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insulation and vents question please help

BlueCalifornia | Posted in General Questions on

i had a 10×16  lean-to shed built (diagram of how the shed is built is attached below)  and i will be using it as my part-time office here in southern California.  after finishing up electrical rough in past few days i started looking online for insulation and type.  this is where i got really confused after having also talking to some spray insulation contractors in the area.  my original plan was to install R13 unfaced batts (24″ on center is how the shed was built) in the exterior wall and roof rafter and then dry wall however after talking to several spray foam contractors, they advise me not to go with the batts because there would be mold issue later down the line because moisture will be trapped between the drywall/batts as there is no ventilation.  shed was built with T11 siding and moister barrier. roof has regular shingles but used a radiant barrier on the backing of the OSB (see attached photo).  not sure if contractors trying to generate more business for themselves by selling me closed cell spray insulation or can i just installed the R13 batts even though i dont have any ventilation? with the pitch of the roof and style, i am not sure what i can do myself to ventilate it.. also the walls.  i live in southern california about 50 miles inland and its usually pretty dry all year round.

maybe i am over thinking it but i just wanted to seek some expert advice on how to minimally complete the project without doing too much unnecessary things that will cost MORE financial burden. 

thank you!

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  1. mr_reference_Hugh | | #1

    You are in either zone 1 or 2 possibly but unlikely zone 3 - depending exactly where you are.

    The assemblies would normally dry to the inside and you would have a vapour retarder on the outside. But this is hot humid climates. It is also for situations where homes are air conditioned or have a dehumidifier.

    Your T11 siding, painted, would act as a vapour retarder, but like not air sealed all that well for a shed.

    Drywall is very vapour open, unless you choose a paint that is a vapour retarder.

    I don’t trust myself what the spray foam contractor is saying. It does not make sense to me.

    If you are in a primarily dry climates, I would think that you just add batt insulation, put an air barrier on the inside (could use drywall) and then drywall. I would use mineral wool batt insulation in this myself instead of fibreglass batt.

    You can search the internet for all the potential problems with spray foam. If the spray foam installer can’t clearly explain the risk of mold, then I am not sure he understands the issue. I would speak to the spray foam installer again and press for a detailed and logical explanation.

    1. BlueCalifornia | | #2

      I am in zone 3 and yes I follow what you are saying completely hence been doing a lot of research myself which has became a little overwhelming because everyone has a different opinion. Thank you and perhaps someone once will chime in here

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