 |
|
        |
|
   |
|
No. 22 "TROUGHING" OF GLASS SHINGLES If, like most Canadians, you have decided to roof your home with asphalt shingles, you may know that there are two different "types" to choose from. These two types are commonly known as "organic" and "glass". These names relate to the type of fibre used to make the base reinforcing fabric upon which the shingle is constructed. Organic shingles are made on a thick felt of wood and other cellulose fibres. Glass shingles are made on a lighter-weight mat of non-woven glass fibres, which are held together with a water-insoluble binder. Both shingle types contain asphalt, are covered with mineral granules and are available in a wide variety of product weights, styles and colours. When properly applied, using quality products, either shingle will perform well. Glass shingles, due in part to their lighter-weight reinforcement, are much more flexible in warm weather than organic shingles. Consequently, when applied to the roof, they often take the shape of (i.e. "telegraph") whatever lies beneath them. This is not as true with organic felt based shingles, as the thicker reinforcement gives the shingle more "body".
As the glass shingles are applied, there is a natural build-up of "layers" of shingles, which is essentially how the finished roof sheds water. In the first few years, as the summer sun heats up the roof, the shingles soften and slowly conform to the shape of the layers underneath. Just above the lower exposed edge of each shingle course, lies the concealed top edge of the shingle two rows lower on the roof. This concealed top edge may form a small "trough" in the unexposed part of the shingle (see diagram). On lower roof slopes (those below 8:12), water that enters this trough (through the shingle cut-outs or joints in the overlying shingles) can travel laterally along the trough, and penetrate the shingle layer through misplaced fasteners or shingle joints. This potential for leaks due to troughing is one of the reasons CASMA strongly agrees with the standard industry requirement to use an asphalt-saturated felt underlayment under glass fibre shingles. The felt provides secondary water shedding protection, and also helps ensure long-term roof system performance.
Additional copies, in English and French, can be obtained by forwarding your request to CASMA via e-mail. To send us your request, click here. |
|
For more information on this subject or other asphalt shingle technical issues, you may contact CASMA by e-mail at casma@casma.ca, or visit our website: www.casma.ca. The information contained in this bulletin is for general education and is not intended to replace advice from a qualified contractor or direction on usage/installation from the manufacturer. Consumers should be aware of the safety hazards associated with work on roofs and, before doing so themselves, should consider following CASMA’s advice of using qualified contractors. This bulletin may be reproduced with permission on condition that it be reproduced in whole, unedited, with attribution of copyright to CASMA. |
© 2008, Canadian Asphalt Shingle Manufacturers' Association
Next Bulletin:
Previous Bulletin:
