A warm roof is a little unconventional, but it solves many common problems. Basically, the difference between a warm roof and a conventional ‘cold’ roof, is that the insulation layer is on the outside of the framing, rather than in the ceiling space or between rafters. The roof cladding is installed directly over the insulation, rather than over rafters or trusses.


This system has a number of advantages.

  • Rigid insulation is used. Rigid insulation, usually made from polyisocyanurate (PIR), generally has better thermal performance than soft insulation with a comparable thickness. It also has a higher fire rating, greater resistance to moisture and is airtight.
  • Avoidance of thermal bridging (where cold meets warm through materials) due to the whole roof being uniformly insulated. This means there is little chance of cold air meeting warm air inside the building. This saves on your heating bill!
  • Less damp air. As a result of the roof structure being at room temperature (warm) due to the lack of thermal bridging, the dew point is on the outside of the building. No water condenses, so there is no dampness in the air or on the structure. In conventional construction, the dew point forms on the internal face of the roofing, due to the warm air rising through the ceiling space meeting the cold roofing product.
  • There is little or no need for ceiling insulation. This leaves your ceiling space clear for wires and more storage. We have never heard anyone complain they have too much storage!
  • Reduction in noise. No more noisy little bird feet or falling acorns.

For thermal performance, a warm roof system is an ideal choice – we recently included one in the design of our Hoeke Cottage renovation.

Questions? We’d love to hear from you. At Mackit Architecture we design bespoke residential architecture for discerning clients. Based in Greytown in the Wairarapa, our team design beautiful, practical and enduring new homes or renovations both locally and New Zealand wide.