Raft foundation query. Pro' opinion please.

[Bouba]

I have a single storey side shed to my end terrace house which was built in 1969 and was passed by building regs at that time.

Currently built with half skin,stretcher bond,2 metre high on a thin oversite concrete slab. It is below the house floor level, as I can see the full airbrick when i am inside the shed.

1. Area is 1.7 wide and continues till end of house wall at rear.

2. Would I be able to use Raft foundation and build another skin of wall in cavity or will it need to come down and use strip foundation. I would like to use it as a habitable room and bring it to current Regs from building control. Also would like to raise wall height and use proper clay roof tiles. Atm it has plastic roof.

Strip foundation means atleast 600 mm wide footings which leaves very little floor area.

 

[tony1851]

Unwise to build the inner skin off the raft because it is an unknown quantity.

If you did use strip footings, you could probably get by with a 400 wide strip (subject to normal ground conditions) as the extension will be quite narrow, and the loads relatively low.

BTW, won't it be a little narrow for a habitable room?

 

[Bouba]

Thanks a lot Tony. As usual you have answered with your knowledge.

I wish to use it as a study room and a loo, and the other half in as kitchen by removing the internal rear wall. Hope this makes sense. Oh and will be going official route.

 

[noseall]

Can you not add a masonry leaf to the outside and let the existing wall become the internal fella?

 

[Bouba]

Noseal: END of terrace. The current wall sits on boundary next to public highway. Local builder suggested Raft and using some sort of screw ties to tie it to the new wall. Did not seem right though but who am i to decide

 

[jeds]

You don't need a cavity wall. Just dry line the existing brick wall.

 

[Bouba]

Its half brick thick but will be rendered on outside. Wont i get damp.

 

[jeds]

No. Line it with thermal laminate plasterboard - Kingspan k17 or k18. It will be fine.