Insulation Between Flat Roof Joists

Measure and cut 2 by 4 inch lumber to fit the gaps between each set of joists.

Insulation between flat roof joists.

1 2 timber strength class and joist size. The insulation is below the deck but above the plasterboard. This method of insulation can also be used to upgrade the thermal performance of an existing roof without affecting the waterproofing system. If you put insulation under the decking and between the joists you lower the temperature of the decking and lower the due point thus bringing it closer to the danger point of being in the building.

The insulation should not bulge past the joist faces. Staple a 4 to 8 mill. Good question theoretically when building a warm roof the vaper control layer goes on the warm side of the insulation. Where insulation depth is restricted by the flat roof construction it may be necessary to install the roof insulation between and below the joists to create a cold deck structure.

Insulation is placed in between the joists underneath the roof surface above. How to install insulation in a flat roof with timber deck insulated above the joists. Refurbishing an existing timber joisted flat roof which has no insulation. Warm deck insulation 1.

Measure and mark the joists at each end of the roof about 4 feet in from the edge. This is used for refurbishment e g. Both these variants require different approaches to insulation which will be covered in this guide. 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 is preferred to have the bulk of the insulation between the joists to reduce any risk of condensation. The majority of domestic cold flat roofs use insulation between and under the joists. Between and under joists. If insulation is placed on top of the flat roof joists and as such the joists are not fastened to the boarding above the depth to width ratio should not be greater than 4.

Lay your chalk line across your two pencil marks and snap a line across all of the joists in between. Depth to width ratio should not be greater than 6. A cold flat roof is one where the insulation is between or between and below the roof joists. How to insulate a flat roof.

The insulation boards should be laid with the plywood face up. Set the quinn therm qrfr ply insulation boards onto a wide 30mm bead of vapour resistant sealant applied to the upper surface of all the joists and cross noggins.