[Source: www.brantfordexpositor.ca, February 28, 2009]
Perhaps it's just my imagination, but don't wintertime temperatures swing more widely than ever these days? Whether these bouts of back-to-back cold and warm weather are "normal" or not, they do cause some Canadian homes to do strange things from coast to coast. Do unexplained seasonal gaps appear along the tops of some interior walls, especially near the centre of your home? Does your house wake you up at night with sudden booming sounds, especially during cold weather? Relax. Neither the booms nor the gaps are signs of serious structural trouble, despite appearances.
For the last 50 years, roofs on most new homes have been framed using factory-built wooden triangles called trusses. These are frameworks made of relatively narrow pieces of wood, connected into an assembly that's both strong and light in weight. Trusses go up quickly and they use smaller, less expensive lumber than traditional, rafter-based roof designs.
And while all this is good, there's a problem. Unless you understand the physics behind trusses, it's quite reasonable to assume that loud sounds and ceiling gaps indicate something seriously wrong with your roof. But appearances can be deceiving.
Most trusses are triangular in shape, with two sloped sides connected at the bottom by a horizontal span of wood that supports the drywall of your ceiling. This bottom section of the truss triangle stays more-or-less constant in temperature and humidity all year long because it's buried within the insulation in your attic. But with the other two sides of a truss -the angled ones that form the actual slope of your roof -the situation is vastly different. These parts are subject to very wide swings in temperature and humidity because the attic space that surrounds them is ventilated and open to outdoor air.
In summer time, as attic temperatures rise, the top two sides of the truss get very hot and bone-dry. In winter, they cool off and absorb moisture, all while the bottom cord remains pretty much the same. And of these two seasonal trends -heating versus cooling -it's the wintertime one that leads to the most unnecessary homeowner distress in a process called "truss uplift".
In some cases truss uplift can cause the ceiling to rise as much as two inches above the tops of interior partition walls. As truss stresses build up in a roof frame, they eventually break free and release quickly, resonating like thunder boom throughout your house. Both the noise and gaps are harmless, though distressing.
Does your house have gaps above interior walls that keep getting larger and smaller, driving you crazy in the process? Here's a fix.
Consider installing some type of crown moulding along the top of the offending walls, but only fasten it to the ceiling. Push it tight against the wall, but don't drive any nails there. This approach allows the ceiling to rise and fall, without you having to see the resulting gaps grow and shrink. Just remember to paint the trim and wall when truss uplift is at its worst -this time is excellent -so no bare gaps appear.
Understanding the physics behind truss uplift won't keep you from waking up the next time your house complains loudly about cold weather, but at least you can fall back to sleep knowing that you don't owe a mortgage worth of money on a house that's about to collapse around you.
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