Monday, September 24
DIY

Q&A with Handy Mac: Is there a risk the wall will collapse over time?

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Glen has a problem with a leaning boundary wall and has sent me photographs of his problem.

Glen has a problem with a leaning boundary wall and has sent me photographs of his problem. Based on his pictures he asks:

Q: Is there a risk the wall will collapse over time? What remedial work should be done to eliminate any further risk of collapse?

A: He points out the extent of fill behind the wall inside the property is a maximum of 850mm.

Like cracks in walls, leaning boundary walls are manifesting themselves more and more following our severe drought, which has caused major disturbances to the ground under foundations. In a house, being a box shape, one side supports another as do the cross walls, so the chance of a collapse is a lot lower than with boundary walls.

There is a common belief among the average homeowner walls will support almost anything. This is the case if the correct type of wall is built for the intended purpose. For example, a 220mm or one-brick wall is not designed to act as a retaining wall, for example in this case, where there is 850mm of filling behind it. The filling will apply forces the wall may have not been designed for.

Many of us are to blame as we merrily raise the height of our walls, assuming the boundary wall we share with our neighbours will support the extra weight.

It is also important that boundary walls are built as per National Building Regulations, with supporting pillars at the construction joints. Usually these joints and pillars should not be more than 7m apart. Local building regulations should be checked and any boundary wall likely to act as a retaining wall should be designed by a properly qualified engineer.

In this case, I would suggest there is a chance the wall could collapse eventually, but before doing anything else I would monitor and check the movement over the next few months.

To fix it, the leaning sections could be supported by buttresses. I am not sure whether they could be built externally as this may be council land. Alternatively, building internally may block your access around the swimming pool, which is quite close to the wall. The pool might also be applying some forces.

As a start, I would suggest you do a little excavation in the flowerbed to find out at what level the foundation is sitting, and what the ground conditions around it are likely to be.

I make no claim to being an engineer and would suggest you appoint one who will suggest some temporary propping to prevent an accident somewhere down the line. The last thing you need is to injure someone in a collapse, or make access into your property easy. The heavy rains may not be helping the situation if there is some form of settlement taking place under the foundations.

*Handy Mac, aka Don MacAlister, is our expert on household DIY issues. If you have a question for him, please send it to don@macalister.co.za or SMS only to 082 446 3859. Find Don on FB: facebook.com/thehandymac

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