Insulation

Insulation is material placed within the structure of a building — walls, floors, roofs, and loft spaces — to slow the transfer of heat. In winter, it keeps warmth inside; in summer, it helps keep heat out. Proper insulation is one of the most cost-effective improvements you can make during a renovation, reducing energy bills and making your home more comfortable year-round.

Common insulation materials

• Mineral wool (rock wool or glass wool) — affordable, fire-resistant, good for walls and lofts. Comes in rolls or rigid batts
• Rigid foam boards (PIR, PUR, EPS, XPS) — high insulation value for their thickness, ideal where space is limited (e.g., insulating walls without losing too much room)
• Spray foam — expands to fill gaps and irregular spaces, good for hard-to-reach areas, but can be controversial if applied incorrectly
• Natural materials — sheep’s wool, cellulose (recycled paper), wood fibre — eco-friendly alternatives growing in popularity

Where insulation is used in a renovation

• Loft insulation — the simplest and cheapest improvement, laid between and over joists in an accessible loft
• Wall insulation — cavity wall insulation (injected into the gap between inner and outer walls) or internal/external wall insulation for solid-walled homes
• Floor insulation — rigid boards laid over or under the floor slab, often combined with screed and underfloor heating
• Roof insulation — in loft conversions, insulation is fitted between and under the rafters with a vapour barrier on the room side

Why insulation matters in a renovation

• Building regulations — any new construction or significant renovation work must meet current insulation standards (U-values). This applies to extensions, loft conversions, and even replacement windows
• Energy costs — up to 25% of heat in an uninsulated home is lost through the roof, and another 35% through the walls
• Comfort — properly insulated rooms feel warmer at lower thermostat settings and are free of cold draughts

Practical tip

When planning your renovation, discuss insulation early with your contractor. Insulation is far easier and cheaper to install while walls and floors are open during construction. Retrofitting it later is always more disruptive and expensive. Ask your contractor to specify the insulation type, thickness, and target U-value in the scope of work.