Repairs: walls

Preliminary checks

Defects in general – and wall defects in particular – should not be considered in isolation, otherwise there is a risk of treating only a part of the problem rather than the whole.

When making a preliminary assessment, bear in mind the advice in texts on building surveys in deciding the extent of the problem. There are 2 main elements to consider at this stage:

  • structural stability; and
  • the wall fabric in more general terms.

Structural stability

Structural stability will either be:

  • immediately dangerous – affecting the safety of the building and its occupants;
  • a progressive defect such as subsidence (which can be very difficult to distinguish from, say, old settlement or shrinkage).

Dangerous structures

Under sections 77 and 78 of the Building Act 1984, a local authority can require the owner of a dangerous structure to make it safe or, in an emergency, the authority can take direct action to remove the danger.

It can be difficult to form a sensible view of whether a building is 'dangerous', so err on the side of caution. If in doubt, a second opinion, or even a third, can save much embarrassment. Many Building Control Officers will be in a position to assist if there is a possibility of a Dangerous Structures Notice being issued.

A Dangerous Structures Notice can apply to parts of buildings as well as whole structures.

Building Control Officers have powers (and a duty) under sections 77 or 78 to enforce appropriate action.

  1. Inspect the building. Does it ‘pass’ or ‘fail’ simple tests such as:
    • excessive bulging;
    • loose masonry;
    • walls displaced by more than one-third of their thickness;
    • ‘significant’ cracks (i.e. cracks that are 15–25mm or greater than 25mm in width)
    • fresh/recent cracks.
  2. If you are unsure of the safety of the wall, seek a second opinion (from a structural engineer).
  3. Public safety is paramount. Liaise with Building Control. Urgent actions might include:
    • demolition;
    • repair;
    • temporary support.
  4. Check the situation with the building’s insurers.
  5. Check with owners/leaseholders/neighbours and any other interested parties. Also, are there any party wall issues?
  6. If the situation is not life-threatening, and works are non-urgent, agree a programme of works within the timescales set out in section 80 (Demolition Notice) of the Building Act 1984 (some minor works are exempt if demolition is required).
  7. Give adequate – usually 6 weeks – notice to gas and electric services if demolishing.

In less extreme cases there are some simple tests to help you arrive at a decision:

  • Carefully thump the wall with the palm of your hand. Think about where you are standing before you do this!
  • A garden wall could be carefully rocked to test the condition of the mortar bonding (it is frightening how many can be readily flexed). Even enclosing walls in a building can sometimes be felt to flex when they are in poor condition and the mortar bond/adhesion is no longer effective.
  • Measure the amount of distortion or leaning out of plumb. Use a long spirit level (minimum 1200mm), with the gap measured at one end by a steel rule, rather than a plumb bob.

For measurements, the rule of thumb is the rule of thirds:

If the wall leans out by one third of its thickness, it is fair to assume the load path through the wall is not stable and the structural integrity of the wall is likely to be prejudiced.

Another option is sighting down the horizontal mortar course joints. This can give a good indication of how much the wall may have bellied-out or sunk locally – perhaps due to made ground, local soft spots, or localised overloading. The latter is not always fatal to a building and is common in properties built up to about 1940. Wide windows with narrow brick piers in between mean that building loads are concentrating onto fairly narrow sections of wall or onto the party walls, causing a recognisable pattern of distortion.

Also consider whether the building has been constructed 'uniformly'. Often gables in older properties are formed in only half brick skins 100mm (4 inches) thick when the rest of the building is in cavity masonry construction. The gable frequently fails, perhaps under wind suction, and starts to lean out before eventually collapsing. This was a common feature following the storms of the late 1980s, when many masonry gables collapsed.

Measurement in these locations can be difficult, be prepared do some serious crawling through the roof space if necessary.

Monitoring using a precision-engineering level may be appropriate in some cases to decide if movement is seasonal. Insurers will generally be involved where trees and shrinkable soils have created a problem and where the foundations have inadequate depth. The insurer may also drive the repair solution.

Be careful – today's partial underpinning can be tomorrow's negligence claim, and many engineering practices are issuing much more robust advice and repair strategies than perhaps they did 15 or 20 years ago.

There was a time when a localised repair followed by a wait-and-see approach was considered appropriate, and generally managed to limit the expenditure on repairs. Building owners and/or their insurers now tend to insist on a final repairs solution, which may require some over-engineering.

Broken flank wall, caused by overloading adjacent to the front door

Stability issues – common problems

  • Insufficiently tied-in building elements – particularly (but not exclusively) when dealing with older properties. Floors, for example, provide a considerable proportion of the rigidity and bracing to the structure.
  • Bowing or rippling to the walls – always warrants further investigation to establish how well the joists are tied in to the wall fabric in both directions. Often houses built in the 1920s and 1930s have joist spans running parallel with the front and rear walls in a terrace. At this time, window openings were becoming larger, perhaps with French casements at the back of the property. Consequently the loads are concentrated in quite narrow bands of brick piers, particularly at the rear of the building, and there is no structural tie-in from front to rear: as a result walls start to bulge and lean outwards.
  • Quality of masonry bonding – bonding for masonry partition walls and load-bearing walls within the building can be of dubious quality. Sometimes there is little more than a butted-up joint with no meaningful toothing-in of the brickwork to lock the structure together between external main walls and load-bearing masonry partitions. Where significant distortions are involved, some of the internal surface and plaster finishes may need to be stripped out to arrive at a robust conclusion about the extent of repairs required. This is unlikely to have been investigated within the remit of a normal condition survey.

It is tempting to cause the minimum amount of disturbance, particularly in residential property where an investigation can cause some distress to the occupants. However, better by far to come up with the right solution.

If the structure is not dangerous, form a view as to whether the problem is going to get worse or not.

Assuming the building does not qualify for a major repair, consider and discuss the following with the client:

  • What is the economic life that the building has to fulfil? Will it be demolished, altered, extended or disposed of in the foreseeable future? Prioritise this against any other repairs.
  • Is there a maintenance programme or budget to consider?
  • Is the defect wear-and-tear, or is it subject – at least potentially – to an insurance claim?
  • Are there any statutory issues (such as listed building status, public buildings with a health and safety requirement, disabled access) that need to be incorporated within the repairs advice.

All of these (and other factors) influence the repairs strategy, and the timing and type and cost of repairs carried out.