CROSS Safety Report
Stability of terraced buildings
This report is over 2 years old
A reporter is concerned about a terrace of four buildings the third of which is being opened up.
Two of the others have no cross walls on the ground floor and he notes that the spine wall in the last building has also been removed.
Key Learning Outcomes
For homeowners and builders:
Be aware that creating an opening in a wall (internal and perimeter walls) can affect the stability of the building
A suitably qualified engineer should be consulted to carry out an assessment prior to undertaking any works on site
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A reporter is concerned about a terrace of four buildings the third of which is being opened up. Two of the others have no cross walls on the ground floor and he notes that the spine wall in the last building has also been removed. This leaves the front eight or nine metres of these buildings with nothing but the glass windows to provide resistance to sway.
It is not, they say, a matter of conjecture that these buildings will eventually collapse. The only question is when. It might be 20 years, but they would be very surprised if it was 100. They find it very hard to believe that it is regarded as acceptable to remove stability of any building, let alone a whole row and has drawn this to the attention of the local building control.
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The statement regarding the involvement of a structural engineer is misleading. Where there is a structural engineer involved, even if appointed for only one unit within the terrace, it is the structural engineers responsibility to ensure that with the removal of the wall there is sufficient stiffness remaining to support the proportion of the side sway loading attributable to that unit.
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This is a well known problem but such work is often carried out by a part time builder, without proper structural engineering input. Building control may not be notified which means no one sees the ‘big picture’ of stability which should be considered for even the most minor of alterations. When there is a structural engineer it is their responsibility, even if appointed for only one unit within the terrace, to consider the wider implications of wall removal.
A structural engineer becoming aware of the situation as described has a duty to pass on any concerns to building control. When there is no engineer, which may well be the case, then overall stability can be compromised and there are many examples of uncontrolled modifications works leading to collapse.
When there is no engineer, which may well be the case, then overall stability can be compromised and there are many examples of uncontrolled modifications works leading to collapse
CIRIA are currently (April 2015) conducting a study into ‘Structural stability of buildings during refurbishment’ and the findings and their recommendations will be important in casting more light on this issue.
Opening up may be fashionable but can be fatal (witness the typical soft storey collapses that occur in any earthquake). A common danger occurs in typical British semidetached houses where one (or both) houses decide to install wide, garden facing French windows in the back wall thereby compromising the back wall stability in side sway. Figure 1 is of a house in San Francisco where the ground floor had been opened up for garaging thereby creating a ‘soft storey’ which failed during an earthquake dropping the building by a complete storey.