Roof framing ideas 1

[JStructsteel]

Got a house with a room in the attic, and the owner wants a full height roof projection. Based on the framing, I was looking at having to do a ridge beam, and rafters. I was thinking that a girder truss each side could be designed for the ridge beam loading. At the other end, the floor joists would have to take the load. Anyone have any other ideas?

 

[jayrod12]

Where is there second floor?

 

[JStructsteel]

Sorry, uploaded only 1 PDF. Here is the floor plan for the attic.

 

[jayrod12]

I think you're kind of on the right track. However in looking at that proposed floor layout, you really don't appear to have enough depth at the sides of the second floor to do attic style trusses. I think you've got to frame out that second floor and just provide beams below your roof framing posts as necessary. Based on that layout you may be better off stick framing that entire roof. You're likely to end up with some posts below the second floor, hopefully hidden in the main floor walls.

 

[KootK]

One option. It would be helpful if you had interior bearing walls and posts available for use.

 

[jayrod12]

I was thinking of framing it the way Koot shows, but that's where I commented about attic style trusses may not be feasible. If they can get them to calc out, then his layout works great. But I have my reservations that the two large ones supporting the ridgebeam and two floor beams will be capable.

 

[KootK]

The ridge beam ought not be a problem as long at it's placed midspan as it appears to be. In that configuration, it winds up just being axial load in the heavy top chords of a multi-ply attic girder. As a slick detail, you could make the peak king post a 2x10 etc for convenient hanger attachment.

For the floor beams, you've got a few options:

1) If conventional attic girders work, peachy.

2) If need be, truss the bottom chord of the attics and carry that through to the whole attic floor system, adjusting stairs etc as need be. This would be kind of slick as you could then truss nearly the entire thing.

3) If need be, place some multiply LVL or steel beams in front of the attic girders to pick up the slack while still retaining the same, fundamental layout.

Like I said previously though, economy will be maximized by utilizing some interior bearing if it's available.

 

[KootK]

Noodling on it a bit more, there might also be some merit switching the direction of the floor framing between girders.

 

[JStructsteel]

Thanks everyone. The whole floor below is a 3 car garage, so no posts coming down. I might end up with some steel framing, I have some in the basement under the garage, so might make use of those columns in the walls and clear span beams where I need.

Its going to be a expensive proposition either way, and this is only the garage portion of the house!

Here is the truss I envisioned on each side of the bump-out area. Very similar to your sketch.

 

[KootK]

Here is the truss I envisioned on each side of the bump-out area.

I'd do the bumpout as over build on the girder attics. You want the sheathing on the main diagonal top chords to brace them convincingly.

 

[JStructsteel]

Sorry, yes, the bump out is just shown beyond.

 

[JStructsteel]

Another thing i am seeing is the truss bearing is on the extension of the overhang. This does not seem normal. For the girder truss I can see this being an issue.

 

[KootK]

Agreed. Those attic girders were aggressive to start with as jayrod12 mentioned. There's no chance that they'd work as tail bearing. The non-girder attic trusses likely wouldn't work as tail bearing either. This you can kind of check yourself as it's mostly just very high bending and shear in the overhangs.

If you're heading in the direction of trusses, the heel heights need to make sense for that. You'll rarely be able to get away with maintaining the kind of bird's mouth geometry that you often find in conventional framing.

 

[JStructsteel]

Ugh. I see now why the architect didnt want to provide any sections or details of this area.

This is a bid job. Would you contact a truss supplier up front, or let it come back that they cant do it for sure?

 

[jayrod12]

Yeah, your architect needs to get a clue. At a minimum, the bottom edge of the bottom chord will need to extend to the far side of the wall. That will push the roof up. Depending on how deep the bottom chord needs to be for all the other stuff going on, it could be a substantial increase in roof height.

Around here, we require a 14" tall heel at the outside face of the wall just for insulation and air gap. That usually allows us to put some fairly robust bottom chords on those trusses when necessary.

 

[JStructsteel]

Yea, even if I goto steel beams, the columns would have to be in the space from the wall so they dont stick out of the roof!

 

[jayrod12]

So tell them the roof has to be higher. At least at the eaves. You could potentially have a lower sloped roof in order to accommodate the ridge height staying as is. But at that same time, the floor system is going to be thicker than the architect shows, so headroom in the attic space will be tight if you don't raise the ridge.

 

[JStructsteel]

Sent them a message. Told them if we leave as is, doubtful that wood will work. If we goto steel, then the columns would be into the space below.

As usual, I look back at the napkin sketch I bid this with, NOTHING showing attic framing required, just a trussed roof.

 

[jayrod12]

Par for the course. Welcome to the lovely world of residential engineering.

Honestly, that sort of thing is why many engineers avoid residential like the plague. Low fees, bidding on no information, constant changes during design, and substandard contractor quality. But it can be profitable if you're good at it.

 

[JStructsteel]

Other than this hiccup, the drawings and info provided otherwise is good after the bid. The whole house and yard I would value at a 1.5 mil investment for the owner. The architect agreed that raising the roof is the way to go, and also gave me the local truss rep to work with to make sure.

I'm only designing the garage portion, since its a 2 story (walk out basement) garage. Not sure who is dealing with the rest of the house, there are some pretty large spans I see. I guess they have it covered.