Insulation and sheetrock install questions

[ole442]

My 24 X 30 garage needs insulation and sheetrock installed and I have questions. I have wood frame with 7/16 OSB Tyvek wrap on the outside with vinyl siding over that. Should I just put fiberglass insulation with the kraft paper towards the inside before putting up the sheetrock? Would that be correct? Any info appreciated.

Thank you,
OLE442

 

[Chris705]

Most likely yes. But it depends on what city you’re too close to?
If you will be predominantly heating your garage the vapor barrier (kraft facing) wants to be to the inside. Predominantly cooling towards the exterior face.

Good luck with your build!

 

[benjamintmiller]

And if you heat and cool and live in zones 1-5, the Kraft facing is unnecessary and you can use unfaced insulation.

(See figures 11 and 12):
https://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers

 

[ole442]

I live in zone 5 and right now, I have AC in summer but no permanent heat for winter just a kerosene salamander type that I use when I work out there. Hope to get a mini split system next spring.

 

[ole442]

So, I should used unfaced insulation in Zone 5?

 

[DC73]

So, I should used unfaced insulation in Zone 5?

That's probably best. Kraft paper is somewhat of a smart vapor retarder. It normally blocks the movement of water vapor but if the interior wall cavity became wet, the kraft paper would open up and allow some drying. But, it would take a longer time. If kraft faced insulation is cheaper or more readily available, it's not terribly difficult to peel the kraft paper off.

DC

 

[matt_i]

I'm going to recommend at least looking at Roxul. Its more expensive yes but I believe a better product than fiberglass, and you get more R-value to boot.

High on the list should be air-sealing, outlet boxes, attic access points, etc. I spent time caulking the rough framing on the inside of the wall cavity. Insulation of any type works best when its complete dead air space inside a stud cavity and there isn't a slow air infiltration thru it.

I wouldn't put less than Type X drywall but also take a look at Type C. As above, incremental cost increase but the fire protection goes way up.

 

[DC73]

I'm going to recommend at least looking at Roxul. Its more expensive yes but I believe a better product than fiberglass, and you get more R-value to boot.

I agree. I primarily went with Roxul for my workshop (all walls, bottom layer of ceiling insulation - top layer was fiberglass to help control costs). Mineral wool has better r-value per inch, blocks sound and air flow better, and has better fire resistance. All around better product than fiberglass. Very happy with the results in my shop.

DC

 

[67CarGuy]

Matt and DC are spot on. Mineral wool beats fiberglass every day IMO. You can easily cut it with a bread knife. Just wear a facemask and proper clothing when you're installing it - you don't want that that stuff in your lungs or on your skin any more than fiberglass.

Mineral wool also will deal with water much better than fiberglass - fg usually just turns into a disgusting mess, while the wool can dry out and go back to doing its thing.

 

[Kaizen]

I agree. I primarily went with Roxul for my workshop (all walls, bottom layer of ceiling insulation - top layer was fiberglass to help control costs). Mineral wool has better r-value per inch, blocks sound and air flow better, and has better fire resistance. All around better product than fiberglass. Very happy with the results in my shop.



DC

What size wall do you have? My dealer didn’t have a 5.5 inch roxsul. Only 3.5 for 2x4 and couldn’t get a good answer to fill the cavity


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[DC73]

What size wall do you have? My dealer didn’t have a 5.5 inch roxsul. Only 3.5 for 2x4 and couldn’t get a good answer to fill the cavity

My walls were 2x4. I'm surprised Roxul for 2x6 walls isn't readily available. I suppose you could do a hybrid installation by installing and then compressing some unfaced fiberglass R13 batts along with a layer of 3.5" Roxul. Compressing the fiberglass will derate the r-value a bit but since the Roxul is R15 to begin with, you'll gain some back and still have a well insulated wall.

DC

 

[Kaizen]

My walls were 2x4. I'm surprised Roxul for 2x6 walls isn't readily available. I suppose you could do a hybrid installation by installing and then compressing some unfaced fiberglass R13 batts along with a layer of 3.5" Roxul. Compressing the fiberglass will derate the r-value a bit but since the Roxul is R15 to begin with, you'll gain some back and still have a well insulated wall.



DC

No kidding. I hate the idea of compressing it but might have to. I’ll have to call manufacturer and see


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[DC73]

No kidding. I hate the idea of compressing it but might have to. I’ll have to call manufacturer and see

Compressing a fiberglass R13 batt into 2" of space will net you roughly R8.5 according to Owens Corning. Add an R15 mineral wool batt to that and you end up with R23.5 overall. A standard fiberglass batt for a 2x6 wall gets you about R21.

DC

 

[slow84lx]

In the DFW area Roxul is readily available for 2x6 walls on 16" centers, not at every home center but most. One of the Lowe's stores is the main stocking center for this area and always has plenty, most of the other stores have limited supply but can get it if asked for.

I'm also in the mineral wool camp. It won't burn with a MAPP gas torch applied to it, it blocks sound very well, and has high R value. After caulking all the stud / joist cavities and utility boxes, and installing the mineral wool my garage is comfortable, even on the hottest days, until I open the door. Huge difference in the comfort in the room above the garage also.

Jonathan

 

[TheOtherChris]

I know Roxul is available in 3.5", 5.5" and 7.25" bat thicknesses as I have used all of the above for different applications.


You can order it through HomeDepot and they will ship it to your local store for pickup.

I very much prefer it over fiberglass.