Uninsulated Flat Roof

Proper ventilation in flat roofs.

Uninsulated flat roof.

If you don t want to put vinyl backed insulation in your roof what other options are there. The type that is right for your flat roof insulation job depends upon the state of the roof expert opinion on the best type and your budget. When you have an un insulated roof you have to live with rather uncomfortable room temperatures inside the home. This means that your approach to insulation will differ from a standard pitched roof.

Traditionally we ve insulated the roof panel to try and keep the temperature on the panel from reaching the dew point. The slate is new and the flat roof is good for another 5 7 years. As a rule any roof with a pitch below 10 is classified as a flat roof. For example a building with material with an r value of r 11 converts to an u value of 0 09 1 r or 1 11 0 09.

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. If moisture has nowhere to go it will gather around joists and eventually undermine the insulation. In most cases there will not be a loft in a building that features flat roofing. The typical u value of an existing uninsulated flat roof is 1 5w m2k.

To achieve this add 100 to 160mm of insulation above the structural deck dependant upon insulant conductivity. R value measures how well certain building insulation materials can resist heat. An uninsulated roof has a u value of approximately 2 5 w m2k however adding insulation can achieve a value of 0 18 w m2k. But a preinstalled membrane may be even more effective at removing condensation.

Ventilation is necessary to allow moisture accumulated inside to escape. The higher the r value the greater the insulation performance. We ll add a vapor barrier so the moist air does not flow up through the insulation and condense on the roof. The target should be to achieve a u value of 0 25w m2k or better.

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. U value has an inverse relationship to r value. How dr pstop can help the answer is a product called dr pstop which is a felt like material with a rubber backer that can be applied to the back side of metal panels that will trap the moisture as the condensation forms. It also lets hot air escape in the summer.

It should be of the maximum available thickness. When determining how much insulation you need don t guesstimate calculate. Flat roofs do not have eaves so there are no soffits holes on the underside to allow air flow.