Get a Price or Request a Brochure

Do Conservatories Need Foundations?

A well-built conservatory is only as strong as its foundations. Without them your conservatory could turn from your dream addition, into a nightmare. This guide takes you through the different types of foundations.

Conservatories need foundations to transfer their weight to the ground. This keeps them safe and stable, even if the ground moves. Without proper foundations, your conservatory could have uneven floors. It could also get damp or even sink.

Conservatory foundations are also subject to some building regulations. If the conservatory has open access to your home and uses the same heating system, then it needs foundations. In this instance, you must lay foundations or your build will be illegal.

How Deep do Conservatory Foundations Need to be?

Conservatory foundation depth depends on the soil and the conditions around it. On average, conservatory foundations should be at least 1000m deep for a small lean-to. For a large conservatory with brick walls, they should be over 1500mm.

The depth of foundations required determines the conservatory designs and the maximum weight. The weight of your conservatory will change if you add walls or a solid roof. This may mean that older foundations need reinforcing.

What’s the difference between conservatory foundations and extension foundations?

The conservatory and extension bases are the same. But the type of foundation you need might be different. The type of foundation depends on the soil, water table and trees. Other factors include slopes, underground drainage, and neighbouring or existing foundations.

Ground Types and Issues that can Affect Conservatory Construction

Clay soil

You need deeper foundations with clay soil because it holds a lot of water, making it more mobile. Clay expands when it rains and shrinks when it dries. Trees can also drain the water from clay, causing shrinkage and even subsidence.

You need deeper foundations with clay soil to overcome its seasonal movement. Clay expands when it rains and shrinks when it dries. Trees can also drain the water from clay, causing shrinkage and even subsidence.

Mixed soil

A common problem for older properties is debris and rubbish left in the soil from previous work. A lot of debris makes a build harder and, in some cases, more costly. This is because you may need more complex foundations.

Reclaimed soil

Homes on reclaimed land are often built on old industrial sites or marshland. This makes the ground unpredictable, so strong foundations are essential. In these cases, raft or pile foundations are best.


Trees can cause movement in the soil, particularly clay, around nearby buildings. Even if you cut down a tree, dead roots can decay underground and make the ground sink. When you plan your project, consider the size and type of tree and how far it is from your new conservatory.


Take care with drains and manhole covers on your property. If you come across them, contact your local authority for advice. You can’t:

  • Build concrete foundations over a manhole.
  • Build within three metres of a public drain or sewer without approval of a local authority.

You can move manholes and drains with permission from your local water authority. This can be a costly option though. If you do move a public manhole, its new location must be accessible without the need to enter your home.

Conservatory Foundation Types

Different soil types can affect homes in different ways. So, what type of foundations do you need for a conservatory? Here are the four main foundation types and how they work.

Strip foundations

Strip foundations are the most common and cheapest to build conservatory foundations. Concrete strips in the soil, sometimes reinforced, support the walls. These foundations work best in dry soil, or soils with a mixture of gravel and sand.

The minimum width of the foundation should be 450mm but it can go up to 600mm. The concrete should have a minimum depth of 225mm. The deeper you need strip foundations, the more costly it will be.

Trench fill foundations

Trench fill foundations are often used where there is loose soil, a high water table or in heavy clay soil. Narrow trenches are dug down to the depth needed, and then filled with concrete. More concrete means more cost, so these can be more expensive than strip foundations.

Trenches should finish no less than 150mm from ground level. For heavier structures or soil factors, trenches are lined with reinforcing material. This adds stability.

Piled foundations

Piled foundations connect structures to deep, solid soil or rock when the soil higher up is weak. Piles are dug, bored or driven down into the ground. The piles support a concrete ring beam or ground beam that spans from pile to pile.

Piles used on conservatories and extensions include helical piles, driven piles and micropiles. Pile foundations are among the most expensive foundation type. That said, they are also the best type when you need deep foundations.

Raft foundations

Raft foundations use a reinforced concrete slab under the whole conservatory. It spreads the load of the conservatory over a larger area, lowering the pressure on the ground. It requires a structural engineer and is often used if you can’t use deep strip or trench fill foundations.

Conservatory Base

Diagram of the foundation base work for conservatories and orangeries from Anglian Home Improvements

A conservatory base is a ground bearing concrete slab that works with the foundations. An Anglian conservatory base is made up of the following:

  • The bottom of the base must have a layer of well consolidated hardcore that is at least 150mm thick.
  • The 50mm layer of sand blinding forms a cushion to protect the damp proof membrane from damage.
  • Concrete slab: A 100mm thick concrete floor slab provides a solid base.
  • Damp-proofing: A layer of damp-proof membrane covers the base. It stops moisture from getting in through the floor.
  • The floor insulation is 120mm thick. This thickness is required by building regulations in England and Wales. This is 130mm in Scotland.
  • Final layer: A 65mm layer of screed, a mixture of sand and cement, smoothed down before a final layer of concrete.
  • Our conservatory bases come with a 10-year guarantee.

Other types of conservatory bases are used when extra height is needed or for sloping ground. These include steel bases and wooden suspended bases. Other materials have advantages and disadvantages and come with their own costs.

Conservatory Foundations Building Regulations

Building regulations apply to all building work in the UK, including conservatory foundations. To ensure peace of mind, it is crucial to research and select a company with accreditations and guarantees. The extent to which building regulations apply depends on the type of conservatory. Before starting work, contact your local authority. Confirm that your plans follow the rules. You can also check if you are exempt.

Building regulations

Buildings regulations help ensure health, safety and energy conservation. Conservatories built on domestic properties are exempt from building regulations if:

  • At least 75% of the roof is completely transparent or translucent. It is made of glass, polycarbonate sheets, or similar material.
  • The walls are substantially glazed and at least half the area of the walls.
  • The floor must be at ground level and doesn’t exceed 30 metres squared.
  • The conservatory is separated from the house by walls, windows or external doors.
  • Any heating system is independent of the home’s heating system. It has its own separate temperature and on/off controls.
  • The conservatory does not contain any drainage facilities.

Building regulations are different from planning permission but you may need both. Always check with your local authority before work starts. If you get your conservatory through us, we take care of this process for you, so you don't need to worry.

Planning permission

You need to secure planning permission before you lay foundations. If your conservatory is a ‘permitted development’, then you won’t need planning permission. We take care of planning applications for you, included in your quote. Read our handy guide for all you need to know about conservatory planning permission.

How much do Conservatory Foundations Cost?

Conservatory foundations can cost several thousand pounds or more, depending on their complexity. Foundations that need more materials and labour will cost more. Typically, it is common to complete the foundations and main works at the same time.

A quote from us for a conservatory includes the complete base and the conservatory. It also covers the material, survey, and installation costs.

Conservatory Construction with Anglian Home Improvements

We have been installing conservatories to the highest standard for over 55 years. We lay the right conservatory foundations to keep it stable, safe and secure. Our conservatories are custom made and come with a 10-year guarantee.

Looking for inspiration for your home? Discover our range of conservatories and find inspiration.

Made in Britain
10-year guarantee
uPVC Windows Price Match
Want to Speak To An Advisor?
Give our team a call on 0800 014 2106

Get a Price

Up to £250 off when you get a
free no-obligation quote.

Please enter your first name
Please enter your last name

To provide you with an accurate quote, we'll call you to arrange a remote or home visit.

Enter a valid phone number

We'll email you if we can't get in touch by phone.

Enter a valid email address
Enter your house number or name

We’ll use this information to store and process your enquiry

Enter a valid postcode
By providing your details you agree to being contacted under the terms of our privacy policy.