I have a porch similar to the one in the picture (that?s not my house)
- posted
10 years ago
I have a porch similar to the one in the picture (that?s not my house)
You can't use the canned expanding foam in large voids, it just turns into one huge empty bubble and does not "go off" very well. It has to be put down in layers for any great thickness & even then not very good. Not possible here I think?
You can use the two component foam for this but a bit dodgy if you can't see what is going on in the void. Probably easiest to take the ceiling down and make a proper job. Can be done over the Winter period too. Make a good job, even a small gap that lets in air will defeat the whole project
You need to be aiming for a continuous thermal "envelope" with no gaps to form thermal bridges.
It would cost you very little to have a roofer repoint the edges, or even to put the whole roof back on. Could replace the felt with something like TLX gold in the process to improve on whatever insulation you lay on the ceiling.
You could work from the inside instead. Take the ceiling down, and replace with a new ceiling and insulation. You should also inspect to ensure nothing is damp above the ceiling whilst you have access. Another option would be to fit a new insulated ceiling below the existing one, but it's harder to get moisture barriers right this way or to check there's no source of damp above the existing ceiling.
Draftproofing the porch from the house might help avoid moisture getting in there from the house air, although not from wet clothes, etc.
Glassfibre, polystyrene bead, cellulose all work in ceiling voids. I'd stay away from expanding foam, it tends to expand with huge forces & can do ser ious damage.
NT
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