Spray Foam Loft Insulation

[sinoba]

Hello everyone.

I'm new to the forums. We moved to a new house last year and had the loft insulation checked and I understand it needs to be raised to newer standards. Had one quote which felt a lot (£6k) to remove old stuff, replace it, raise joists, and then re-board. I don't know whether (a) that's a lot or (b) it needs doing in that way. Thoughts on that? But also, is spray foam for the underside of the roof a cheaper alternative?

 

[zrock]

Not sure i understand why you had a inspection, and really do not understand why it has to be raised to newer standards unless your doing renos and pulled a permit for that.

Spray foam would give you a better insulation value but not sure it would be cheaper since im not sure what you mean by raising joists?

 

[Pinesmoke]

We CSF a new build 3 years back and it is very good from various angles. We live in a latitude that has a high sun angle during the summer and the AC doesn't come on until late afternoon. Air change has to be addressed since we pretty much have a balloon we live in.

Costs here are a bit higher than standard inso with the installation (alot of square footage in the walls and roof). Moisture control is a thing to think about as well. We didn't insulate the ceiling over the living area. The installers said every foam roof system they put in with ceiling bats cause issues long term.

Pluses and minuses but we are happy with the foam system.

 

[stoveliker]

Do you know why ceiling bats result in issues when there is foam under the roof decking? (I understand that the bats may not be needed for thermal insulation if the foam is sufficient, but that's besides the point, I think, as I assume the problems are moisture related - but how, especially if the bats are unfaced (and thus no vapor barrier)?)

 

[Pinesmoke]

It was a pretty generic remark he made when I brought it up. I would also assume it was the vapor barrier. Most inso , especially existing before foam, has the moisture barrier.

I can say I don't miss it since the CSF roof spray does the trick. I realize I do end up heating/cooling the air up there some but my bill to run the HP is pleasantly low for a place this size.

 

[John Galt]

Do you know why ceiling bats result in issues when there is foam under the roof decking?

Having closed cell foam and fiberglass bats can be disastrous. Warm moist air will be on one side of the bat and cooler air on the other, it doesn't matter if it's 4 ft. of attic or the bat is touching the foam, there is still air. The dew point could occur somewhere between the two layers or inside the bat and the moisture will condense. I'm not saying it's catastrophic in every case but it certainly is in some cases. You need the warm air to contact the foam to keep the dew point from being inside of the house.

 

[stoveliker]

Thanks. That makes good sense.

 

[EatenByLimestone]

Insulation removal is a horrible job. That leads to high prices.

 

[stoveliker]

I've always wondered what would happen if one has a leak in the roof and needs to replace some sheeting. Pulling that off will ruin the sprayfoam envelope.

 

[EatenByLimestone]

There are enough things that can separate the fo as m from the sheeting I’d replace the sheeting and not worry about it. I’ve seen “pros” spray sheathing that was too wet. I bet it had pulled off it by the time they left the job.

 

[stoveliker]

Yes, but I would expect pulling sheets adhering to the foam off, might also result in cracks in the foam layer (which kills the vapor barrier that it is)

 

[EatenByLimestone]

If the foam was attached to solid wood, it’d probably be impossible to do. You may be able to use a circular saw to cut the sheathing into small sections and then tear little parts off at a time. But t try often wood wouldn’t be that bad. One could only cut the rotten area out and then lay in a small section.