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.
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.
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.
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.
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.
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:
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.
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 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 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 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 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.
A conservatory base is a ground bearing concrete slab that works with the foundations. An Anglian conservatory base is made up of the following:
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.
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.
Buildings regulations help ensure health, safety and energy conservation. Conservatories built on domestic properties are exempt from building regulations if:
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.
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.
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.
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.
