brickeyee Your point about RH of winter air seems well taken. What was missing from the Carson Dunlop explanation, I think, is that attic air in a home is often more humid than air outside the attic due to leakage from the conditioned to unconditioned space. Here's how another P.E. describes truss uplift: "A problem that can occur with this system causes cracks in wallboard over time. In recent years, attic insulation usage has increased, which ends up covering the bottom chord of the truss. This tends to keep the bottom chords warm and dry while the top chords absorb moisture and expand. The top cord expansion causes the top chords to lift, pulling up the bottom chord as shown in Figure 1, hence the term truss uplift. " Charles C. Roberts, Jr., Ph. D., P.E. My untrained guess would be that the lengthwise shrinkage of grain does not relate to the length of the wood but to which portion of the tree the wood was cut from. Here's a longer explanation: "Truss uplift is caused by wood's natural response to moisture exposure. This response occurs when humidity changes differentially in two areas (an attic floor and attic ceiling, for example). A truss's top chords expand as their moisture content increases. Problems resulting from truss uplift are most common with flat-bottomed trusses in homes during winter when a truss's bottom chords, often covered by insulation, are kept warm and dry while its top chords are exposed to moisture from condensation. During winter months, warm, humid air emanates from buildings' interior use and occupants. The uplift movement occurs because, as the truss's upper components resize themselves under the differential moisture conditions, internal tensile stress occurs in the truss's web members, which then pulls up the bottom chords (and the attached ceiling drywall), resulting in a separation along the wall-to-ceiling juncture of the drywall. To put this into perspective, consider a truss with top chords made of two members, each measuring 30 feet in length. The total movement anticipated from winter swelling caused by the truss's moisture content increasing is a 0.72-inch expansion per side, or a 1-inch total rise of ridge above the bottom chords. And once a crack forms inside a home, additional moisture generated by occupants and their activities can escape into the attic, travel to the cold attic ceiling surface, condense on the truss's top chords and cause further truss uplift. " Lucas J. Hamilton manager of building science applications, CertainTeed Corp.'s Insulation Group For interest, I will forward this thread with a request for comments to Carson Dunlop. lzerarc As I said, different places, different practices. I've changed only reluctantly. Seeing those spindly stuck-together 2x2s gives me a visceral reaction and I have to rationalize using roof trusses. However, my engineer says they're much better done now than ever and with wall lengths less than 50 feet uplift is rare. None of this applies to warm climate homes.

You might find it much easier to take the whole roof off and replace it, especially if you want to make the wall taller. Sounds like you're re-roofing anyway, so you're most of the way there. Just do it once and right. Either stick build it or use trusses, it will probably cost about the same either way. Saving the old material doesn't seem worth the effort.

We just recently built a house owner/builder. Our interior walls were up before the trusses, but like PPF stated above, the trusses sat on the exterior walls for support and didn't need the interior walls. That said, I designed the house to have a very simple roof. If you have a complicated roof, you might have some interior bearing walls which means some of your trusses have to sit on the interior walls for support. The other problem could be that due to the current building boom, truss manufactures are really busy. Last year, our trusses were almost 4 weeks delayed. I think this year things are worse.

I designed and sold materials for a stick framed wood structure with a very similar design to this in the main entry. It turned out beautiful, builder was very talented. I don't have photos, sorry. Also it was about 10 years ago so I don't remember the costs. We used engineered parallel chord truss and built decorative beams on the underside. It was easy to insulate due to the unusually large heel height. The parallel truss is limited on span, so not sure if you could get to 35ft or not... Engineered timber trusses are another avenue to check out. They are quite expensive though, so be prepared. I sold 3 at 25' span 6/12 pitch last year for $9k each. We had to site assemble them due to difficult terrain not allowing them to be delivered whole. Insulation needs o be planned ahead of time. Rigid foam can be installed on top of the sheathing with the metal roof on top. This is a very effective way to insulate a roof, although a lot more expensive than typical fiberglass blown. Lastly, this look can be achieved with a large (very large) engineered ridge beam and conventional rafters. I've done this type of construction on numerous builds. Everyone is always amazed at the shear bulk of the ridge beam, almost every framer has questioned if the engineer got it right... Insulating is limited to the size of the rafter, so spray foam is usually the best option here. I'm usually against spray foam, but in this application not much else can fit the bill. 3rd party HVAC design is critical on a project like this. Really need someone that has experience with spaces similar to this. I agree with others that these spaces are known for having problems, but those issues can be mitigated for the most part by proper planning and execution. Explain your concerns when you interview them and your builder. If the only answer is "install a few fans" then maybe they aren't the right fit. Best of luck