ashrae 90.1-2007 - commercial bldg envelope insulation

[syarn]

existing shell building; 1 story; 6000 sf; climate zone 4 (NJ); type IIB; no sprinklers.

existing exterior shell wall assembly - 8" CMU, 2" airpace, 4" brick veneer, no insulation in airspace or CMU cores as far as we know...

interior fit-up scope plan review is requiring exterior wall insulation.

since the wall is existing; insulation is most easily added on the interior side which unfortunately begins to move the dew point towards the interior....with the new 2007 ashrae 90.1 the need for CI (continuous insulation) is introduced....

so what is the detail to apply R-9.5 (CI) over the masonry exterior wall and OR if it is considered steel frame R-13 cavity + R-7.5 (CI)?....this seems like new territory....never seen 2" rigid foamular for example attached to inside face of CMU..???

we were thinking of going with 1-1/2" of foamular glued or anchored to the interior CMU and than set 3-1/2" metal studs with faced batt.....

this energy code seems to not account for this scenario as opposed to building new and putting the CI in the exterior side air space......keeping the dew point closer to the exterior side.

any comments or thoughts?

 

[Mr. Inspector]

In PA you are supposed to use the 2009 IECC not ashrea. I know NJ has there own codes. I usually see sprayed on foam on the inside.

 

[mtlogcabin]

Thought foam was limited to a maximum 4 inches on exterior walls?

 

[syarn]

to get R9.5 c.i. eg with icynene I think around 2.5" would do the trick...

however termites, vapor barrier & covering the foam above the finsihes ceiling to the deck issues would concern me....

at this point we are working on the bldg owner either showing the shell architect drawings with the rigid foam in the airspace between brick or CMU OR certifying in a letter that 2" of rigid is in the exterior airspace.

 

[syarn]

now owner hiring engineer to do a comcheck...

 

[coloradocode]

You may want to check out Building Science Corporation's website www.buildingscience.com. They may have a white paper that addresses your issue.

Rick, Section 501.2 of the IECC allows ASHRAE 90.1 as an alternative. Does PA delete that option out of the code. If they do, they may be in violation of the DOE requirements for the good old stimulas money, if you care.