Insulation in extensions

This is general information, not a survey, design, legal or Building Control decision. The correct scope and standard depend on the property, work, date and regulatory route.

An extension introduces new thermal elements: the floor, walls, roof, windows and doors are designed as a coordinated envelope. Junctions and continuity can matter as much as the headline U-value.

Do not assume that upgrading an existing retained wall or floor is identical to designing the new extension. Feasibility, moisture, reveals, thresholds, planning constraints and the approved route may change what is reasonable.