New Double Stud Wall Assembly with Rock Wool & Smart Vapor Retarder
We’ve been inspired to test a new double stud wall assembly on First Steel that may be used in future projects like reNEWBOLD. There is a 2.5 minute video below walking through the basics of the wall assembly. You will find more details below the video to feed your inner building science geek’s thirst for knowledge and discussion.
If you’d like to see this wall in person before we close it up, please attend our mid construction event tomorrow evening between 4PM and 8PM. Use the Facebook Event to RSVP and find out more details. We hope to see you there. As a side note, anyone interested in the reNEWBOLD project should strongly consider attending as one of the homes is a beta model for the homes in South Philly.
New Double Stud Wall Details
- Double 2×4 wall on 24″ centers
- 2″ gap between studs with no staggering of studs
- ZIP sheathing on exterior
- R15 Roxul ComfortBatt Rock Wool Insulation for 24″ center wood 2×4 framing
- 2″ AFB Roxul Rock Wool Insulation in 2″ gap between walls
- Certainteed MemBrain Smart Vapor Retarder on outside of interior stud wall
- R15 HD Ecobatt unfaced insulation on 24″ centers in interior stud wall
- All electric and utilities on interior wall inside of the vapor retarder
- 5/8″ Type X Drywall
That’s it for the assembly. I’ll try to address some additional detail I didn’t have time for in the video.
The rock wool insulation is very unique product that is used a lot in Europe and also in the US in commercial fire rated and sound proofing applications. What’s great about it is how well it completely fills the cavities. It does not droop or sag at all like typical fiberglass batts. It also does not absorb moisture and will not produce mold which makes it perfect for installing during construction and prior to being completely dried in.
In our first test houses, we found it was easiest to frame up the entire house with the exterior stud walls and treat the interior stud wall just like the other interior framing. That allowed us to get the house tight with the ZIP sheathing product and come back to insulate the exterior wall at a relaxed pace once the main framing of the house was completed.
I am still a bit torn on the effectiveness of the vapor retarder, especially when we have the ZIP sheathing and vented rainscreen on the exterior keeping us dry and a thick layer of drywall with multiple coats of paint on the interior. I know people will chime in saying I’m wrong not to have this interior vapor barrier and hopefully I will learn more from the comments in this post to help make a decision on future projects.