Different layers, different jobs
Sarking or underlay can support weather control, while bulk or reflective insulation addresses thermal performance. Metal-roof systems may also require condensation management.
Questions for the specification
- What existing insulation remains?
- What product and R-value are proposed?
- How is roof-space ventilation considered?
- How will condensation be controlled?
- Are clearances around electrical services maintained?
- How do solar and penetrations affect the installation?
Whole-building context
Ceiling insulation, roof colour, ventilation, glazing and air leakage all affect comfort. A roof product should not be presented as the only performance factor.