[aaron_a]

Trying to price out an attic renovation project right now. Architect specced full depth fiberglass insulation for an unvented cathedral roof (2x6 rafters).

Emailed the architect and said this needs to be changed, as it doesn't meet current code for an unvented roof. Architect said since its not an attic, its a habitable space, it doesn't apply.

R806.1 Ventilation required. Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space by ventilating openings protected against the entrance of rain or snow. Ventilation openings shall have a least dimension of 1/16 inch (1.6 mm) minimum and 1/4 inch (6.4 mm) maximum. Ventilation openings having a least dimension larger than 1/4 inch (6.4 mm) shall be provided with corrosion-resistant wire cloth screening, hardware cloth, or similar material with openings having a least dimension of 1/16 inch (1.6 mm) minimum and 1/4 inch (6.4 mm) maximum. Openings in roof framing members shall conform to the requirements of Section R802.7.


806.1 specifically mentions enclosed attics AND enclosed rafter spaces.


806.4 only mentions attics

R806.4 Unvented attic assemblies. Unvented attic assemblies (spaces between the ceiling joists of the top story and the roof rafters) shall be permitted if all the following conditions are met:

1. The unvented attic space is completely contained within the building thermal envelope.
2. No interior vapor retarders are installed on the ceiling side (attic floor) of the unvented attic assembly.
3. Where wood shingles or shakes are used, a minimum 1/4 inch (6 mm) vented air space separates the shingles or shakes and the roofing underlayment above the structural sheathing.
4. In climate zones 5, 6, 7 and 8, any air-impermeable insulation shall be a vapor retarder, or shall have a vapor retarder coating or covering in direct contact with the underside of the insulation.
5. Either Items 5.1, 5.2 or 5.3 shall be met, depending on the air permeability of the insulation directly under the structural roof sheathing.
5.1. Air-impermeable insulation only. Insulation shall be applied in direct contact with the underside of the structural roof sheathing.
5.2. Air-permeable insulation only. In addition to the air-permeable installed directly below the structural sheathing, rigid board or sheet insulation shall be installed directly above the structural roof sheathing as specified in Table R806.4 for condensation control.
5.3. Air-impermeable and air-permeable insulation. The air-impermeable insulation shall be applied in direct contact with the underside of the structural roof sheathing as specified in Table R806.4 for condensation control. The air-permeable insulation shall be installed directly under the air-impermeable insulation.


Although it does mention "spaces between the ceiling joists of the top story and the roof rafters"

Am I correct in thinking this still applies?

 

[ScipioAfricanus]

For all of the non-vented attic assemblies I have spec'ed out all of them have required rigid foam insulation directly under or over the roof decking. All the cities that I have done this in expected and required this assembly. Just as you have been interpreting it.

Andy.

 

[mski]

Trying to price out an attic renovation project right now. Architect specced full depth fiberglass insulation for an unvented cathedral roof (2x6 rafters).

Emailed the architect and said this needs to be changed, as it doesn't meet current code for an unvented roof. Architect said since its not an attic, its a habitable space, it doesn't apply.

R806.1 Ventilation required. Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space by ventilating openings .

What's in bold is my interpretation. The ceiling material is being applied directly to the rafter. Ventilation required per R806.1

 

[Morning Wood]

2x6?!? Closed cell man. The only way to get anywhere near enough insulation.

 

[music9704]

What's in bold is my interpretation. The ceiling material is being applied directly to the rafter. Ventilation required per R806.1

That's how I would read it.

 

[aaron_a]

Thanks.

Between this and what I've read elsewhere it seems like a recipe for disaster to install only fiberglass against the deck.

 

[Morning Wood]

Fiberglass against the deck is ok. BUT, only if you do a few other things to make it right. Air seal outside and inside of roof assembly and have foam board on the exterior of the roof deck so the dew point is not in the fiberglass.

 

[aaron_a]

Fiberglass against the deck is ok. BUT, only if you do a few other things to make it right. Air seal outside and inside of roof assembly and have foam board on the exterior of the roof deck so the dew point is not in the fiberglass.

Yeah, this is a remodel situation and the owner would prefer to keep the existing slate roof intact. So anything on top of the deck isn't an option. From what I understand we can apply 4" of xps against the deck, sealed around all edges. Then attach 2x4 with gussets to the existing rafters and fill with r-13 to meet the r-30 minimum of n1102.1

Closed cell seems like the simplest, but I'm hesitant to spray than in a house where people are inhabiting. Unless they decide to go on a vacation for a bit...

 

[PatChap]

Is building out the rafters a few inches to get some space an option? Unvented attics are terrible ideas, despite the code.

 

[aaron_a]

Is building out the rafters a few inches to get some space an option? Unvented attics are terrible ideas, despite the code.

I think we're gonna have to regardless. The valley jack rafters are a few inches deeper than the common rafters. gonna make for a difficult time hanging sheetrock...

 

[fireguy]

Contact the B/O and get a written opinion.

 

[B.D.R.]

I would ask the archy for a detail drawing (not a clip and copy).
Spray foam seems to be the only option.
Shouldn't be too bad if they are gone for the day.
But I am expressing an opinion without pictures

 

[Morning Wood]

I hear you on the closed cell with people living in the place. That stuff smells like cancer.

 

[TimNJ]

Who's paying the architect?

It is his responsibility to come up with a drawing that will be passed by the code official to get a permit approved.
If the code official rejects the design it's back to drawing board for the architect.

Spray foam seems the only viable option. You aren't going to get much R value in a 2x6 bay.

 

[aaron_a]

Who's paying the architect?

It is his responsibility to come up with a drawing that will be passed by the code official to get a permit approved.
If the code official rejects the design it's back to drawing board for the architect.

Spray foam seems the only viable option. You aren't going to get much R value in a 2x6 bay.

Client is paying for the architect. It's a small residential project with no structural changes, so the building dept doesn't require drawings to issue a permit. That being said, it still has to pass an inspection.

I was just hoping to get that detail sorted out in the beginning to avoid a change order later on.

Gotta love doing other peoples homework.