Insulating A Flat Roof Without Ventilation

Like other roofs insulating a flat one requires ample ventilation a vapor barrier and sealed bypasses.

Insulating a flat roof without ventilation.

Cold roof a very bad idea. However in many situations the insulation may need to be primarily or entirely below the flat roof membrane and between the roof joists if so what are the best options. Any type of roof from tpo to epdm can be either hot or cold. How much ventilation does a flat roof need.

Hot roofs have the roof deck then insulation then the roofing material. Proper ventilation in flat roofs. It depends on where the insulation is installed. There is a common misconception that flat roofs are difficult to insulate.

Should i leave out the soffit vent. Flat roof insulation cross section a great example of this is powerdeck f insulation board which is both rot resistant and highly durable. Depending on the weather and usage of the roof during its lifespan the insulation board may still be in a good enough condition to re use when the time arrives to replace the roof itself. This is then covered with a further weatherproofing layer.

Since you currently do not have ventilation and it sounds like you have access to the attic the most cost effective insulation technique you can use is to spray closed cell foam using spray foam kits around the perimeter of the roof between the roof surface and the ceiling to a nominal depth of at least 2 inches to prevent air infiltration. Also there is a soffit vent but none at roof peak. It also lets hot air escape in the summer. Ventilation is necessary to allow moisture accumulated inside to escape.

The material that works best depends largely upon preference in a given situation. Is there any advantage to trying to get any insulation in between the 2 8 rafters. The answer depends on the type of roof you have. Insulating a flat roof requires ventilation above the insulation.

Cold roof systems are highly inadvisable as insulation from the inside will inevitably lead to the formation of condensation. When renovating an older home whose roof rafters are only 2x6 really 5 1 2 x 1 5 in dimension the available space for insulation and ventilation is limited therefore limiting the options for a combination of good under roof ventilation and high insulation r values in the cathedral ceiling. To produce a hot roof rigid insulation is fitted outside above the weatherproofing. Unvented flat roofs a technical discussion flat roofs have often been built with the insulation all on top of the vapor closed drainage plane as this avoids dew point condensation issues inboard of the roofing.

This misconception is so strong that some people actually choose to not get flat roofs because they are worried about the roofs not being properly insulated.