Foundations and bases for Conservatories

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a friend recently bought a conservatory for pennies from the yellow ads paper. hes erected it straight onto his patio which has slabs which cant be more than about 3in thick. it all seems solid enough for now.

ive had a look into diy conservatories and fancy having a go myself maybe something around 3m square. Id like to do the foundations and base properly though. Ive read varying opinions of how deep the foundations should be. have you guys any opinions on how deep foundations should be and is it possible to dig too deep and weaken the house foundations?

 

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have you guys any opinions on how deep foundations should be and is it possible to dig too deep and weaken the house foundations?

Yes you can undermine your house foundations, which can result in your house walls settling and a variety of cracks forming..
Just match the depth/type of your current foundations with the new.. (dig a trial hole next to the existing footings if unsure of depth)

In the end a conservatory is not an extension to the property, it is not a livable area of the house, it will get too hot in the summer and freeze in the winter.. conservatory foundations depend on how long you think the conservatory will last.. your friends conservatory on paving slabs will probably sink/move in the next 5 odd years and need some rebuiling/repairs.. most band new conservatorys last from 10-25yrs depending on quality.. most house extensions are built to last 50 years+..

That said, proper foundations depend alot on what natural material they found onto.. so are you on clay, chalk, peat, limestone, aluvium, sand, gravel, silt, sandstone, glacial boulder clay or other?