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.