Cold Flat Roof Insulation Thickness

Achieving a u value of 0 20w m meaning your roof will be better insulated than your walls will need 120mm thickness of rigid foam or 200mm of mineral wool or natural insulation.

Cold flat roof insulation thickness.

Kingspan and recticel are the two of the most well known flat roof insulation brands and they re firm favourites of insulation superstore customers. Insulating a flat roof with recticel powerdeck u recticel s powerdeck u offers 0 024 u value for thicknesses 120mm or more so it s a great thermal insulator as well as a strong and stable board for structural integrity. This is used for refurbishment e g. The target should be to achieve a u value of 0 25w m2k or better.

120mm of kingspan tr26 or similar will make the. Additionally attic condensation and leaks will make fiberboard wet. Refurbishing an existing timber joisted flat roof which has no insulation. It has only 1 r value per inch and is always installed in 0 5 inch thickness.

It allows insulation to be added without having to replace the waterproofing on. To achieve this add 100 to 160mm of insulation above the structural deck dependant upon insulant conductivity. With a flat roof this issue does not arise but the u value constraint and the amount of insulation needed is just the same. Unless the joists are exceptionally deep there is also likely to be a requirement to install insulation to the underside of the joists as the upper 50mm of joist space is usually required to be left clear for ventilation purposes.

Fiberboard is not an insulation. The typical u value of an existing uninsulated flat roof is 1 5w m2k. It should be of the maximum available thickness. A ventilation gap usually 50mm should be provided between the top of the insulation and underside of the roof covering to allow the air to flow across.

Cold deck flat roof the thickness of insulation required will vary depending on the material you decide to use and the manufacturer s specification. A cold flat roof is one where the insulation is between or between and below the roof joists. The insulation is below the deck but above the plasterboard. A ventilation gap usually 50mm should be.

Therefore you get practically 0 r value out of it. Between and under joists. If you are upgrading the roof to meet current thermal requirements then the thickness of insulation will vary depending on its thermal conductivity.