How high will the deck be?

The deck will be raised 279mm above the top of your joists. This is to allow for a full depth of loft insulation (up to 350mm, measured from the floor of the loft) plus an air gap above the insulation and below the boards. This essential air gap is there to allow air to flow over the insulation, thereby taking away any humidity which might otherwise condense on the underside of the boards and cause damp. LoftZone took advice from the Buildings Research Establishment for the size of the air gap during the design phase – hence the 279mm.