Sloped ceiling insulation problem

Robert_H

I have a 100ish year old house in Norwich CT.

The ceilings of all the rooms in the second floor of the house are bisected by the roof so that in one case there is 5 feet of flat ceiling and 4 feet of sloped ceiling. When I moved in the house there were several inches of cellulose between the (flat) ceiling joists on which I have rolled out unfaced batts of fiberglass.  However, the sloped areas which obviously only have a few inches of space and very limited access have some cellulose which has been nested in by squirrels and mice. (long since evicted and barred from entry).  Some of the bays have no insulation at all. I’m trying to figure out how to correct the insulation in the sloped areas.  

One issue is that there was a fire in the house ages ago which basically burned the roof off. Some of the burned stubs of the rafters are still there and new rafters were sistered to the old ones and some were completely replaced. The result is that the spacing’s are not conventional and are inconsistent. I tried once to cut a batt of insulation to fit and feed it in with a long stick with a nail in the end. This worked a little but the batt kept catching on the roofing nails and low and behold the replacement rafters were not spaced exactly the same, top to bottom, so the bay tapers and the batt was bunching up.  I lost a lot of skin that day and gave up.

I thought of blowing in more cellulose but how would I maintain the required are space above it? Because of the limitations I already mentioned it’s impossible to use the spacing material available at hardware stores.



If I want to just completely fill the bays with cellulose, I am  “unvented” and need to insulate the roof deck which means replacing the shingles, Which are only ten years old.  I understand I could have the bays filled with foam and would not need to insulate the roof deck.  I do a lot of DYI but this seems like something that should be done by a pro.



I had an insulation contractor over and he did not want to touch it. He wanted to remove the fiberglass batts I rolled out in the attic and blow in more cellulose arguing that not much heat is lost through the sloped areas and poor the fiberglass is.  There may be a little truth to that but if I stand in the room on a sunny day I can feel the heat radiate off the slopped ceiling.



I really hate having this area that I can’t seem to do anything with.  I will be grateful for any comments and ideas on this.

Jamie Hall

You have company...

the sloped ceiling areas in the upper floor rooms of the place I care for are uninsulated.  And likely to remain so, for many of the reasons you mention: getting insulation into them while keeping venting is pretty close to hopeless, unless you go with foam.  Which really is a professional job.



Also, there is a serious downside to foam in some cases (not all): unless your plaster or sheetrock (but particularly plaster) is really really strong, there is a very good chance that the foam will simply pop it off the rafters as it expands.  This would rank somewhere between a nuisance and a catastrophe.



Myself -- I left it alone.  I'm not losing enough heat through those ceilings to worry about.

Robert_H

Nice to know I'm not alone

Thanks for your comments Jamie

JeffM

similar house (no solution)

I've got a similar construction in my 1890 home - recently spent a day in the attic snaking cable TV wires into the master bedroom which was quite a chore! The sloped segments of my ceilings/roof are filled with loose cellulose (not so loose anymore in some areas), though I've got a slate roof so it may have different venting requirements.

NRT_Rob

I don't see

how spray foam helps compared to cellulose here. if you fill the bay right to the roof decking and the singles are on the other side, that's usually a problem unless the cladding (shingles in your case) is itself vented. if the shingles are vented underneath then you don't need venting in the insulation assembly under the deck. am I missing something?

Zman

Spray Foam

Rob,

My understanding of this is that if you fill the void without 100% air sealing and the correct r value, you create a condensation issue which leads to rotting ect.

If you use the correct amount of closed  cell foam insulation based on the relative humidity and design temp in your area you eliminate the condensation and have the best possible assembly.

It is kind of like, why does moisture form on some refrigerators and not others in varying climates?

I may stand corrected on some of this, but that is the general idea.



Carl

NRT_Rob

I dunno

I only know that venting cladding in any insulated roof assembly is kind of a strong recommendation.

Zman

It works

Rob,

What I described does work. A great deal of attention needs to be given to the details.

Carl

NRT_Rob

fair enough

good paper on the issue here: http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting

Zman

Thanks

Thanks,

That is a good read. I will throw it in the file. These things are so handy when you are trying to explain concepts to folks.Fine homebuilding also did a great one on ice dams.

Carl

Robert_H

Thanks Rob

That's an excellent read on the subject, thorough and concise.

NRT_Rob

yeah

I kind of love buildingscience.com for that.