Conservatory Foundations Should Be Determined By Ground Conditions, And Not By You!

Published: 25th February 2011
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The ground conditions on which a conservatory is built have a critical effect on the lifespan of a conservatory. Poor base-work can lead to a variety of problems from leaks to the risk of full-scale collapse. This article explains a series of techniques to identify problems before the base is built.

This is an area where surveyors need to be actively vigilant - get it wrong and the associated costs to rectify could be astronomical, not only at point of build, but years later if the conservatory moves or subsides and is covered by your warranty.

Your company will almost certainly have clauses in the contract to cover unforeseen. In other words during the build if you come up against bad ground conditions, and you need to carry out more costly foundation works, you can go back to the customer and ask them for more money to cover the costs of any additional unforeseen works.

In the event that additional works are required, your customer could refuse to agree the additional payment, leaving you with the choice of carrying out the extra work at your own expense, or cancelling the contract and returning the site back to its original status again at your own expense.

What choice do you make, especially if you have ordered frames and roof?

Both the options above will massively reduce your profits and in some cases you will make a total loss.

Ground conditions can be deceptive and many sales-people may miss tell-tale signs. You won't really know what's in the ground until you dig a hole in the ground, or employ a professional company to carry out tests and a ground survey.

The choice of foundation design is ultimately your call. It must be of correct design and sit on suitable bearing material.

I have highlighted some precautions you can take during the survey process to minimise the chances of getting it wrong, and increase your chances of getting it right.

Gain as much information off the customer and neighbours as you can on survey, information at this time could determine the final foundation design and cost.

Ask the customer if they have any knowledge of the construction of their property. Have they got any architects drawings, do they have their NHBC details?, did they see the property being built, do they know what type of foundations were used and how deep, were they standard strip foundations, deep strip, trench fill , raft design, or was it piled foundations etc?

Speak to the customer or neighbouring house owners to see if there have been any problems on extensions or conservatories within close proximity of your proposed build.

Look around at the general lie of the land, try to determine if the ground is made up or filled ground where the conservatory build is proposed. Are there big drops or rises or steep slopes to neighbouring properties to help identify made up ground? Was it reclaimed land?

Are there any drainage runs under the conservatory? Look to see if there is pattern glass above identifying a bathroom, look for boxed in soil vent pipes inside lower rooms identifying drainage. Is there any kitchen drainage in the close vicinity? Check invert depths and flow directions of any manholes. There may not be manholes in your customer's garden, so check in properties either side.

Any gas appliances near the proposal which may indicate gas mains services below ground.

Take any trees in the vicinity into consideration when designing foundations.

Does the customer know if radon gas is present in the area and was a radon barrier built into the house? Even if it is an old house, it may not have a radon barrier built into the foundations but you will still need to build a radon barrier into your conservatory to protect your customer.

Speak to the house builders

If the builders are still on site speak to the Site Agents and ground workers they will have all the ground and foundation information you need, and in general are very helpful and will provide you with ground information. Most house builders will want you to get it right. If they are not forth coming with the information for you, they have to provide it to the home owner, get the home owner to contact them.

Contact the NHBC

Speak to the NHBC on behalf of the customer, they will sometimes provide you with the required foundation information. Again if they won't provide you with the information, they must give it to the home owner, get the home owner to contact them.

If you are building near trees you can purchase an NHBC foundation depth calculator - Easy to use. Simply line up a tree height and tree distance, then read off the foundation depth

Contact the local building control officer

You will have probably have dealt with local building control officers in the past, you should have built up a relationship with them. If you are unsure of ground conditions, phone them and ask them what the general ground conditions are in that area is there a high water table? Is it reclaimed land and is there methane present? Is there radon gas present? Has there been any mining activity in the area? What is the composition of the ground locally is it silt, sand, gravel, rock, or are there clay soils present in the area? Ask them if they have had any ground problems on extensions or builds in the close proximity. All of these questions will determine the design of foundation you require. The building control officers generally take quite kindly to you enquiring and will help you and offer advice, as they can see you are trying to act professionally and build correctly. They would normally rather help you rather than have to become involved in any future disputes.

Contact your local piling company

You will probably have used a piling company in the past, they will have in depth knowledge and locations of bad ground on record and again depending on your relationship with them are normally only too happy to provide you with any information.

Finally, Remember you don't determine the foundation design required! The ground conditions do!


Steve Williams worked as a Senior Installation Manger at the largest home improvement company in the UK for over 10 years. He now works as Business Development Manager at RPS RoofWright, developers of the World's Favorite Conservatory Design Software. For a FREE trial of our professional software visit

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