• Two diagonal \ and / cracks at lower part of bay window.
  • Can not tell if they are visible from inside as there is wall paper.
  • None of the neighbours seems to have any cracks.
  • Crack width seems at most 1 mm as was unable to squeeze-in a 1p coin.
  • There appear to be no other cracks inside or at the back of the house.
  • There are also mirror fault lines in the window sill, but I suspect they are just countours of the three-part stonework; or are they?
  • The front "garden" has a weird open D ~ 30 mm metal pipe/tube sticking out upwards -- looks like a super-short bin.
  • East London location.

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  • Is that wall frame or masonry? May 15, 2021 at 18:29
  • I suspect (based on geraintdavies.co.uk/stone-repair/bay-window-restoration) the wall is brickwork and window sill is stone. May 15, 2021 at 19:06
  • Perhaps you are seeing signs of London becoming Venice... close to the Thames? Really it is age and settlement.
    – Solar Mike
    May 15, 2021 at 19:14
  • @SolarMike Relatively -- it is just above the boundary of the flood zone. Looking at satellite imaging data it also seems close to subsidence red zone; although this street is meant to be green zone -- the next parallel one is starting to hit the red zone though. May 15, 2021 at 19:28

1 Answer 1


The cracks are caused by settlement, evident by the separation of the window sill and the wall. I suspect the settlement is caused by water. What you can do is 1) repair the concrete walkway and apply the flexible sealant to the concrete-wall joint, and 2) grade the ground, or correct the slope of the concrete walkway, to allow water to flow away from the building, also the downspout, if any.

After the corrective actions, patch the wall and monitor the situation. If the cracks reappear soon afterward, then you might need to contact a structural/geotechnical engineer to check/work on the foundation.

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  • I have added an extra image of the window sill fault line; since they mirror -- I have assumed they are part of three-piece stone work. Or do you mean vertical separation of the window sill plane from the wall; that I did not notice, but could potentially see that in the second photo. May 15, 2021 at 19:09
  • Thank you for clarifying. Do you think there is some probability of this being subsidence? May 15, 2021 at 19:44
  • Sorry, I forgot to attach the photo that pointing to the problem. London is notorious for having soft clay, combined with water and time, the foundation settles. The problem seems minor for now, with proper remediation, you can delay costly repair to a much later date if it is inevitable. Do not forget to seal this joint too., so no moisture will get under the window.
    – r13
    May 15, 2021 at 19:53
  • I suggest checking around the house carefully for cracks and separation of the concrete walkway and the wall, and take notes. After sealing the cracks/joints, re-inspect at least once a year.
    – r13
    May 15, 2021 at 19:57
  • By bigger repair down the line, do you mean underpinning? May 16, 2021 at 7:33

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