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Indigo139
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# Posted: 12 Apr 2025 10:37pm
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Hey all,
I'm trying to design a 12'x20' cabin with a loft and vaulted ceiling (8/12 roof pitch). Is one beam for the loft (6' or 8' from the back gable wall) enough to stabilize the side walls with just a ridge board and collar ties? Do I need to put a second beam near the other gable end? Or should I give up on my dream of french doors and just do a ridge beam?
Any advice is greatly appreciated!
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travellerw
Member
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# Posted: 12 Apr 2025 11:11pm - Edited by: travellerw
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I'm confused.. Do you mean vertical posts?
Just an FYi.. We have a 16X28 Gambrel roof with a 2/3 loft. We have no vertical posts.
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travellerw
Member
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# Posted: 12 Apr 2025 11:20pm - Edited by: travellerw
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Hmm.. After thinking.. I think I know what you are asking.
A traditional roof would require vertical supports depending on the distance (with a loft).
Look into an LVL beam. Pretty sure a laminated beam 3 X 1.75" X 16" could carry that load. OF course it depends on a ton of factors that an engineer could help with (is there snow loads for example).
That brings up a other problems though. Even a 1.75"X 16" X 20 ft LVL beam is darn heavy. You would probably need a picker truck to lift each lamination in place (3 required for the whole beam).
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DaveBell
Moderator
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# Posted: 13 Apr 2025 03:49am - Edited by: DaveBell
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If you use 2x6x10 16"OC for the wall studs you can build the loft bottom at 7' above the floor and have a 2' knee wall for the loft. Or 2x6x12 wall studs for a 4' knee wall in the loft.
Ties. https://www.nachi.org/collar-rafter-ties.htm
Your loft joists become rafter ties but adding collar ties is OK. Always overbuild to prevent cabin problems. Whether the loft is half the length or full length of the cabin, put in the collar ties. Gives you something to hang lighting from.
Do not (ever) put the loft joists on top of the wall. IRC wall standards do not account for added loft weight (dead and live loads). Add wall studs attached to the existing wall studs cut shorter to mount the loft joists on top of. The loft load will be transferred to the foundation independent of the roof loading on the walls. See the IRC for joist size.
I do not understand this two beam thing. Can you draw a picture and post it?
Use Simpson Strong Ties for you roof to wall connections and other connections. I used H1 ties.
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DRP
Member
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# Posted: 13 Apr 2025 06:50am
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In summary, collar ties and rafter ties perform different functions, but both are essential roof-framing members,
Quoting: DaveBell Do not (ever) put the loft joists on top of the wall. IRC wall standards do not account for added loft weight (dead and live loads). Add wall studs attached to the existing wall studs cut shorter to mount the loft joists on top of. The loft load will be transferred to the foundation independent of the roof loading on the walls.
Typically the floor or ceiling joists on top of the wall plate provide the required rafter tie. Conventional platform wall framing does support floor and roof safely. Balloon framing as decribed is unconventional, requires thought engineering-wise and fireblocking-wise. Dropping the joists down the wall creates a bending moment in the wall and a connection problem at the top plate to rafter. The "loft kneewall" is the sketchy condition that should be corrected by using a ridge beam.
You can have a ridge beam supported on a post that runs down to a header beam over the french doors. The header is supported by king and jack studs on either end. Those girder and header tables are in chapter 5 or 6 of the IRC.
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Indigo139
Member
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# Posted: 14 Apr 2025 01:12pm
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Thanks all!
I was getting conflicting information on whether or not a support post for a ridge beam should be on a door header. Good to know that's actually an option.
The beam I mentioned would go from side wall to side wall (12' long at 7' height) with loft joists running the shorter length between it and the gable wall. I agree that running joists the other way would add more stability. I'll keep researching materials and figure out what's best for me (as a 5'2" female).
I don't currently have framing design software, but once I finalize a design I'll put up a visual here for comments. Thanks again!
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Brettny
Member
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# Posted: 15 Apr 2025 06:50am
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The ridge beam would need to be 20'? If so I wouldnt do it. Just build the building wider. Lofts suck to get into and live with. They are also really hot and for me terrible to sleep in. I wouldnt they to over engineer a building until you have tried to just make it wider or longer.
The physical ability just to lift a 20' ridge beam in may need scafolding and 4 grown men. Much less the support needed built into the building.
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gcrank1
Member
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# Posted: 15 Apr 2025 08:40am - Edited by: gcrank1
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We had a 12x12 mostly stand up loft in our 1st cabin, 12x24 self-built '83-'84 when we were young and vigorous. As the years and injuries piled up the loft became an issue. The only thing Id use a (short) one now for would be seasonal stuff storage.
The vaulted ceiling we still have on the new pre-built 12x28 and do use a pair of small 120vac ceiling fans run off lfp bat/inverter mostly to mix the air throughout during heating season.
But its your dream  , just giving an ime
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jsahara24
Member
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# Posted: 15 Apr 2025 08:47am
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Have you thought about scissor trusses?
We installed two 25' long x 14" high LVLs in our cabin, that took 4 men up on scaffolding 20' high, and it wasn't easy....
Lofts do tend to get hot, but with a large ceiling fan we are able to keep the temps within ~3* of the downstairs...
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