Appendix 5: Resilient Reinstatement
Many of the techniques described in this appendix should only be carried out by specialist contractors with the correct skills and equipment. For a list of such contractors, contact the British Damage Management Association (BDMA) on info@bdma.org.uk or visit their web site www.bdma.org.uk .

Most of the information in this appendix relates to flood resistant design and construction, but in some cases, local flood defences which protect only one or two houses might be considered. For more information about these, an excellent paper by P. Bowker of HR Wallingford was published in the September 2002 issue of Municipal Engineer.

Flood Damage to Dwellings

Current research indicates that climate change will bring increasingly wet weather with more severe extremes in the winter. If a property is flooded it should ideally be reinstated in such a way that future floods will cause less damage. Some suggestions are shown below.

Building materials can be affected in different ways by a flood, but repair is more a function of the type of materials than the duration of flood;

plasterboard and chipboard will always have to be replaced even if the immersion time is small. Consider alternative materials if possible.

timber can be dried out to an acceptable moisture content, provided it does not warp

masonry can usually be dried out although the finish may be different

There are two basic types of materials used in a house

materials which although vulnerable, are easy to replace, (e.g. drylining/plasterboard) or

more robust materials which suffer little damage, but may take a long time to dry out and require skilled labour to replace (e.g. plastered masonry).

Effect of flood on different materials

1. Masonry and concrete

No serious effect, but takes a long time to dry out.

Lightweight concrete may expand on wetting and shrink on drying, causing cracks.

Wet masonry, especially in foundations and external walls, will be vulnerable to freeze damage.

Foundations built on sand or gravel can be weakened by flood waters, check them carefully.

Resilient Reinstatement

If walls have to be rebuilt, ensure that adequate ventilation and drainage is provided. With cavity walls, holes may be needed to help drainage (see also comments on insulation). Ensure that a proprietary waterproofing solution is applied to the external walls.

2. Timber

Swells and may distort. This could cause serious damage to the rest of the building. Timber based panelling may suffer permanent weakness if wet for a long time.

Chipboard, even if to the BS for flooring, will expand and may need to be replaced.

Resilient Reinstatement

Ensure that waterproofed chipboard (or preferably marine plywood or solid timber) is used.

3. Rendering

Cement based rendering should not suffer but may be hard to clean and will be at risk of frost damage for several weeks.

4. Cladding

Tiles, GRP and plastic should be only slightly affected. Timber siding may distort and need to be replaced.

5. Metals

Metal sheeting will have accelerated corrosion, even aluminium - especially after a sea water flood. Also wall ties, nails and fixings, and metal window frames.

Resilient Reinstatement

Ensure that stainless steel fixings are used in vulnerable areas.

6. Insulation

Quilt insulation below suspended floors is likely to compact and not recover following wetting and will need to be replaced; preferably by rigid slabs.

Reflective foil sheets will hold water and should be perforated with holes.

Mineral fibre and expanded polystyrene panels in cavity walls should self drain without problems. However, blown in cavity insulation could have problems; polystyrene beads can be washed out, urea formaldehyde can be crushed and low-density mineral and glass fibre insulation can be displaced, creating voids.

Resilient Reinstatement

Ensure that replacement insulation is not vulnerable to soaking or movement. Rigid slabs are ideal, or if polystyrene beads are used, ensure that they are used in conjunction with waterproof adhesive.

7. Floors

Suspended floors are likely to be less affected by shallow floods than solid floors, simply because the floor level tends to be about 200 mm higher than solid floors.

Joists built into walls are more vulnerable than joists supported on hangers.

Access will be needed below all solid floors to ensure that sewage and silt can be removed.

Floor surfaces of boarding on top of insulation are likely to float during a flood and usually have to be replaced.

In the last ten years, building regulations have raised the insulation standards for new buildings, and this has led to the practice of insulating floors to meet the new standards. A typical method is the so-called "floating floor" where polystyrene insulation is laid on the floor and then covered with either chipboard or cement. Flood water can become trapped in this insulation layer, and has to be removed. Where the insulation is covered in cement this can either be done by digging up the floor, which is expensive, or by using high pressure suction pumps combined with high pressure injection of dry air until the humidity of the exhaust air reaches a satisfactory level. This can take up to three weeks and is obviously a job for a specialist contractor.

Resilient Reinstatement

Ensure that waterproofed chipboard (or preferably solid timber) is used, ensure adequate access is available to voids under floors and if possible that these voids have drainage holes, which can be cleaned. Consider fitting a sump pump under the floor to help keep flood waters low next time.

If replacing the floor in the ground floor of a property, If the ceilings are high enough, serious consideration should be given to raising the height of the floor above the flood level.

8. External Walls

A wall with a clear cavity will dry out more effectively than a solid wall. A wall with cavity insulation may take a lot longer to dry out.

Some insulation materials can have a capillary action, which draws floodwater up to the upper floors.

Check for ventilation holes in the outside skin; these will speed the removal of water from the cavity.

Resilient Reinstatement

When a wall has fully dried out, treat it with a proprietary waterproofing solution.

If a property is so badly damaged that the walls need to be rebuilt, consider raising the floor height and the damp proof course above the danger level, and ensure that foundations are adequate to avoid water scour.

9. Internal Walls

Stud partition walls will need replacement of the plasterboard sheets, the studs should be allowed to fully dry out first, if warped they will need to be replaced.

Solid partition walls will be less affected, though drying out will take longer

Panel partitions (e.g. two sheets of plasterboard with a honeycomb centre) will need to be replaced.

Resilient Reinstatement

Consider laying the boards horizontally, so that next time only the lower sheets will need to be replaced.

If a suspended timber floor is also being replaced, the internal walls should rest on masonry under the floor structure. If the walls rest on the floor, and the floor has to be replaced again next time, then the walls will also have to be replaced.

10. Doors and windows

External solid timber doors are unlikely to be affected, though some distortion may occur. Stripping the paint off the doors will help them to dry out more quickly. Remove them from their hinges and lay them flat while drying to reduce warping.

Hollow core doors will need replaced.

Windows will be only slightly affected, although metal windows could corrode from salt water and double glazed units may be damaged if water reaches the edges. If water enters a sealed double glazed unit the unit will have to be replaced.

Hollow UPVC window or doorframes could fill up with water containing contaminants which might be difficult to remove.

Resilient Reinstatement

If new woodwork is to be installed, specify a micro porous paint finish, or for hardwood, use an external micro porous protective stain rather than a varnish. This protects the wood from water, but if the wood does become wet, it allows the water to escape and the wood to dry out, avoiding blistering, peeling or warping.

11. Skirtings and door facings

These will almost always have to be removed if only to investigate the underlying materials and allow drying out. They are difficult to remove without damage and it should be assumed they will need to be replaced.

12. Floor finishes

Sheet and tile finishes can be affected by damp; adhesives will deteriorate. Blistering may occur for several months. Ceramic tiles are usually resistant to wet conditions, but if they are on a solid base, they may have to be removed to allow drying out.

Resilient Reinstatement

Most laminated floor finishes will need to be replaced after flooding. Water-resistant laminates are expensive (over £15 a square metre) but may be worth considering if the insurer approves.

13. Drains

Floodwater can enter the building through the drainage systems. External storm water drains will be silted up and gullies will need emptying.

Resilient Reinstatement

Consider installing non-return valves, but these will need regular maintenance and may not be suitable for multi tenure properties.

14. Central Heating Systems

Pipe work is unlikely to be damaged unless the water contains salts. Pipe work insulation could become saturated. Electric storage radiators will need replacement.

Warm air ducts can fill with water and will need to be drained and cleaned. Oil tanks in the garden could float away, allowing oil to escape and contaminate property.

Resilient Reinstatement

Consider moving heating appliances and the central heating boiler to less vulnerable positions. Ensure that oil tanks are well secured.

15. Gas supplies

Water may get into pipes, e.g. through pilot lights. Pipes may have to be purged.

In some areas, the gas supplier may insist on replacement of all copper piping if it has been immersed in seawater.

Resilient Reinstatement

If replacing pipework, re route it at a higher level.

16. Electricity

For safety, the affected wiring and sockets should be replaced. Initially, ensure that there is no risk of fire from flooded wiring.

Resilient Reinstatement

Ideally new sockets should be at least 450mm above floor level to reduce the risk of damage from future floods. Wiring should be routed through the ceiling and loft wherever possible.

17. Telephone, TV aerial and similar wiring

These are usually in conduits. Water in conduits can cause problems and can take a long time to drain. Before reinstating, seek advice from the supplier concerned.

18. Sanitary and kitchen fittings

Sanitary ware is usually unaffected.

Kitchen units will distort and need replacing. Units resting on plastic legs may survive a shallow flood. Gas cookers are less vulnerable than electric, but oven insulation may deteriorate regardless of whether it is gas or electric.

Resilient Reinstatement

New kitchen cabinets should be the type which sits on plastic legs rather than those where the chipboard sits on the floor. Gable ends and plinths may still have to be replaced after a flood and should be installed in such a way that they can be easily removed. This will also assist drying out.

Temporary flood defences for individual properties

There are a number of products available which can give temporary protection against flooding. One of the most comprehensive systems is the " Neptune " system produced by Floodskirt Ltd. A copy of their recent press release is reproduced below, as it shows the issues which need to be addressed when considering the installation of a private flood defence for an individual property.

PRESS RELEASE

The Neptune Flood Defence System, as manufactured by Floodskirt Ltd, recently passed a second severe real life test, witnessed by the National Press and TV when Yalding was flooded by a breach of the River Beult.

On Monday 30 December 2002 , a flood warning triggered the owner, Duncan Hewett, of Riverside Cottage, to swiftly deploy the system's skirt around the external walls. Unfortunately, in doing so, he damaged one of the zips but was able to execute an emergency temporary repair with back up advice from the manufacturers.

The test commenced when the river rose to a height of over 760mm (2'6) above the surrounding ground level completely flooding the area around the property for some 30 hours.

The rubber skirt came into immediate use as the waters rose as did the system's non-return valves preventing back flow up the drains. The next danger, hydrostatic pressure/rising ground water, would have flooded the cottage from the inside. However, the system's sump pump, located inside the garage, activated and is still running to remove thousands of gallons of water that would potentially enter the property from under the foundations all the time the river level is higher than the ground floor.

Rising ground water is a very real problem and will enter a building through the face of external walls below ground level and via service ducts. Whilst concrete foundations are impervious, walls are not and underground tanking is as essential as protection above ground. The Neptune Flood Defence System covers this situation by protecting below ground walls with a torch on bituminous membrane. No other system offers protection like Neptune .

Due to the damaged zip, sump pumps located behind the skirt were put under extra pressure but still coped with the situation and the property was not flooded thus saving insurers a potential claim of over £70,000 and the owners the heartache of again having to leave their home for some 12 months for remedial works.

Whilst the system is not cheap, it is far cheaper than flooding!

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