bill1952
SAWHORSE
Can an a-frame dwelling be built prescriptively and comply with the IRC? Or does it require an RDP?
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A-frame dwelling
- Thread starter bill1952
- Start date
Beniah Naylor
SAWHORSE
Can you post a picture? I think I know what you are talking about, but not sure.
bill1952
SAWHORSE
Lots of images. Pitch varies. (Was there a consensus in another thread that 60° or greater from horizon was a wall, less was a roof?) I've seen 1,2, and 3 stories. Help?
Beniah Naylor
SAWHORSE
If ceiling heights can be met, I see no reason you can't build one prescriptively.
SDS
Registered User
Does prescriptive code limit pitch to 12/12 max?
mtlogcabin
SAWHORSE
2018 IBC
[BF] EXTERIOR WALL. A wall, bearing or nonbearing, that is used as an enclosing wall for a building, other than a fire wall, and that has a slope of 60 degrees (1.05 rad) or greater with the horizontal plane
[BF] EXTERIOR WALL. A wall, bearing or nonbearing, that is used as an enclosing wall for a building, other than a fire wall, and that has a slope of 60 degrees (1.05 rad) or greater with the horizontal plane
bill1952
SAWHORSE
So if it is a wall by definition, just use the IRC requirements for a wall? 2x4s 16" on center?
I'm guessing at least some share my hesitancy as far as the sloped walls complying with the intent of the code structurally. It's hard for me to disregard snow load but at 60° and (in my thinking) metal "siding", I doubt if there is much snow load.
Clearly a form of building that did not get much attention when the IRC was drafted.
I'm guessing at least some share my hesitancy as far as the sloped walls complying with the intent of the code structurally. It's hard for me to disregard snow load but at 60° and (in my thinking) metal "siding", I doubt if there is much snow load.
Clearly a form of building that did not get much attention when the IRC was drafted.
mtlogcabin
SAWHORSE
You could get a lot of snow buildup at the wall and ground which may cause water issues. Your typical wall construction of 8" above grade for wood will probably not be enough.
I don't think a 2 X 4 wall can comply with the energy code.
See it all the time. 2x4 with CI.
Beniah Naylor
SAWHORSE
bill1952
SAWHORSE
Practically, it seems a lot of plans use a double 2x6 4' on center (been there) to reduce the number of piers, the usual foundation. Does that put it out of reach of prescriptive design for everyone (except Wayne)?
The water/snow pile issue - several designs use p.t. double 2x6s so sheathing and floor are well above grade. But those are basic design problems that can be addressed prescriptively.
A lot of piers or a few with a big header across them or a continuous foundation wall, 2x6 on 24" centers, and balloon framing, might all fit prescriptive requirements.
The water/snow pile issue - several designs use p.t. double 2x6s so sheathing and floor are well above grade. But those are basic design problems that can be addressed prescriptively.
A lot of piers or a few with a big header across them or a continuous foundation wall, 2x6 on 24" centers, and balloon framing, might all fit prescriptive requirements.
steveray
SAWHORSE
Post and pier foundations supporting BWP gets engineered....R602.10.9
bill1952
SAWHORSE
That "designed in accordance with accepted engineering practice" phrase which according to some requires an RDP. Is that your interpretation?
SDS
Registered User
I had to dig a bit as I couldn't remember where I'd read it....no, nothing in the IRC that I can find, so not applicable to this thread.
It was in the 2018 AWC's wood framing construction manual, prescriptive roofs are limited to 12/12.
Yankee Chronicler
Registered User
It depends on the state. In my state, by law, anything that requires engineering must be performed by a professional engineer licensed in this state. We have an exemption for the design of single family residences under the architecture practice laws, but there is no corresponding exemption for the practice of engineering.
Inspector Gadget
Registered User
It *can* be done in Canada, so I'm assuming the same on the other side of the 49th. My little cabin in the woods runs R20-plus with 2x4 walls....
bill1952
SAWHORSE
IRC requires R25 here so I'm guessing 2" of rigid foam CI rather than 1".
I think the only issue I struggle with is structural framing.
Inspector Gadget
Registered User
Aye. North of where I am, insulation requirements increase. Also new Codes, NECB, pushing for more all the time.
Mr. Inspector
SAWHORSE
How do you know how to insulate if you do not know if they are roofs or walls?
Joe.B
Registered User
I don't have a reference to point to, just my gut instinct. I would consider it a roof system, not walls.
Joe.B
Registered User
And if you look closely at the picture in post #3, there is a very short wall.
bill1952
SAWHORSE
It's wall if 60° or greater from horizontal. Maybe the sample image isn't, but for that issue and the question, assume it is. If there was a ceiling near the apex and the thermal barrier was at the ceiling, then roof insulation (R49 here).
Paul Sweet
Sawhorse
It's a bit of both. It's a wall when it's 60 degrees or more from the horizontal, but functionally it's a roof. I wouldn't trust any wall siding materials to shed enough water. The studs will probably have to be 2x6 or 2x8 because they would be longer than 12 ft. (IRC Tables 602.3(5)&(6)). It would be best to use rafter span tables to size the studs. This will be conservative for snow loads, but wind loads could be significant.
If you have rigid foam outside the sheathing it will probably be necessary to cover it with plywood or OSB to nail the shingles to, and this should have an air space between the foam and sheathing. It could get complicated fast.
If you have rigid foam outside the sheathing it will probably be necessary to cover it with plywood or OSB to nail the shingles to, and this should have an air space between the foam and sheathing. It could get complicated fast.
steveray
SAWHORSE
Studs longer than 12' get engineered...
R301.3 Story Height
The wind and seismic provisions of this code shall apply to buildings with story heights not exceeding the following:
- For wood wall framing, the story height shall not exceed 11 feet 7 inches (3531 mm) and the laterally unsupported bearing wall stud height permitted by Table R602.3(5).
Exception: A story height not exceeding 13 feet 7 inches (4140 mm) is permitted provided that the maximum wall stud clear height does not exceed 12 feet (3658 mm), the wall studs are in accordance with Exception 2 or 3 of Section R602.3.1 or an engineered design is provided for the wall framing members, and wall bracing for the building is in accordance with Section R602.10. Studs shall be laterally supported at the top and bottom plate in accordance with Section R602.3.