Check the rules governing the start of work. A scheme may set an eligible expenditure period or require certain steps before you buy materials. Before paying a deposit, find out how earlier invoices are treated. Agree how changes to the scope should be documented and costed if opening up the roof reveals additional work.

An energy audit looks at how the building works as a whole. The roof, walls, windows, ventilation and heating all influence energy demand. Choosing a material before assessing these elements can lead to unnecessary expense. Damp problems or air leaks may need attention first, or the planned works may need to be reordered.

Ask which indoor temperatures, occupancy patterns and existing wall and roof conditions the auditor assumed. The findings should be detailed enough to specify the work. A recommendation to insulate the roof still needs a thickness, junction details and installation requirements. If you are applying for public funding, check the scheme’s requirements for the audit and the completion documents.

Compare materials at the same required thermal resistance or at the same target performance for the complete wall or roof. PIR boards with low declared thermal conductivity can achieve that target at a smaller thickness than many EPS, XPS or mineral wool products. This can matter at eaves and thresholds or where loft space is limited. Use the declared conductivity of the specific product in the comparison.

Check fire requirements, moisture exposure, loads and the permitted application as well as thickness. XPS can suit assemblies exposed to water, while mineral wool can suit designs that call for a non-combustible core. Assess the quoted material against the project requirements before comparing the price per cubic metre.

Include fixings, seals, protective layers and finishing work alongside the boards. A roof retrofit may require changes to flashings, eaves, drainage and chimney junctions. On walls, allow for window and door reveals, the plinth and connections to adjoining elements. Omitting these details can reduce performance even if the insulation itself is the correct thickness.

Distinguish the cost of all technically necessary work from the expenditure eligible under the scheme. The quotation should identify the scope, units and quantities. Check that the area claimed follows the scheme rules and the audit. Only add cutting waste to the claimed area if the documents expressly allow it. Check how the estimate separates materials, labour and tax. The scheme may calculate eligible costs on a different basis from the supplier’s quotation. Resolve differences before signing or paying a deposit.

Keep records identifying the product, its declared properties, the quantity purchased and the thickness installed. An invoice that says only “building materials” can make verification difficult. Specify in the contract what substitutions are acceptable. A different facing or board type may affect performance even when the trade names sound similar.

Photograph the work before it is covered. Images showing the joints, fixings and continuity of the insulation make handover easier. Keep records confirming which work was completed. The expected energy performance applies to the whole assembly. Gaps in the insulating layer or unresolved thermal bridges can undermine that performance even when the board meets its declared specification.

Before work ends, check which supporting documents you need to submit and when. Find out in advance whether the scheme requires a further document recording the condition of the building after the retrofit. The contractor, auditor and owner should describe the scope and the installed solutions consistently.

Treat the grant as one part of financing the project. The insulation should also meet the building’s practical and technical needs. Good design limits energy losses, and careful installation helps deliver the expected result. Use the application and the final claim to document the work identified through the assessment of the house.