Insulation

"With a loft conversion we need to maximise thermal performance but retain the space."

A retained roof slope would generally mean a rafter that is now insulated where it previously wasn’t.

If you are insulating between the rafters you typically need to provide a 50mm ventilated airspace between the felt and the insulation.

Many new or recent roofs have a breathable membrane that allows you to dispense with the ventilation gap - this would result in a hybrid roof - check with the membrane manufacturer or Building Control officer before proceeding.

If the rafter isn’t deep enough to accommodate the right thickness, use the depth you can and increase the insulation thickness below.

Ceilings are the easiest part of a dwelling to upgrade, layering extra insulation into the loft has a dramatic effect on fuel bills - but ensure that you provide safe access for storage and maintenance.

Placing a layer of XT/TL Thermal Liner to the underside of the joists, eliminates thermal bridging, meets the U-value target and will allow the loft space to be floored.

Extra battens can be added to make the joists wider to allow Thermal Liners to be butted and fixed to the underside.

Ensure that any downlighters installed are fully sealed to avoid heatloss and that they are fire proofed.