|
| Author |
Message |
chrisser
Member
|
# Posted: 15 May 2015 02:56pm
Reply
Like a lot of people here, planning a cabin with a loft and want to maximize ceiling height up there.
A neighbor built a cabin about the same size and had me over to look at how he did it and give me some ideas.
He built an 8' high box, then added a 2' high wall and set the rafters on it. Used collar ties up top. I think it was a 4/12 pitch
From reading this forum, I looked at that and thought it was a bad idea. Mitigated by a metal roof, and probably limited snow load, but still probably not something I want to sleep under during a windy snow storm.
Been thinking of ways I'd do it differently and read a lot of posts.
Have an idea that I haven't seen posted and was wondering what you guys thought...
What if the joists on the lower box were extended so they stuck out past the walls? Then the short wall is erected on top, and the rafters are set on the short wall. The short wall carries all the vertical load.
But then, if planned right, those joist extensions could intersect the rafters outside the building (easier with a steeper pitched roof). This gives rafter ties much lower than would be had by just having them in the lower 1/3 of the rafter and it makes it very easy to box the rafters in with a soffit - essentially the second floor joists do triple duty - floor joist, rafter tie, and soffit structure.
Is this a sound configuration? Does this method have a name already?
|
|
Just
Member
|
# Posted: 15 May 2015 04:40pm
Reply
My idea , I haven't built it but one similar . IMO it would be safe.
|
|
MtnDon
Member
|
# Posted: 15 May 2015 05:51pm
Reply
It could work. How to make the rafter meet the ceiling joist and have the required strength is the main issue. Well, that and any building inspector if there is one. That joint would be bearing half the roof weight in a normal rafter roof, as well as the horizontal forces.
Think ahead to how to insulate the roof and short loft side wall before starting to build. It may be best to treat the small triangular area as conditioned space and exten insulation in/on the roof down to the ceiling joist. Then insulate the soffit and then the main floor side wall.
|
|
Don_P
Member
|
# Posted: 15 May 2015 08:56pm
Reply
Many older homes do something similar. The one I'm working on now is 14' wide with 16' ceiling joists that cantilever over the walls, forming the overhang. The rafters have just a level cut and rest on the ceiling joists. In older work there was often a flatways board nailed on the top of the cj's called a raising plate that the rafters were nailed to. On these I'll plate both sides of the joint with scrap plywood and plenty of nails to reinforce the tired connection there. Trusses also often use a cantilevered overhang to gain more useable space. Stick framed I would probably build the walls full height ~10' and run a let in ledger at 8' to rest the cj's on.
|
|
Just
Member
|
# Posted: 15 May 2015 09:11pm
Reply
Quoting: chrisser planning a cabin
There are other options , have you decided on a size and are there height restrictions ??
|
|
toyota_mdt_tech
Member
|
# Posted: 15 May 2015 10:00pm
Reply
How about scissor rafters, not scissor trusses. I have this idea in my head. OK, you have your rafters in the V or pitch you want. Now take a large tie like a 2X6 or more and run it up like a scissor on one side, then do the same on the opposite side, then fill in the cross point with a board the full length and you have the scissor rafter. I dont know if this makes sense. I wont have time to sketch is up, headed out of town.
|
|
toofewweekends
Member
|
# Posted: 15 May 2015 11:24pm
Reply
Chrisser, so how is the construction you want to avoid different than most two story houses, other than the second story has really short walls? The weight of the roof is transferring to the walls one way or another, and the collar ties (and the connection to the top plate) if correctly done are stopping the rafter spread. I see a lot of cabins up here done the way you describe, but have never heard of a squished sleeper (although with Alaska snow loads, the roof pitches are steeper). What am I missing?
|
|
razmichael
Member
|
# Posted: 16 May 2015 06:24am
Reply
Why not consider a ridge beam and rafters? You don't mention cabin size but an appropriately sized LVL beam, although adding some cost, might simplify the build (rather than trying something more complex) so might even be cheaper in the end if you factor in time and effort. It does impose a couple of other design constraints (need to provide support down to the foundation) but I would see it as an option to get your headroom.
|
|
|
chrisser
Member
|
# Posted: 16 May 2015 06:50am
Reply
I've read many threads and have considered a ridge beam, various trusses, etc. If I were to do a short 2nd story wall, I'd use continuous wall studs rather than have that hinge point of the separate wall.
I thought extending the ceiling joists might be an easy way to overcome the structural problems with the short wall wanting to spread the rafters when no rafter ties were used. I would think that with birds mouths on the rafters at the top of the short wall, all the vertical loads would be transferred to the wall once the ceiling joists insured the rafters couldn't spread.
|
|
razmichael
Member
|
# Posted: 16 May 2015 08:15am - Edited by: razmichael
Reply
Obviously there are many ways to skin this cat - if you are dealing with building inspections, anything out of the ordinary may cause some heart-ache without engineering support (and the associated cost). I used 10' walls so the loft joists had plenty of space without feeling tight over your head, a ridge beam (3 LVL beams - I would need to go back to verify the dimensions) and Gambrel roof. The gambrel roof option would likely be harder to do if you have a serious inspection regime but I did not really need to worry about this. Built them based on agricultural building codes and beefed them up anyway. They do take much longer to build! This provide about 13 feet of the 16 (outside dimension) width with full standing headroom and about 8 feet in the middle up in the lofts. Cost of the LVL's was much less than I expected and they delivered with a crane truck no extra charge (I was planning to put each up one at a time and then bolt them together). The beams are 24' long but supported at 16 feet by the deck wall and extend over the deck (the loft sits above the deck). The rafters hang off the beam (strapped over the top and ties to the top plate.
|
|
Don_P
Member
|
# Posted: 16 May 2015 08:54am
Reply
Attached is a sketch I had on the computer. I think I'd do it a little differently but I think it could be done prescriptively.
|
|
chrisser
Member
|
# Posted: 16 May 2015 01:14pm
Reply
That pic is exactly what I had in mind.
I have no inspection to worry about, but I still want to do things right.
|
|
soundandfurycabin
Member
|
# Posted: 17 May 2015 06:34am
Reply
I think your configuration is sound. As long as the rafter/joist attachments are per code, you are still tying the rafter ends together.
If you are in Canada, you can likely even eliminate the short walls. 2x10 joists that carry only roof loads are allowed to cantilever 24", while 2x8 joists that carry only roof loads are allowed to cantilever 16". I would just run a 2x4 bearing plate about 10" in from the cantilevered end for the seat cuts to sit on and still have adequate overlap of the rafter and joist.
Possibly you could even argue that the 24" cantilever limit applies to the location of the bearing plate, and the overlap portion for tying in to the rafter can extend beyond that. But that gets into a very gray area, so I would confirm with the inspector before counting on being allowed to do that.
This does increase the rafter span so check that the rafter size still works.
|
|
|
