The biggest weak point in my opinion is that if there is a roof leak you won t find out until the wood is rotted.
Spray foam under roof deck.
It is not the end of the world.
No interior class i vapor retarders e g plastic sheeting are installed on the ceiling side attic floor of the.
Yeah you probably still breathed some of it but not as much as you will now with spray foam on the roof deck.
Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls.
Moisture generated indoors or that infiltrates into the home is responsible for the bulk of the moisture in an attic insulated with spray foam on the underside of the roof sheathing.
Spf is not a greater risk under a roof deck than the risk associated with sips.
The spray foam definitely has its merits.
This construction approach was first used in the 1970s and it has been implemented much more widely since it was first included in the international code council s icc model building code in 2007 irc section 806 4.
By encapsulating the attic and leaving the old insulation up there that filth is in your conditioned space.
Lstiburek takes blame for bad language.
Spf is not a greater risk under a roof deck than the risk associated with commercial compact flat roofs with multiple layers of insulation sandwiched between roof membranes and metal and wood structural decks.
It s not coming from above the roof and it s not some new moisture source resulting from the spray foam.
Just make sure you overdo your roof when the roof is installed.
Your indoor air quality may get worse.
Polyurethane or polystyrene spray foams can provide thorough coverage to roof rafters and attic walls in much less time than is needed for other materials.
I ve done a lot of work in energy efficient building and design.
Open cell spray polyurethane foam ocspf and closed cell spray polyurethane foam ccspf insulation sprayed to the underside of roof sheathing is a popular strategy for increasing roof insulation levels in all climate zones.
Spray foam under roof decks.
How spray foam should be installed on the underside of the roof decking the unvented attic space is completely within the building s thermal envelope.
Where wood shingles or shakes.