Apparently we are the only ones enforcing this part of the energy code

[MASSDRIVER]

General question here: We go to great lengths seal up walls, yet go to greater lengths to vent attics and crawlspaces. If wind wash is such a terrible thing, why are we not enveloping our insulation fully to prevent it? If we create sealed cells, could we therefore use a lower r-value of insulation? Why treat a kneewall in an attic differently than the roof?

Brent.

 

[jar546]

General question here: We go to great lengths seal up walls, yet go to greater lengths to vent attics and crawlspaces. If wind wash is such a terrible thing, why are we not enveloping our insulation fully to prevent it? If we create sealed cells, could we therefore use a lower r-value of insulation? Why treat a kneewall in an attic differently than the roof?Brent.

Slowly and carefully read the first 48 posts in front of yours and you will see the answer.

I for one am a fan of unvented attics. My new house has one. That will eliminate the knee wall issue.

 

[MASSDRIVER]

Slowly and carefully read the first 48 posts in front of yours and you will see the answer.I for one am a fan of unvented attics. My new house has one. That will eliminate the knee wall issue.

I will. I didn't.

Brent.

 

[jar546]

I could be wrong you know. I've been known to be wrong every now and then. I have a special fork for eating humble pie

 

[RJJ]

We all have that fork at times.

 

[kyhowey]

Please list the Code section this is from.Thanks

Table 402.4.2 Air Barrier and insulation inspection component criteria

The first component "air barrier and thermal barrier", last sentence in the criteria "Air-permeable insulation is inside of an air barrier." I slightly misquoted it from memory adding the "must be" instead of "is".

 

[Francis Vineyard]

I too enforce the air barrior in knee walls. But I am not sure if house wrap can be used. Can house wrap be exposed in a crawl space?

Not familiar with this type of configuration but this section R302.10.1 would apply (major brands are class A). I've contacted manufactures in the past and though they recognized it as a air barrier they only provide installation for exterior applications.

Note as brent posted #48 it can tear when not attached to a solid wall membrane in accordance to the manufacturer's guidelines.

R302.10.1 Insulation.

Insulation materials, including facings, such as vapor retarders and vapor-permeable membranes installed within floor/ceiling assemblies, roof/ceiling assemblies, wall assemblies, crawl spaces and attics shall have a flame spread index not to exceed 25 with an accompanying smoke-developed index not to exceed 450 when tested in accordance with ASTM E 84 or UL 723.

Exceptions: 1. When such materials are installed in concealed spaces, the flame spread index and smoke-developed index limitations do not apply to the facings, provided that the facing is installed in substantial contact with the unexposed surface of the ceiling, floor or wall finish.2. Cellulose loose-fill insulation, which is not spray applied, complying with the requirements of :Next('./icod_irc_2012_3_par069.htm')'>Section R302.10.3, shall only be required to meet the smoke-developed index of not more than 450.3. Foam plastic insulation shall comply with :Next('./icod_irc_2012_3_par208.htm')'>Section R316.

 

[Francis Vineyard]

Over the weekend I was searching EarthCraft guidelines for a different issue (they don't allow a return pathway in unvented crawl spaces) and noted in their earlier version specifically did not require the attic knee wall to be encapsulated but now the newer versions do!

Keeping up with this stuff is like herding cats being chase by wild dogs.

Francis

 

[markw]

Ive been soooooo waiting for this topic to come up. After much reading, I think the air barrier, when defined as a "system" not just an individual component, can be installed on the interior or the exterior as long as it is approved and installed correctly. The ceiling under a vented attic must have the air barrier also-so if I have a t+g ceiling under this vented attic is it an approved air barrier?? Big neg dude- its gotta be gyp board,or you need to add an approved air barrier to the bottom of those trusses before running your t+g. Thats what I tell big Jim contractor on a new job and he looks at me like "are you F-in nuts". Right or wrong-Its what you learn after you know everything that matters.... The code only requires the air barrier in the exterior thermal envelope-Right? and it must be in alignment with the insulation-Right? So soffits/knee walls that are exterior facing will require it.Ok clear as mud.

 

[bptp32]

I totally agree with JAR on this one. I require an air barrier on the "exterior" side of a knee wall that is exposed to a vented attic area. Table 1102.4.2 in the Residential code mandates "air permeable insulation is inside of an air barrier". Inside an air barrier means totally encased in an air barrier. Fiberglass R values can be reduced by almiost 30% if air is allowed to wash across the stud cavity due to the venting of the attic area. The only exception that I would allow would be if the rafter bays are insulated and venting in the individual bays is in place (air-permeable insulation not air-imperable insulation). Great topic. Thanks Bob