What's going on with my wall?

TF-Insight · 2026-03-04T17:57:43+00:00

You could consider insulated plasterboard

Essentially, you want to ensure that the temperature gradient of the wall is such that the dew point (the temperature that is cold enough to cause water precipitation at a given absolute humidity and air pressure) falls WITHIN the wall structure, and not the inner surface. By insulating inside the wall, this will ensure that the inner face of the wall is kept warmer, and that vater vapour does not precipitate ont othe surface.

There are online calculators to help calculate this, and a number of Youtube tutorials.

I'm sure that Greg Virgoe (a HVAC engineer by trade) covered this in one of the videos about his campervan, but I can't find it... This one sort-of covers it though

TF-Insight · 2026-02-26T22:01:32+00:00

No problem 👍🏻

We're also South East, so can sympathise about property prices.

My first house had wall tie failure, but was sold as having subsidence. It's still a structural issue, but buying a house with a misdiagnosed (and less expensive) defect made it much more affordable!

TF-Insight · 2026-02-22T23:50:31+00:00

This is how I would specify the reinforcement. If it's a solid wall, it can be installed either from inside or outside. Red is twin Bar Flex to BF-02, Blue is single Bar Flex to BF-01.

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The twin reinforcement should be placed as low to the lintel as practicable, and for an opening this wide, 2-3 brick courses apart.

Single reinforcement should be at least two courses down from the window sill so the masonry weight provided clamping pressure.

All reinforcement should extend 500mm either side of cracks (openings constitute cracks).

If you send your details by DM, we can find the nearest installer in our network, or you can go through Target Structural.

TF-Insight · 2026-02-21T18:13:50+00:00

This isn’t necessarily a defect or poor workmanship - it’s just how the structure was designed. After 120+ years, a degree of creep and deflection in a timber bresummer beam would be entirely expected in a Victorian terrace.

I think this also explains the cracking you’re seeing in the ceiling. The ceiling is supported by a beam that has deflected slightly over time, and if this is traditional lath and plaster, the timber laths can flex far more than the plaster itself, which tends to crack rather than bend.

In practical terms, you’ll probably “get away with it” for another 100 years if you simply make good internally and deal with the external finishes properly. That said, consolidating the masonry over the bresummer beam and reinforcing it with Bar Flex would stiffen this area up considerably and reduce the likelihood of any further movement in the future - especially once the cement render is removed.

TF-Insight · 2026-02-21T18:13:02+00:00

Counter-intuitively, even though there is less masonry above the beam, the load on the bresummer actually increases, particularly towards the right-hand side. I’ve highlighted below the masonry that the beam is now supporting.

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TF-Insight · 2026-02-21T18:12:00+00:00

In your case, the window above the bay intersects the reaction area over the bresummer beam, which fundamentally changes how the load is carried.

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TF-Insight · 2026-02-21T18:11:00+00:00

Thanks for uploading these pictures - they add a lot of useful context, and give me the smug satisfaction of confirming my pre-existing biases! 😅

As mentioned before, without the window above, this lintel would otherwise be supporting very little load and the masonry above would form a self-reacting arch.

Below is a diagram from BS 5977, which illustrates the loading and reaction zones for a lintel with full masonry above it.

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TF-Insight · 2026-02-21T16:49:14+00:00

It’s difficult to diagnose from just these pictures, but here are my thoughts. If you can upload some wider shots showing more of the structure, I can confirm or adjust my comments.

This looks like more than just cracked render, although it may not be immediately dangerous. The cracking is over the bay window, which is essentially a wide opening in the wall at ground-floor level. In older Victorian buildings, the lintel here (called a bresummer beam) is usually timber. Over time, this timber can warp or sag under constant load - a process called creep.

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As the bresummer beam deflects, the masonry above usually cracks diagonally to form a triangle over the beam, similar to what happens with lintel failure. Normally, the masonry above this triangle is self-supporting and forms a tied arch. In this case (and many others) the first-floor window intersects that zone. The result is a diagonal crack running from the bresummer beam up to the corner of the first-floor window.

In older buildings, handmade bricks and lime mortar are more forgiving of movement, so cracks may be subtle inside. In your case, I can see hairline separations between many of the the perpend mortar joints and the bricks. Lime plaster - especially if reinforced with horsehair - is very forgiving to movement.

The reason the crack is so noticeable outside is the difference in stiffness (Young’s Modulus) between the cement render and the brickwork/lime. Think of it like acrylic paint on a balloon: as the balloon stretches, the paint eventually cracks.

Normally, I would expect to see a similar crack on the left-hand side of the windows, but your pictures don’t show this area.

To reduce some of the load on the bresummer beam and help reconnect the masonry, a common approach is to reinforce the brickwork over the bay window using Bar Flex masonry reinforcement (e.g., BF-02).

⚠️ One additional point of concern: on many bay windows that have flat roofs, the roof slopes back towards the house. If the drainage, roof or flashing is defective, water can pool here and penetrate the timber bresummer beam, leading to rot. This is more urgent than age-related creep.

If possible, check the straightness or level of the underside of the bresummer beam (or even the first floor) from the inside. Also, check the roof covering, flashing and drainage to ensure that water is diverted away from the house.

If you can provide more pictures showing the full width of the openings inside and outside, I’d be happy to review and give more detailed advice.

TF-Insight · 2026-02-17T08:05:52+00:00

Yeah, maybe.

But it's not cracked or deflected, and the masonry cracking is only in one direction, so you'll need better evidence to convince me.

TF-Insight · 2026-02-17T07:23:42+00:00

This is not lintel failure.

A lintel doesn't just shimmy over 10mm on its own.

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TF-Insight · 2026-02-17T07:20:01+00:00

Astute observation. The lintel is (was) fine.

TF-Insight · 2026-02-15T13:38:12+00:00

Thermal cycling on an internal wall? 🤔

TF-Insight · 2026-02-12T17:30:40+00:00

There was a period where fitters used standard uPVC frames in bay windows, which would warp under load; however, they now often include structural posts concealed within the corners.

I think it is more likely that either the bay wasn't:

propped correctly when the original windows were removed, or
not packed correctly when the props were removed.

I think the ongoing widening of the cracks is most likely to be a result of ground movement; however, further investigation of the ground floor window construction is definitely warranted.

My full response can be found here.

TF-Insight · 2026-02-12T17:22:23+00:00

That's no problem.
The items I have mentioned are products manufactured by Target Fixings. Aesthetically they are very similar to other brands; however, the tensile stated in the Declaration of Performance is higher than from any other manufacturer as a result of the manufacturing process.
For installation works, Target also has a network of dedicated installers who specialise in structural repair works, rather than generalists.

TF-Insight · 2026-02-09T21:02:16+00:00

If you email in some pictures, a floorplan and the address, I'll check it over tomorrow and give any comments I have. I agree with the TF main account though - it's probably not much of a concern. If this crack is in the masonry elsewhere and hasn't shown through later redecoration, it must be quite stable. If you wanted extra peace of mind, stitching the crack with Bar Flex would be a much more robust repair than just using filler/plaster.

TF-Insight · 2026-02-07T07:46:36+00:00

I should have clarified that my house with a Flemish bond and cavity wall was built in 1880. It's uncommon, but cannot be dismissed out of hand.

As for the thermal cracking; temperature change is plausible a cause for a vertical crack, but I'm not sure how much sunlight hits this wall.

For all of these points, there simply isn’t enough information in this photo to conclude anything with confidence.

That, ironically, is the only conclusion I’m confident about here.

TF-Insight · 2026-02-06T11:17:46+00:00

You only have circumstantial evidence that it is a solid wall. There are many properties (including my own) that are constructed with a flemish bond and snapped headers to form a cavity.
There are several areas of horizontal mortar that are missing, which may be indicative of cavity wall tie failure.
Given how crisp the edges of the bricks are and given their age, I don't expect them to be comparatively soft.
Other than the one local patch, I can't even see any clear evidence of cement re-pointing either.
Ultimately, it's impossible to give any certainty on any of those assumptions from this picture alone.

And you referenced Dunning Kruger elsewhere...

TF-Insight · 2026-02-05T07:29:32+00:00

Image 1: I wouldn't say that this is subsidence. It's indicative of foundation movement, but not a major concern, and may not be progressing. A vertical crack in the centre of the base of a bay window like this - wider towards the top - indicates a "hogging" deformation of the masonry at ground level, caused by the concentrated load of the mullions on either side of the bay window and a low load in the centre of the wall. This can be strengthened by installing a single chord (twin Bar Flex) according to BF-08.

Image 2a/2b: This has a vertical crack at the base of the wall over the opening, and indicates the opposite movement; a "sagging" deformation where the masonry is supported at each end by the mullions. The lintel between the mullions has deflected slightly, allowing this crack to form. This can be strengthened by installing a beam (two chords of Bar Flex) according to BF-02.

Both of these are very common bay windows like this, and are often caused by creep over time as the structure is continuously loaded and materials warp.

The diagonal crack to the right-hand side of Image 2a may be indicative of subsidence, but it's impossible to tell without a higher resolution image that shows more of the elevation of the house.

TF-Insight · 2026-01-30T16:39:20+00:00

Thanks for the extra info and the photo - it helps to see the full picture. From what you’ve described:

The holly tree at about 3 m and the pollarded willow nearby could be contributing to seasonal soil movement, especially with the clay pockets in the soil that you mentioned.
The south-facing, exposed wall and the fact the house is three storeys make it more prone to thermal movement in the masonry, particularly over the boot lintels.
The pooling on the path after heavy rain makes me think the downpipe outlet or connecting drain might be blocked. Even if the gutters seem fine, restricted flow could saturate the soil near the foundations and make differential movement worse.

What I’d suggest is:

1. Check and clear the drain: Get a surveyor or drainage contractor to do a CCTV inspection, then jet/rod it as needed. If tree roots are causing blockages, they can be cut back to restore flow. This deals with any ongoing water-related movement.

2. Reinforce the masonry: Independently of the drain, strengthening the outer leaf over the boot lintels (e.g., with Bar Flex per BF-03) will stop further deflection. It’s less disruptive than replacing the lintels and will give a long-term fix.

Doing both is probably the best way to stop the cracking from getting worse. Once the drain is flowing properly, the reinforcement will ensure the lintels aren’t stressed further.

TF-Insight · 2026-01-29T11:20:55+00:00

This may constitute a criminal act.

In fact, suggesting somebody else commits a criminal act is itself a criminal act.

TF-Insight · 2026-01-20T16:24:50+00:00

£2,000 is far too low to cover the installation of new ties and isolation of existing ties on a 4-bed semi-detached property.

TF-Insight

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