[Greenbuilding] embodied energy was Polyiso strength on roof (ErgoDesk)

[John Salmen]

Yes and no - my concern was venting with exterior wet air in a well sealed and insulated building i.e. no stack air from the interior. Underside of ply sheathing in well interior sealed code vented (1:300) homes had still discoloured (fairly common here in poorly interior sealed houses).  So the question remained as to whether venting made it worse or not – but since I have to vent by code for a standard truss assembly it is a moot question

 

So the remaining question is about using materials that can deal with the moisture cycling and that is why I am wondering about cellulose over the long term. The increased moisture causes it to settle more and it seems to clump more.  Ply sheathing seems fine for cycling moisture but blackening would indicate that moisture levels do get in the 20% range and that could support mold growth in cellulose.

 

Good study done in my area below

 

http://smtresearch.ca/sites/default/files/resource/Highly%20Insulated%20Ventilated%20Wood%20Framed%20Attics%20in%20Cool%20Marine%20Climates.pdf

 

From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Alan Abrams
Sent: December-13-14 11:09 AM
To: Green Building
Subject: Re: [Greenbuilding] embodied energy was Polyiso strength on roof (ErgoDesk)

 

< I would guess new trusses as being the least material / lowest cost / highest benefit / integrity. Moisture conditions in the attic would be a concern – from experience I can say that venting with wet winter air is not effective. Cellulose fill is moisture tolerant but that is not the same as moisture cycling.>

 

I assume it would follow to make the ceiling a vapor barrier--no cans, fans; sealed junction boxes, etc. (Smart membrane behind sheet rock?) 

 

Another way to frame this is: are the moisture problems you are finding associated with exfiltration from the interior, or from ambient conditions?

 

AA

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