# Internal Wall Insulation for Solid Walls: A Practical Guide

Homes built before about the 1920s usually have solid walls with no cavity, and they lose far more heat than modern cavity walls. Where external insulation isn't an option, perhaps because of planning, a conservation area or a period street frontage, insulating from the inside is the practical route.

## Is the wall ready?

Internal insulation should only go onto a dry, sound wall. Before you start:

-   Find and fix the cause of any damp, such as failed pointing, leaking gutters, high ground levels or a bridged damp-proof course.
-   Remove loose or blown plaster.
-   For traditional stone or lime-built walls, get advice on moisture first. These walls rely on drying out and can be harmed by the wrong build-up.

## Choosing a board

-   **[PIR insulated plasterboard](/collections/insulated-plasterboard)** gives the most insulation for the least thickness, which matters in small rooms. Many have an integral vapour control layer.
-   **[Polystyrene-backed plasterboard](/collections/polystyrene-backed-plasterboard)** is a lower-cost option where a slightly thicker build-up is acceptable.

Every millimetre of insulation comes out of the room, so it's a trade-off between performance and space. If you're upgrading a wall as part of a wider renovation, building control may expect it to reach a minimum U-value, so check before you choose a thickness.

## Fixing methods

### Dot and dab

Bonding boards straight to the wall with adhesive is quick and saves space. Apply a continuous ribbon of adhesive around the board edges and openings, plus dabs across the middle, and add mechanical [fixings](/collections/fixings) as the board manufacturer specifies. The continuous perimeter stops cold air circulating behind the board, which is a common cause of hidden mould.

### Battens or metal lining

On uneven walls, fix the boards to timber battens or a [metal wall lining system](/collections/wall-lining-syatem). This also leaves a service void for cables, so you don't have to cut into the insulation.

## Details that make or break it

-   **Window reveals:** insulate them too, even with a thinner board. Uninsulated reveals are where condensation and mould usually appear first.
-   **Floor and ceiling junctions:** keep the insulation continuous where you can, and seal the board edges.
-   **Vapour control:** tape the joints of foil-backed boards, or add a separate vapour control layer, so warm moist air can't reach the cold wall behind.
-   **Services and heavy fixtures:** plan sockets and radiators before boarding. Radiators and wall cupboards need fixings that go through to the masonry.
-   **Kitchens and bathrooms:** use [moisture-resistant plasterboard](/collections/moisture-boards) on any areas you aren't insulating.

## Typical materials list

-   Insulated plasterboard (PIR or polystyrene-backed)
-   Drywall adhesive and mechanical fixings, or a lining system
-   Foil tape or a vapour control [membrane](/collections/membranes)
-   Thinner insulated board for window reveals
-   [Beads](/collections/beads), jointing tape and compound

## Solid walls near you

Solid-walled terraces are found right across England, including [London](/pages/insulation-supply-london), [Manchester](/pages/insulation-supply-manchester), [Leeds and Yorkshire](/pages/insulation-supply-leeds) and [Bristol](/pages/insulation-supply-bristol).

Not sure which board or thickness to use? Send your wall details and room sizes to sales@nextdayinsulationltd.co.uk and we'll recommend a build-up.

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> Source: [Next Day Insulation](https://nextdayinsulations.com/pages/solid-wall-insulation)