The Secret Life of Your Home’s Roof
Standing outside and looking up at your homes roof does not really tell you very much about the actual structure that keeps the rain off your head. What you see is just the surface.There may be asphalt shingles on it; there may be wooden shakes, maybe even pieces of corrugated tin. What is most important for the successful functioning of your roof is what lies underneath this surface.Let's take a deep breath and go under the shingles for a look-see.
The Bare Bones of Roof Support
Built up on top of your house frame, rising above the ceiling is the roof deck. This is a framework of wooden boards. Just as a skeleton creates the shape of an organic body, these heavy planks of wood form the internal structure of your homes roof. It is on this wooden framework that everything else that comprises the roof of your home will be attached.
On top of this framework you will find, especially on newer homes, sheets of plywood or oriented strand board (OSB), also known as particle board, nailed over the top of the framework trusses. These sheets of wood are set in a staggered formation and with a small gap set between each one to allow for the expansion and contraction that fluctuating temperatures will produce.Older homes more frequently use 2" x 6" planks to cover the roof deck framework.
While this surface does appear to be a solid roof, it is not. This aspect of your roof, like the muscles of the body, help give extra strength and fill out the form of the finished roof. Over these flat wooden sheets you will find the final layer of hidden protection for your roof.
The underlay material can be either roofing felt or the more effective but more expensive fiberglass or fire resistant materials. These large sheets are rolled out and nailed down over the deck sheets like a thin carpet.
Being water resistant, they prevent water seepage or blow back from getting to the wood underneath and allowing rot to develop. This material is what keeps the gaps between boards from leaking. Your shingles will ultimately be nailed onto this surface.
The Extra Metal Bits That Keep The Water Out
DRIP EDGE and RAKE EDGE
While not all building codes require these to be installed on a roof, they are very important for the longevity of a wooden roof. They are metal strips that go along the ends of the roof deck at the eaves troughs and gable ends. Since these parts will be seen along the edge of the roof, they are available in many colors so as to better match the overall color scheme of the home.
While not necessary, houses without these drip edges tend to rot quicker and need replacement more often. It is almost a guarantee that a roof without a Drip Edge will require a case by case replacement of rotted wood any time the roof is resurfaced.
CHIMNEYS and SKYLIGHTS
Since these items push up through your roof, they need special treatment to prevent water from cascading through the roof and into the living quarters. Each of these needs a metal "back pan" which sticks up 1" to 2" and diverts water flow away from the object.
Each side of the chimney or skylight also has a metal flange that goes under the shingles across the roof deck. These metal strips are sealed with tar for waterproofing and the other end attached likewise to the side of the chimney or skylight structure. These items are usually enhanced with a tar coating to further seal any potential leaks away from the main body of your roof.
VALLEYS and PEAK LINE
Another place where metal is needed in your roof is where right angle sections meet. These natural troughs have increased amounts of water funneled into them and with greater pressure. Installing a metal trough to carry the runoff down to the eaves or guttering is critical to avoiding water penetration and damage in the structure of your entire house.
The "closed" style of valley is made by just weaving the shingles themselves along the angle of the roof at this join. There is a much greater chance of system failure and extensive water damage over the protection given by the "open" system that builds the metal valley and merely attaches to the shingle section.
Since this style of valley incorporates tarring across the seam between metal and shingle, there is very little chance of system failure and leakage. As an extra bonus, the metal used in the open system can be obtained in a wide variety of colors so that it can be used as part of the decorative aspect of your overall home decor look.
Just like the valleys, the ridge line needs to be strengthened against the elements. A good ridge line is also of metal and covers the peak of the roof. Rather than being put in place before the shingles go on, the ridge line is put on after the shingles are in place. This way the flanges go over the top of the shingle upper edge. Tar is then used to aid in water repelling along the peak of the roof structure.
Again, the major concern is expense, but paying a bit more can have long-term savings by minimizing the need for repair or replacement. It is sometimes the difference between a roof lasting 30 years instead of the more average 20 years or less of an economy built roof.
So there you have it. Regardless of the outer layer of skin on your homes roof, the shingles, it is the underlying structure that makes a roof strong and weatherproof. While the cosmetic aspect has its specific uses depending on the overall climate in your area, it is the body under the shingles that makes the ultimate difference.