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Bulging or Leaning Masonry Walls - Building Defect Analysis

Bulging or Leaning Masonry Walls

16th Century Cottage with distortion to masonry walls

Typical Causes of bulging or leaning masonry in old solid walled buildings

It’s a fairly common occurrence to survey old solid walled buildings and find some distortion in the masonry; the walls often found to be bulging or leaning to some degree; and indeed we’ve encountered two such properties within the last four weeks, the latter case was particularly interesting and forms the subject of this blog. 

16th Century Cottage with distortion to masonry walls
16th Century Cottage with distortion to masonry walls

The building in question is a 16thcentury building, originally built with an Oak timber frame and brick infill panels. In fact the building was originally separated into three small cottages but over time was converted to a single large cottage. The building is grade 2 listed but has been derelict for some years but about to undergo substantial renovation and improvement works. With that in mind we were commissioned to carry out a full condition survey, focussing on structural condition and causes of dampness within the property. Little remains of the timber frame and the external envelope of the building is now of solid walled construction; only two timber end frames exist internally, along with the timber roof structure. which is now almost wholly supported on the external masonry walls.

Checking for Distortion in the Masonry

A 2 meter spirit levels shows a bulge of 80mm to the front wall
A 2 meter spirit levels shows a bulge of 80mm to the front wall

Commonly we’ll use a simple plumb bob and line or a large spirit level to. check for distortion in masonry. A large spirit level can be used quickly and effectively, and in this case we noted bulging to both the front and rear walls of the property. The front walls were at a much reduced height due to the cat slide roof, and despite 80mm of distortion, they were less worrying than the 50mm distortion measured to the rear wall, due to the greatly increased height of the wall.

50mm bulge measured to rear wall
50mm bulge measured to rear wall
Checking masonry distortion using plumb bob and line
Checking masonry distortion using plumb bob and line

Acceptable Limits for Leaning or Bulging Walls

Generally speaking you should be concerned with anything more than 25mm of distortion as it lowers the stability of the wall. There is a general rule known as the V3 rule, which asks that you consider the walls centre of gravity. When viewing a 225mm solid wall in profile, a plumb line dropped from the head to the foot of the wall, which passes through the walls centre of gravity, will not fall outside that centre of gravity at the wall base, (if the wall is perfectly vertical.) Where walls are leaning or bulging then the plumb line will fall outside that centre of gravity, and should be considered unsafe, where the plumb line falls beyond the outer edge of the wall base. In these cases you should seek advice from a qualified structural engineer.

V3 Rule
V3 Rule

Common Causes of Bulging or Leaning Walls

Bulging of the walls is caused by a number of factors: 

  1. Vibration from road traffic. 
  2. Increasing the floor loads or building on additional floors 
  3. The original walls being insufficiently thick in relation to the height. 
  4. Lack of lateral restraint between the external walls and floor joists, beams and partitions. 
  5. Thermal or moisture expansion of the walls outer surface

In our experience, the type of bulging seen in older buildings built with lime mortar, such as this, is often a lack of lateral restraint. It is a well-known principle that lateral restraint should be provided to arrest any potential movement in the masonry walls, and this is usually achieved by building floor joist ends into the masonry, or by bonding in internal partition walls at right angles to the outer wall. In this particular case, lateral restraint was meant to be provided by the first floor joists, running from front to rear in the building. However, when viewed internally, the joist ends were set in sockets cut in the central spine bresummer

Joists. supported by sockets cut into bresummer
Joists. supported by sockets cut into bresummer

Visual Inspection of Joist Ends

In this case visual inspection was fairly straightforward, since all the floor joists were fully exposed. However, it is more common for the floor joists to be hidden as they are sandwiched between the ground floor ceiling, and upper floor. Often, we may need to take up floorboards at first floor level to inspect joist ends, and in particular, to assess how they are tied to the masonry walls, and whether lateral restraint is being provided.

The joist end lap joints, seen above, are seen to have pulled clear of the sockets cut into the bresummer, which accommodate them. Ideally, these lap joints would have been secured with oak pegs, but they are unfixed, and have simply pulled clear of their sockets as the external walls have bowed. This technical detail was simply unable to provide the lateral restraint required by the front and rear walls of the property.

When checking some joist ends, we found as little as 20mm of bearing surface at the joist ends, which essentially tells us, that if another 20mm of deflection occurs to the outer walls, then the floor joists could collapse.

Only 20mm of bearing surface to joist end
Insufficient bearing surface to joist end

The floor joists are now too short and cannot be re-used, unless the outer walls are taken down and rebuilt so as to be perfectly vertical again. In this case, the joists should then be able to be fully inserted back into their sockets formed in the spine bresummer. However, with the amount of deflection measured, the walls should be perfectly stable, so long as adequate lateral restraint in re-instated to prevent further ongoing distortion in the masonry. Joists will be replaced with longer joists which will be adequately tied into both the outer masonry walls, and the central spine bresummer.

7 responses to “Bulging or Leaning Masonry Walls”


    good posting! I’m looking forward to seeing your post, will you make it like this again?

  2. Simon Holloway avatar
    Simon Holloway

    Can anyone confirm that a cob wall with an over all lean out from top to bottom of 10 degrees to 18.6 degrees is irretrievably and liable to collapse please?

  3. Zena avatar

    What about if it bulges in the middle? I’m looking at an old Semi detached cottage at the moment which has kitchen in the basement lounge above, bedroom 1st floor, the garden sits next to the house, but the tall 3 storey wall bulges in the middle. I’m unsure if this is just because it’s an old, basic build dockers cottage of it is about to fall down

    1. Joe Malone avatar
      Joe Malone

      Hi Zena,

      There are acceptable tolerances, so it really depends how much the wall is bulging. Sounds like you’ll need it properly inspecting by a qualified structural engineer.

      As I’ve explained in the blog, this normally occurs due to lack of adequate lateral restraint.



  4. John avatar

    I am looking at buying a 3 storey 1840’s property in London. I have a report from a surveyor that says that the ground floor walls are essentially straight and true but that there is a bulge that starts at the first floor (what the surveyor describes as a “belly”) and that he has estimated that this belly is around 100 mm away from where it should be (I note your estimation that 25 mm is cause for concern so 100 mm sounds like it could be catastrophic!)

    My question is, is it possible to take the wall down row by row and re-build the wall taking care to make sure that the re-built wall is obviously level and true but that it is also appropriately anchored to the floors? I know that the first reaction will be that it will be expensive – but leaving that aside – is this a workable solution and is this likely to give a more permanent solution to the bulge issue than trying to pin a wall that seems to me to be in the process of failing?

    1. Joe Malone avatar
      Joe Malone

      Hi John,

      It’s first important to understand why the wall has bulged in this way, and you may know from my blog that it is usually caused by a lack of lateral restraint. Internally, look at where the wall is bulged. Is it connected to internal spine walls or joist ends? You may need some invasive investigation work to understand why this has happened, and that may mean taking up floor boards etc. Also ask if any internal spine walls may have been removed during previous renovations?

      The works you describe would need careful design by a qualified structural engineer, particularly as it relates to temporary structural support, but yes, it is possible, and yes, it will be expensive. You absolutely must understand the cost of these works before you consider proceeding with this purchase!

      Yes, 100mm of deflection is significant but it can be stabilised with tie bars and wall plates, which of course would be a significantly cheaper option. Of course, then you have to consider the impact on any future sale if you were to buy this property.


      Joe Malone

  5. Richard avatar

    Hi Joe,

    Thank you for posting this.

    If I drop a plumb line down the side of my solid stone wall house, how many mm off plumb does it need to be before I need to worry?

    Kind Regards,


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