Kitchen Extension on slope

[Lift span]

Hi All,

 

I’m trying to figure out the best way of building my rear extension.

 

Due to the sloping ground I’m thinking of just building a wall approx 6m long. Then using 3m beam and blocks resting on that wall out from the existing kitchen wall. Then, a steel frame with a flat roof with a rubber covering. 

 

However, due to the existing terracing, I’m not sure how I would build the sides as I would like to avoid removing the existing terracing. I was thinking of concrete lintels to act as a bridge?

 

I’ll have to get a structural engineer involved but I wondered if anyone had any better ideas.

 

Thanks,

 

 

[Piers]

It all sounds quite heavy duty to me.

 

Have you considered building using timber frame?

 

You could use helical pile foundations which require no digging and no concrete. If access is an issue you don't even need a digger for these as they can be installed with a hand-held machine.

[Lift span]

Thanks for the reply.

 

Timber frame is an option however the extension is mainly glass. 

 

I’m now thinking that I could just  build on the existing retaining wall as I’ve dug inspection holes and the footings are deep. The extension would be 0.5m smaller but the kitchen would still be a good size.  A steel goalpost construction could then be used on top of that wall.

 

I’m wondering if I could use concrete lintels below the DPC level to span the 1.5m gap from the house to the wall and then build on there.

 

See below:

 

[ProDave]

With SE input, you might be able to cantilever out from that existing wall to get the size you want.  He would want to inspect the foundations to satisfy himself of their load bearing capacity and indeed I am pretty sure building control would only allow you to build up from that with calculations from a SE.

 

the foundations are probably deep because the site probably sloped originally and the level terracing you now have is probably all made up ground.

[Lift span]

Thanks for that ProDave.

 

We probably don’t even want to go beyond the wall. I think on top of the wall is all we need for space. 

 

You have hit the nail on the head though as to why we may have problems going out further. I reckon it is all made up ground so we would have to go very deep or use an alternate expensive foundation system.

 

How would we bridge the gap over from the house to the retaining wall though?

[Russell griffiths]

Looking at the pic the garden wall has some steel bolts in it, these where either put in to prevent it tipping or have been put in after it has moved. 

I cant see for the life of me how any structural engineer would want to qualify that that wall is good enough for a new build extension 

i would rip the lot out and get it properly designed. 

You say the foundations are thick, but that’s your opinion, on that slope I would want a minimum of a 1m deep below the bottom of that wall. 

As a massive stab in the dark your original computer pic looks to me to be a nice glass box with flat roof, build cost £25,000.