Wall ties and cavity insulation
What does a bulging outer leaf suggest, and why is it not automatically subsidence?
A bulge in the outer brick leaf of a cavity wall, often with horizontal cracks, can mean the ties are no longer holding that leaf to the inner one. Subsidence is movement of the ground under the building. The patterns differ: tie trouble sits in the brick courses of one leaf; ground movement tends to taper around openings and continue into the plinth. A survey from the ground cannot see the ties.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
Cavity walls depend on ties. When mild-steel ties rust they expand and crack the bed joints, and the outer leaf can bow. The Energy Saving Trust’s cavity guidance assumes a wall that is suitable to fill, which a bulging leaf is not, until someone has dealt with the structure. A visual survey records the bulge and the cracks. A borescope inspection is a separate instruction.
The Association of British Insurers describes subsidence as foundation movement. Do not start with underpinning because a gable bows at mid-height. Ask the surveyor which pattern they saw. If ties are the concern, ask a firm that will inspect ties, and ask the lender what they need. There is no RICS national price for tie replacement. The number of ties is what changes the quote.
What should you ask your surveyor?
- Is the bulge in the outer leaf only, or is the whole wall leaning from the ground?
- Are the cracks in level courses, or diagonal over openings?
- Did you see the cavity, or is a tie inspection still to be done?
What are the typical next steps?
- Do not fill the cavity while the leaf is bulging.
- Photograph the elevation in raking light so the bow is visible.
- Get a tie inspection if the purchase depends on it. Do not deduct an underpinning sum for a wall-tie pattern.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
Can render hide a bulge?
It can soften the look of it. Cracks in the render and a shadow line still show. The survey should say if render stopped them seeing the brick.
Does one bulging gable mean the whole house needs new ties?
Not on this page’s say-so. Exposure and the ties that are seen decide that. Ask the inspector to say which elevations they checked.