PART 1: VENTILATION
When it comes to roofing, it’s easy to focus on making sure everything is sealed up tight. In a way, this makes sense because gaps, seams and junctions are the points most vulnerable to leaks in a roof system. But while sealing your roof against leaks is important, it’s just as essential to allow your roof to “breathe”. That’s where roof ventilation comes in. Why is roof ventilation important? Without proper ventilation, heat and moisture will build up in your attic. Over time, this will cause your roof sheathing and rafters to rot, insulation to wear out and shingles to buckle. It basically damages your roof from within.
Ventilation also helps reduce the temperature difference between the roof surface and its underside, which is the key to preventing ice dam formation during winter time. Roof Ventilation Requirements How your roof should be ventilated depends on where you live. Ventilation guidelines may vary according to the climate and weather conditions particular to an area. Generally, though, the amount of ventilation your roof needs is dictated by the dimensions of your attic. DO allot at least one square foot of net-free ventilation area for every 150 square feet of attic floor space.
PART 1: VENTILATION
DO try to strike a balance between the amount of exhaust ventilation (vents at or near the ridge) and intake ventilation (vents at the soffits or eaves). In a balanced ventilation system, a 1:300 vent-to-attic-floorspace ratio is allowable. DO make sure the airspace between your roof deck and insulation is at least two inches deep. This applies to cases where continuous roof ventilation is required—usually when the attic space needs to be conditioned as a living area or for mechanical use. DON’T overstuff your attic. You’ll want to make sure that all ventilation units are never blocked off.
Keeping your attic as clear as possible isn’t always easy. (Where else will you store your off-season clothes, Christmas ornaments and embarrassing baby pictures?) But if you must use the space for storage, stack your boxes low and remember to leave space around your vents to facilitate air flow.
PART 2: INSULATION
Ventilation and insulation are the dynamic duo of auxiliary roof components. They work hand in hand to keep your roof energyefficient and in good shape by building upon each other’s benefits. Where ventilation keeps the air in your attic moving, insulation keeps heat transfer at a minimum, preventing an imbalance in indoor air temperature. The Value of R-Value R-value is a measure of your roof insulation’s ability to resist heat transfer. The higher the R-value, the greater the insulation’s thermal resistance. Roof insulation with high R-values offer the greatest benefits if you live in climates that require plenty of indoor heating or cooling. The range of recommended R-values for roof insulation tends to be wider in hot climate zones because heat gain prevention also factors in sun control measures like reflective roof coatings. Like ventilation, roof insulation helps you save money in two ways: by extending your roof’s service life and by helping you save energy. A properly insulated roof makes your home easier to heat in winter and cool in summer. It minimizes energy loss and keeps your HVAC system from getting overworked. According to the Department of Energy, a well-insulated roof can cut your heating and cooling bill by 10% to 50%!
PART 2: INSULATION
Roof Insulation Options • Wood fiber flat boards of insulation made out of organic (wood, cane or vegetable) fibers, binders and fillers; an asphalt coating makes this type of insulation moistureresistant • Perlite also in board form; composed of particles of perlite (a type of volcanic glass), organic fibers, binders and sometimes concrete
• Polyisocyanurate another type of rigid thermal insulation; a “sandwich” made of a closed-cell foam core bonded to different types of facers
• Sprayed polyurethane foam an expanding foam made from the reaction of two liquid components that harden once they are applied directly onto a surface Roof Insulation Tips For unfinished attics: DO insulate over and between the floor joists to completely seal off the living spaces below. For finished attics: DO insulate between “knee” wall studs, ceilings with cold spaces above, and between the rafters and studs of the roof and exterior walls.
PART 3: PENETRATIONS
Roof penetrations are often the weakest link in a roof because they essentially cut holes through layers of roof material. This is why most issues concerning penetrations have to do with the collars and seals used around them. Common roof penetrations include plumbing stacks, bathroom exhaust vents, roof vents and combustion vents. If your roof has one or more of these, you’ll know that flashing is your best friend. What is roof flashing? Flashing refers to waterproof sheets (usually metal) that are fabricated into different shapes and fitted over roof discontinuities and around penetrations. The I-Codes don’t have specific requirements for flashing, save for one: the flashing material must be resistant to corrosion and installed in a way that prevents water intrusion.
Roof Penetration & Flashing Tips DO install a cricket or saddle if you have a penetration wider than 30 inches in the direction parallel to the roof ridge (or perpendicular to the slope). A cricket will prevent water from pooling on the penetration’s uphill side. DON’T use mortar chimney caps. Mortar isn’t as durable as concrete and has the tendency to crack and spall (deteriorate on the surface) in cold climates.
PART 3: PENETRATIONS DO follow the “2-10 Rule” for combustion vents. With a few exceptions, all chimneys and combustion vents must:
a) extend at least two feet higher than any part of a roof within a horizontal distance of 10 feet and b) be at least three feet in height on their shortest side.
DON’T mix metals that come in direct contact with one another unless the two metals are close together on the galvanic scale. This will prevent galvanic corrosion, the tendency of active metals to deteriorate rapidly when in contact with a passive metal in the presence of water.
DON’T repair corroded flashing around penetrations. It must be replaced. Optional: DO paint flashing to make it last longer but DON’T paint bare galvanized metal without first cleaning it with lacquer thinner.
Patriot Roofing 1623 Stone Drive NW Gig Harbor, WA, 98335 253-265-6868 (253) 448-8222.
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