Am I the only one who thinks spray foam isn't always the answer for attics?

I had a guy out to quote attic insulation on my house near Nob Hill last month and he pushed spray foam hard. Everyone on here seems to love it but I went with blown-in fiberglass instead for about $1,200. My neighbor did spray foam three years ago and now he's dealing with a roof leak that's impossible to trace because the foam hides everything. Has anyone else run into issues with spray foam trapping moisture up there?

3 comments

3 Comments

david_hayes17h ago

Wait, your neighbor paid extra for the privilege of having his roof leak become a mystery game? That's hilarious in the worst way. I swear spray foam sales guys act like it's magical unicorn dust that solves everything, but they never mention the part where you can't find a single leak without tearing half the roof off. My buddy had a similar issue where a small drip turned into a full mold situation because the foam trapped all the moisture up there like a sealed tupperware container. Blown-in fiberglass lets the attic breathe and if something goes wrong you can actually see it before it becomes a nightmare. Sometimes the boring old-school stuff is just smarter, even if it's not as sexy to talk about at parties.

abby_chen13h ago

Sealed up like a tupperware container" is exactly it (and now I'm never gonna unsee that image). My neighbor's contractor actually admitted later that foam works great in some climates but in our foggy SF microclimate it turns attics into a moisture trap with no way out. I did a ton of research after getting that quote and read about a study from some building science guys that showed fiberglass actually outperforms spray foam in attics when it comes to drying potential - spray foam can lower the roof deck temp enough to cause condensation on cold nights, especially with older roofs like ours. Plus with blown-in you can just vacuum it out if you ever need to rewire or move plumbing, which felt like future-proofing for like $3,000 less than the foam quote.

kelly.dylan13h ago

Wait why does nobody talk about how spray foam basically bricks your roof for the future? @david_hayes you nailed it with the hidden leak thing but it gets even worse - my buddy had a house with spray foam and when he wanted to install solar panels the roofers couldn't even walk up there because the foam made the decking all spongy and weak from moisture that never dried out. That tupperware comparison is dead on because once that seal is made the wood up there just rots from the inside out with no way to spot it until the roof actually sags. I feel like theres a whole generation of homeowners getting sold on this stuff without hearing the horror stories from people who already went through it. Old school blown-in might not impress the guys at parties but at least you can sleep knowing your roof isnt turning into a science experiment.