An assessment can also identify jobs worth doing together to avoid opening up the same area several times.

Before pricing the insulation, check for leaks, damp and structural damage. Deal with those problems before covering them. A flat roof may need wet layers removed, while a pitched roof may need timber or flashing repairs. Both affect the budget. A preliminary quote prepared without a site visit should identify work that cannot yet be priced reliably.

Compare quotes for the same scope and thermal performance. Include boards, accessories, labour, delivery and substrate preparation. Add scaffolding or access equipment, flashings and waste disposal. For over-rafter insulation, include the fasteners and alterations at the eaves. Work omitted from a quote may still be necessary.

Check how the contractor measures the area and calculates waste. Dormers and penetrations need more cutting and detailing than a simple slope. Agree who will remove and refit existing equipment. Ask how any additional repairs discovered when the roof is opened will be priced. Clear terms make it easier to compare quotes and prevent disputes during the work.

PIR with low thermal conductivity provides high thermal resistance in a relatively thin layer. In an existing building, this may help retain headroom or make a terrace threshold easier to detail. Consider the whole junction. A higher board price can be offset if it avoids other building work. Compare two itemised estimates to see whether that applies to your project.

Equal thicknesses of different materials may provide different levels of insulation. First establish the required U-value for the whole element, then specify the layers to achieve it. Check how the material handles loads and moisture and whether it meets the fire requirements. A saving from choosing an unsuitable grade can disappear with the first repair.

Start with the difference in energy demand before and after the upgrade. Account for the heating system’s efficiency and the cost of the energy supplied. For a heat pump, use its seasonal performance rather than a single favourable catalogue value. A standing charge may still be payable in full. Apply the estimated reduction only to charges that vary with consumption.

Assume the same occupancy and heating habits in both calculations. Raising the indoor temperature after the work uses part of the potential saving but may improve comfort. A change in household size can also affect hot-water costs. Allow for the weather when comparing years. A mild winter alone cannot demonstrate the performance of the insulation.

To find the simple payback period in years, divide the investment cost by the annual monetary saving. If you are calculating the owner’s outlay after an awarded grant, deduct that grant from the investment cost. Record the energy prices and the work included. Payback is an estimate under those assumptions. It does not automatically account for future tariffs, borrowing costs or system maintenance.

If a worn roof already needs replacing, make two calculations. One covers the whole refurbishment. The other covers only the additional cost of better insulation compared with the roof work already needed. Keeping them separate avoids charging the insulation for work that would have gone ahead anyway. For a large project, test several energy price scenarios.

Check funding conditions before signing contracts or incurring costs. Eligibility can depend on documentation, scope, deadlines and material specifications. Some invoices may not qualify. Distinguish an awarded grant from one you merely hope to receive, and allow for the time between payment of invoices and receipt of funds.

If the project includes replacing the heating system, size it for the building after the upgrade. Insulation and heating improvements can also reduce emissions from fuel use. At handover, keep product documents, photographs of concealed layers and inspection records. After the first heating season, review consumption and system settings to see how the investment performs.