After many years of manufacturing roof curbs, AVP’s customers want to have insulation inside curbs to control condensation. A roof curb is a box that acts as an extension from the roof deck. This extension provides a mounting platform for a roof vent or exhaust fan.
AVP uses Johns Manville’s Foil Faced Polyisocyanurate Board Insulation. This provides a smooth surface resistant to absorption. As moisture laden air moves through the roof curb to the vent or exhaust fan, there’s no loose insulation to absorb moisture. Instead, the moisture will pass through the insulated roof curb and vent directly outside. Polyiso has the highest R-value per inch of any rigid board insulation. This insulation meets both CFC and HCFC-free specification requirements.
After seeing the industry’s practices, AVP sought to improve insulated roof curbs. The industry standard was to use fiberglass insulation. However, fiberglass insulation acts like a sponge by holding onto whatever passes by. Often, when an attic or HVAC duct exhausts moisture, fiberglass will trap some of the moisture on the way out. It’s common to see the bright yellow insulation turn completely black. This can also lead to the growth of mold and mildew on the insulation.
AVP uses 1” thick board with an R-6 value for the RC-12 to RC-48 models. Fiberglass insulation for 1” is around R-3 value. The ridged board provides double the amount of insulation value available per inch of thickness. The models RC-3 to RC-10 use a ½” Johns Manville’s Foil Faced Polyiso Board Insulation. This ½” board provides an R-2.7 value.
AVP has 3 height options for flat or low slope roofs. For climates with minimal snow or no snow at all, a 6” height is sufficient. In moderate snow climates, AVP offers a 12” high curb. Lastly, high snow climates should use an 18” high curb. As a result, providing additional height allows for installation in all climate zones. With a wide range of widths from 6” up to 51”, these curbs can support many roof vents or fans.
An important reason for the use of a roof curb is for a roofing manufacturer's warranty. Many EPDM, PVC & TPO roofing manufacturers require roofing penetrations to be secured by a curb and a boot. Check with your roofing materials supplier to purchase a boot that slides over the aluminum curb.
The boot provides a manufacturers-approved attachment to the roof deck’s membrane. The upper end of the boot folds into the curb. Then the curb mount flange goes over both the boot and curb. This will provide a perfect seal from the top.
An additional benefit to using a roof curb is it can act as a hatch or access entry port. The roof vent or exhaust fan can be easily removed. As a result, allowing for quick access to ductwork, electrical lines, or maintenance in the attic below.
Traditionally, roofers build wooden boxes on the roof at the time of the membrane installation. Using pre-build aluminum curbs reduces the time and need to build the wooden boxes. This will also lower the risk of injury during installation by lowing the time spent on the roof. In addition, any chances to damage the roof in the building process are also lower.
Another safety feature is that aluminum curbs are not flammable. The majority of curbs vent out heat from range hoods or HVAC units. This can cause wooden curbs to burn. However, aluminum will not burn, rust, or corrode. Aluminum curbs are safer and easy to clean.
Shop roof curbs on AVP’s website: roofvents.com.
AVP also offers the 6 inch tall roof curbs on HomeDepot.com.
