Can your cracked walls be repaired or is it subsidence?


If the exterior walls of your house have cracks, how can you tell if they are easily repairable or are something far more serious such as subsidence?

This is when the ground the property sits on starts to sink undermining the very stability of the house, causing major damage to the building, which to remedy, is expensive.

A recent report by a leading comparison website suggested that to repair cases of subsidence average about £10,000 so like most defects, if caught in the early stages, the final bill to repair would be lower than that.

Firstly, it is probably wise to lay out exactly WHAT subsidence is and what causes it.

Subsidence is defined as….

“the downward movement of a building foundation caused by the loss of support of the site beneath the foundation”.

Source: Institution of Structural Engineers and the Association of British Insurers

So in essence it is the downward movement, or sinking, of the very ground that your house stands on. You don’t need to be a construction professional to realise that the implications of this happening are very bad.

What causes houses to start sinking?

There are various reasons why houses start to sink so here are the most common:

  • The house is built on clay soil which starts to dry up and shrink, often caused by nearby trees.
  • Trees themselves, if large and old, can burrow deep under your home, cracking the foundations.
  • Leaking main water pipes under the house, washing away the soil the foundations sit on.
  • Undiscovered old mine workings, as has happened very recently in west Cornwall, where old mine shafts re-open as their “cap” fails.
  • Ground heave. Often caused by UPWARDS pressure as the ground under the home fills with water, often after tree removal.
  • Landslips, often occurring on clifftop and seaside homes and you can learn more about coastal erosion here.

So how can you tell if your home has that sinking feeling?

Spotting the signs of building movement is quite easy and would normally follow this course:

  • Look for evidence of cracks outside. Fractures that run from the top to the bottom of the house is a usual sign
  • Check for cracks internally too. If the crack runs from the inside wall to the outside, this is BAD and you should call a surveyor to advise.
  • Doors and windows may not close properly, or even open at all.
  • The visual appearance of the exterior doesn’t quite seem right.
  • Cracks in the walls are wider than 2mm and often run around doors or windows.
Cracked render on a wall

This single story extension suffered movement and opened up this crack, which we had to cut out and fill with an epoxy resin mortar to stablise it.

What can be done to fix subsidence?

The most common form of fixing particularly bad incidents of subsidence in property is underpinning, which entails digging out an area around where the foundations have failed, supporting the house with steel props, removing the bad section of foundation and then rebuilding a brand new section in it’s place. The average cost of this work is, as mentioned earlier, about 10 grand.

If you do discover this problem in your home you should first contact your home insurance company and check you are covered for this. It is worth noting that underpinning is often cited as a last resort as in many cases, removing the CAUSE of the problem (e.g. intrusive tree roots) can often STOP it happening any more but again it is recommended you get a survey done.


This shows a severe crack which opened when the newer extended section of the house "settled" at a different rate than the older section (on the right)

This shows a severe crack which opened when the newer extended section of the house “settled” at a different rate than the older section (on the right)

So what cracks are not due to building movement?

In most cases if you are checking out the condition of the external walls of your home and you find cracks, more often than not these are cracks in the SURFACE covering of the home, such as pebbledash or render, and should not cause any alarm as they are (fairly) easily repaired.

The best way to tell if the cracks simply need to be cut out and filled, or if the cracks signify an area of render that has become detached away from the wall is to lightly tap the affected part with a hammer or a chisel.

If the implement gives a dull “thud”, the cracks are probably just surface fissure cracks and simply need to be cut and filled. If the chisel gives a ringing or hollow sound, that means the render is “blown” and would need to be taken off and replaced to match.

Removing hollow render is essential if exterior decoration is to be carried out.

If this is NOT removed and simply painted over, not only is that the “cowboy builder” method which will come back next year and bite you in the ass, it is also the least cost-effective way because if the problem is not attended to it will get much worse and spread across the wall, costing you a lot more in repairs than you think, PLUS allowing damp to enter the wall.

Would NPA textured wall coatings be flexible enough to cure the cracking?

I won’t beat about the bush here, no they won’t.

Our coatings are specially made with flexible pliolite resins which aid elasticity as this demonstration shows, however there is a limit to this and such products are NOT a sticking plaster for major cracks, nor are they a quick and cheap fix. If your house has cracked external walls, whether they are surface cracks or something worse, we cannot and will not apply our system to a house that is sinking!

If we were asked to work on your home, we would only be able to do this AFTER the house had been underpinned and had stopped moving. A surveyor can attach markers that span across a crack and measure movement. They are sometimes used after repairs have been done to make sure the property has stabilised.

Only then could we apply our wall coating system. As we guarantee the exterior surface coating will not crack, we ourselves need to be sure of that also, to avoid any You can read what our warranty covers here which of course come out of our pocket not the clients.

Is is safe to buy a home that has been underpinned?

In most cases yes it is but you would be advised to pay for a very good structural survey BEFORE you make an offer, to reassure yourself the job has been done right and it will not happen again.

Also bear in mind, and most people don’t know this, that if you DO buy a previously underpinned house you may find your home insurance policy for the new house will have very expensive premiums, so try and negotiate a lower price with the vendor based on this fact.

You should not have any issues with getting a mortgage on a property like this, especially if the problem has been fixed.

So if my home does not have subsidence, what’s wrong with the walls?

If you are certain that cracks in your home are not the result of building movement then this means that the weatherproofing ability of the surface outside your house has been degraded over time and work is needed to the walls to fix and repair the cracks.

After repairs it is preferable to commence specialist over-coating and weatherproofing with a flexible paint or durable wall coating such as the NPA system, and free advice can be given to you about this, so please give us a call today on 0800 970 4928 or click the CONTACT button on the screen.

Thanks for reading.

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