A bowing or bulging wall has moved out of plumb, usually because something that held it in place has failed: corroded wall ties, missing restraint at floor or roof level, roof spread pushing the wall outwards, or movement in the foundation. The right repair depends entirely on which of these is responsible. A chartered structural engineer assesses the wall first; the work may then involve restraint straps or ties, helical anchoring, wall tie replacement or, where the wall is too far gone, a partial rebuild.
What causes a wall to bow?
Masonry walls are strong when pressed down on and weak when pushed sideways. They rely on being held at intervals, by floors, by the roof, by cross walls and, in cavity construction, by ties linking the two leaves. When one of those connections fails, the wall can lean or bulge, often slowly over many years. The main causes we see described in engineers’ reports are:
- Corroded wall tiesIn cavity walls, old mild steel ties rust and expand, or simply snap, leaving the outer leaf free-standing. It can then bulge, often with horizontal cracks in the mortar. Our wall tie replacement page covers this in detail.
- Lack of lateral restraintGable walls, and walls where floor joists run parallel rather than bearing into them, may never have been properly tied to the floors and roof. Without that connection, tall walls can drift outwards.
- Roof spreadIf roof timbers have been altered, overloaded (for example with heavier concrete tiles replacing slate) or have decayed, the rafters can push the tops of the walls outwards.
- Foundation movementSubsidence or heave beneath part of a wall can rotate it, producing a lean rather than a bulge. That is a foundation problem first and is handled through subsidence repair.
- Removed or altered wallsTaking out a chimney breast, internal wall or floor without proper support can leave a wall less restrained than it was designed to be.
How do you know if a bowing wall is serious?
Some older solid-brick walls have had a slight bulge for a century and are not getting worse. Others are moving. The things that tend to concern engineers are a bulge that has appeared or grown recently, cracks opening at the corners or around windows, gaps appearing between the wall and internal floors, ceilings or staircases, bricks displacing or mortar falling out, and doors and windows distorting in their frames. Bowing combined with horizontal mortar cracks every few courses often points towards wall tie failure; a wall leaning as a whole with tapering cracks elsewhere suggests the foundation may be involved.
If a wall is bulging noticeably, cracks are opening quickly, or a ceiling or floor near it looks unsafe, keep people away from that area and get urgent professional advice. Your council’s building control team deals with dangerous structures. If movement has damaged a gas pipe and you smell gas, leave the property and call the National Gas Emergency Service on 0800 111 999. Please do not try to prop or brace a wall yourself.
How is a bowing wall assessed?
The engineer measures how far the wall is out of plumb and over what height, inspects the crack pattern, and checks how floors and roof connect to it. That may mean lifting a floorboard to see whether joists are tied in, looking in the loft at the roof structure and wall plates, and using a borescope through a drilled mortar joint to look at the ties inside the cavity. Where the cause is unclear or the wall may still be moving, monitoring over a period of months, with tell-tales or survey targets, shows whether it is stable. A structural engineer survey brings all of this together into a written assessment and recommendation.
What are the repair options?
| Repair | What it does | Used where |
|---|---|---|
| Lateral restraint straps or ties | Connects the wall back to floors, joists or roof timbers | The wall has lost or never had restraint at floor or roof level |
| Helical anchoring or remedial ties | Stainless steel ties fixed through the wall into a sound backing structure | Outer leaf has separated, or a solid wall needs tying to cross walls or floors |
| Wall tie replacement | New stainless ties across the cavity; old ties isolated or removed where needed | Corroded original ties in a cavity wall |
| Crack stitching | Helical bars bonded across cracks to restore continuity | Cracking associated with the bow, once the cause is addressed |
| Partial rebuild | Taking down and rebuilding the affected section, tied in properly | The wall is too far out of plumb to be safely restrained in place |
| Foundation repair or underpinning | Deals with ground movement under the wall | The bow is a symptom of subsidence or heave |
Often a scheme combines several of these. Restraint holds the wall where it is now; it does not usually pull a badly bowed wall back to vertical. The engineer decides how far out of plumb a wall can be and still be safely retained, and where rebuilding becomes the sensible option. Cracks associated with the bow are typically repaired with crack stitching once the wall is secured.
Do bowing wall repairs need Building Regulations approval?
Structural repairs such as rebuilding sections of loadbearing wall, or work that affects the stability of the building, generally fall under Part A of the Building Regulations, and Building Control involvement is common. Smaller restraint work may be treated differently; the engineer and Building Control confirm what applies. Where the wall is shared with a neighbour, as with gable walls on semis and walls in terraces, the Party Wall etc. Act 1996 may apply, and a party wall surveyor handles the notices.
Which Merseyside properties are prone to bowing walls?
We see this most in older housing. Victorian and Edwardian terraces and villas, common in Birkenhead and Wallasey, often have tall gable or flank walls and floors that were never strapped to them, and exposed coastal walls take a lot of weather. Inter-war cavity-walled houses, such as many in Old Swan and across south Liverpool, are the generation where mild steel wall ties have often reached the end of their life. We carry out engineer-designed wall restraint and rebuilding work across the region as part of our underpinning and structural repairs on Merseyside.
What affects the cost of a bowing wall repair?
The cause and the chosen repair matter most. Restraint straps to one gable are a very different job from rebuilding a two-storey section of wall. Other factors include scaffolding and access, the height and length of wall involved, whether floors or ceilings must be opened up inside, temporary support during rebuilding, matching bricks and mortar, Building Control and party wall fees, and any foundation work if movement below ground is part of the picture. We price the engineer’s specification, not a guess.
Worried about a bulging or leaning wall?
Call 07777 659786 or fill in the form. Tell us which wall it is, whether it is new or getting worse, the age of the house and anything you have noticed inside, such as gaps at floors or ceilings. We will call back, talk it through and arrange a visit, with an engineer’s assessment where needed. More about our work as a structural repair contractor for Liverpool homes is on the homepage.
Frequently asked questions
Is a bowing wall dangerous?
It can be. A slight, long-standing bow in an old solid wall may be stable, while a bulge that is growing, or one with cracks opening at corners and floors, may need urgent attention. Only an inspection by a structural engineer can say. If it looks unsafe, keep people away and get advice promptly.
Can a bowing wall be pushed back straight?
Generally, no. Restraint ties and straps are designed to hold a wall in its current position and stop further movement, not to pull it back. If a wall is too far out of plumb to be safely held, the engineer will usually specify taking down and rebuilding that section.
Does home insurance cover a bowing wall?
It depends on the cause and the policy. Gradual deterioration such as wall tie corrosion is often treated as wear and tear, while bowing caused by subsidence may be covered under the subsidence section. Check your policy and speak to your insurer, who decides whether any claim is accepted.
How long does a bowing wall repair take?
Restraint strapping or remedial ties on a single wall may take a few days once access is in place. Partial rebuilding, especially at height or where floors must be supported, takes longer. Building Control and party wall requirements can add time before work starts, and it always depends on the property.
Why is my gable end wall bowing?
Gable walls are tall, and many older ones were never strapped to the roof or floors, so they lack lateral restraint. Roof spread, failed wall ties in cavity gables and exposure to wind and rain can add to it. An engineer will look at the loft, floors and ties to find the cause.