• Decide between two insulation location strategies:
   - Insulation between + below rafters (AKA ‘ventilated’ roof)
   - Insulation between + above rafters (AKA ‘unventilated’ roof)
• Examine roof timbers for rot, damp and infestation
• Avoid recessed lighting
• Cables less than 50mm away from plasterboard should be enclosed in metal conduits
• Ensure air tightness by making the vapour layer continuous, sealed at joints. Services should be located on the warm side of the layer.
• If services have to go behind the vapour layer, create a service zone to limit puncturing the layer. Seal holes.
• Ensure roof space ventilation to prevent condensation:
   - pitch less than 15° – 25mm continuous air gap at eaves
   - pitch more than 15° – 10mm continuous air gap at eaves
   - use ridge ventilation at pitches of over 35°
• Confirm with the insulation manufacturer the expected u-values and suitability of planned construction particularly where condensation control is required.

Insulation Materials: Phenolic foam, Polyisocyanurate and polyurethane, Extruded polystyrene give the best performances followed by Expnded polystyrene, Woodfibre boarding and Cellular glass, and can be used above, between and below the rafters. Cellulose, flax, sheep’s wool and mineral wool slabs can be used for between rafters

• Adding insulation above the rafters maximises the roof space but can add overall height to the roof – which might be difficult to reconcile within a terrace situation.
• Specify interlocking insulation boards where possible and seal joints.
• Ensure that the space between the wall and roof insulations is continuous at eaves.
• Air cavities where occurring between the vapour control layer and the u/s of the insulation should be sealed top and bottom.
• When using rigid insulation between the rafters, ensure that the joints are taped and the junction between the rafter and insulation is sealed with foam (leave a 5mm gap).

• Decide between a cold ‘ventilated’ or ‘unventilated’ roof
   - design for a ‘ventilated’ roof space when using an impermeable bitumen felt
   - design for a ‘unventilated’ roof space when using a permeable sarking felt
• Ensure that the roof insulation butts up against the wall insulation to avoid thermal bridging.

• Locate insulation above the roof deck.
• Avoid locating insulation below the roof deck (cold deck).
• (if insulation cannot be added above the roof deck, consider applying insulation to the ceiling)
• Insulation boards should be rigid ie loadbearing
• Check with the insulation manufacturer the suitability of the insulation for the construction method.
• Ensure careful detailing at edges and parapets.
• Ensure on-site that falls are correctly constructed to avoid ponding.
• Consider the impact from rain noise.
• Try and reduce incidences of membrane penetration (eg vent pipes etc).

• Check that insulation materials are compatible with the bonding materials used with the membrane.
• Voids within a timber roof should not be ventilated to the outside

Insulation Materials: Cellular glass, Mineral wool slab, Cork, Strawboard, Phenolic foam, Polyisocyanurate, Polyurethane, Expanded polystyrene.

• Advantages: Insulation can be applied over existing membrane; The insulation can effectively protect the membrane against damage.
• Disadvantage: Rainwater percolating between the joints in the insulation can cool the membrane leading to possible condensation problems beneath it. This effect will also compromise the u-value of the construction.
• Check that the existing roof can support the new load of insulation and ballast.

Insulation Materials: Cellular glass, Wood fibre board, Mineral wool slab, Phenolic foam, Polyisocyanurate, Polyurethane, Expanded polystyrene.