Venting in non-conditioned attic space

[ccanney]

Hello,
I have a building with an exterior, non-insulated roof deck. The space is open air but with a covered roof structure. This roof is constructed of steel joists and will have a hard lid ceiling. Per CBC 1203.2 I know that venting is required when enclosed rafter spaces are created with the ceiling applied directly to the underside of the joists. However, as the space below the ceiling/roof is open air and uninsulated I am questioning whether this venting is required. My understanding of the venting requirements are that they are required due to the temperature differential between the insulated building areas and the attic space which allows for moisture build up. In this scenario there is no insulated space on the roof deck.

 

[mark handler]

Venting is required for several reasons.
Roofing manufactures require it for most roofing, for their warrantee. the unventilated attic space "Cooks" the asphalt or plastic in the roofing due to the heat.
Contact your roofing manufacturer.

Proper ventilation of your roof helps address excess heat and moisture that can otherwise wreak havoc on your structure. Heat and moisture buildup causing predictable but different problems in hot and cold climates; areas with hot summers and cold winters can suffer the effects of both.

• When it’s hot outside, the sun beating down on the roof can increase the temperature in the attic. Exposure to this excessive heat can warp the roof sheathing and distort and prematurely age the roofing. If the attic floor isn’t evenly and adequately insulated, that heat can radiate down into the occupied areas and make it more difficult and costly to keep the space comfortable.
• In locales where the temperature drops below freezing during the winter, warm air escaping into the attic from the heated space below rises to the underside of the roof deck. As the roof deck warms, the bottom layer of accumulated snow on the rooftop begins to melt, causing water to trickle down the roof. Once the runoff reaches the cold outer edge, it refreezes into ice. When this happens repeatedly, an ice dam forms along the eaves, blocking the escape of further runoff. Once the water has nowhere to go, it can back up under the roofing. A properly installed self-adhered underlayment is a final defense against ice damming. This tear-resistant, waterproofing product seals tight around nails. It helps prevent water overflow from entering exterior walls or the attic where it can saturate the floor insulation, ruin the drywall underneath or get into the interior walls.
• Humidity, generated from your occupied area or from outside, that enters a cool attic condenses into a liquid when it meets colder surfaces. Over time, that moisture can cause deterioration of the roof system and interior structural elements or ruin the attic insulation. In a warm attic, the moisture can allow mold and mildew to flourish and put added strain on the cooling equipment.