wacky cabin roof ... 2x4 rafters laying flat

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Old 11-05-13, 10:49 AM
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wacky cabin roof ... 2x4 rafters laying flat

Hi,

2 years ago I bought some land with a 16x40 1960s-era cabin on it. The cabin was in rough shape. In 2008 the roof collapsed under extreme snow. The owner rebuilt the roof, clearly without checking any sort of how-to guide. It's in a remote area and permits and the like aren't a worry.

The guy fashioned some home made trusses out of 2x4s oriented to the FLAT side. These are installed every 24". The bottom chord is nailed to the top plate of the walls. Each half of the truss is nailed to a 2x4 lengthwise beam and a 2x8 "nailer" board above it (not quite all the way to the ridge). Every 10 feet, a 2x8 width-wise beam crosses below the 2x4 beam. These 2x8s are notched and hung on the walls. The roof is sheathed in 3/4 OSB and shingled. No leaks. See crude diagram.

Obviously it's a total sh*tshow and the best remedy would have been set a match to it in March and rebuild. But money and time wouldn't allow such a proposition. Further, the building is still useable, being a decent size, and it would be a shame to waste so much material. So I decided to shore up the existing arrangement. I sistered 2x6 rafters to every 2nd truss and added stubby struts/props to tie these to the top of the walls. I also added permanent posts in 3 places- where the 2x8 crossbeams go beneath the 2x4 lengthwise beams. In half the building I also built a wall under the center beam.

Just curious if anyone has any thoughts on this matter (other than you should have torched it already...) i.e. what else should be done to remediate this. Does the 2x6 rafter (every 4') and structural post solution seem adequate? I'm almost worried about adding too much More weight to the roof structure (if I sistered every truss instead of every 2nd one). The sistered rafters are now a robust looking L shape, and the trusses do have web ties which direct the load to the middle. I'm thinking there is only about 4-5 feet of "unsupported" span on each of the non-sistered 2x4s... which seems reasonable? At least this thing has nice big overhangs. And it made it through last winter (HEAVY snow) with no noticeable changes.
 
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Old 11-05-13, 01:20 PM
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Welcome to the forums! Thanks for the drawing. It helps to explain it a little. Pictures would rocket, if you can. What you have is a modified Queen truss, but the truss part is too close to the middle to do any good. Laying the framing on the side was......OK, dumb. Trusses seldom can be made in the field and be of much good. Design has much to do with the weight it can handle. the queen truss can handle spans up to 22' I believe, so it is well within limits. I would rather see a vertical member from the bottom chord to the top since you obviously have snow load.

Sistering may add weight with little benefit. Making a tee of the rafters would be the next option.

Hang in there, as we have a bunch of qualified people that may be able to give you better information. A structural engineer may help...........but he may run, so you may be faced with doing this the best you can.
 
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Old 11-05-13, 01:59 PM
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Thanks for the welcome, and the reply.

You're right, a structural engineer would probably collapse at the sight of this place (and some nearby properties are even worse... picture a 24x24 tree house with haphazard porches and decks all on rotting stilts 20 feet off the ground...) And there are really no funds to being in any pros.

The thought behind sistering with the 2x6s was to replicate a "regular" roof system as much as possible and eliminate the possiblity of deflection of the undersized and wrong-way 2x4s.

I'll see what I can do for pictures in a bit. Should have some.

I'm not sure I am familiar with the term rafter tee, I am picturing a collar tie...?
 
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Old 11-05-13, 02:24 PM
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Making a tee of the rafters, is basically what you suggested. You have a flat rafter, and I was thinking of doing the regular rafter beside the flat one, fastened to the flat one. Is that what you were thinking? It sure would boost the rigidity. Not exactly a "tee", but more of an "L">
 
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Old 11-05-13, 10:28 PM
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Yup the L shaped rafter is what I was going for when I added the 2x6s alongside every 2nd truss (some screwed on & some nailed, in both cases about 8" apart along the length of the rafter). Between that and the posts I'm hoping I'm covered. There is a center floor beam which the posts are positioned over. That floor beam rests on cinder blocks as do the 6x6 edge or "foundation" beams.

After no issues last winter I'm just trying to decide if there is anything more I should do to this insane roof before attaching some kind of ceiling to the underside of the truss arrangement and hiding the whole mess. Certain trusses do have the vertical member midway along the truss you mentioned...it's very haphazard. I can't believe the guy spent all the cash on lumber, osb, shingles, to do it this way. Oh well that's why it was so cheap.

Here are a couple of pictures to illustrate. The far end of the cabin before I built walls and added paneling- you can see the post and the 2x6s. Also an exterior shot.
 
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Old 11-05-13, 10:31 PM
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whoops. something went wrong with the pic. here is another try.
 
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Old 11-06-13, 02:16 AM
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OK, so the rafters are fine, just the ceiling joists are flat. Much better scenario, if that is what it is. I would "strongback" the joists with a 2x on top full length, or along side.
 
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Old 11-06-13, 06:38 AM
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Aaah, that picture isn't the best actually. It's not just the ceiling joists. In that pic you can mostly see the 2x6s I added on, and some of the other rafters onto which buddy had actually scabbed on some correct-orientation 2x4s (for short lengths, a few feet here and there - not all way from center to wall). I believe he put those on because the edge of his osb roof sheathing panels weren't quite centered over the existing rafters so he needed to add some material to be able to nail them down.

This picture shows what is really going on (from the outside). I reclaimed these old windows so took this picture. You can see the 2x6s I added and the original flimsy rafters. (I've since cleaned up the roof edge with a PT fascia board and drip edge also.)

The place isn't accessible in winter except by snowmobile so I always have to keep my fingers crossed things will work out and the roof will hold. There is barely a square angle in the place...everything is a little wonky. But it seems pretty solid. Likely, my main concerns are still security (lots of low lifes around) and critters.
 
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Old 11-06-13, 09:08 AM
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Wow, it's a wonder that it didn't fall down the first winter
I'd add more 2x6s so every rafter has one!
 
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Old 11-06-13, 09:59 AM
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Quite a conglomeration there! I was waiting for your pix to show up before commenting, as I wasn't quite certain of what you were dealing with just based on your written description. The "waviness" in the shingle roof is really striking, along with the natural ventilation (visible vertical light streaks) in the attic.

I think if it were mine, and I wanted to do something to make me sleep better at night when the 100-year, 6-ft. deep snowstorm hits, I'd be inclined to add more vertical 2 x 6 rafters where you had skipped doing them earlier. Also, adding vertical web members at all panel points that don't currently have them, and some vertically-oriented full-length 2 x 6 ribs on any that don't yet have them wouldn't hurt, either. Centering the latter on top of the bottom flat 2 x 4s would be a more effective way to go under extremely heavy loading conditions (in an inverted "T" configuration, instead of creating "L's"), as such will prevent the bottom of each truss from wanting to rotate and kick out of plane. Glue and screw everything, of course.

Bolting some welded rebar cages on all of the windows might lessen the likelihood of broken windows, courtesy of the local low-lifes (I mistakenly thought we had all of them down here, south of the border!).
 
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Old 11-07-13, 06:07 AM
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Thanks for the suggestions. I'm definitely going to add vertical 2x6s on the rafters I skipped before, and beef up the webbing. Unfortunately there won't be time to do anything more before this winter. So we'll see how things shake out in the spring. My feeling is that with the posts in the middle, and being only 16ft across, it would be pretty hard for the thing to cave in. I hope. Last winter we had a LOT of snow and it seemed fine, but who knows how close it really was to catastrophe. As for the natural ventilation, haha, buddy did a board-and-batten siding (must have spent a mint on the sanded pine boards) but forgot the battens. I'll be putting those up next year too. In the meantime, at least I can run a propane heater worry-free.

As for the low-lifes, well, it's kind of a catch-22. The more deterrents there are to entry, the more the sketchies might try and get in. Many people in the area just leave their places unlocked with notes that there is nothing to steal and please don't trash the place. I lock the door, but being not visible from the trail has helped me so far I think since these guys go for the easy targets. Pretty much all you can see from the windows are old furniture, toys, and mouse traps. No reason to enter. I'm more concerned they might want to use the diamond windowpanes as target practice.
 
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