Is Winter a Bad Time to Build? How UK Extensions Deal with Rain, Cold Weather and Frozen Conditions

When homeowners start planning an extension, many people will advise: “Don’t start during the rainy season, do it in summer — it will be much faster.”But the UK is nothing like Hong Kong — it rains all year round. If builders had to stop every time it rained and wait for everything to dry completely, most UK extensions would never be finished.

That’s why many HK families doing their first extension in the UK often worry:“Does work stop when it rains?”“Will wet timber rot?”“Can bricklaying still continue?”“What if it’s cold, wet and things start freezing — will that delay the whole project?”

In reality, the UK construction industry is very used to working in wet weather. Most stages don’t fully stop just because of rain; instead, builders adjust based on the stage of construction, material behaviour and safety considerations. A typical extension goes through several key stages — foundations, brickwork, timber structure, roofing membrane, insulation, plasterboard and internal finishes — and each of these responds differently to weather.

What truly slows a project isn’t rain, but cold + moisture + freezing conditions. When temperatures drop close to or below 0°C, the ground, mortar, concrete and even timber surfaces can freeze. This is not something that simply resolves when the rain stops — construction often must wait for temperature to rise again. For example, mortar can’t set properly in freezing weather; concrete shouldn’t be poured below freezing because its strength will be compromised; and frozen soil may feel hard temporarily but becomes unstable again when it thaws.

Timber, on the other hand, can tolerate getting wet — UK timber is treated — but it must not stay wet and cold for too long without the chance to dry. Builders usually cover the structure with tarpaulin to protect it. Indoor works such as plastering or skimming are also avoided in very cold weather because moisture cannot evaporate properly, causing extremely slow drying or cracks.

So the idea that “winter isn’t good for building” has less to do with rain and more to do with how cold and frozen conditions affect specific materials. That said, winter extensions are absolutely possible — they just tend to require more careful planning, more protection, and sometimes slightly more time.

If you’re unsure how your extension should be scheduled through winter, or want advice on protecting materials and avoiding delays, feel free to send us a message — we’re happy to provide practical, experience-based guidance.

— ArchiKei