Hanging a small roof off of a wall?

[MushCreek]

I'm going to build a small shed roof over the doorway of my barn. Right now, the slider hardware is bolted to a ledger, and the rain pours down inside the door if the wind comes out of the south. The plan is to build a short (3-4') roof all the way across, covering the door hardware, and providing additional shade and rain shielding when the door is open. I'm going to build little trusses, topped with 2X4 purlins and tin roofing. The question is- How do I attach these little trusses to the wall? The bottom can rest on the external ledger, so shear is taken care of, but I'm trying to figure out the best way to secure the top. The wall is already sheathed with 5/8" T1-11. I could either use loooong carriage bolts, all the way through the studs, or I also thought of cutting a slot through the siding on either side of the studs so I could use metal straps nailed to the studs and to the trusses. Any other ideas?

The wall is very stoutly built, and our snow load is only 10 lbs/ft. I'm going to cut an angled slot in the siding to slide flashing into on top of the tin roof. Between the angle, and ample caulking, the flashing should keep the bulk of the water out. It is a barn, after all.

Here's a pic of the truss and wall:

[Redoverfarm]

First thought would be to use "lag" bolts in either 1/4" or 3/8" dia X 5-6" bolted through to the wall studs.  Just allow you purlins to overhang 1" and tin 1" beyond that.  Flashing should probably be at least 6" both directions at the top.  I have also seen just a rain shield boxing made to cover the sliding track which would shield the track and water but would not give you an overhang to stand under.

[flyingvan]

I was thinking lag bolts too, but run in at an angle so over time they don't pull out the same direction they went in

[Don_P]

I've done a bunch of similar overhangs at 2' and less. With them I took scraps of ply or osb and cut the profile of the roof on them. Then we made 2x pieces to nail the ply gusset to (you don't have to nail it all to the same side) It guaranteed everthing was the same and prefabbed it for easy work up on the ladders. Those sit on a notch for a 2x4 wall ledger like yours and I nailed them well. I sheathed those in ply and nailed that sheathing to the wall as well, a top purlin could be done the same. As it gets bigger I would think about it harder. I see it as rotating about the ledger and think about it as if it were a framing square sitting on the ledger, one leg extends out from the ledger and a load hangs from that at the overhang width, the other leg runs up the wall and at some height there needs to be a connection capable of resisting the rotation that's trying to happen. If the overhang is say 4' and the wall leg is 4' then every pound of vertical load is a pound of withdrawal resistance needed for a lag or screw into the wall framing. Minimum design load is 20psf live, you're no more than 5psf dead load, 4'x25psf x 2' spacing=200lbs withdrawal, and that was very conservative, I hung the entire load out on the gutter. The wind under it will produce the same force at the bottom of the wall leg, another fastener there.

I'd go read labels on the thinner shanked structural screws (fastenmaster, oly's). They're easier to work with and I think you'll easily get it out of them.

[MushCreek]

Don- I understand what your saying, and that is precisely my concern with fastening them well. The roofing panels are 4', so the roof extends out about 3-1/2'. I could certainly cut them down if it looks like too much load for the wall studs. The bottom ledger is through-bolted through the quad-2X12's because it has to support the very heavy doors. I'm still thinking about through-bolts, but it would be a lot of work. I'd have to temporarily hang the trusses, and drill from the inside out to be sure I was centered on the studs. I'll look at the various timber screws to see how they stack up.

I'll completely sheathe the two outermost trusses, but want to leave the interior ones open for a timber effect. I was thinking about making them out of 4X4's on 4' centers, but that doubles the load on each one. Do you think that's too much load for the wall studs?

[PEG688]

  Why not install a 4x6 stud  inside,  above the header, connect the 4x6's to the adjacent stud with ledger lock bolts , staggered 12" OC. The thru bolt the truss to the 4x6, the 4x6 could even be installed on the flat so you'd create a 2" space for any wires that may be in the wall and so the thru bolts would not have to be recessed into the 4 by.

This would create plenty of withdrawal strength, and I'm sure you'd never rip the sheathing off and pull the whole works thru the wall this way.

I'd lengthen the vertical 4x4 on the exterior as much as possible to create more distance to spread the load into the header.

Is the header braced laterally inside , or is it really as drawn, no lateral support inside?


You could make the roof-let a steeper pitch so snow load would slide off sooner as well.   

[MushCreek]

4X6's would certainly stiffen up the wall, and give me plenty of bolt surface. 4X4's are a lot cheaper though- do you suppose they would be enough?

I'm not sure what you mean by lateral support of the header. Do you mean the header over the door opening, the quad 2X12? It rests on a 6X6 post on either side of the opening.

I can't lengthen the vertical by much because the roof slope would eventually get in the way. I could increase the roof pitch easily- what's a good pitch to shed snow? As shown, it's only a 5/12 pitch. A steeper pitch would also reduce how far out the edge of the roof would be, reducing the load on the top of the truss.

[PEG688]

4X6's would certainly stiffen up the wall, and give me plenty of bolt surface. 4X4's are a lot cheaper though- do you suppose they would be enough?


Just more surface area , I'd think that would spread the point load a bit is all, stronger is better.   /color]

I'm not sure what you mean by lateral support of the header. Do you mean the header over the door opening, the quad 2X12? It rests on a 6X6 post on either side of the opening.

    Is there a ceiling your not showing in the drawing? Something to stiffen the header from deflecting inward?  If you mentioned how long it is, the header, I missed that.




I can't lengthen the vertical by much because the roof slope would eventually get in the way.

I'd suggest just bringing it down just above any trim on the existing door , maybe a couple of inches between the post bottom and the existing trim top, maximize it's / there length. 



I could increase the roof pitch easily- what's a good pitch to shed snow? As shown, it's only a 5/12 pitch. A steeper pitch would also reduce how far out the edge of the roof would be, reducing the load on the top of the truss.

  If it wouldn't clash with the existing roof of the building pitch I'd go at least to a 6/12 , best shedding pitch  would be starting at a 8/12 or greater.

Not having the total picture,  these are just suggestions.

G/L PEG

[MushCreek]

This rooflet goes on the gable end of a gambrel roofed barn. The roof pitches are 12/7 and 7/12, so the roof pitch doesn't matter all that much. It is a barn, after all, so appearance is secondary to function, as long as it doesn't look weird.

[Don_P]

For you wind will control, that was the 20psf, vs your 10 psf snow load. This is up or down and the end corners are going to take the worst hit. But for wind you are really shackling against short impacts rather than long term loads, most things get to multiply allowables by 1.6 to acoount for the short term nature of the loading. Pitch for snow shedding is not really critical... in this southern instance.

Using heavier studs would be a good thing, they are easier to be sure you got a good connection but if you hook to the 2x studs well they can handle the withdrawal. As the load increases the connection of the stud top and bottom is something to look at, some simpson A35 or 55 framing angles with nails down and into the studs can resist that shear to a point. PEG's point about laterally supporting the header is a good one. If that is a flexible stack of stud,header,stud something inside needs to stiffen that up.

I've been enjoying train depots lately, check out the bracketing supporting the various platforms, there are some nice designs. I had Michelle hanging out the window with a camera in Bristol the other day.

[MushCreek]

The loft floor is a substantial diaphragm just above the header. The upper walls are built on top of it. I'll definitely add some brackets to beef up the loaded studs, and make sure the top and bottom plates of the upper wall are well-fastened.

The end corners are close to the roof structure, so it is a stronger, stiffer area anyway.

[PEG688]

The loft floor is a substantial diaphragm just above the header.

There ya go , that doesn't show in the drawing , one can never assume something is there to help with lateral  support  I was asking about.

  I think you'll be good , I would still use thru bolts vice lag screws/ bolts.   Nice big washers or maybe 1/4"x  3"x3"  bearing plates if you had some left over from the build ,  on the top bolts,  on the inside. Those would never pull thru.   

[flyingvan]

If I'm picturing that correctly, with the loft diaphragm a little above the header, could you just extend your rafters right through the wall, supported by a ledger, then have them continue on diagonally to tie in with the loft joists?

[MushCreek]

I'll re-draw the sketch to show the loft framing. It's not drawn exactly right- the 2X10 floor joists sit on top of the header. It had occurred to me that I could go right through the wall with the rafters and tie them directly to the wall studs. My contractor recommended I remove a strip of sheathing so that I could get the flashing properly up behind the sheathing. With the wall open, the roof rafters could just overlap the studs and be fastened securely. Fitting the strip of sheathing would be harder, though, having to notch around the rafters. Eventually I plan to tighten up the structure and insulate, so I need to be able to caulk it all tight. I'm not putting any kind of soffit under this little roof; it will all be open; so I'd like it to not look too cobbled together.

[MushCreek]

Here's a re-do. I increased the pitch to 12/12, which reduces the total projection to less than 3', and lowers the outside edge, which will offer a little more shielding of the open doorway. I eliminated the vertical member altogether. The roof rafter is attached directly to the wall stud, which is exposed by removing a strip of sheathing, which also would facilitate proper flashing.

I see two issues- attaching the bottom strut firmly to resist uplift, and re-sheathing the piece removed, having to work around the roof trusses. I could use right angle metal brackets to secure the bottom strut to the existing exterior ledger, I guess.