Insulation Between Rafters Flat Roof

Piling up pieces of rigid foam.

Insulation between rafters flat roof.

Isover glass mineral wool gmw is another option for the between rafter insulation as a roll or batt. Rigid foam also does a better job of stopping air flow as long as it s carefully sealed at the edges. The flexible nature of gmw means that the roll or batts can be accurately cut and friction fitted between the rafters thereby minimising air gaps and maximising thermal performance. With a warm roof the usual process is to split the insulation into two layers.

Install ventilation baffles into the space between the rafters before you install the insulation usually by stapling into place. Common rafter depths range from 100mm to 200mm. Between and under joists. Most types of rigid foam insulation have a higher r value per inch than fiberglass batts.

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. This limits the maximum thickness of the insulation between the rafters to between 50mm and 175mm. Refurbishing an existing timber joisted flat roof which has no insulation. If your attic is going to be converted into livable space then you will need to insulate the roof rafters.

This is used for refurbishment e g. Then install r 30 fiberglass batts between the rafters. The flexible nature of gmw means that the roll or batts can be accurately cut and friction fitted between the rafters thereby minimising air gaps and maximising thermal performance. Breathing roof with low resistance lr underlay with this option insulation fully fills the rafter space without an airspace between the insulation and type lr underlay.

If 180mm is to be installed then 100mm board might be introduced between the rafters there has to be a minimum 25mm air gap between the insulation and the underside of the tiles or slates with an 80mm board running across the rafters. A cold deck flat roof will typically require insulation to be installed between the roof joists to comply with building regulation requirements. The insulation is below the deck but above the plasterboard. Insulation between the rafters can be designed in two ways.

A cold flat roof is one where the insulation is between or between and below the roof joists. Installing stacks of rigid foam between rafters is slow fussy work but it might make sense for a do it yourselfer. Framing this out and buying 30 r fiberglass insulation will cost you about 50 more than just buying 5 inches of polyiso equivalent of 30 r.