What You Should Know About Truss Uplift

20 February 2018
 Categories: Construction & Contractors, Blog


Have you ever noticed that there is a gap between the ceiling and the interior walls during some months of the year? Read on and learn about roof truss uplift (a phenomenon that could explain that gap).

What It Is

Roof truss uplift describes what happens when a gap of several inches is created between the ceiling and the interior walls of a building. This truss uplift usually takes place during the colder months of the year. The trusses settle back onto the walls when the weather gets warmer. People who observe this phenomenon for the first time may mistakenly think that the ground underneath the building has settled.

Why Truss Uplift Occurs

Why do roof trusses lift off the ceiling in some months of the year and not in other months? Today, buildings are constructed with plenty of insulation materials to increase the thermal performance of those structures. Consequently, the lower sections of the truss assembly (the bottom chords) end up being encompassed by the insulation materials that have been used to prevent heat loss from the interior of the building.

Those bottom chords therefore stay warm throughout the year because of the insulation covering them. The chords start contracting/shrinking as they lose moisture.

In contrast, the upper chords of the roof truss system aren't protected by any insulation. Consequently, they experience greater temperature variations as determined by the conditions outside. Those upper chords absorb moisture during the cold months and expand or elongate. This elongation exerts an upward pull on the bottom chords that have been contracting as they lose moisture.

This explains why a gap will develop between the ceiling and the walls. The onset of the warmer months causes the upper chords to lose the moisture they had absorbed. Consequently, they will contract to their original dimensions and the truss system will settle back onto the walls. This cycle repeats itself as the season changes.

What Can Be Done About It?

Roof truss uplift may not pose any structural issues to your building. However, several measures can be undertaken to combat the cosmetic problems that result. For instance, the builder can install some form of decorative moulding in the places where the walls meet the ceiling. This moulding is fastened onto the ceiling so that it moves with it whenever truss uplift occurs. The movement of the moulding hides the gap created during truss uplift. Secondly, the drywall used to make the ceiling can be left unsecured to the walls at carefully selected points so that the drywall can flex during truss uplift. No gap will be visible when that happens.

For more information about roof truss uplift, contact companies like Prefab Technology Pty Ltd.