When is it worth adding insulation below a sandwich panel roof?

Record how the building is used today. A roof designed for a warehouse may now cover a much more intensively heated space. Changes in indoor temperature and humidity affect how the assembly performs. Compare the original design assumptions with current conditions to establish the scope of the retrofit.

Distinguish heat flow through the panel from losses at junctions and through air leakage. A cold strip at the eaves or a draught under a flashing can point to a defective detail. Insulation fitted between structural members may leave that defect untouched. Inspect under conditions in which the problem is apparent.

Include the walls, industrial doors and ventilation in the assessment. If they account for much of the loss, work on the roof alone may have limited impact. Compare the options for the whole building over its actual heating periods. Thickness alone gives no reliable estimate of savings.

Insulation above the existing roof may require a redesigned assembly with a waterproof membrane or replacement of the panels. Check load capacity, fixings, wind actions, material compatibility and drainage before selecting the build-up or deciding how to attach it.

Survey parapets, eaves, rooflights and service penetrations. Additional thickness may mean raising flashings or altering outlets. Establish whether the existing covering is suitable to remain. Investigate damp or damaged materials before deciding whether they can be incorporated.

Insulating below the panel reduces the heat reaching its inner facing, which may then become colder. If humid indoor air gets behind the new insulation, condensation risk can increase. Check airtightness and the vapour resistance of the proposed layers.

Show how the airtight layer continues past walls, supports and services. A simplified vapour diffusion calculation cannot account for air flowing through gaps. Detail each layer’s function and its connections to adjoining elements, including the edges around structural members.

The insulation, framing and lining add weight. Design the suspension to transfer it to members that can carry it. Check the existing assembly and design the fixings before suspending a ceiling from any part of the roof. Include equipment that will remain above the lining.

Assess how the extra layers affect fire performance and access for maintenance. Check service penetrations and decide how the roof will be inspected afterwards. A concealed leak can go undetected for longer. Provide access at locations that need regular inspection or repair.

Compare junction repairs, supplementary insulation and, where appropriate, panel replacement. For each, record the expected thermal improvement, moisture risk, cost and interruption to use. Better seals may deliver much of the benefit. In other cases the main shortcoming is heat loss through the panel itself.

Agree acceptance criteria before work starts. Include substrate condition, airtightness, fixings and continuity at junctions. Document concealed layers and approved changes. Reinspect previous problem spots after the first heating season and compare the result with the retrofit objective.