Uninsulated Flat Roof

The typical u value of an existing uninsulated flat roof is 1 5w m2k.

Uninsulated flat roof.

The higher the r value the greater the insulation performance. 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. 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. 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.

Traditionally we ve insulated the roof panel to try and keep the temperature on the panel from reaching the dew point. Reduce extreme temperature fluctuations inside your home. 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.

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. 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. The slate is new and the flat roof is good for another 5 7 years. This means that your approach to insulation will differ from a standard pitched roof.

It also lets hot air escape in the summer. If moisture has nowhere to go it will gather around joists and eventually undermine the insulation. If you don t want to put vinyl backed insulation in your roof what other options are there. In most cases there will not be a loft in a building that features flat roofing.

While insulation for a flat roof is expensive and can account for as much as 25 of the total installation cost there are a number of important benefits to having it in place. When you have an un insulated roof you have to live with rather uncomfortable room temperatures inside the home. 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.

As a rule any roof with a pitch below 10 is classified as a flat roof. But a preinstalled membrane may be even more effective at removing condensation. When determining how much insulation you need don t guesstimate calculate. Proper ventilation in flat roofs.

Reference table for u values u value is the coefficient of transmission i e the transmission of heat through the materials which compose the building s envelope or outer shell. It should be of the maximum available thickness. Ventilation is necessary to allow moisture accumulated inside to escape.