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Roof Curbs With Insulation

AVP manufactures Insulated Roof Curbs with Foil Faced Board Insulation

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. 

 

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  • RC-12-H6-Ins | 6 inch tall roof curb

  • RC-12-H18-Ins | 18 inch tall roof curb

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. Below, you'll see on the left is AVP's insulated roof curb - smooth water resistant surface . While on the right, is the fiberglass insulated roof curb.

  • 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.

AVP uses Johns Manville’s Foil Faced Polyisocyanurate Board Insulation. Polyiso has the highest R-value per inch of any rigid board insulation. This insulation meets both CFC- and HCFC-free specification requirements. After the insulation is placed, foil tape is used at the top and bottom to ensure moisture does not get behind the insulation. In addition, the corners are calked to also prevent moisture.

 

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.

 

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.

Benefits

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. There is a liability to roof damage when roofing crews are building wooden curbs. The roofing crew needs to hoist heavy, and often sharp, lumber onto the soft membrane roof. Then they need to cut, saw, and nail or screw together these wooden curbs. As a result, this often leaves small sharp pieces of wood and nails littered on the roof. This is commonly walked on causing damage to the new roof.


In addition, many times these wooden curbs are not square, and the roof vents or exhaust fans do not fit properly. This then leads to rebuilding the curbs.


When purchasing pre-built aluminum roof curbs, all the construction liability is eliminated. Aluminum roof curbs lower the time spent on building curbs and keep the roof safe from additional damage.


Another safety feature is that aluminum curbs are not flammable. The majority of curbs vent out heat from range hoods or HVAC units. This allows for the possibility of wooden ones to burn. However, aluminum will not burn, rust, or corrode. Aluminum is safer and easy to clean.


AVP also supplies curbs as an independent part. With a wide range of widths from 6” up to 51”, these curbs can support many roof vents or fans.


Shop roof curbs on AVP’s website: roofvents.com