Build upon existing conservatory footprint

[Sismithin]

Hi folks,

I’m just looking for some initial guidance really. I have a conservatory on the back of my 100 yr old house. This was built about 20 years ago long before I moved in. Originally there was a long coal shed/store built on the site which was demolished, and new foundations built up to what’s exists today.
I would like to turn the conservatory into a proper single story extension, however keeping the cost down the dream would be to build upon the existing dwarf walls and turn into something like the attacked picture with a slate roof and skylights.
The inside is plumbed, plastered and has a radiator so very little work actually needed.

As you can see the land slopes considerably through to the gable side where the ground level is 5ft lower then the right hand side.

From peoples experience what is the likelihood I would be able to build upon the existing footprint without having to dig new foundations and considerably increasing the cost?
How does the land gradient fall into the mix? Since the entire base is stat upon a huge mound of earth which has been there since the day the house was built.
There is absolutely no sign of movement at all but again this is only a light conservatory on top so not really a good indication.

I appreciate in advance, anyone’s input.
Kind regards
Si

 

[jasonzyx]

You will have to expose the existing structure that you wish to retain, in order to reassure the Building Inspector that it is sufficient and conforms to modern requirements.
That may mean accessing the cavity, if there is one, to inspect any insulation, if there is any, and exposing the foundations to inspect those.

 

[^woody^]

what is the likelihood I would be able to build upon the existing footprint without having to dig new foundations

1 in 10.

So if nine people in the road have already done it, you will be the unlucky one. Or something like that.

 

[jasonzyx]

Doesn't it mean if one person in the road had already done it like that, the other nine couldn't?

 

[Sismithin]

Thanks for the replies.
There is no cavity it’s just early with a concert slab and DPC on top. It would be a shame to dig this up to insulate but I guess wouldn’t take too long and cost a great deal. I would be taking the tiles up and continuing the new laminate from the kitchen and putting underlay insulation down (which probably won’t meet regs on it’s own)

I guess the dilemma is I don’t want to spend to much money finding out I can’t do it, is there anything I can do in the first instance so I know if its feasible?

Should I lift the block paving and try digging two holes to see how deep the existing footings are first.

As you can see from photos attached - inside it’s plastered (and has electrics and radiator already) and I have temporary removable wooden doors in a arch which was built with a steel across so no structural work needed to connect the two so should keep the costs down.

Thanks again

 

[^woody^]

You certainly can't build off it if it is just a slab.

 

[Sismithin]

You certainly can't build off it if it is just a slab.

Yes it’s not just a slab, these side wall does extend down into the ground considerably but to wha depth I don’t know

 

[jasonzyx]

I suspect that that brickwork is imperial, and matches the 100 year old house.
In which case it's probably more like 50 years old.
Best stop digging, and assume you'll need new foundations.
Or start digging to expose the existing foundations for the Building Inspector to inspect. But the floor slab will need replacing anyway, and the brickwork on the foundations will need replacing or another way found to meet current regs.
Also bear in mind that any new foundation for the proposed extension may need to extend below and under (for a little way) the house foundations.
Until you expose the existing it's all guess work.
You won't need to expose all the existing, just enough to satisfy the BI.

Let's not go into whether the heating can be isolated from the rest of the house.
I bet that fan don't work on that radiator.

 

[Sismithin]

Thanks Jason,
I assume the old outhouse which ran along that existing wall was completely levelled and rebuilt, on that photo above you will see the bottom 5 courses of bricks are metric and then they reused the old bricks to build the conservatory walls.

The rad is not isolated it’s apart of the house system unfortunately.

It does seem like a bit of a pipe dream then, I can’t afford to demolish the entire thing and rebuild it as it will cost far to much. Looks like I will keep the crappy conservatory for now
Thanks for the input at least I know now to forget it.

Oh no that stove fan was just placed there on the window sill and I’ve not moved it yet, excuse the other mess too

Thanks again

 

[jasonzyx]

I think there is an approximate estimate for the percentage cost of a building to 'get out of the ground' compared to the whole cost of the building. Obviously it depends on circumstances.
Maybe one of the pros on here might help.
I found this

https://www.quora.com/What-is-the-percentage-cost-of-structure-and-finishes-in-house-construction

Also found this

https://www.homebuilding.co.uk/how-much-will-your-project-cost/