Planning thin wall insulation for a house close to the plot boundary

Inside, measure clearances to windows, radiators, doors and fitted furniture. Include finishes, adhesive or framing. Ten centimetres of insulation can take more than ten centimetres out of the room once the full build-up and uneven existing masonry are allowed for.

For a wall 5 m long, a complete lining projecting 0.10 m into the room takes up about 0.50 m² of floor space. The example covers one wall. Where several walls meet, account for overlap at corners. Even a small reduction in a bedroom can affect where the bed fits.

A PIR board with lower thermal conductivity can provide the required resistance at a smaller insulation thickness. Check moisture safety and reveal details before selecting the thinnest option. Saving a few millimetres may make little difference to a difficult junction.

Mark the finished wall line and check it against window sashes and door leaves. Keeping them easy to open can matter more in practice than the floor area lost. Check clearances before finalising the thickness.

Internal insulation changes the temperature profile through the wall. Assess existing moisture, rain protection and exterior coatings. Walls inaccessible from outside deserve particular attention, as a concealed leak may be difficult to locate and repair later.

Gas-tight aluminium facings need continuous joints and an assessment of drying potential. Resolve wet masonry before covering it. Where timber is built into the wall, assess conditions around it after the retrofit. A basic U-value calculation does not cover that risk.

Difficult junctions often occupy little area, such as the wall-to-floor junction, a narrow reveal or a partition meeting the outer wall. A break in insulation can leave a cold strip. Determine how far the insulation should return onto adjoining surfaces by assessing the particular junction.

Check that windows will open fully after lining. The internal sill and curtain rail may need alterations. Maintain a usable clear width at doors. A thermally effective detail must also allow normal use of the room.

Moving radiators, sockets or pipes may cost more than the price difference between two board thicknesses. Establish these works before construction. Anchor heavy equipment in a suitable substrate. A rigid insulation core does not give the board the loadbearing capacity needed for heavy fixtures.

A service void on the room side reduces penetrations of the air barrier but takes up space. With plasterboard-faced insulation, check the installation instructions for joints and penetrations. A neatly finished plasterboard joint does not establish that the layers behind it are airtight.

Inspect joints before they are covered. Keep photographs of insulation terminations, cable routes and fixing points. Mark areas on a drawing where drilling will require a check. This modest record makes later changes to fixtures easier.

After completion, check the ventilation and heating controls. Observe corners during the first heating season. When only one wall is improved, comfort and energy consumption still depend on the whole building. Estimate any percentage saving using a calculation for that building.