I need help with Massachusetts Chap 13
Ok, I’m with a architecture firm in Milwaukee, Wisconsin. We have been retained to design a multistory building in Massachusetts and are having problems with the energy code. Obviously we have no experience working in Massachusetts.
Some criteria:
- B occupancy
- 99,000 sq ft
- 3 stories
- Masonry veneer cavity wall construction
- Climate zone 13a
- 20% glazing area
Now typically our standard wall construction (inside-out) is drywall, vapor barrier, R-19 Batt in the 6″ stud cavity, exterior gypsum board sheathing, air infiltration/moisture barrier, 2″ air cavity, masonry veneer. This was all fine until a product rep pointed out that our wall construction wouldn’t pass the Mass. energy code due to the lack of a continuous insulation layer and the vapor barrier was located on the wrong side of the wall. The rep sent us a sketch of their typical wall section: drywall, empty stud cavity, gyp. bd. sheathing, vapor barrier, 2″ R-13 high performance rigid insulation, air infiltration/moisture barrier, air cavity, masonry veneer. Research shows that Mass. requires a R-3 continuous layer of insulation. So we had planned on swapping the rigid insulation sheathing for the gyp. bd. sheathing. We never did understand how the vapor barrier could be on the wrong side of the wall as Mass. is a heating climate and we had the barrier on the warm side. We also felt the exterior rigid insulation was a pretty funky and expensive way to get less R value so we concluded that it was probably that person’s unique method of wall construction. We felt the issue was resolved, until we started talking to some contractors. The contractors are reiterating what the product rep had previously said: the vapor barrier goes outside of the sheathing and is covered by rigid insulation. Looking at the code further, 1304.1.2 states the vapor barrier can go on the inside face of the studs, provided “All joints, holes, imperfections and penetrations of the vapor barrier shall be taped tight with a vapor barrier tape recommended by the vapor barrier manufacturer.” Ok, I guess it’s going to be a bit difficult to make the junction boxes vapor tight, but is that the sole reason why designers are jumping to a exterior vapor barrier?
To complicate things, we have run several different ComCheck (Mass.) combinations.
- R-20 cavity 0 continuous fails “to meet mandatory requirement” Probably referencing to the missing continuous insulation.
- R-19 cavity R-3 continuous passes 21%
- R-13 cavity R-3 continuous (code min) passes 20%
- R-21 cavity 0 continuous passes 19%
We find it fascinating that R-20 would fail to meet the continuous insulation requirement while R-21 (6″ high performance batt) would pass. Thoughts?
Certified boat fetish.
Replies
I have been told by several building officials that chapter 13 in tree opinion should be eliminated or at least heavily revised ,To make some kind of since .
BLAME MEL FINK !!!!!!!
The scenario you first described made sense to me. We've done lots of compliance checks here in Ma. you have to to get the building permit. I use RESCHECK 3.6 for MA.
See if the specs are any different for them, I don't know the direct link but Google bbrs in ma. and follow for energy and you'll get RESCHECK. Just a thought, up the roof value and you don't have to worry too much about the walls, or trade off on mechanicals and you don't have to worry about either. Good luck.
David
The advise you've been getting is right on the mark. With a metal stud wall, we typically never install batt insulation and especially a vapor barrier on the inside. This really is a carry over from residential construction. As a business use group, once a new tenant moves in and the space is reconfigured, it's almost guaranteed the batt and v.b. will be torn up and compromised.
Because you need a minimum continuous insulation outside the studs, we typically beef this up to meet the minimum insulation requirement. The membrane or fluid applied air/vapor barrier is put over the gyp board or (even better) dens glass, thus placing it on the winter warm side of the insulation. Most important (and the trickiest) is keeping the air barrier continuous up over the roof edge and onto the roof. Make sure you specify the nice brick ties that penetrate the rigid and get right to the dens glass.
This link has a wealth of information and some very good details: http://www.mass.gov/bbrs/energy.htm
Yep, I've been to the site and have the details printed up and handy. I guess the biggest question is why wall design A is the regional standard vs. the more affordable and better insulating wall design C. Is it because of the state's anal concern about vapor barriers? That's the only reason I can see for using design A.
Certified boat fetish.
That was kind of the argument when the new commercial energy code came out a few years back. Massachusetts realized that the vapor barrier is way, way less important to the envelope design compared to the air barrier. The amount of vapor passing through an air leak is nearly a magnitude larger than simple vapor permeance. Buildingscience.com is another good source for info on this.
We're finding that Assembly C isn't cheaper or better insulating. By code, you have to have R-3 minimum continuous insulation. There's a labor cost associated with that. Beef it up to R-7, the labor costs are just about the same and you're done with insulation. No interior insulation or vapor barrier needed. Run COMcheck with R-7 continuous and 0 cavity and see what you get.
The big concern here with the vapor barrier and metal studs is the vapor barrier is never going to be installed correctly and you can nearly guarantee condensation forming on the metal studs. With the rigid outboard of the wall the studs stay at approximately the indoor temperature.
Ok, thanks for the explanation!
Certified boat fetish.