Insulating a 1990s house internally while retaining its facade

Archived drawings are a useful starting point but may differ from the as-built structure. Check masonry thickness at openings and establish whether the wall has one, two or three layers. Investigate any cavity. A carefully chosen inspection opening can prevent numerous incorrect assumptions.

Record later alterations as well. Replacement windows or new render may have changed operating conditions. Identify where the house loses heat most quickly. Insulating every wall internally may not be the first priority: the main problem could be a floor junction, roof or major air leaks.

Will the house be heated as it is now? Are changes to the boiler, ventilation or attic use planned? These answers affect the required result. Consider the building as a whole so that insulation of one wall fits the subsequent stages.

A U-value calculation helps assess the additional layer, provided the material data are correct. Do not promise bill savings solely from an improved U-value for one element. Energy consumption also depends on ventilation, temperature, building services and how occupants use the house.

Inspect the roof, flashings, plinth and services. Even a small leak may have persisted for years in an older house, and a new lining makes it harder to detect. Establish whether the masonry is dry and whether it will still be able to dry after the build-up changes.

Internal insulation changes temperatures within the existing wall, making a moisture assessment necessary. Simple models do not cover every water-transport mechanism, particularly in heterogeneous or damp walls. Additional investigation is part of the refurbishment in these cases and helps avoid trapping moisture in the masonry.

A composite board with a factory-applied plasterboard facing is one option. Different versions are intended for dry rooms and spaces with increased humidity. Check the permitted conditions for the complete composite. Reduced water absorption of the facing does not remove the need for ventilation or protection in areas exposed to water.

Check whether the quoted thickness covers the whole product or only its PIR layer. Room measurements must allow for the complete lining and fixing method. Similar appearance does not guarantee equal thickness, resistance or classification. Specify the exact version and properties rather than simply “PIR with plasterboard”.

Locate cables, sockets and pipes before installation. Older services may need checking during the refurbishment. Do not accommodate electrical work by casually cutting out large sections of insulation. Plan airtight joints and service penetrations beforehand.

Cable penetrations and boxes should maintain the airtight layer. Use details intended for the chosen boards. Plan radiator, cabinet and bracket fixings separately, transferring their loads to suitable supporting construction. Decisions left until the end often lead to cuts or holes through finished insulation.

Check window reveals and sills, and assess the ceiling junction. These areas often remain cold after refurbishment. A thick board across a large surface cannot solve an uninsulated strip left at its edge.

A junction detail may require insulation to return along an adjoining wall; do not guess its length. Allow for furniture and valve access. In an older house, a trial area can reveal the total thickness, flatness and alterations needed before work extends to every room.

Photograph the substrate, fixings and seals. A smooth finished wall does not reveal the quality of concealed layers. Retain board labels and records of the other materials used to support later repairs and alterations.

Maintain effective ventilation after refurbishment and observe the wall through the first winter. Confirm thermal and formal requirements for the actual scope of work; the year of construction alone does not determine them. The aim is a dry building element used correctly, rather than merely a fresh surface ready for paint.

No. The wall’s actual construction and condition matter more.

Often it can, but check its resistance to water ingress and how internal insulation affects the masonry’s ability to dry.