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Dave G Posted: Mar 09, 2017 08:59 PM	Living roof I have a customer that is installing a living roof on his house, it has to have a R50 rating. He was wanting 10 inches of open cell sprayed between joists and then 2 inches onto the open cell for the vapor barrier. Not sure if this is a good idea as hard to have consistency of 2lb on the 1/2 lb. Thinking the best would be 2lb first and then 1/2lb. Thoughts?
mark moyer Posted: Mar 16, 2017 11:37 AM	i would apply the closed cell foam on to the roof substrate,,,i would be thinking out at 3"....4 would be better..you could then apply open cell over the closed cell foam to achieve higher rvalue. obviously, an all closed cell system would be best for this assembly...6" depth or there abouts otta work. you will have, by design, an roof assembly that does not allow for the "normal" wetting and drying of that assembly,,,as occurs normally with good design and build practices. you will be dependant on good ventilation practices in the structure. build tight, ventilate right i believe it goes... with appropriately sized mechanical ventilation i would not see a reason for a vapor retarding media over this assembly...in fact,,,i would prefer that any moisture migration, as is normal in the world,,,would be allowed to move into and out of the assembly,,,managed by the mechanical systems,,,rather than risking moisture being "trapped" between the 2 vapor retarding media..(there is no perfect application in this not to perfect world). now,,,forgive me,,,but i can only think of a reason or two to put a garden on my roof,,,and the ones i have been invloved in end up bein darned perty weedbeds after time.. last i knew roofs were put over structures to keep the assemblys below dry....now lets see,,,add dirt,,,water,,,weight...ah the warm fuzzy turns into a fuzzball... foamdude

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Comments

Dave G

Posted: Mar 09, 2017 08:59 PM

Living roof

I have a customer that is installing a living roof on his house, it has to have a R50 rating. He was wanting 10 inches of open cell sprayed between joists and then 2 inches onto the open cell for the vapor barrier.
Not sure if this is a good idea as hard to have consistency of 2lb on the 1/2 lb. Thinking the best would be 2lb first and then 1/2lb. Thoughts?

mark moyer

Posted: Mar 16, 2017 11:37 AM

i would apply the closed cell foam on to the roof substrate,,,i would be thinking out at 3"....4 would be better..you could then apply open cell over the closed cell foam to achieve higher rvalue.
obviously, an all closed cell system would be best for this assembly...6" depth or there abouts otta work.

you will have, by design, an roof assembly that does not allow for the "normal" wetting and drying of that assembly,,,as occurs normally with good design and build practices.
you will be dependant on good ventilation practices in the structure. build tight, ventilate right i believe it goes...
with appropriately sized mechanical ventilation i would not see a reason for a vapor retarding media over this assembly...in fact,,,i would prefer that any moisture migration, as is normal in the world,,,would be allowed to move into and out of the assembly,,,managed by the mechanical systems,,,rather than risking moisture being "trapped" between the 2 vapor retarding media..(there is no perfect application in this not to perfect world).
now,,,forgive me,,,but i can only think of a reason or two to put a garden on my roof,,,and the ones i have been invloved in end up bein darned perty weedbeds after time..
last i knew roofs were put over structures to keep the assemblys below dry....now lets see,,,add dirt,,,water,,,weight...ah the warm fuzzy turns into a fuzzball...
foamdude

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