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I have a Cape Cod style house that was built in 1945 with an attic as a living space. The trusses are 2x6, 16" apart, and don't span more than 15' across. Do I need to reinforce these trusses or should they continue to hold up? If so, how should I reinforce them?

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Welcome. Here is the wikipedia page for 'trusses' en.wikipedia.org/wiki/Truss ... perhaps you mean floor joists? Photos would help. – mike Oct 31 '13 at 6:15
@mike I think you are obviously right, so why not edit? – bib Oct 31 '13 at 20:21
@bib - I was looking at safety harnesses etc this afternoon. The packaging stated that the tie-in anchors must be nailed off into 'trusses' . . homedepot.com/p/203191839 . . . bizarre. I'd be surprised if trusses (in the wikipedia sense) are designed for any forces other than downward loads and a bit of wind shear. – mike Oct 31 '13 at 23:22
@mike - Though trusses are designed to support mainly vertical loads, they develop significant secondary stresses axial to the members, so truss top chords, especially when tied together via roof sheathing, are typically capable of resisting the astounding 5k lbs force the anchors are supposed to resist, even though not explicitly designed for. To OP - sorry for the OT talk. How can you be sure it was intended as living space? That is pretty light floor framing even in 1945. – bcworkz Nov 1 '13 at 4:42
@bcworkz - couldn't quite follow your line of reasoning. I agree it's OT. Upon reading their terminology, I figured 'truss' to have broader meaning than I had understood it. I was expecting 'rafter', not truss. OED: 6a Building, etc. A framework of timber or iron, or both, so constructed as to form a firm support for a superincumbent weight, as that of a roof or bridge. . . . So I suppose the framework of a stick-framed roof fits with that definition. – mike Nov 1 '13 at 5:27

Unless you are putting unusual loads up there (king size waterbed, full kitchen, concrete sculptures), normal bedroom/living room furniture and a couple of people should still be fine.

Ceiling cracks in the lower level will be the first indication of undue stress.

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Span tables at: http://www.awc.org/calculators/span/calc/timbercalcstyle.asp

Suggest 8-11 ft max span for a 2x6, depending on species.

So this is unsafe.

The reverse calculator suggests a 2x10 would do it.

I'd suggest getting an engineer in to look at it.

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The OP said 2x6. But your answer may be the same. – bib Oct 31 '13 at 20:22
I meant 2x6. Fat fingers. – Chris Cudmore Oct 31 '13 at 20:24

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