Overcladding

Many high rise blocks and social housing tenements have now been overclad with external wall insulation to make the flats warmer. If not properly done, however, condensation can occur.

Overcladding is a form of external wall insulation.

Low rise blocks

In low rise blocks of flats, the method used is to fix insulation boards on the outside walls and then apply render over the boards. Frame and panel systems are also sometimes used. This type of insulation has commonly been carried out by local authorities and housing associations to blocks of flats built of concrete block or brick where they have the majority ownership. Grants may be available but these don’t usually include for insulating walls outwith flat ownership.

Application

To avoid cold bridging, the insulation should be continuous. Proper installation may require pipes to be removed and replaced to the outside of the insulation. A plastic cover over the pipes is not an adequate solution. External insulation should also be carried down to below ground level and not stop at the internal floor level. Otherwise significant heat losses occur at the skirting level in ground floor flats which generally are the hardest to heat. Old concrete cills should also be treated, either by applying GRP cills over the existing cills or by insulating the cill and using an extender aluminium cill to protect it.

This type of insulation is not suitable for stone walls as it is not permeable.

The use of insulated render can also be considered.

High Rise Blocks

High rise blocks are overclad with rainscreen cladding behind which insulation is fixed to the original external walls. The external skin of the cladding is usually fixed to a metal frame bolted to the original. Aluminium and resin bonded panels are often used.  New windows are often installed at the same time. These systems have caused concern in England as the type of boards used and the lack of fire-stopping are a risk. Building regulations in Scotland are different and this fire risk has been found in only a very few blocks of flats.

Maintenance or improvement?

Adding insulation is now defined as maintenance so only requires the majority of owners to agree.

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Overcladding projectJohn GilbertAreas around pipes and balconies have not been insulated

 

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Thermal image of overcladding project aboveJohn GilbertThe cold spots are shown white and orange. These are where condensation is likely to occur

Problems

Grants for insulation do not cover the provision of over-cladding on walls which are not part of individual flats. Moving pipes and adding overcladding below floor level is also excluded from funding.  Where these grant levels were not topped up, many parts of the building were left unclad and cold bridging occurs.  This results in localised condensation damp and mould inside flats and the cold areas can extend for a 1 metre around the gaps in cladding.

Further information

Energy Saving Trust 'Home Insulation: Solid Walls'