Digging out the floor questions..

[andygo999]

Hello
I'm a newbie...wondered if someone could help with some questions i have about digging out a floor.
We live in a 200-year-old terraced cottage with stone walls and flagstone floor.
We plan to install solar powered underfloor heating under the flags in the living room.
While we've got the flags up we're thinking about digging down a metre or so to lower the height of the floor and give us more headroom.
I'm wondering about the consequences and or possible problems to look for while doing that..especially..
* Damp - the internal floor will be lower than other internal floors the level outside and (though it slopes away steeply)
* Support - will digging out the floor cause problems for supporting walls?
* Cost - how expensive could this be - room is around 10m x 3m
* What other things should I be concerned about - budget for.
any help much appreciated
Andy

 

[Shytalkz]

From a structural pov, the first thing that springs to mind is that you are likely to end up well below the existing foundation level. If you dig out wholesale, without first underpinning, you're not likely to have a house for much longer.

It can be done, but underpinning is around £600-700/m, so it's not cheap at 26 lin metres of that. DIY is of course much cheaper, but you need to know what you're doing, if you're not going to end up with cracks to the superstructure, as the building settles onto its new foundation.

 

[roy c]

If the cottage is 200 years old I would be very surprised if has got any foundations at all. Where about are you?

 

[chessspy]

Hi, andy,
The point about the founds is a good one,
I once dug down on a similar building and found it was built on bales of wool.
good luck.






not so much a job, more a way of life.

 

[JohnD]

perhaps the original occupants were three little pigs

 

[Shytalkz]

If the cottage is 200 years old I would be very surprised if has got any foundations at all.

It has a foundation of some description, be it corbelled brickwork, lime-based clunch, faggots or wool bales, etc. Foundation as a term does not necessarily mean 600 wide gen1 trenchfill ya know .

 

[andygo999]

Thanks for the replies.
I feared that it might need underpinning...but amazed it costs so much. Will it really cost £15-£18k ??
maybe we'll just live with the low ceiling after all then!

 

[JohnD]

it won't hurt to dig a small trial pit beside a wall to gave a look. you never know your luck - maybe it used to have a cellar.

 

[chessspy]

Hi, andy,
Underpinning is expensive as to do it properly it needs to be done in sections in the correct order or the building needs to be propped up whilst the pour in setting and packed.
Could you could consider heightening the ceiling?
I once added 3 ft to an old property in Beverly called Nanny Goat Farm.
Ok it means a new roof etc but the cost should compare and you could get a lot more room out of it, in my example 3 more bedrooms.
(and a 3 car garage with inspection pit, but thats another story)

 

[Shytalkz]

Will it really cost £15-£18k ??
maybe we'll just live with the low ceiling after all then!

It will if you get a contractor to do it all for you. Do it yourself, with some dayworks labour and it will cost a lot less.

You just need to limit the amount of excavation you do at one time, keep each bay to around 1m length, ensure that no greater than 25% of any wall is unsupported at any time, excavate in a sequence, so that subsequent excavations are not adjacent to one another, don't dig any adjacent bays within a min of 48 hours of one another and, most importantly, ensure that the underside of the existing footing is adequately pinned up with 1:3 cement/sand drypack (or overfill the excavation and poker the concrete in), before you start digging the next lot in the sequence out.

I've just done 13m of underpin x an average of 1m deep below footings for around £1300 for labour and materials (8 tonne ballast, about 45 bags OPC, 8 man days' labour, 1:5 mix). Admittedly, I didn't need to get rid of around 18 tonnes of spoil, as I could lose that on site and I blagged a poker vibrator off a mate, but it's worked out at around a seventh of the going rate. Removing the spoil in skips would have added say another £600 or so, but would still have resulted in a great saving.

As with most things, project manage it yourself and you can make considerable reduction in cost.

 

[andygo999]

Thanks again for the replies.....
not sure I fancy taking on anything structural - am sure the neighbours will be relieved - but do appreciate the info - esp Shytalkz - thanks v much.
We'll live with the ceiling and spend the money elsewhere.
great forum btw
Andy