Insulating A Flat Roof Without Ventilation

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.

Insulating a flat roof without ventilation.

Insulating a flat roof requires ventilation above the insulation. A cold roof or hot roof. To produce a hot roof rigid insulation is fitted outside above the weatherproofing. The old roof was tar and gravel so the switch to tpo should show significant change.

Ventilation is necessary to allow moisture accumulated inside to escape. Proper ventilation in flat roofs. It depends on where the insulation is installed. Is there any advantage to trying to get any insulation in between the 2 8 rafters.

Hot roofs have the roof deck then insulation then the roofing material. 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. Also there is a soffit vent but none at roof peak. How much ventilation does a flat roof need.

Should i leave out the soffit vent. Cold roof a very bad idea. Any type of roof from tpo to epdm can be either hot or cold. The answer depends on the type of roof you have.

There is a common misconception that flat roofs are difficult to insulate. This is then covered with a further weatherproofing layer. It also lets hot air escape in the summer. 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.

Like other roofs insulating a flat one requires ample ventilation a vapor barrier and sealed bypasses. Flat roof insulation cross section a great example of this is powerdeck f insulation board which is both rot resistant and highly durable. I have an insulation factor of about 8 10 plus the reflectivity of the white tpo. Cold roof systems are highly inadvisable as insulation from the inside will inevitably lead to the formation of condensation.

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.