So if you're anywhere in the UK right now, you really don't need
me to tell you what the weather's like.
No, just look out the window. Exactly.
It's February 2026 and the the weather charts we're looking at,
they're just a solid wall of blue.
It has been absolutely relentless.
Relentless is the perfect word. And you know, usually when we
talk about this kind of weather, this constant soaking rain, the
conversation's pretty surface level, isn't it?
Oh yeah, it's all about the commute being a disaster.
Or, you know, the park turning into a swamp.
Right, the usual complaints. The national pastime.
But for this deep dive, we're going, well, we're going way
below the surface. We've got a stack of
geotechnical surveys, climate data, engineering reports, and
they're all flagging something a bit more significant.
We're talking about what all this water is actually doing to
the ground under our feet. And that's a really important
distinction. This isn't just about water
falling on the ground. This is about how the ground
itself reacts when it's been waterlogged for for months on
end. And specifically, it's about
this collision right between our 21st century climate and, well,
19th century houses. Precisely.
That's the core conflict we're unpacking, right?
You have hundreds of thousands of homes in London and the
southeast. All those beautiful Victorian
terraces, the Adordian semis, the houses built between what,
1900 and the 30s? Yep, and they're all sitting on
this geological ticking clock. The London Clay, the.
London Clay. That's the antagonist in our
story today. OK, but before everyone starts
staring nervously at their skirting boards, let's just be
clear The sources we're looking at, they're not predicting A
catastrophe, are they? No, no, not at all.
And that is a crucial disclaimer to make right up front.
This isn't about alarmism. I mean, these houses have stood
for over a century. They've been through world wars,
the Blitz, plenty of bad winters.
They are robust. What we're discussing here is
more of a professional risk assessment.
It's about shifting our mindset away from just maintenance and
more towards, you know, structural understanding.
So it's about knowing the mechanics of the soil to keep
them standing for another 100 years.
Exactly. It's not magic, it's just
engineering. Right.
So let's start with the engine driving this whole thing.
The atmosphere, the climate data and the sources is, well, it's
pretty stark. It is.
It's a fundamental shift in the baseline.
If you look at the records, and the UK has amazing records going
back over 120 years. Yeah, winters now are roughly 10
to 20% wetter than they were in the early 1900s.
And that's not a fluctuation, that's a trend.
And the physics behind that is it's something called the
Clausius Clapeyron relation. It sounds like a mouthful,
doesn't it? But the concept is actually very
simple. It's just that warmer air holds
more moisture. The rule of thumb is for every
1°C of warming, the atmosphere can hold about 7% more water. 7%
That feels like a massive compounding factor.
It's not linear. Not at all.
You warm the planet, you're essentially loading the dice for
a heavier rainfall. The atmosphere is a bigger
sponge. And when you squeeze a bigger,
wetter sponge. More water comes out, but
there's a second factor that the 2026 data really highlights.
And I think this is even more critical for homeowners.
It's the delivery. You mean the weather system
stalling the blocking patterns? That's it.
The jet stream is well, it's wobblier.
So instead of a storm blowing through in 24 hours, it just
parks itself over the Southeast for a week.
So the ground never gets a chance to dry out.
It never gets that crucial intermission.
It's just soak after soak after soak.
And this is where the geology, the London clay, becomes the
villain of the piece. Eocene era deposits.
It's all across S northwest London.
In the geotech world, this stuff is famous.
Maybe infamous because it's highly plastic.
OK, when you say plastic, you don't mean like a plastic bag?
You mean it's moldable? I mean, it's reactive, its
volume, its strength, it all changes depending on how much
water is in it. Now, usually when people think
of clay and rain, they think of heave.
Yeah, that's the classic idea, right?
The ground gets wet, it swells up and it pushes the house up.
Which can happen, yes, but the sources are pointing to
something different. In a year like this, with such
prolonged deep saturation, we're seeing a loss of sheer strength.
This was the real aha moment for me in the reading.
It's not just moving up and down, it's it's losing its
integrity. Precisely.
Think about walking on a clay field in summer.
It's like concrete. In a normal winter, it's sticky.
But in a winter like this one, you sink.
You sink. Your boot goes 6 inches into
this, the slurry. The clay is softened.
It's turned to soup. But the bearing capacity just
drops. The ground literally can't
support the weight it used. To And that's where the age of
the house is the critical factor.
You know, if we were talking about a modern building,
something like the Shard, it's sitting on deep piles.
Right, they go down meters and meters.
They bypass the soggy layer completely, but we're not
talking about skyscrapers. We're talking about the classic
Victorian terrace. Which is a heavy, brittle brick
box and crucially it is very shallow foundations.
I was actually amazed by the numbers.
The reports say strip foundations are only maybe 300
to 600mm deep. Sometimes less.
That's. I mean, that's barely a foot or
two in the ground. By modern standards it's
negligible. You're sitting right in that
zone of maximum moisture. Change the Victorians and you
can't blame them. They were building for their
time. They just assumed the ground was
a constant. They dug down till it felt firm,
laid some bricks and stopped. They never imagined a climate
where that firm clay turns to soup for three months straight.
And the house itself is so rigid.
Solid brick walls, no steel frames.
Nope. It relies on gravity and mass to
stay put, and it's all held together with lime mortar.
Now, I've always heard that lime mortar is a good thing, that it
lets old houses breathe. It is good.
It's what we call sacrificial. It's a cushion.
It allows for tiny movements without cracking the bricks.
But even long has a limit. It's not elastic.
It's not elastic, no, So the ground softens unevenly and say
there's a leaking drain on one side of the house.
So 1 patch of clay gets softer than the other.
Exactly. You get differential settlement.
One side sinks into the soup, the other stays put.
The whole box twists. And that's when you see the
cracks, the stepped cracking around the windows and doors.
That's the building trying to tell you it's being stressed.
The masonry is shearing. There is another layer to this
in the research that honestly, it gave me the creeps a little
bit. It's what's happening under the
floorboards. Yes, the suspended timber
floors. A classic feature.
And the mechanism is just terrifyingly simple.
These houses have air bricks to keep air flowing underneath.
But in a year like this? The ground level is so high and
there's so much surface water that those vents get blocked or
even submerged. So the void under your house
basically becomes a damp cave, a reservoir.
You might not have water coming through your carpet, but
underneath in that dark space, you've got standing water for
the very least 100% humidity. And that moisture has to go
somewhere. And timber is like a Wick, the
joists just absorb it month after month.
You're not just looking at warped floorboards anymore, you
are creating the perfect conditions for wet rot or dry
rot. Which is a silent killer for a
house. You don't know what's happening
until. Until the piano goes through the
floor or you get that musty mushroomy smell that just will
not go away. It's a biological attack
triggered by a hydrological event.
OK, so that's a grim picture for winter.
Soft ground, sinking foundations, rotting joists.
But let's play this forward. Eventually, the rain has to stop
and the forecast suggest we might flip into a hot, dry
summer. Which brings us to what the
insurance industry calls the double whammy.
This is the scenario that keeps structural engineers up at
night. Because you'd think drying out
is good, right? The ground gets hard again, the
sinking stops. Problem solved.
You would hope so, but clay has a long memory.
When it dries, it shrinks, and because it's currently so
saturated, the potential for volume reduction is huge.
So it's like a sponge you leave on the side of the sink, It just
shrivels up. Exactly, and this is where
vegetation really comes into play.
The sources are very clear about the role of trees in this phase.
Because trees get thirsty in the summer.
Very thirsty. A large tree, an oak, a Willow.
It's basically a hydraulic pump. In a hot summer, that tree is
fighting to survive. And it will aggressively pull
moisture from the soil. We call it matrix suction.
So the tree is literally sucking the water out from under your
house. Aggressively and unevenly.
If you have a big tree near the front of the house, that area
dries out and shrinks much, much faster than the back.
So in winter the house sank because the ground was too weak
to hold it, and in summer the house sinks or twists because
the ground is physically pulling away from it.
The. Cracks might look the same to
you, but the physical cause has completely reversed.
It's a brutal cycle of fatigue. Expand contract.
Soften Harden. You're just bending a paper clip
back and forth. Eventually the masonry, the
warder, it gives up the snaps. So.
If I'm a listener standing in my hallway right now and I'm
staring at a crack, how do I know if it's just old house
charm or something much worse? That's the $1,000,000 question,
isn't it? We need to be precise.
Subsidence is a very specific insurance term, but really every
old house moves a little. Yeah, doors stick in the winter.
That's normal. That's character.
It becomes a claim when the distortion is permanent or it
affects how the house works. If a crack is jagged, wider than
a pound coin, maybe 3mm, or if you can see daylight through it,
that is not character. If a door frame is so skewed you
have to shoulder barge it open, that implies the geometry of the
house is changing. And the advice in the articles
is interesting because the first line of defense isn't call an
engineer, it's check your gutters.
Sounds so boring, doesn't it? But it's the most important
thing you could do. It's all about water management.
How so? A blocked, overflowing gutter is
dumping hundreds of liters of water in one concentrated spot
right next to your foundation. You're basically creating your
own mini subsidence event. So fix the gutters, make sure
patios slope away for the house, keep the air bricks clear.
Control the variables you can control.
You can't stop the rain, but you can stop it pooling against your
brickwork. Let's talk about monitoring,
though, because the problem with cracks is psychological.
You see one, you panic, you stare at it every day and you
think, is that bigger? And our memory is just awful for
that sort of thing. Anxiety makes it worse.
You convince yourself it's moving when it isn't.
Right. And this is where the source
material brings up a tool called Crack Guide.
It's an app from Auk company Survey All Now.
We're not selling it, but the tech is fascinating.
It uses Lidar. It's a brilliant use of consumer
tech. The newer smartphones have Lidar
scanners built in, you know, for photography and AR games.
This app just repurposes that sensor to map the surface of a
wall in 3D. So it's not just taking a photo,
it's measuring the depth and the width of the crack.
It creates a digital baseline. You scan the crack today, you
scan it again next month. The AI overlays the two scans
and tells you with sub millimeter precision if and how
it's changed. That completely changes the
conversation instead of calling a surveyor and saying I've got
bad vibes about this wall. You hand them a data log.
On February 15th it was 2mm. On March 15th it's 2.5.
That trend line is gold dust for an engineer.
It tells you the rate of movement.
Is it accelerating? Is it stopping?
We can diagnose the root cause so much faster.
It basically outsources the anxiety to an algorithm.
And that's key. Often the app will show you that
the crack hasn't moved even though you were sure it had.
That's Peace of Mind. So to pull it all together, then
we've got a climate loading the dice with more rain, we have
this very sensitive geology that reacts to it and an aging
housing stock caught in the middle.
Sound daunting when you stack it up like that, but I think it's
important to remember how resilient these buildings are.
They're tough old things. They survived the blitz, the
Great freeze of 63, the drought of 76.
They are not fragile. But they're not invincible.
The key phrase from our sources that stuck with me was informed
observation. Yes, we have to stop viewing the
ground as this static concrete platform.
It's not. Especially not London clay.
The ground is a living, breathing participant in the
life of the building. It swells, it shrinks, It's
soft. And it's the climate changes
that participant is getting a lot more active, a rowdier
neighbor. Right.
So our relationship with our homes has to evolve.
We have to be active stewards, not just passive occupants.
We have to understand that water cycle.
A shift from home ownership to home partnership.
I like that and using the tools you have, whether it's a ladder
to clear a drain or an app to track a crack.
Here's a thought to leave you with then.
If our homes are becoming more dynamic and our ability to
monitor them is becoming so much more sophisticated with AI, are
we moving to a future where the house effectively self diagnosis
where your wall sends you a notification saying my
foundation is slipping, please check the oak tree.
The smart home of the future might be less about voice
activated lights and more about structural survival.
It's a fascinating, if slightly unsettling thought.
Something to think about next time you're out in the rain
clearing those air bricks. Stay dry.
Keep watching the walls. And thanks for listening to this
deep dive. Take care.