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Jim Baird

site built truss

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Before it was so easy to pick up a phone and order some trusses or maybe a glue lam beam the site carpenter had to make long spans somehow, so he did it this way.
Have been seeing these in brick ranches lately.  Anybody else here?

PB070334.JPG

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I've seen a few like that.  One vital element that's missing here is the lack of lateral rigidity at regular intervals on the 'internal rafter'.  It's got compressive forces in it so if you don't install lateral support along it's length, it might deflect sideways and the whole thing fails like a house of cards.

It's like the rafters on a house under construction: until you fasten the roof deck to the rafter, the rafter can sway sideways.

If this house has been that way for 40 years, I might not make a big fuss over it.  If it's recent construction, I'd punt it.

Does the top of this internal rafter join to the roof system above?

Edited by Marc

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...lateral support on the bottom is the regular spaced ceiling joists?  This is a carport (no insulation), and they needed something to make a 20 ft span on which to rest ceiling joists of 9 ft or so.  From below, after 59 yrs, you can see a little sag across the span.  I'm sure the top is tied to something, but not at intervals down the slope.

Not bad, huh?

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When I was still working as a carpenter in the late 1960's we built more than a few roofs like that, only thing I don't see is some collar ties but maybe that was something done locally. Yes, the double beam at the bottom is the support for the ceiling joist, we would put that in anytime we had no supporting walls underneath. Ends of the doubled up 2xs rest on the end of the last 6 inches of the support wall inside and then on the exterior wall. Need to have doubled up 2xs stud under this area. And yes, you will still get some sag, but usually not much, maybe a 1/2 inch in the length. If this was inside the home, you almost always have a crack in the drywall right under the beam. 

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14 hours ago, Jim Baird said:

...lateral support on the bottom is the regular spaced ceiling joists?  This is a carport (no insulation), and they needed something to make a 20 ft span on which to rest ceiling joists of 9 ft or so.  From below, after 59 yrs, you can see a little sag across the span.  I'm sure the top is tied to something, but not at intervals down the slope.

Not bad, huh?

Not bad at all.  A connection at the top transfers some of the stress from the interior rafter pair to the roof system.

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Those purlin supports actually put downwards pressure on the ceiling beam, no?

The beam seems to be hanging on nails. I would have expected plywood gussets. But who am I to criticize the carpenter at this point?

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Hard to see the details, but it looks like crap to me. Probably a lot wrong with the design and construction details, but many poor site built trusses work because many roofs may never see a full design load.

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Thanks, Mark.

I agree that it looks "country".  It looks like an attempt to transfer loads to outside walls, as trusses do, hanging the beam off the peaked rafters, as well as hanging the ceiling joists of the carport.

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Jim,

I see them from time to time on about 60-70s ranch homes. They're always over a double car garage where the home owners didn't want a post. I have no idea what they're actually called. The ones I've seen that are untouched seem to hold up pretty well.  

It's either these type of beams or some doubled up 2x8 or 10s sandwiched between a steel flitch plates that always seem to sag. 

How was it holding up? 

Kiel 

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18 hours ago, palmettoinspect said:

 

How was it holding up? 

 

...as noted in an earlier post it was built in 1959 and looks good from below, though the ceiling was plywood that likely adds some stiffness to the whole thing.  Like Mark noted, in residential you don't see very much in terms of loads on anything, especially when it comes to a one level ranch.

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