11.4   Cool Roofs for Mobile Homes

Cool roof coatings reduce summer cooling costs and improve comfort by reflecting solar energy away from the home's roof and slowing the flow of heat into the home. They are shown to reduce overall cooling costs by 10-20%, and are a good choice for mobile homes or site-built homes with low slope or flat roofs. Cool roof coatings are usually bright white, and must have a reflectivity of at least 60% to meet the Energy Star or equiva­lent requirement for cool roof coatings.

Cool roof coatings are usually water-based acrylic elastomers, and are applied with a roller. They can be applied over most low-sloped roofing such as metal, built-up asphalt, bitumen, or sin­gle ply membranes. Some underlying materials require a primer to get proper adhesion-check the manufacturer's recommenda­tions for asphalt-shingle roofs.

Surface preparation is critical when applying any coating. The underlying roofing materials must be clean so the coating will stick. Repairs should be performed if the existing roofing is cracked or blistered. Roof coating won’t stick to dirty or greasy surfaces, and they can’t be used to repair roofs in poor condi­tions. Observe the following specifications when installing cool roof coatings.

ü       Install the coating when dry weather is predicted. Rain, heavy dew, or freezing weather, if it happens within 24 hours of installation, will weaken the coating’s bond to the underlying roofing.

ü       Protect any nearby windows, siding, or automobiles from splatters. For roller application, use a large brush for the edges, and a shaggy 1 to 1 1/2-inch roller on a 5- or 6- foot pole for the field. Run the coating up the roof jacks and other penetrations to help seal these areas. Install at least two coats, with second coat applied in the opposite direc­tion to the first to get more complete coverage. Allow a day for drying between coats.

ü       Clean the roof of loose roofing material and other debris.

ü       Wash the roof with a water/tri-sodium phosphate (tsp) solution, or comparable mildew-cide, and scrub brush. Better yet, use a pressure washer.

ü       Buy the highest quality coatings, and look for those that are specifically formulated as mobile home roof coatings.

ü       Reinforce any open joints around skylights, pipe flashing, roof drains, wall transitions, or HVAC equipment. For build-up asphalt or bitumen roofs, repair any cracks, blisters, or de-laminations. Use polyester fabric and roof coating for these reinforcements and repairs by dipping fabric patches in the roof coating and spreading them over the existing roofing, or by laying dry fabric into a layer of wet coating. Smooth the patches down with a broad-knife or squeegee to remove bubbles or wrinkles. Allow any repairs to cure for 1 to 2 days before applying the topcoat.

ü       For metal roofs, sand any rusted areas down to sound metal. Install metal patches over any areas that are rusted through, followed by polyester patches as described above.