Insulating small area of roof / ceiling - IECC exemption?

[Jay]

Hello....not doing too much commercial work I am looking for guidance on a small project. Commercial office building has a small 10 x 9 greenhouse type wall/roof assembly that was built in the mid-80's. Owner wants to replace with wood frame assembly with solid roof and new window wall. I have a question about insulation...

The area for new roof framing works best with a 2 x 6 rafter in order to maintain the wall height for windows. Ok with the rafter span. Looking to avoid spray foam insulation if possible. I see that per IECC we are required to have R-38. Can anyone please steer me in the right direction as to where I might find an exemption in the current energy code for such a small area? Not sure if C503.3 building envelope for existing buildings helps without me analyzing the entire building? I am going from full fenestration to solid roof. Common sense we will be better off. Thanks!

 

[classicT]

Not sure that you will find an exception....

But if it were me, I would go with the U-factor method. Insulate the void with batt, and add some continuous insulation on the top of the deck. Would mean a TPO roof, but I would be that is doable.

Otherwise, 2x10 rafters are in your future.

 

[steveray]

I would try to prove equivalency to what is there and treat it as more of a repair than new and see if the BO buys that...

 

[Jay]

Thanks for the replies. I emailed the Building Inspector and will see what he has to say.

 

[Mr. Inspector]

Try https://www.energycodes.gov/comcheck. Maybe with more insulation in the walls and better windows it will work.

 

[steveray]

Any paperwork on the existing windows? Can you get a U-factor?