Kitchen extension on slope over terrace

[liftfan]

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,

 

[Notch7]

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

The cheapest option is to remove the existing terracing, or at least the parts in the way.

You need 150mm void below block and beam, which means ground level will need to be roughly 450mm below FFL.
At either ebd, you cheapest option is to remove terracing and trench out for foundation. You could do pad and steels encased in concrete, but the extra work and cost of SE cslcs means its not worth it.

If you want terracing beyond the extension you could fit block and beam, with the beam resting on the outer skin of the extension.

 

[Leofric]

How about getting an architectural designer involved to prepare drawings showing the construction required to comply with Building Regulations. The structural engineer will deal with structural matters ,obviously, but they won't specify/draw all the construction as required for the builder and the bldg. regs application. As far as any other ideas go, there are always various forms of construction that can be used for walls , floors and roofs etc.

 

[^woody^]

The extension, and extension foundations are separate to any raised deck/patio/terrace that will be around it. A suspended floor would be normal for any extension on a sloping site.

 

[liftfan]

Thanks for the info.

I’ve done a bit of digging and the existing retaining wall looks to have fairly substantial footings. I’m now thinking it would be easier and cheaper just to build off that instead.

Would it be ok to span across from the house to the wall using a concrete lintel as shown in blue in the picture. The span is 1.3m so minimum 1.6m lintel?

On top of the lintel would be brickwork to the existing dpc on the left of the picture.

The overall construction would be a steel goalpost sitting on top of that old retaining wall but built up to the existing DPC.

Obviously needs structural engineer input but I’m just after some practical advice.

Ta.

 

[Leofric]

Aren't you going to apply for building regulations approval with architectural working drawings

 

[liftfan]

Yes I’m going to do the drawings in consultation with the engineer. I designed and built the extension on my last place and have done the drawings for other aspects of this renovation that required planning permission.

Just wondering if anyone has a clever solution to this little problem rather than just removing the whole lot!

Cheers!

 

[Notch7]

I’m just after some practical advice

It could well be cheaper to remove the existing and start from scratch.

 

[^woody^]

wall looks to have fairly substantial footings

Substantial may not be the same as sufficient.

And the width of that in the photo, looks nothing like the width of that in your drawing. Generally it's a waste of time trying to build on existing things and being constrained if it is nothing like the size of what you want or could potentially acheive by building from scratch

 

[liftfan]

Yes, all fair points. It’s more the how I would do it rather than the why!

I’m thinking two 140mm deep by 100mm concrete lintels could be used to span the gap then build on top of them.
On the side I’m looking at there is only a small wall to build with a window above. I could use timber frame for a the wall so that side would not be carrying much weight anyway.