Question 1

What is a screed, and what is a damp proof membrane?

Accepted Answer

A **screed** is a levelling layer laid over a structural floor to provide a flat surface for the finish; a **damp proof membrane (DPM)** is a barrier preventing moisture rising from the ground through the floor.

**Screed.** Usually a sand and cement mix, or a flowing **liquid screed** based on anhydrite or cement, laid to a specified thickness over a concrete slab or insulation.

**What it is for:** achieving level and flatness to the tolerance the floor finish requires; burying underfloor heating pipes and providing thermal mass around them; and providing a surface suitable for the covering.

**What to know about it:**

**Drying time is the constraint.** Traditional sand and cement screed dries very slowly — a frequently cited rule of thumb is around a day per millimetre for the first 50mm and considerably longer thereafter. A 75mm screed can take months to reach the moisture content a floor covering requires.

**Laying a floor covering over damp screed is a classic and expensive failure**, producing adhesive failure, blown tiles, cupped timber and trapped moisture. **Measuring moisture content before laying is essential**, and estimating by appearance is unreliable.

**Liquid screeds** dry faster and go on thinner, though they require different preparation and some need surface laitance removing.

**Damp proof membrane.** Normally heavy polythene sheet, laid beneath the slab or between slab and screed.

**Why it matters.** Ground moisture rises through concrete by capillary action. Without a barrier it reaches the floor finish, destroying timber, lifting vinyl and causing persistent damp that is repeatedly misdiagnosed as rising damp in the walls.

**What makes one work or fail:**

**Continuity is everything.** A membrane is only as good as its weakest point — laps must be taped and overlapped adequately, penetrations sealed, and edges **linked to the wall damp proof course**, so there is a continuous barrier around the whole floor.

**Punctures during construction** are common and invisible once covered.

**Termination at the perimeter** is where most failures occur.

**Liquid-applied membranes** are used over existing slabs where lifting the floor is impractical.

**Insulation position** relative to the DPM matters, and should follow the design rather than convenience.

Question 2

How long does a flat roof last?

Accepted Answer

Anywhere from ten to fifty years depending entirely on the material and the detailing — and the reputation flat roofs have for failing comes almost entirely from one older material and from poor

Question 3

What is a vapour barrier and which side does it go on?

Accepted Answer

A vapour control layer (VCL), often called a vapour barrier, is a membrane restricting water vapour from passing through a building element into the insulation and structure behind it. Why it exists.

Question 4

What are the best materials for roofing repair?

Accepted Answer

Choosing the best materials for roofing repair involves considering durability, cost, and climate. Options include asphalt shingles, metal, slate, tile, EPDM, and TPO, each with unique benefits.

Question 5

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 6

Are damp surveys from damp-proofing companies reliable?

Accepted Answer

Frequently not, and this is one of the clearest conflicts of interest in home maintenance: the company diagnosing the problem sells the treatment, and the treatment they sell is rarely what old

Question 7

What is subsidence, and what should you actually do about it?

Accepted Answer

The downward movement of the ground beneath a building's foundations, causing the structure to move with it. It is the most feared word in home ownership, and the fear is disproportionate to how most

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