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Old 02-16-2014, 01:10 AM   #1
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Converting rafters to trusses


This is yet another "removing a load bearing wall" topic. I know you guys are probably tired of these questions, but I searched and couldn't find a thread on what I am proposing to do.

I am reasonably sure this is a load bearing wall, as it sits over a beam in the crawl space. Also, the roof structure is stick built, not trusses, so the framing would not support itself over a 28 foot span. And the way the rafters are braced makes doing any work in the attic a real PITA. (And I have several wiring, HVAC and plumbing projects planned that require attic work) So, to make the roof self supporting and open it up for access, I am wondering if I can convert the existing framing to a Fink, or "W" truss. Attached are two drawings, one of how it is now, and the other of what I propose to do. The wall to be removed is about 15' long. The rafters and ceiling joists are 2X6, the bracing is 2X4. The truss members I would add would be 2X4.

I already know the standard answer "Consult a structural engineer", and I plan to do so before doing anything. I just wanted to get some additional input first.
Thanks.
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Converting rafters to trusses-existing-structure.jpg   Converting rafters to trusses-proposed-change-truss.jpg  

ArTrvlr is offline   Reply With Quote
Old 02-16-2014, 06:07 AM   #2
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Converting rafters to trusses


As you noted, only a structural engineer can give you a straight, useful answer. Too many location-specific variables involved (wind, snow load, etc.) to even hazard a guess.

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Old 02-16-2014, 07:32 AM   #3
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Converting rafters to trusses


In the old days of construction, wooden trusses were sometimes stick framed using wooden gusset plates. I haven't seen a stick framed truss built within the last 50 years, probably because essentially all modern trusses are factory fabricated using steel nail plates that are shot into position using a special compressed air gun. The lumber for trusses is sized and specified by the truss engineer at the factory.

If I understand you correctly, you are not proposing to replace your stick framed roof with trusses, rather you are proposing to field convert the existing stick framing to truss framing. This may work, but it assumes that the existing framing is the correct size and grade to be used in the F truss you propose, and it assumes you can install plates in the field that will work.

You already know that you are going to need an engineer to determine if the existing lumber will work. I doubt there are any truss manufacturers who will take on the project, since their plates are not designed for field installation, and they probably do not have insurance to cover a field retrofit of stick framed lumber. So this will be on you, your engineer, and a contractor if you decide to hire one. Best to check with your local code enforcement official if this is going to be OK with them, and what sort of documentation you are going to need. Where I live, if you can get a registered professional engineer to sign off, the building inspector will let you do just about anything. No stamp, you need to go strictly by code, and retrofitting a stick frame roof to a truss is way beyond code.

Best of luck.
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