One common question that’s often asked is, How deep should conservatory foundations be? It is a difficult question, there is no distinct standard on conservatory foundations. Even in the UK’s Planning Portal, there are plenty of limits on heights, sizes, boundaries and materials, but no defined depth for foundations. In some cases a Building Control approval is required for a conservatory extension, they will apply guideline standards to which the local authority Building Control department work, but again this is not the same for all cases.

Do I need foundations then?

In short, Yes. Even a very lightweight conservatory needs a well thought out foundation. Heres what we think you need to consider when building a conservatory footing;


1. Size matters.

A deep enough excavation, based on the size and weight and construction of your conservatory. For example, a wooden single-storey lean-to may only need up to half metre base, with proper damp proofing. Whereas an Orangerie style conservatory will need a much deeper foundation of say 900mm and around 40 to 80mm depending on the walking above being single or double depth.

clay soil conservatory

2. Ground Conditions

This can affect the size and shape of your foundation. It all depends on your soil type, if your area is a greenfield or brownfield development, and soil erosion or if your conservatory is built on an incline.
Clay soil, for instance, holds onto water a whole lot more than say chalk and is subset able to expansion and shrinkage. Without these being addressed, you could end up with cracks forming, subsidence or even worse total failure.

tree roots

3. Trees

Yes trees, If you build near a tree you need to consider the roots. Even if you dig down now and don’t see any now, ask yourself if it is going to affect the conservatory base in the future.

wet wall conservatory

4. Nearby drains and the water table.

You don’t want water seeping in, so building above the water table and having sufficient drainage helps. A layer of damp proofing is advised in any case.

Complete Project Management (CPM) has a team of Conservatory specialists working across Devon. We are more than happy to visit your property and see what sort of work is needed. Our specialists will provide a free quotation and expert advice.

So, is there anything you don’t do? No. We do it all.

If you require our services for any conservatory, extension or General building then contact our helpful office manager Donna on 01392 925 045 or email And we will be able to book a convenient date and time for your quotation. Contact us today for your FREE no hassle Same Day Quotation.