Cathedral ceiling ventilation
#1
11-25-15, 07:09 PM
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Cathedral ceiling ventilation
Hi guys.
I am from BC Canada
This is my first owner project. I am building a small garage house at my backyard. There are no attics in this house. All cathedral ceiling.
My framer just finished the roof today. And i have noticed there are NO venting space in all of the ridges.
The roof is constructed by 2x4 (12 inch on center) laying perpendicular on to the 2x10 rafters (16" O.C). So there are an inch and half air space between the roof sheeting and rafters.
My framer said all the garage houses are built like this....
Because there are skylights and dormers, most part of the roof can not be ventilated from one side of the rake soffit to the other side of the rake soffit.
From what i see, i can only ventilate the roof from air going under the eave soffit and out to the rake soffit, or or vice versa. I am planning to add those plastic rafter vents( baffles) between each rafter from the eave soffit all the way up to the ridge to create an extra one inch air space. so that the air can also move vertically up under the 2x4.
so my question here is....will my cathedral ceiling be well ventilated?
I have attached some pictures here for reference.
View image: IMG 20151124 142353
The front
View image: IMG IMG_20151124_141220
The Back
View image: IMG_20151124_141045
Eave soffit and skylight
View image: IMG_20151124_141045
Last one the closed vent ridge.
Any advice would be great. Thank you guys.
I am from BC Canada
This is my first owner project. I am building a small garage house at my backyard. There are no attics in this house. All cathedral ceiling.
My framer just finished the roof today. And i have noticed there are NO venting space in all of the ridges.
The roof is constructed by 2x4 (12 inch on center) laying perpendicular on to the 2x10 rafters (16" O.C). So there are an inch and half air space between the roof sheeting and rafters.
My framer said all the garage houses are built like this....
Because there are skylights and dormers, most part of the roof can not be ventilated from one side of the rake soffit to the other side of the rake soffit.
From what i see, i can only ventilate the roof from air going under the eave soffit and out to the rake soffit, or or vice versa. I am planning to add those plastic rafter vents( baffles) between each rafter from the eave soffit all the way up to the ridge to create an extra one inch air space. so that the air can also move vertically up under the 2x4.
so my question here is....will my cathedral ceiling be well ventilated?
I have attached some pictures here for reference.
View image: IMG 20151124 142353
The front
View image: IMG IMG_20151124_141220
The Back
View image: IMG_20151124_141045
Eave soffit and skylight
View image: IMG_20151124_141045
Last one the closed vent ridge.
Any advice would be great. Thank you guys.
#2
11-25-15, 07:32 PM
I'm not comfortable with an approach that doesn't have a definite ventilation strategy. One inch of vent space is below the recommendations and I suspect the remaining space for insulation will fall short of meeting your minimum code requirements. Did you start with an engineered building plan?
I'm not sure where you are in Canada so tell us what the code requires where you are.
Also, what is planned for a high vent opening, I can't tell from the pictures. Is there going to be a ridge vent? Are you planning on any recessed lights?
Bud
I'm not sure where you are in Canada so tell us what the code requires where you are.
Also, what is planned for a high vent opening, I can't tell from the pictures. Is there going to be a ridge vent? Are you planning on any recessed lights?
Bud
#3
11-25-15, 10:27 PM
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Hi Bud
thank you for your reply.
I live in Vancouver.
Actually there are an inch and half gap between the 2x4 and 2x10 rafter.
And i am planning to increase that gap by putting plastic baffles between the rafters.
There are no venting at the ridge. (I thought there would be)...
And Yes i am planning to install some recessed lights.
Thank you
thank you for your reply.
I live in Vancouver.
Actually there are an inch and half gap between the 2x4 and 2x10 rafter.
And i am planning to increase that gap by putting plastic baffles between the rafters.
There are no venting at the ridge. (I thought there would be)...
And Yes i am planning to install some recessed lights.
Thank you
#4
11-26-15, 05:13 AM
IMO, you absolutely need high venting and a ridge vent can be cut in at the last minute before the final roof goes up. They could be waiting to cut the sheathing bact to avoid too much rain/snow.
The vent path should be continuous. I'm not sure from the pictures and description where that will be. Probably my problem, not yours.
I don't know the difference between a code and a by-law, but Vancouver is now showing R-50 for ceilings. Whether that extends to cathedral ceilings or not is for you to determine, but R-50 would require over a foot (maybe 15") of fiber insulation. It doesn't look like the current construction is planning on that much insulation.
New Vancouver Building Bylaw 2014 – Insulation Values and Energy Efficiency (VBBL 2014) | One SEED Architecture + Interior - Greater Vancouver, BC
FYI
Bud
The vent path should be continuous. I'm not sure from the pictures and description where that will be. Probably my problem, not yours.
I don't know the difference between a code and a by-law, but Vancouver is now showing R-50 for ceilings. Whether that extends to cathedral ceilings or not is for you to determine, but R-50 would require over a foot (maybe 15") of fiber insulation. It doesn't look like the current construction is planning on that much insulation.
New Vancouver Building Bylaw 2014 – Insulation Values and Energy Efficiency (VBBL 2014) | One SEED Architecture + Interior - Greater Vancouver, BC
FYI
Bud
#5
11-26-15, 05:41 AM
Member
That to me is some of the strangest roof framing I've ever seen.
What's the reasoning behind the 2 X 4's on top of the 2 X 10's?
I can see those 2 X 4's cantilevered out so far just sagging in a few years.
No fascia boards on the ends of the 2 X 10's?
That narrow roof that runs under that big window on the right looks way to close the bottom of the window, that space is need to be able to flash the window.
I'd worry there's not enough support for the sheathing on the sides of those dormers with just 2 X 4's butting up against the walls like that with no blocking between them nailed to the walls.
What's the reasoning behind the 2 X 4's on top of the 2 X 10's?
I can see those 2 X 4's cantilevered out so far just sagging in a few years.
No fascia boards on the ends of the 2 X 10's?
That narrow roof that runs under that big window on the right looks way to close the bottom of the window, that space is need to be able to flash the window.
I'd worry there's not enough support for the sheathing on the sides of those dormers with just 2 X 4's butting up against the walls like that with no blocking between them nailed to the walls.
#6
11-27-15, 09:31 PM
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Hi Bud thank you for your reply.
The vent path is continuous, it just has to take a 90 degree turn.
And the R value for cathedral ceilling is 28 in here. so a 2x10 rafter has enought depth for the insulation i believe.
The vent path is continuous, it just has to take a 90 degree turn.
And the R value for cathedral ceilling is 28 in here. so a 2x10 rafter has enought depth for the insulation i believe.
#7
11-27-15, 10:15 PM
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Hi joe
The city coding has limited the roofing design. I did not intended to get this complicated roof.
The 2x4 is for increasing the ventilation inside the roof. And also for rain sheltering.
I would put gutter at the end of the 2x10s
which window?
Anyway, do you know how should i roof the this part?( the part between the fascia and sheeting.) Should i cut the fascia board to create a large gap between the sheeting and the fasica board so i can lay my shingle under it? if not how do roofers normally do it?
The city coding has limited the roofing design. I did not intended to get this complicated roof.
The 2x4 is for increasing the ventilation inside the roof. And also for rain sheltering.
I would put gutter at the end of the 2x10s
which window?
Anyway, do you know how should i roof the this part?( the part between the fascia and sheeting.) Should i cut the fascia board to create a large gap between the sheeting and the fasica board so i can lay my shingle under it? if not how do roofers normally do it?
