HRV Heat Recovery Systems & air tightness using only spray foam

[@stevene2812]

In older homes would you always need an hrv after spray foaming the attic?

[@jericho9653]

With a block 2 storey wpuld ypu not be better putting 300mm rockwool between attic joists and airtight the ceiling ratger than have all your heat get as far as the rafters?? I know tge hrv will be in attic but is there really a need for 9inch apray between rafters in attic

[@ablowick]

sure - rockwool is an option along with an airtightness membrane - but do a cost copmarison and foam would beat the combination - also we are spraying an average of 6 inches here not 9

[@imnothere220]

Am I crazy in thinking this is just a bad idea? I mean, its covering in ducting with a spray product making it inaccessible forever?

[@ablowick]

okay so ducts by their very nature are inaccessible in that if you wanted to access them say for cleaning, access would be from the duct boxes and transitions which we don't spray over. The flexible pipes themselves by definition are sealed to be airtight . We spray over them to insulate them and prevent condensation occurring inside the duct when warm air hits the cold roof felt behind if the duct is touching the roof felt. So we aim to get foam between the duct and felt. Finally these ducts will be slabbed over using drywall so irrespective of foam or not they are going to be largely inaccessible - thank for the comment in any event

[@imnothere220]

@@ablowick thank you!