Flooding and Historic Buildings

Although most historic buildings are very durable and relatively resistant to flooding compared with much modern construction, they can still suffer substantial damage.

Older buildings behave differently to modern ones and as a consequence need much more careful attention after flooding. They are often built with more permeable materials like timber, lime mortars and plasters and soft bricks which will absorb water but need to be able to dry slowly.

Repair works need to be considered in relation to how the building is constructed and the materials used. One solution does not fit all. 

image of flooding in Worcester

English Heritage has prepared guidance to assist those who live in, own or manage historic buildings that are threatened by flooding:

Advice is provided on preventative measures as well as on the inspection, conservation and repair of historic buildings after flooding. Click on the links below for further information: 

Preparing for Flooding  

  • Carry out basic building maintenance to minimise potential damage.  
  • Are building drainage systems working efficiently?
    Check any adjacent land drainage such as ditches and water courses for blockages, particularly after heavy rainfall.
  • Check external ground levels are not too high adjacent to the building. These should be at least 150mm below internal floor level and damp proof course level.
  • Prepare an emergency home/family flood plan and flood kit.
  • Check insurance cover. Are there any special provisions for historic buildings?

Flood Resistance Measures to Keep Water Out  

Flood protection can reduce flood damage by as much as 50 – 80% by limiting the amount of water entering the building and the damage it causes.

Consider having a flood protection survey from an architect or building surveyor who has experience with historic buildings and flooding damage. Try to understand how the property is constructed - what is significant and vulnerable to flooding? What measures would be most appropriate? Could flood protection measures be positioned away from the property?

The following protection measures can help

  • Adding aperture protection devises, such as door guards and air brick covers. These may only keep water out for a limited period, depending on the level of flood water, but they will allow time to move valuable possessions to safety and restrict the entry of debris. A range of certificated (BSI) products are available. Water causing flooding to a depth greater than 1m should not be held back because of the risk of structural damage.
  • Using temporary flood barriers consisting of interlocking units kept in place by the weight of flood water can be useful, but will require storage. 
  • Avoiding products which aim to provide an impermeable barrier to the external wall of the property such as coatings or tanking. These are best avoided for traditional construction as such systems can trap damp within the structure of the building not allowing the fabric to dry naturally.
  • Avoiding extensive hard surfaces around a building as this increases run-off and restricts water absorption by the ground. 

Measures to Minimise Damage if Flooding is a Possibility  

There are many quite simple measures that can be carried out to a property so that, if flood water does enter, the damage is minimised.

  • Installing or moving electrical circuitry above potential flood level.
  • Having any vulnerable electrical equipment such as freezers raised above potential flood level.
  • Adding backflow valves to plumbing.
  • Adding a built in pump for cellar areas or sub-floors that are particularly vulnerable to flooding.
  • Ensuring that a few floorboards across a room can be lifted when flood water subsides. This will help to avoid permanent board deformation, assist drying and allow water to be pumped out of the sub-floor void.
  • Retaining lime plaster as this is porous and will dry out with the main wall. Modern gypsum plaster is slightly soluble and will become detached.
  • Avoiding composite wood materials such as chipboard and fibreboard which will be ruined so are best avoided for fixtures such as kitchen units. Historic solid doors will be much more water resistant than modern hollow doors.

Minimising damage from Remedial Work after Flooding    

Properties that are insured will be inspected by the insurers’ loss adjuster who may in turn bring in a surveyor to establish and specify the extent of repair works required depending on the extent of damage. A recovery contractor appointed by the insurers would then be brought in to carry out repair works.

Historic buildings can be particularly vulnerable at this stage as works may be specified that are inappropriate and damaging or include extensive removal of historic fabric. The appointed contractor may also have little or no experience with working on historic buildings.

Consider the following:

  • Make a comprehensive photographic/video record of the damage.
  • Inform your insurance company that you need a loss adjuster/recovery contractor experienced with historic buildings. Where insurers and loss adjusters have instructed inexperienced contractors a great deal of unnecessary damage has resulted.
  • Obtain advice from the local planning authority’s conservation officer who has expertise with older buildings about the works and establish whether any consent is required before any stripping out work or repairs are put in hand.
  • Obtain independent advice from architects or buildings surveyors experienced with old buildings and who know local contractors suited to this type of work.
  • Beware of bogus contractors who can take advantage of flood victims.

Good Practice Advice on Remedial Works    

Ideally remedial works and drying should start as soon as is practical after any contamination issues have been dealt with and the building made safe. If the property is insured, drying should start as soon as agreement is reached with the insurers that remedial works can begin. 

  • Pump out basements and sub-floors when flood waters have receded to a safe level.
  • Remove damp items and sodden floor coverings because these impede drying and trapped moisture encourages mould growth and decay. Contaminated items may have to be discarded unless cleaning is viable.
  • Either open windows and maximise air flow with fans or blowers (quadrupling air flow across a surface doubles the rate of drying and discourages mould growth) or seal areas and use dehumidifiers.  Heat and forced air movements should only be used if there is significant ventilation, otherwise warm humid air will be dispersed around the building causing potential secondary damage in the form of condensation and mould growth elsewhere. 
  • Dehumidifiers will only remove water from the large pores of the material and become a waste of resources when the volume of accumulating water in the receiving vessel diminishes significantly.  This is because loss of moisture from small pores is controlled by capillary forces and only time and ventilation will remove it.  Intensive dehumidification may produce superficial drying but deeper moisture will migrate to the surface again when capillary pathways have become re-established.
  • Be cautious about applying expensive wall coverings until a wall is thoroughly dry (12 months or more) because there may be damage caused by salt migration if there were localised pockets of wet material that were not located. Moisture distribution within a wall is highly variable and could not be accurately established without demolition.
  • Moisture meters can be useful but the results need to be interpreted with care. These meters are measuring some electrical property of the material and not moisture. Results are entirely inaccurate and unreliable in materials other than timber, and timber moisture readings become increasingly inaccurate above about 18%.  Meters are useful for monitoring changes but always take several readings and use the same meter. Plotting readings in skirting boards can be helpful but ensure that the part of the board tested is actually in contact with the wall (often the top edge). If the meter indicates that the skirting is dry (mc < 15%) then this is likely to be correct.
  • Meters and loggers recording temperature and relative humidity can be useful, particularly if the instrument is sealed for several hours behind a square of polythene. This method is particularly valuable for testing damp stained or salt damaged areas because these phenomena may actually indicate that a wall has dried rather than it is currently wet. If the wall is significantly damp then the humidity recorded will rise until it is in excess of about 80%.
  • Move large items away from walls and open cupboards or voids to encourage drying. Dry rot and other decay problems will not occur provided that drying proceeds and moisture does not become trapped. The removal or treatment of timber items in case they decay at a later time is unnecessary.
  • The removal of panelling, floors or lime plaster in a legally protected building may cause unacceptable damage and require permission. If the works proposed seem destructive then the local conservation officer should be consulted. There is often a tendency for justifiable exposure work to become enthusiastic demolition. Historically important materials should only be removed by persons with appropriate skill and experience and with thought given to appropriate storage and recording.
  • Keep a detailed photographic record of every stage of the flood damage and subsequent restoration.

RELATED PUBLICATIONS

  

Further Flood Advice

Find out more about flood advice from heritage insurance providers Ecclesiastical

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