Locate the thermal boundary
An insulated roof slope and a cold loft above an insulated ceiling are different assemblies. Decide whether the roof space will be heated and identify the airtight layer before detailing stairs, access hatches, ventilation ducts and chimneys. Moving that boundary after installation can leave inaccessible gaps. The roof drawing should show how the selected boundary connects to the wall enclosure all around the building.
Rain and indoor moisture
The covering sheds rain, while joints, abutments and penetrations remain vulnerable locations. Underlay, drainage paths, ventilation spaces and drying potential must work together for the selected roof type. A vapour-control layer is not a substitute for watertight detailing. Adding an arbitrary membrane can restrict timber drying, so membrane selection should follow the moisture assessment rather than a universal layer recipe.
Rafters and summer conditions
Timber interrupts insulation placed between rafters. A justified continuous layer can reduce that effect, but its connections still need design. Rooflights and roof orientation influence solar gains. In occupied attics, review external shading, ventilation opportunities and internal heat sources as well as insulation. Insulation thickness by itself cannot establish whether summer temperatures will remain acceptable.
Inspect while details are visible
Check valleys, eaves, ventilation outlets and wall-to-roof connections before finishes conceal them. Record hidden layers with photographs linked to drawings and plan airtightness testing while repairs remain possible. Solar panels require coordination with structural capacity, fixings and access for roof maintenance. Start with a thermal-boundary and drainage diagram; compare covering materials within that assembly rather than choosing the covering as an isolated product.