At first glance, the answer seems obvious. Every building needs something to stand on. Even a garden shed will shift and buckle if you plonk it straight onto grass.
But conservatories are not quite houses. They’re lighter. Less formal. Built more for the sun than the structure. And that’s where the confusion begins.
If you’re thinking about adding a conservatory – that bright room at the edge of the home where mornings start slow and evenings stretch out – you’ll want to know how deep it needs to go before it starts going up.
Yes, They Do
A conservatory needs foundations. Maybe not the same depth as the main house. But something solid.
Without foundations, the room moves. Slowly at first. Then all at once. The Glass cracks, the doors jam, and water sneaks in.
It doesn’t matter how lovely the frame is, or how neatly the floor’s been laid. If the ground underneath hasn’t been taken seriously, it will all come undone.
How Deep Should They Be?
There’s no single answer. Soil changes. Trees grow. Water tables rise and fall. But a few basic rules tend to hold.
- Strip foundations: The most common. A trench is dug – usually 450mm to 1 metre deep – and filled with concrete. The walls then rise from there.
- Trench-fill foundations: These are similar, but the trench is filled almost entirely with concrete. They are faster to build and require less brickwork.
- Pile foundations: Used where the ground is poor – full of clay, peat, or made-up rubble. Concrete columns are drilled deep into the earth to reach something stable.
Builders will usually test the soil before deciding. If they don’t, ask why. Guesswork isn’t good enough.
What Happens If You Skip It?
It might seem tempting. Especially if you’re told the conservatory is “lightweight” or “modular” or “only temporary.”
But it doesn’t take much movement for glass to crack. Or for a roof panel to come loose.
Even a small shift in the ground can ruin the fit of the doors or tilt the whole structure ever so slightly—enough to notice, enough to regret.
Worse still, insurance won’t cover problems that come from bad groundwork.
You don’t need to build a nuclear bunker. But you do need something better than paving slabs and crossed fingers.
Planning Permission and Building Control
You don’t usually need planning permission for a conservatory. As long as it’s single storey, under a certain height, and not too big, you’re probably fine.
But Building Regulations still apply. And that includes rules about foundations.
- The structure must be stable.
- It must not affect the main house.
- It must not cause heat loss or drainage issues.
If your conservatory joins your home and you plan to knock through the wall, the foundations must meet the same standards as the rest of the house.
No shortcuts.
Think About Trees
It’s easy to forget what’s underground. Tree roots can reach further than you’d think – three times the height of the tree in some cases.
If you have large trees nearby, your builder should consider this. Deeper foundations may be needed to avoid future movement.
And don’t assume a stump is harmless. Roots don’t rot quickly. When they do, the soil sinks. The building goes with it.
Conservatory Base Options
You’ll hear different terms from different builders. Some talk about “dwarf walls” or “floating floors.” Others will push for concrete slabs or pre-fabricated bases.
Here’s a simple breakdown:
- Traditional base: Dig, pour, build. Long-lasting. Best for uneven ground or large structures.
- Concrete slab: Quicker, but only good if the ground is flat and solid.
- Steel base systems are fast to install, sit on adjustable legs, and require less digging. However, they are usually more expensive.
Don’t pick on price alone. The cheapest option now might be the most expensive later.
FAQs
Do all conservatories need foundations?
Yes. Even small ones need a stable base. The depth and type will depend on the ground, the size of the conservatory, and how it connects to the house.
Can I build a conservatory without digging foundations?
Technically, yes – but it’s a false economy. Without proper foundations, the conservatory is likely to shift or crack over time.
How deep should foundations be for a conservatory?
Usually 450mm to 1 metre, but it depends on the soil and nearby trees. A builder should assess this before starting work.
Do I need building regs for a conservatory?
If it’s separate from the house, usually not. But if you’re knocking through or adding heating, insulation, or drains – then yes.
Can tree roots damage my conservatory?
Absolutely. They can dry out clay soils or rot away and cause sinking. This needs checking before you build.
A conservatory can be the brightest part of your home. A place where winter mornings don’t feel quite so grey.
But only if the ground beneath it holds steady.
Get the foundations right, and the glass will stay true. Skip them, and you may end up rebuilding from the ground up – quite literally.
Planning a Conservatory? Start from the Ground Up
Book a site visit today and get expert advice on the right foundations for your conservatory. No guesswork. No shortcuts. Just solid ground and honest answers.
