Zone 6 Wall Insulation/Vapour Barrier Question

[Schumi]

I am now ready for insulation on my 35X40 detached garage build. I plan to seal all gaps/seams with foam, then insulate the 2x4 walls with Roxul R-15. I installed Tyvek between the OSB and Hardieboard exterior siding. I do plan to keep the garage heated/cooled year-round.

My question is this: do I need a vapour barrier between the Roxul and the drywall in Kansas City?

Any other suggestions/tips are welcome.

 

[stm317]

Yes you need a vapor barrier on the inside of the insulation. If the Roxul has a facing, the facing may act as a vapor barrier but it depends on materials and how it's installed. The simpler option might be to use unfaced insulation and plastic sheeting.

 

[DC73]

There are some building science experts that hang out here: http://www.greenbuildingadvisor.com/qa

They would be your best source of reliable info. There are also some good articles on the site regarding vapor retarders (building scientists are getting away from using the term vapor barriers). Whether or not you need a vapor retarder and where it needs to go is very climate dependent. Don't get this one wrong or you can create problems for yourself down the road.

DC

 

[Schumi]

stm317 - I am going with Roxul as it has a true R-15 and is friction fit/easier to install.

DC73 - That is what I understand as to getting it right. I've searched greenbuildingadvisor for vapor/vapour barrier, but hadn't tried retarder. Thanks for the tip on terms.

Roxul doesn't even offer a faced product, which got me wondering if I even needed one. With the OSB sheathing, then Tyvek, then Hardiboard, it just wasn't sure.

 

[DC73]

DC73 - That is what I understand as to getting it right. I've searched greenbuildingadvisor for vapor/vapour barrier, but hadn't tried retarder. Thanks for the tip on terms.

I use Roxul R15 in my workshop walls and was very happy with the choice.

Here are some links to articles that might help you:

http://www.finehomebuilding.com/membership/pdf/174534/021264084-87-EnergySmart.pdf

https://buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers

https://buildingscience.com/documen..._term=0_194890bc8c-35739b2ea6-63891105#foot05

https://buildingscience.com/documen...sheet-310-vapor-control-layer-recommendations

http://www.greenbuildingadvisor.com...-when-you-put-plastic-vapor-barrier-your-wall

Pay attention to the dates that articles about vapor retarders/barriers were written as the science is evolving and the most recently dated articles tend to have the best and most current information.

DC