Question 1

What is the difference between cavity wall and solid wall insulation?

Accepted Answer

The difference is **what kind of wall you have**, which determines both the method and the cost — and getting the diagnosis wrong is expensive.

**Which do you have?** Homes built roughly from the 1920s onward in the UK generally have **cavity walls** — two leaves of masonry with a gap between them, tied together. Older homes typically have **solid walls**, a single thickness of brick or stone. Clues: a wall around 260mm or more thick suggests a cavity; brickwork showing alternating headers and stretchers (a **Flemish bond**) suggests solid; uniform stretcher bond suggests cavity.

**Cavity wall insulation.** The gap is filled by drilling holes in the mortar and injecting mineral wool, polystyrene beads or foam, then making good. It is comparatively **quick and cheap**, needs no internal or external disruption, and is usually completed in a day.

**The important caveat:** cavity fill has a troubled history. Where properties were unsuitable — exposed to driving rain, with existing damp, poor construction or debris in the cavity — the fill has **bridged the cavity and transmitted moisture to the inner leaf**, causing damp problems that are expensive to remedy. The cavity exists partly to stop water crossing. A proper survey assessing exposure and wall condition is essential, and reputable installation carries a guarantee.

**Solid wall insulation** must be added as a layer, internally or externally.

**External (EWI)** — insulation fixed to the outside and rendered or clad. Better performance, no loss of internal space, no disruption to living, and it protects the wall. But it is expensive, changes the appearance (often needing planning permission, and generally unsuitable for listed buildings or conservation areas), and requires extending eaves and adjusting sills.

**Internal (IWI)** — insulated boards on inside walls. Cheaper and can be done room by room, but **loses floor area**, requires removing and refitting skirtings, sockets and radiators, and carries a real **interstitial condensation** risk if detailing is wrong.

Question 2

Why do old houses need to breathe?

Accepted Answer

Because they were built without a damp-proof course or a cavity, and are designed to absorb moisture and release it again. Sealing them with modern materials traps that moisture inside the fabric,

Question 3

What is a cavity tray, and why does it matter?

Accepted Answer

A barrier built into a cavity wall to collect water that has crossed the outer leaf and direct it back outside — and missing or badly installed cavity trays are among the most common causes of

Question 4

Which cracks in walls are serious and which are normal?

Accepted Answer

Most cracks in a house are cosmetic. A small number indicate structural movement, and the difference lies in width, shape, location and whether the crack is changing over time — not in how alarming

Question 5

What is a lintel and why does it matter?

Accepted Answer

A lintel is a structural beam spanning the top of an opening — a door, window or archway — carrying the load of the wall above and transferring it to the masonry on either side. Why it is necessary.

Question 6

What actually works for soundproofing a room?

Accepted Answer

Sound travels as vibration through structure and as airborne pressure waves through gaps, and effective treatment addresses both. Almost everything sold as soundproofing addresses neither, which is

Question 7

What are the best practices for home insulation installation?

Accepted Answer

Effective home insulation installation enhances energy efficiency and comfort. Key practices include choosing the right insulation type, air sealing, and regular maintenance.

Related Questions