Tim Kampert from IBACOS-PERFORM presents the causes of truss uplift, its impact on quality and customer satisfaction, and best practices to mitigate it in your projects.
I would never live in a truss house unless I built it to ensure all mitigation steps were taken. I’ve seen several truss houses with gnarly wall/ceiling gaps and even ceiling failure.
Uplift in trusses is also an issue when solar panels are added to a large hip truss roof. This is mostly where long 2x4 rafters are supported on side-to-side cross-trusses below them, and the rafters are just fastened down with an upward-facing toenail from the truss below, and not with a block and a couple A35F clips, or similar, showing prior Uplift load design consideration. A toenail is fine for normal gravity download forces, and normal broad windloads, but not 150‐300+ lb. uplift point loads right above it. Solar Panel installation companies are usually run by Electrical Contractors hiring remote online 'discount' engineers if the City requests an Assessment and Calcs due to the local Wind zone. The Solar Contractors have installers and office staff who are often clueless when one mentions the engineering 'Load Path', as I have found out. Uplift on my own 9 rear solar panels (covering 200 sq ft) over the Kitch/Fam/dining 'Great Room' was calculated at 4100 lbs. total, with local design Vmax=120 mph and prevailing winds from the North. Tiles lift up and chatter at 45+ mph winds, and wind pressure in the attic and over the ridge lifts the downwind (usually south) roof sheathing, so actual tile roof deadload weight alone (about 21 psf if no heavy mech./misc in the area) cannot be counted on in a windstorm 75+, hence the Code-required traceable 'load path' below each panel footing, theoretically tying it down to the foundation. An upwards toenail is NOT going to hold that added panel uplift force down, and all it takes is a strong 3 second gust at just the right angle to open up the roof like a sardine can. The wind and rain can then do much further damage. Please do a video on this issue, since it is often missed by solar companies, engineers who do not physically inspect the attics (as is common, post-C-19) or who are not 'hands-on' familiar with wood framing (thus sending weird details that do not even apply!), and by City inspectors without a journeyman carpenter and/or engineering background [...like me] that is often needed to recognize an overlooked structural issue. Usually an Electrical 'combo' City inspector is sent to inspect Solar Installs, so they may also overlook missing Load Path (downwards) connections inside the attic of added stabilizing blocks, clips, and/or small straps, including rafter to truss, truss to topplate, and truss-to-truss, or angled braces, for Load Paths that jog sideways or that need to be spread over 2 or 3 trusses to stay within deflection limits and not overstress the wood. The roof ply is not considered 'structural' when it comes to bending Uplift loads of load paths, and it is treated more like posterboard. Visioning the Load Paths like a string on a roof-level (red?) balloon at the panel footing's point load and following the 2x framing downwards and tied to an anchorbolt at the foundation makes the Load Paths easier to figure out. It also always follows the stiffest members. Ensure the connections exceed the calculated uplift including nearby contributary loads from adjacent panel footings, and that the cross-truss top chords can handle multiple point loads and maintain the
Unfortunately we are dealing with this problem after the fact. We have lived in our home for 3 years and the same areas keep cracking. They have been retaped but every winter it happens again. I’m assuming that installing f clips would be difficult at this point? Or could that still be done from the attic when they cut screws loose? Our current plan to fix it is by cutting screws loose within 12 inches of wall and installing blocking to allow the ceiling to flex. We do not currently have truss clips. Would it still be necessary to install them? I don’t completely understand the lateral movement part.
Here's what Graham Davis at IBACOS says: I would love to get pictures from (you) that show both the cracking and the exterior elevation of the home so I could see the basic roof design. I would also like to know what region the home is in. But aside from those selfish desires, my response to the reader is that they are on the right track. Eliminating the nails through the ceiling drywall that are within 12” of the interior walls is the best fix. The two methods to consider: 1. Cut the nails with a multipurpose tool (Vibrating saw with an offset blade). If the rock is secured with screws, I would highly recommend option 2. Screws don’t cut as easily as nails, and are pretty easy to locate and remove from below. Locate the nails with a magnet type stud finder (old school device) and pull them from below. Either option will require drywall patches after the nails are cut or removed, therefore, the second option is probably preferred. Installing drywall clips is not likely necessary. The ceiling rock tends to rest on the wall rock at the edges. As for the installation of truss clips (STC, DTC or other) These are not really necessary at this finished stage. The trusses are most likely secured to the interior walls using toenails. The question is, when the trusses are moving (during seasonal transition or due to temperature changes in the evening) do the occupants hear and annoying popping sounds coming from the ceiling? If so, I would recommend cutting the toenails connecting the trusses. With all the drywall in place and finished, it will likely provides sufficient stability where installing truss clips won’t be necessary. If any lateral movement of the walls seems to be a problem (walls that feel a bit unstable) DTC clips could be added later, but I doubt they will be necessary. Toenailing trusses to non-load-bearing walls, or using truss clips, are not typically required by structural engineers in a house design except where long walls exist with no intersecting walls on either side. I hope that helps! Sorry for the delayed reply! Pro Builder
Thank you! I really appreciate the response. I am checking to see if the trusses are secured by toenails to the walls. If they are, will we have any continued problems when the trusses uplift? If they aren’t, should we go ahead and install the truss clips? I have photos of my home elevation and pictures of the truss uplift damage to the walls. Can I email them?
