How do I insulate this ceiling ? (Cathedral ceiling)

[someguy11]

My garage has sloped roof ends. We put a loft in the attic where the regular rafters are.

At the ends, I removed the stringers between the end walls and the regular rafters and created a mini cathedral ceiling. We plan to hang bikes up in that space, hoisted up there by winches.

How do I insulate this part of the roof ? Do I need an air space between the insulation and the roof seething ? Should I fir them out to 2x6 ?

I don't think I have enough budget to spray foam it.

Ideas or advice ?

These images are rotated. Don't know how to rotate them to the correct orientation.

http://www.garagejournal.com/forum/attachment.php?attachmentid=504946&stc=1&d=1449944288

http://www.garagejournal.com/forum/attachment.php?attachmentid=504947&stc=1&d=1449944288

 

[hippie2cams]

Just put insulation between rafters and cover with sheetrock

 

[jives]

Read this:

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling

See other articles on the same website. Then go here:

http://buildingscience.com/document...ented-cathedral-ceiling-ucc-in-vancouver/view

 

[FordTruckWench]

At the ends, I removed the stringers between the end walls and the regular rafters and created a mini cathedral ceiling.

Was the roof supported by engineered trusses? I see some remnant joining plates where the roof meets the wall...

 

[someguy11]

Was the roof supported by engineered trusses? I see some remnant joining plates where the roof meets the wall...

I met with the engineer that designed the roof for the garage and the stringers between the wall and the roof trusses were strictly for holding up drywall. They did not play any role in the roof structure.

FWIW, I had the very same question before we removed them. The trusses alone are incapable of carrying a load perpendicular to the wall so I doubted the stringers were carrying any load tensile or compression load. That prompted me to track down the supplier and engineer and ask.

 

[someguy11]

Read this:

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling

Wow. I knew there were special issues with insulating a cathedral ceiling, thus the question to the forum. That is a great article. I need to give this a bit more thought. Had I known it was that complicated, I might not have removed the stringers.

Having said that, I love having the extra height on the ends.

I guess I might have to get it sprayfoamed.

What is really interesting is that we put an offer in on a house that had a huge cathedral ceiling with pot lights in it. It was built in 2009. The offer wasn't accepted. I think I dodged a bullet there. The offer was subject to a building inspection and in the back of my mind I was leery of that ceiling, so I would have checked it out prior to finalizing the purchase. But still !

 

[someguy11]

Our roof is almost impossible to vent because the sloped portions do not meet at the ridge. I'd have to build a volume at the top of the sections that somehow met and vent that. Hmmm....

This sounds like a lot of work, but our family has 8 bicycles that take up about 40 ft^2 of floor space, so it is no small gain to insulate the ceiling and hang them up there.

 

[ForceFed70]

Wow. I knew there were special issues with insulating a cathedral ceiling, thus the question to the forum. That is a great article. I need to give this a bit more thought. Had I known it was that complicated, I might not have removed the stringers.

It's not too hard. The baffles are cheap and just staple on, then it's just a matter of drilling some venting holes and applying the bat insulation as per normal ontop.

 

[someguy11]

It's not too hard. The baffles are cheap and just staple on, then it's just a matter of drilling some venting holes and applying the bat insulation as per normal ontop.

From the article: "A vented cathedral ceiling only makes sense if the geometry of your roof is simple. You need a straight shot from the soffits to the ridge." I don't have that.

 

[someguy11]

From the article: "If you want to install a combination of closed-cell spray-foam on the underside of the roof sheathing and air-permeable insulation between your rafters — an approach sometimes called “flash and batt” — the building code requires that spray foam (or, arguably, rigid foam insulation) be “applied in direct contact with the underside of the structural roof sheathing” and that the foam insulation meet the requirements “specified in Table R806.4 for condensation control.” These are the same minimum R-value requirements mentioned above, ranging from R-5 in zone 1 to R-35 in zone 8. Moreover, "The air-permeable insulation [for example, fiberglass batts or cellulose insulation] shall be installed directly under the air-impermeable insulation.""

Hmmm.... So I could install foam board insulation between the 2x4s and seal it to them with closed cell spray foam. Then I could install batts underneath that.

The problem is that I don't want to insulate the roof to R38. I'm only going to heat the garage to a bit above freezing most of the time and only to 60F when I am working in it. This article makes it sound like I need 10" rafters to prevent condensation problems.

Read more: http://www.greenbuildingadvisor.com...ild-insulated-cathedral-ceiling#ixzz3uE0o7yEl
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[DC73]

Hmmm.... So I could install foam board insulation between the 2x4s and seal it to them with closed cell spray foam. Then I could install batts underneath that.

The problem is that I don't want to insulate the roof to R38.

You may not need R38 but pay particular attention to that article and others on the site about the amount of foam you need for your climate to avoid condensation issues.

You could install the foam board with batts underneath but the foam board could be a lot of work. Might consider enough spray foam to avoid condensation issues and then finish with batts.

DC

 

[Voi]

Hmmm.... So I could install foam board insulation between the 2x4s and seal it to them with closed cell spray foam. Then I could install batts underneath that.

The problem is that I don't want to insulate the roof to R38. I'm only going to heat the garage to a bit above freezing most of the time and only to 60F when I am working in it. This article makes it sound like I need 10" rafters to prevent condensation problems.

I haven't read that article in a while but there is how much foam you need in your area to avoid condensation with an un-ventilated roof and then there is how much batt you need to reach the total recommended R value for your area. So in your case just worry about how much foam you need.

Even in my area the 3.5" of space between rafters is sufficient to meet this recommendation. At least that's what I recall.

Or are you required to meet a certain R value for this space according to a permit?

 

[Jack T.]

Look up "CrossVent". It's essentially adding another roof, but it works. I tried insulating our cathedral ceiling below the deck and covering it with pine tongue and groove, but had problems with condensation since there was no way to vent it. Bit the bullet and went with the cross vent and it works well.

If I had left a space between the insulation and underside of the roof deck the roofer showed me a system where vents could have been cut into the roof deck near the eave and allowed air movement to a ridge vent.

Check with a local roofer who does commercial work. They run into cathedral ceiling issues all the time.