Insulation Between Rafters Flat Roof

This limits the maximum thickness of the insulation between the rafters to between 50mm and 175mm.

Insulation between rafters flat roof. Then install r 30 fiberglass batts between 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 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. 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.

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. Refurbishing an existing timber joisted flat roof which has no insulation. 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. It should be installed on tapered 2x furring strips in order to slope the surface of the roof to drains.

Isover glass mineral wool gmw is another option for the between rafter insulation as a roll or batt. 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. Rigid foam also does a better job of stopping air flow as long as it s carefully sealed at the edges.

This generally would not be a sufficient thickness to achieve the u values required to meet building regulations and more insulation would need to be added. The insulation is below the deck but above the plasterboard. Piling up pieces of rigid foam. Between and under joists.

Installing stacks of rigid foam between rafters is slow fussy work but it might make sense for a do it yourselfer. A cold flat roof is one where the insulation is between or between and below the roof joists. Insulation between the rafters can be designed in two ways. Most types of rigid foam insulation have a higher r value per inch than fiberglass batts.

Common rafter depths range from 100mm to 200mm. 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. With a warm roof the usual process is to split the insulation into two layers.