ? RW is a decent product ...
Nothing is going to seal like foam
wolfhawk73
Well-known member
Whats everyone doing with Rock wool and vapor barriers? Seeing mixed info on the web, and looking for what everyone here has done. My gut says vapor barrier.
NO to a plastic vapor barrier, especially in Georgia. You basically need an 11-month winter for that stuff to be effective.
If you really want to go down a rabbit hole, follow this guy:
https://www.buildingscience.com/users/joseph-lstiburek
Find his videos on YouTube. He might change how you do the entire system. By the time you're about 2 hours in, you'll want to rip the walls of your house apart to do it better. Fascinating stuff, and he's got a great sense of humor.
I'm in the pacific northwest... even with roxul, we use plastic VB inside, and something more permeable outside. (I used tar-paper, and metal siding). The 'warm' side of the wall is meant to be the inside. Moisture is pushed to the outside by heating the building.
You probably have to flip this practice around in a warm climate when you actively cool the interior space for long periods.
The main thing is - don't use two types of air-tight material. (Traps moist air, that can't vent, and causes wood to mold/rot.) And I wouldn't use full interior spray foam due to it making future changes much more difficult with your sheathing, studs, and utilities all glued together.
You probably have to flip this practice around in a warm climate when you actively cool the interior space for long periods.
The main thing is - don't use two types of air-tight material. (Traps moist air, that can't vent, and causes wood to mold/rot.) And I wouldn't use full interior spray foam due to it making future changes much more difficult with your sheathing, studs, and utilities all glued together.