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Bad weather
This section gives guidance on good building practice during wind, rain and snow.
High winds
Britain is the windiest country in Europe and one of the windiest in the world. Building regulations require British buildings to be designed to withstand wind speeds ranging from 85 mph (37m/s) in the south of the country to over 120 mph (54m/s) in the far north of Scotland.
Nowadays, modern computers can forecast the approach of wind storms accurately several days before they reach Britain. Prediction of the exact course of the storm and wind speeds is harder.
Despite improvements in forecasting, there is still little advice available to the public and homeowners on how to lessen the worst effects of wind storms. The meteorological office operates a severe weather warning service to warn of approaching strong winds or storms.
Response to severe weather warnings
When a severe weather warning is issued the following precautions should be taken:
Before a storm:
- Secure loose objects such as ladders, garden furniture or anything else that could be blown into windows and other glazing and break them;
- Close and securely fasten doors and windows, particularly those on the windward side of the house and especially large doors such as those on garages;
- If available park vehicles in a garage, otherwise keep them clear of buildings, trees, walls and fences;
- Close and secure loft trap doors with bolts, particularly if roof pitch is less than 30 degrees;
- If the house is fitted with storm shutters over the windows ensure they are closed and fastened;
- If chimney stacks are tall and in poor condition, move beds from areas directly below them.
During a storm:
- If you do go out, try not to walk or shelter close to buildings and trees;
- Keep away from the sheltered side of the boundary walls and fences - if these structures fail they will collapse on this side;
- Do not go outside to repair damage while the storm is in progress;
- If possible, enter and leave your house through doors in the sheltered side, closing them behind you;
- Open internal doors only as needed and close them behind you;
- Do not handle or lay sheet materials in strong winds - force 5 - since membranes may be damaged (In force 5, force of wind is felt on the body). On some roofs work may have to stop at lower wind speeds for safety reasons;
- Do not permit bricklaying or rendering in strong winds - force 6. (In force 6, force of wind makes it difficult to walk steadily). Walls that do not yet have adequate returns or other restraint against movement may need to be propped if such winds are forecast;
- Inspect for damage if strong winds occur soon after construction.
Rain and snow
Providing precautions are taken, it is possible to continue building successfully in any weather conditions likely to be encountered in the UK. Elaborate precautions such as heated working enclosures however, are rarely economically justified. Care must be taken on laying concrete only when weather conditions are suitable, both at the time of laying and throughout the curing period. Weather protection may be needed in addition to other measures taken (such as a covering of damp sand to promote curing).
If air temperature is low enough to delay initial set, concrete over sites will not develop their full strength. If heavy rain falls on a freshly laid slab, the fines may be washed out, and the concrete surface will be weak and crumbly.
Concrete
Do no permit mixing or laying of concrete when the air temperature is below 2 degrees C nor when it is expected to fall below 2 degrees C within the next few hours.
- local conditions may increase risk of low temperatures (e.g. frost hollows, seek local knowledge);
- temperatures are lower on higher ground by about 0.6 degrees C for every 100m height above sea level;
- Check that aggregates are not frost-bound;
- Providing air temperature is above 2 degrees C, and if concreting cannot be delayed, frost bound aggregates must be thoroughly heated;
- Do not permit unprotected concrete slab to be laid in more than the lightest rain or snow showers;
- Protect fresh concrete if rain or snow is likely.
Flat roofing
- Do not handle or lay sheet membranes when the air temperature is low enough to reduce their workability -generally less than 5 degrees C for heavier types or 0 degrees C for lighter types;
- Some membranes are more tolerant than others of low temperatures. Check manufacturers' recommendations for 'conditioning' and unrolling before laying;
- Do not lay membranes on damp or frosted surfaces or when any rain, sleet or snow is falling;
- Do not lay a greater area of hot applied adhesive than will stay fluid until the membrane is laid;
- Protect immediately, day work joints in warm deck roofs with a fully bonded lap.
Brick laying
- Do not permit bricklaying or rendering when the air temperature is below 2 degrees C, nor when it is expected to fall below 2 degrees C within the next few hours;
- Check that the aggregates are not frost-bound;
- Frost bound aggregates must be thoroughly heated;
- Do not permit bricklaying or rendering when rainfall exceeds the lightest of shower;
- Rendering applied to saturated walls will almost certainly become detached;
- Rain can weaken mortar and stain face work (note need for adequate protection of materials prior to use);
- Ensure that green brickwork and render are protected from rain and possible overnight frost.
For more information, contact the Building Control Section.
07 October 2008
