Truss Lifting: What is it and How to Fight it
Are you noticing that your ceiling looks almost warped?
This is just one of the visual indicators that your roof trusses have lifted. It can also look like the trusses are lifting away from the drywall.
In the more than 16 years we have been in business, we have dealt with a fair amount of truss lifting. That experience means we can explain what truss lifting is, what causes it, and how to fix it.
Now let’s get started.
What is Truss Lifting?
Truss lifting, or truss uplift, is when wooden trusses shrink, or cures and the bottom-most piece bows upwards and is most noticeable in the middle.
Truss lift is mainly an issue with wood frame construction homes where the non-load bearing drywall walls meet the ceiling. As the lift occurs it pulls that ceiling drywall up.
This happens particularly in homes where the trusses or drywall isn’t properly secured. It can show itself as a nail pop, so it looks like the nail is pushed in because the drywall or wood is being pulled away.
Rarely does mean there are structural concerns. It is something that is more of a cosmetic blemish.
What Causes Truss Lift?
Truss lift happens when the wood expands and retracts with the change in temperature.
Basically, when the outside air gets inside your home which has a different temperature, then this affects the wood. Poor insulation is likely to blame for this air leakage. This coupled with wood, which isn’t a great insulator, to begin with, is a perfect storm for truss uplift.
Now it’s science time.
The upper portions of the trusses are in the attic where the air is colder and drier. The traditional insulation in your attic is slightly warmer and is located in the lower portion of the truss.
Wood is a hygroscopic material, which means it tends to absorb moisture from the air. Breaking this down, the top portion of the truss is cold, the bottom portion is warm, so the bottom will have a higher moisture content. This moisture content can also lead to problems with mold and mildew in the attic.
This temperature difference and difference in moisture content is what causes the truss to bend. The upper truss in the cold dry air shrinks, thus pulling up the bottom part of the truss causing it to curve upwards.
As the truss curves upwards, it takes the drywall ceiling with it. If the walls aren’t secured properly at the floor, the truss can pull the walls up with it.
Roof Truss Repair
If your trusses have lifted, it’s not the end of the world and can be fixed.
To fix truss uplift, you’ll need to get into the attic and start the work before it gets too hot.
You’ll need to remove the nails that connect the trusses to the interior walls and install L shaped clips in their place, according to Ask the Builder. After you install the truss clips, nail a board on top of each interior wall that will overhang it by at least an inch on each edge. This lip will act as a bumper if the truss attempts to lift again.
You can also avoid truss lift all together by updating your insulation.
If you update your insulation with a material like foam, then you can create an air seal in the attic. This air seal will prevent the temperature difference in the attic that essentially created the truss lift.
If you want to learn even more about this air seal and how it can be beneficial to your home, check out the Learning Center on our website.
About Eric Garcia
Eric brings his knowledge and training in building science, training in spray and injection foams from the manufacturers, more than 8 years installing foam insulation, as well as selling and managing in the foam insulation industry. He is also BPI and Dale Carnegie certified and has taken several building science courses including air sealing and building envelope. Eric’s responsibilities include overseeing and giving support to all of the branches of the RetroFoam of Michigan company, office, estimates, and installs. He is also the Professor of Foam on our educational YouTube series Foam University. Even when Eric is off he is usually still “working” or thinking about work, but when he can get away he enjoys camping, hiking, hunting, and woodwork.