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Old 12-14-2009, 03:59 PM   #16
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Attic Framing Confusion...


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Originally Posted by pyper View Post
In my house the rafters are undersized. They're true dimension 2x4s with a 15' span (about 20 feet long). Those 2x4s that go up on an angle serve to cut the span. They didn't put one on every rafter, but there are various pieces nailed across the rafters that seem to effectively distribute the load. Well, that, and the tongue and groove decking.

Measure the span of your rafter, and look it up in a span chart. If your rafters are undersized for the span, then the 2x4's are there to prevent sag.

being that your ceiling joists are also under-sized, the 2x4's aren't preventing much of anything. it's just the way these things were built, before building codes and span charts. oddly enough, some framers will still post their long rafters/hip/valleys down to practically nothing.

sometimes it's even called out on the drawings

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Old 12-14-2009, 04:17 PM   #17
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Attic Framing Confusion...


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being that your ceiling joists are also under-sized, the 2x4's aren't preventing much of anything. it's just the way these things were built, before building codes and span charts.
Not true -- the 2x4's come down on a load bearing wall (where the joists are tied together).

If they did come down on under-sized joists mid-span they would be pretty pointless.
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Old 12-14-2009, 04:22 PM   #18
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Attic Framing Confusion...


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Not true -- the 2x4's come down on a load bearing wall (where the joists are tied together).

If they did come down on under-sized joists mid-span they would be pretty pointless.
you lucked out on that one most of the time these struts just land in the middle of nowhere. is there a center girder in your house?
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Old 12-14-2009, 04:43 PM   #19
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Attic Framing Confusion...


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you lucked out on that one most of the time these struts just land in the middle of nowhere. is there a center girder in your house?
My house is build "beam on pier."

There's a 12x14 grid of brick piers with 6x8 oak beams connecting them. The center wall is on a beam, just like the end beams. I calculated that each beam can carry about 10,000 lbs.
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Old 12-14-2009, 04:52 PM   #20
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Attic Framing Confusion...


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My house is build "beam on pier."

There's a 12x14 grid of brick piers with 6x8 oak beams connecting them. The center wall is on a beam, just like the end beams. I calculated that each beam can carry about 10,000 lbs.
sounds like a solid SOB
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Old 12-15-2009, 01:35 AM   #21
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Attic Framing Confusion...


Pyper, you have purlins and struts, to shorten the span of the rafter to use smaller material: second page, middle picture: http://books.google.com/books?id=1fI...20ties&f=false

The O.P. drew a horizontal member tying and supporting the struts, which sounds like there is no bearing wall directly below the ridge board. I agree, have a Structural Engineer look at it for plan of attack.
Be safe, Gary
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Old 12-15-2009, 11:12 AM   #22
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Attic Framing Confusion...


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Pyper, you have purlins and struts, to shorten the span of the rafter to use smaller material: second page, middle picture: http://books.google.com/books?id=1fI...20ties&f=false

The O.P. drew a horizontal member tying and supporting the struts, which sounds like there is no bearing wall directly below the ridge board. I agree, have a Structural Engineer look at it for plan of attack.
Be safe, Gary

The top of a bearing wall is a horizontal member. I wouldn't want to read too much into a rough sketch.

Not that it matters to the OP, but I don't have purlins -- just struts and collar ties. There are assorted horizontal members tied on diagonals across the bottoms of the joists. I really think it's the roof decking that distributes the load.

Regardless of what's going on, the only rule we had when we did the recent work was "no cutting into the stuff in the attic."

I'm definitely not endorsing the construction method used in my house, but it seems to have held up. I had also considered going in and beefing it up with actual purlins and more struts, but then I decided not to, on the basis that there didn't seem to be any problem and I definitely don't want to create one.
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Old 12-16-2009, 02:41 PM   #23
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Attic Framing Confusion...


Pyper, I, too, have found many older roofs systems with struts tied to purlins, struts tied to rafters and 6’ non-continuous nailers going perpendicular to the rafters. As you mentioned in your post: “various pieces nailed across the rafters that seem to effectively distribute the load.” Sometimes these nailers will have two struts (each end), and sometimes, only one for a 6’ long nailer. I wonder if these were used to support the installer as he was up there, and later, after sheathing, removed the nailer that tied them (the shorter nailers together for the proper layout) together. Interestingly, I find mostly 12’ long 1x6 or 1x8 boards on roofs, maybe to make it easier for the carpenter and his apprentice to install them without moving much. Yet they had access to 1st growth lumber in long lengths, like rafters. Perhaps I misunderstood you; I apologize if I offended you.
A lot of the time there is not a bearing wall close below (2-4’), so the struts land on a strongback or single board on edge. This is what I understood the drawing to be. A picture is worth…….
Be safe, Gary
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Old 12-16-2009, 03:17 PM   #24
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Attic Framing Confusion...


Perhaps I misunderstood you; I apologize if I offended you.


[/QUOTE]

No offense taken Gary. I think the best we can say is in the old days each carpenter probably had his own ideas about how to frame a building, and some of them were better than others.

It would be great if we had a photo instead of a sketch.

In my house the "assorted nailers" seem to be diagonal braces that keep the rafters from racking. They're mainly 2x2, and pretty long. They go at any odd angle (probably depending on the length at hand).

I know that the wood used to frame my house is a lot stronger than modern wood -- some of the studs are so hard a screw will break off if you don't drill a pilot hole.

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