Your roof structure is designed by an architect, held together by trusses, fastened in place with framing nails, and covered with sheets of plywood or OSB board. This is the basic foundation, lying beneath the shingles you see when looking at your beautiful home from your sidewalk.
If you pop your head into your attic you may see different sizes of wood trusses varying from 2ft in width to 10ft in width, or even beams as thick as 10ft by 10ft. These differences will depend on the year your house was constructed, the design style of your neighborhood and the personal preferences of the original home builder, designer and original purchaser. Whatever size, type or style of the framing trusses installed, this is what holds the top of your house in place and allows a roofing professional to install a system to keep water out.
In the Calgary area it is typical to see 2ft by 6ft truss widths on homes constructed prior to 1980, which have been fastened using framing nails, and installed by hand with a framing hammer. These homes were installed in a style referred to, in the industry, as “stick framed”. Stick framing basically means a big pile of lumber is dropped off on site and framers, often journeymen carpenters, put trusses together one piece, or one “stick” at a time. Whereas buildings which were constructed after 1980 often have pre-manufactured truss assembled in a factory, stamped by an engineer, delivered to site on a flat top truck and installed using pneumonic air nail guns designed for exterior construction use. There are pro’s and con’s to each type of installation style. Older homes were often built by journeymen carpenters one hand-nail at a time, arguably with more care and attention, however much slower than modern times. Newer homes are built much more quickly by tradespeople with relatively less training and who are relying more on machinery and technology. Newer homes are built more rapidly though, to deal with the growing demands for more houses at lower prices.
On top of the truss system goes your plywood or OSB board which provides a surface area to install asphalt shingles, rubber tiles or some other roofing material type, all of which are designed to keep weather and moisture out of your home. Without a roof deck installed on your house, there would be nowhere to install your roofing products. And of course without the shingles, your roof deck would rot away due to exposure to the sun, rain, snow and ice.
On newer houses, sheets of plywood or OSB boards are fastened on top of wooden trusses in your attic to form the roof deck. Plywood and OSB boards are installed in a staggered formation with small spaces between them. These small spaces are to allow for minor amounts of expansion and contraction during freeze/thaw cycles, as well as moist or dryer climate periods.
Older homes sometimes have lengths of 2ft by 6ft wood planks installed instead of plywood or OSB board. These planks can sometimes have small spaces between them. If these spaces are too large then nails from your asphalt shingle system may end up protruding between planks and not actually be fastening shingles to anything. Rely on your professional contractor for advice and best practice guidelines if this occurs. When the time comes for you to replace your roof system, your roofing contractor can replace any and all damaged wood and make minor corrections to original construction framing if needed.
Remember, if your roof deck is rotting or damaged in any way people walking on your roof could potentially crack or break through the wood, causing further destruction to the roof system, such as damage to the shingles, and to the person who walked on it! Most roof decks, however, can withstand a little bit of exposure to water or ice before they need to be replaced.
In conclusion, the top of your home is put together with a truss system, which supports a roof deck where your waterproof roofing system is installed to keep your home dry.