Felt roofing, sometimes referred to as tar paper or roofing felt underlay is a layer of protection installed between the roof deck and the final layer of roofing material giving your roof an extra layer of defence from the outer elements whilst providing an extra layer of insulation for your home.
Felt roofing is made from natural materials like wood cellulose or synthetic ones like fiberglass fleece or polyester. This is then coated and treated with a waterproofing agent such as bitumen, which does an excellent job of repelling water. It is usually sold in two types of 36 inches wide, large rolls being 15 pounds or 30 pounds.
How long does a felt roof last?
Your felt roofing is the final layer between your roof and your home. How long a felt roof lasts depends on the type used and the conditions that the roof is exposed to. Asphalt felt can last between 20 and 30 years while the new rubberised or synthetic asphalt felt can last between 25 and 35. Your felt roof longevity relies on regular inspections and maintenance with roofing experts recommending an inspection at least every three or five years.
Types of felt roofing:
- Shed Felt – Which Shed Felt Do I Buy?
Shed felt usually is used to waterproof a non-habitable building such as a shed, kennel or summerhouse. It is made from a compressed cloth-fibre base which provides strength and flexibility. Some are coated with bitumen making it waterproof. Going in for a bitumen coated one is best as this lasts longer.
Super Shed felt is a longer-lasting polyester reinforced felt considered by many experts as the best value for money. It boasts a lifespan of up to 15 years with its durable waterproof membrane which easily outlasts both standard and heavy-duty felt.
Standard shed felt is designed with a 5-year life expectancy in mind, and heavy-duty felt is double that while super shed felt boasts 15 years. The longevity can change depending on the quality and type of fiber used in manufacturing.
Heavy Duty Shed Felt is typically manufactured with twice the number of materials than a standard shed felt. It is two times thicker than ordinary felt, and the green mineral finish is made with coarser grains. Heavy Duty Shed is originally designed to be used on a two-layer flat roof system, providing a durable top sheet. It is used when extended longevity is needed beyond that of a standard shed felt.
Do I need to glue the new felt onto the roof?
Not the first layer. The first layer of felt must be nailed to the roof decking and not glued together with adhesive. The second layer is where the glue is needed. You can glue the second layer to the first nailed layer and the third layer to the second.
How many rolls will I need?
Roofing materials are specified in squares with 1 square equal to 100 square feet. Felt roofing is sold by the roll, which is equal to one square each. Felt rolls are usually 36 inches wide x 144 inches long for type 15# felt, and 72 inches long for type 30# felt. A 15-pound roofing felt covers about four squares and a 30-pound covers about two squares.
Which shed felt will make it watertight again?
Shed felts are made from a compressed cloth-fiber base, and most are coated with bitumen to make it waterproof. Always pick a bitumen composition for a watertight solution.
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