Preserve Granulated Roofs with Cool Roof Coating
Granulated Roofing — Inexpensive and Popular
Granulated roofing was standard long before energy efficiency and extended longevity were issues. Factory-manufactured granulated roofing is used as the top or exposed layer in many built-up roofing systems. It is relatively inexpensive and quite popular.
Granulated roofing is available in different weights, from thin-roll roofing for homes to thick 90-pound cap-sheet for commercial roofs. The product is basically an asphalt binder with scrim reinforcement and colored mineral granules of 30-to-50 mils embedded into the top asphalt surface.
These granules are intended to add UV protection to the asphalt binder and color to the roof. Granulated roofing is found on both standard built-up roofs (BURs) and on some modified-bitumen asphalt roofs. This type of roof is popular because of its lower installed price (particularly the non-modified type) and because no further finishing is required once the rolls are installed.
Solar Destruction: The Down Side of Granulated Roofing
- Granulated roofs reflect very little solar energy. White granules are the most reflective color but reflect only about 20%-to-23% of the solar energy that strikes it; red and gray granules reflect even less.
- Granulated roofs tend to be hot in summer and capture heat that will radiate into the structure below, increasing cooling costs.
- The roof dries out because of the heat that is absorbed and the unprotected asphalt around the granules. Over time granules are released from the surface. The rate of granule loss increases, exposing ever more asphalt to solar destruction.
- As the amount of free gra nules increases, wind and water push them into piles in low areas on the roof. Here the granules may slow down water drainage and cause moisture to be held against the roof surface for prolonged periods, increasing the weathering damage to the surface.
- Once a granulated roof is worn out, it typically requires an expensive tear-off and replacement.
Increase the Energy-Efficiency and Longevity of a Granulated Roof
Elastek elastomeric roof coatings can solve the problems of a granulated roof if the roof has remaining service life.
- Coating the roof will make it an energy efficient “cool roof.” (Note, due to the grainy surface, coated granulated roofs are slightly less reflective than smooth built-up roofs.)
- Granules will be significantly more securely anchored for the long term. Even when the surface coating wears away, granules will still be secured.
- Applying Elastek elastomeric coatings will help to seal lap seams and other problems areas and strengthen the roof membrane. Use Elastek Super Seal and PolyTek fabric.
- Tear-off can be deferred for many years.
- Coating a granulated roof changes it from a heat island to a sustainable, renewable roof — cleanable and easy to re-coat.
- Energy efficiency can be renewed time and again by simple recoating of the roof.
- The cost/benefit analysis would be very dramatic.
- A coated roof will ease stress on air conditioning units, extending their service life.
Granulated Roof Coating Tips and Techniques
- Blowing, sweeping, or hosing may be adequate cleaning.
- The initial coating applied to a granulated surface will largely migrate below the surface and adhere the granules in place. (Note: More coating will be needed for the first coat — coverage decreases.? Coating thickness needs to be 10 mills dry per coat.)
- Always roll the first coat to push the coating down into the granulated surface.
- If asphalt emulsion is used for a first coat, two coatings of elastomeric will still be required.
- Apply the second coat as usual.
NOTE: Some commercial built-up roofs are built with smooth-ply sheets and a coat of hot-mopped asphalt on which loose granules are cast. Such roofs present coating challenges because of the excessive amount of granules used. Such roofs should be bid with an allowance for the cost of preparation.
