Conservatory Foundations and Footings - what should they be installing?

As most conservatories are exempt from Building Regulations approval or inspection, there is no set standard you can quote for the conservatory foundations or footings. In other words each conservatory supplier and installer will construct what they think will be suitable foundations for the conservatory.

As they are a business designed to make money, they will want to maintain or improve on any margins on the job any way they can. It has been my experience when acting as an inspecting surveyor for client who has had a failed conservatory extension, that most of their sales specifications will be very vague and lack any real detail on what they will be installing for the conservatory foundations and footings.

This means that they can install whatever they want or consider to be just adequate to support the conservatory as there is no set standard or specification they are following. Most homeowners would not know the various types of sub-soil that demands different types of foundations being depth and size.

This is perhaps why out of all the complaints for building failures or defects, conservatories account for the largest proportion. A conservatory footing foundation only needs to settle by 15mm in order to pull it away from the existing house wall for it to be a failed and defective building.

So what should be the correct foundations for a conservatory? Well look at it like this. The Building Regulations require a minimum of 1M deep foundations for controlled building works and for most sub-soils this is sufficient and conservatoires would be no different. Therefore ask you conservatory supplier if their foundations will be down to this 1M depth as a minimum starting point. If not ask them why and what their engineered solution is for having lesser depths foundations.

Many conservatory installers have installed footings or foundations at around the 600mm depth and this can work if the sub-soil is exactly the same at the 1M depth so the theory is why go any deeper? This logic works well if the sub soil is virgin soil and of good load bearing capacity with no shrinkable clay content eg - chalk. Most conservatory foundations are trench fill of around 450mm x 450mm size.

Some conservatory installers have built a combined conservatory floor and foundation in one pour which is usually a reinforced raft foundation and these can work well without the need for going deep for traditional foundations and footings. However, every conservatory raft foundation should be engineered designed and based upon the type of sub-soil on the site.

If you have doubts as to what the exact foundations or footings will be for your own conservatory, simply ask them for specific construction details and ask them the relevant questions. Remember that any deficient conservatory foundations that may cause excessive settlement will probably not reveal itself until many months afterwards when you have already parted with your money. Why not consider employing your own site visiting surveyor to monitor and approve the works during constriction? It could be money well spent and avoid corner cutting.