Subsidence Damage to Drains
If the subsoil in which the foundations of the building are set in contracts, it could allow the footings to very slightly move. This can be brought about by the drying out of the ground due to drought, or by nearby trees drawing moisture out of the soil. The first you will know about this is cracking along the mortar joints of the brickwork in a local area. If this occurs, then the same underground movement could put enough stress on the drainage pipework to make it crack, or to displace one or more joints.
Tree root growth around the pipes could also literally push the pipes aside. Once a pipe is cracked, or the jointing compound at a displaced joint is damaged, water will gradually escape and wash away the finings surrounding the pipe. This in turn compounds the problem, and allows even more movement. In the meantime, any nearby tree root growth will gravitate into this wet area, and eventually grow through the crack or joint, ultimately blocking the drain at this point. This of course puts pressure on the pipe joints upstream of the blockage, and any slight defect will allow seepage into the ground, thus starting the same problem in another area.
Our advice is, if you notice new cracking of the brickwork joints, tell your insurance company, and ask them to send a Buildings Surveyor to check it out.
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