With a flat roof this issue does not arise but the u value constraint and the amount of insulation needed is just the same.
Cold flat roof insulation thickness.
Additionally attic condensation and leaks will make fiberboard wet.
It should be of the maximum available thickness.
Between and under joists.
Therefore you get practically 0 r value out of it.
The typical u value of an existing uninsulated flat roof is 1 5w m2k.
Fiberboard is not an insulation.
To achieve this add 100 to 160mm of insulation above the structural deck dependant upon insulant conductivity.
Refurbishing an existing timber joisted flat roof which has no insulation.
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 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.
While insulation for a flat roof is expensive and can account for as much as 25 of the total installation.
A cold deck flat roof will typically require insulation to be installed between the roof joists to comply with building regulation requirements.
The target should be to achieve a u value of 0 25w m2k or better.
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.
It has only 1 r value per inch and is always installed in 0 5 inch thickness.
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.
120mm of kingspan tr26 or similar will make the.
The insulation is below the deck but above the plasterboard.
This is used for refurbishment e g.
A ventilation gap usually 50mm should be.
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 deck 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.
