Foundations for Building a Conservatory


A conservatory is one of the most popular and useful ways of extending the living area of a home. Available from either a specialist company or bought from a larger DIY store, they can often be installed without the need for planning permission or detailed building regulations. Although the use of an architect or structural engineer is not mandated, thorough planning needs to go into the build to avoid future problems. As with any construction project, the end result will only be as strong as the foundations upon which it is built!

What is a conservatory?

The generally accepted definition of a conservatory is a structure having at least 75% of the roof and 50% of the walls constructed from translucent material. This is partly based on the rules for a house extension that does not require planning permission. If planning permission is to be waived, then additional requirements are:

  • The floor area must be less than 30 sq m.
  • It must be built at ground level.
  • The conservatory must be separated from the main building by good quality lockable doors (and windows if present).
  • There must be a separate, thermostatically controlled heating system.
  • There can be no sanitary or drainage equipment, such as a sink or toilet.
  • The glazing must use appropriate toughened or safety glass.
  • The conservatory is not connected to a listed building.

The Planning Portal, a joint venture between the Ministry of Housing, Communities and Local Government has a section on building regulations for conservatories in England and Wales, where you can find out more detail.

Does a conservatory need foundations?

Legally, you do not need foundations for a conservatory, however we HIGHLY recommend that you have them! Building a smaller conservatory without foundations might seem like a good way to reduce the project spend, however it is likely to bring you far greater problems and costs in the long term.

Despite their construction, even small conservatories are heavy and the downward force they exert directly below the walls. This will quickly cause the ground to compress and for gaps to form, allowing water ingress and structural instability. Whilst shallow foundations may solve this problem, they will be more prone to general subsidence, including the seasonal expansion and shrinking of clay soils.

How deep do conservatory foundations need to be?

The exact depth of your foundations will vary, depending on the nature and stability of the soil. As a guide, 600mm depth may be suitable in hard and stable ground, 1000mm for softer soils with up to 1500mm in particularly fragile or problem prone areas. The government building regulations have more detail on best practice in this area.

The aim of the foundations is to provide frost proofing, vertical and lateral stability for your conservatory. Getting your foundations right is vital to the ongoing and stress-free enjoyment of your new living space!

Common problems with conservatory foundations

There are two common problems when planning for the foundations of a conservatory. Trees and drains.

Trees have root structures that can cause significant soil shrinkage, especially in dry spells. Whilst this risk can be mitigated by the use of deeper foundations, trees will also have a root protection area around them, designed to ensure the tree’s ongoing viability and health. Together with the risks from branch or tree collapse in strong winds, trees can be problematic for conservatories and their foundations.

Drains and sewers form a different problem for the siting of foundations. The need to allow the ongoing functioning of these vital services means that you cannot build directly over a manhole. Also, you cannot build within 3 metres of a public drain or sewer, without approval from the local water authority. If your foundations are in close proximity to public sewers, you should contact your local water authority before you start any work. There is often an option to move manhole covers or drains, but there is likely to be a cost involved.

How can ABC Anchors help?

We hope we have explained why good foundations are the key to a long and happy relationship with your conservatory. In the majority of cases, simple concrete foundations of the appropriate depth will be all that is required. In areas where subsidence or soil stability is an issue, ABC Anchors offer a range of solutions that can help. Give us a ring on 01380 850885 to see how we can be of assistance.

We already helped one customer with their new conservatory. And they were very happy with the result. Read the full case study here.