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Framing walls for a flat roof


Jeff123's Avatar
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10-11-06, 06:48 AM   #1  
Framing walls for a flat roof

This may need to be in the roofing forum, but here goes.

I'm framing a garage with a flat roof. The roof will slope 6" from one wall to the other along the length of the ceiling joists/rafters. The length will be approximately 20'4". I have a couple questions.

1. How do I frame the walls to get the slope? I can frame one end wall 6" higher than the other, but what do I do about the side walls? Are they the same height at the short end wall or do they need to be framed so they taper up from the short wall to the tall wall? If the side walls are short, how do I make the connection at the corner with the tall wall since I won't be able to tie them together with the top plates? Do I need a rim joist, or do I just line up a joist with the outside of the top plate on the side walls, which will give me something to nail sheathing to? I'm using engineered joists.

2. With this low slope, do I need to worry about how the joists attach to the top plates? By that I mean do I need to bevel the top plates or do anything else special?

3. For the garage door header, the engineer spec'd a beam of three glulams. The total width is 1/4 inch narrower than the walls (2X6). Do I need to worry about adding a 1/4 inch filler? Should I connect these with carriage bolts or just nail together? The engineer did not spec one way or the other.

3. On some garage doors I have seen there was a bottom plate under the header running from cripple to cripple on either side of the door instead of resting the header directly on the cripples. Is this necessary? Is it just to give something to nail trim to?

Hope this is clear. Thanks for the help.

 
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Jack the Contractor's Avatar
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10-13-06, 06:30 PM   #2  
Lots of questions here. Hope I touch on all of them. You build your back wall and front wall. One taller then the other. for the end or side walls, you build them with a taper to fit. Since your using engineered joists, I wuld put a rim joist on the outside of each end so they are not exposed to the weather. They sit on the top sills, toe nailed twice on each side with #16 sinkers, and then you must use a wall to joist metal hanger.
for your garage door headers, you will have to put in at least one piece of 1/4 plywood or osb so they are the same width as your wall studs. Use double cripples on each side (like a 3x6") and set your header on these and attach. For three glue lams, power nail two of them together, nails on each side, put in at an angle, then add the plywood filler and the other lam beam and nail in place to the other two. These nails can go in straight. I would leave out the board under the header.
Hope this all helps. Good Luck

 
Joe Carola's Avatar
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10-14-06, 08:21 AM   #3  
Jeff,


You don't have to taper the top plates because the pitch is so small. It's only a 5/16/12 pitch or 1.41.

Build your back wall 6" higher than the front wall. Plumb and brace and sight both walls. Nail a rimboard across the top plates of the front and back walls. Cut the I-joists to fit in between the rimboards.

Nail a rimboard on the outside of two I-joists and nail one on one side of both front and back wall top plate in between the to rimboards you already have nailed up flush to the outside and do the same on the other side. Those two now represent the side walls top plates and angles you need to frame.

With those two in place just nail top plates to the bottom of those flush with the rimboards because the rimboards are flush with the framing. Now you can frame your two side walls putting a 1.5 on the saw if you want.

Install the rest of your I-joists in between the rimboards nailing then into the top plates and facenailing from the rimboard into the I-joists with whatever size nail is code in your area.

As far as packing out the : for the header. Just nail the three together first and see what you will need, because when you nail three lvls together they usually dont equal 5-1/4. Sometimes theyre 5-3/8.

The 2x you see on the bottom is just to flush everything up and adds no extra strength. Nail one on if you can and have enough space for the cripples above because sometimes the cripples are to small and code wise you cant put small cripples ion and you have to keep the header tight to the bottom of the top plates and then fir down the bottom of the header to the desired height.

 
Jack the Contractor's Avatar
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10-14-06, 05:11 PM   #4  
Jeff:

Joe gave good info, but do not cut your engineered joists. They are engineered for strength and stability and are not meant to be cut. However, on the other hand, they are your joists so I guess you can do whatever. We do not know where you live so do not know your codes. Good Luck

 
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10-14-06, 05:37 PM   #5  
Posted By: Jack the Contractor Jeff:

Joe gave good info, but do not cut your engineered joists. They are engineered for strength and stability and are not meant to be cut. However, on the other hand, they are your joists so I guess you can do whatever. We do not know where you live so do not know your codes. Good Luck
Jack,

What do you mean an I-joist is not meant to cut? They have to be cut to length. I use I-joist all the time and cut them.

 
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10-14-06, 08:36 PM   #6  
Joe:

I am not going to argue with you about this. In Jeff's first letter, he said he was using engineered joists, not I joists. These are different then I joists. They may look the same, but an engineered joist is different.

Jack

 
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10-14-06, 09:46 PM   #7  
Posted By: Jack the Contractor Joe:

I am not going to argue with you about this. In Jeff's first letter, he said he was using engineered joists, not I joists. These are different then I joists. They may look the same, but an engineered joist is different.

Jack
Jack,

Who said anything about arguing? I'm just trying to figure out what your talking about, that's all.

He said Engineered joists. I-joists are considered engineered joists.

http://www.apawood.org/level_b.cfm?content=prd_joi_main

http://www.ebuild.com/guide/products/productSpecifier.asp?catCode=1889

I take it that he's talking about I-joists. What type of joists are you talking about that can't be cut?


Last edited by Joe Carola; 10-15-06 at 11:10 AM.
 
Jeff123's Avatar
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10-16-06, 05:46 AM   #8  
Framing Flat Roof

Thanks for all the info. This really helps. Just so there is no ongoing dispute let me clarify. I was using engineered and I-joist interchangably. I think the engineer spec'd Trusjoist TJI 35S joists (sorry, don't have my plans handy). I believe these can be cut to length, but I will follow whatever instructions come with them.

 
Jeff123's Avatar
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10-16-06, 07:19 AM   #9  
Framing Flat Roof

Joe,

As an alternative, could I build the front and side walls to the same height, tying the corners together with overlapping top plates, and just build the back wall 6" higher and tie the side walls to the back wall with metal plates plus the normal corner stud nailing (I think code in my are - Kentucky - would allow this). Sheathing would also overlap helping to tie it together. This would be easier for me to do and the side walls don't seem to be bearing any weight since the joists rest on the front and back walls, so do I really need to taper up the side walls? The max space I would have between top plate and bottom of joist would only be 6" so I would be able to nail on sheathing and still be within code. Code in my area requires nailing on sheathing with nails 6" oc on the edges.

Something else, since I am building close to the property line, the city is requiring 1-hour fire rating from both sides for the wall next to the property line. How do I get this? I am planning on using something like Hardi plank on the outside. Do I use a fire rates sheathing for the outside and drywall on the inside?

Thanks again.
Jeff

 
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