Building additional floor - rules re underpinning + public land

[eshroom]

Background:

I own a 2 story converted terraced office on a strange plot. It is fronts the pavement, therefore no space at all to front. 90% of the rear belongs to a neighbouring apartment block with a tiny 3m2 walled off courtyard in one corner belonging to me.

I have got planning permission to add an additional floor.

The building mas built some time between 1910-1930 according to ordinance survey maps.

Having spoken to engineers there are a few possible scenarios, but many questions remain and I hope someone on this forum might be able to offer some advice.

Engineers have suggested trial pits will be needed as the additional load to the building is probably going to be 40%-50%. I have been advised the building is on London clay (as a most likely, but also best case scenario), but have no idea what the foundations look like.

So that raises the first challenge. Trial pits on neighbour's land and also public footway. Do I have any rights under the Party Wall etc Act 1996 to dig on either of these? How easy is it to actually get permission to dig on public land?

Second, if the trial pits show that underpinning will be required, then the question is similar to above do I have a right to underpin via neighbour's land and public land? Would underpinning under public pavement be crazy expensive?

Regarding the building, given the period it was built in and the purpose of the building (shop with accommodation above) does anyone have an opinion as to what the foundations might actually be made of?

 

[^woody^]

Party walls have a room on the other side of them, not a path. You have no rights to dig across a boundary.

Engineers always recommend trial pits. But the foundation for a two storey house will support a three storey house.

 

[endecotp]

Irrespective of trial pits, you're probably going to have to errect scaffolding or something on this land, aren't you?
So talk to the council and neighbours and see what they say.

 

[eshroom]

Party walls have a room on the other side of them, not a path. You have no rights to dig across a boundary.

Engineers always recommend trial pits. But the foundation for a two storey house will support a three storey house.

Apparently not. 2 engineers expressed doubts but quoted for coming down. Another had a long phone chat with me just to lay out why he didn't think I should waste my money with him (as he was very sure the building would likely not support an additional floor without underpinning).

I have spoken to neighbours who have been quite open to the idea of trial pits, but as the flats have multiple freeholders there are still hoops to jump through.

 

[^woody^]

How can they say that over the phone.

I'd love to know why an existing two storey house foundation is so inadequate that it just can't take the small amount of extra loading of an additional floor.

 

[wessex101]

Probably because a property of that age will have a very shallow foundation and no professional would be prepared to stick their neck out and and state that it could take the extra weight and certainly not without inspecting trial pits.

Its much easier to say it will be fine from an anonymous keyboard (which it probably will) if your PI premiums aren't in jeopardy. The OP has the option to ignore professional advice and just crack on with it.

In answer to the original queries you do not have a "right" to underpin from neighbouring land for development purposes but something could probably be arranged/negotiated especially if the party wall act comes into play. The other option is underpinning internally but that would mean disturbing the floor with excavated concrete pins or mini-piles.

 

[^woody^]

Its much easier to say it will be fine from an anonymous keyboard

It is easy because it is common sense.

If an existing two storey has such inadequate foundations for just a single extra floor (which as you may know, the extra loadings are small), then it will already be susceptable to foundation movement as the seasons change and will be at risk now.

 

[wessex101]

Yes its common sense but when did that ever make any difference. We now now live in a society where packets of peanuts have to have warning notices that they may contain nuts, where's the common sense in that?. Hell I'll say it will be fine, we all know it will be fine. One of the reasons I quite like spouting nonsense on here, I can prattle on all day saying all sorts of crap knowing full well my PI premiums are safe. Its very liberating compared to how I speak to my clients.

 

[eshroom]

Thanks for all the replies, they have helped.

Regarding the foundations being labelled inadequate without underpinning by one local engineer, he explained he was familiar with buildings in the area of the same period. This being a lightweight building on (he presumed) 2 step brick foundations on London clay. He felt so sure about this that he didn't want to even charge me to inspect said foundations.

I will go ahead and dig some trial pits and get an engineer out. Maybe we can get away with using lightweight construction for the additional floor.

 

[motorbiking]

Party wall act covers more than wall/rooms adjoining your land, but it doesn't help you. In this scenario its their to protect the neighbour. If you need to place foundations on other's land, you'll need to acquire the rights to do so. It may be possible. There is a fair chance your building is currently sitting on 12" of poorly nocked up concrete.
Access to neibouring land act 1992 is worth a read. But doesn't enable you to build foundations for your extension. It could however allow you to carry out essential repairs to your current foundations. However, the fact you have planning might alert anyone to your real intent.
http://www.legislation.gov.uk/ukpga/1992/23/section/1

 

[bernardgreen]

I'd love to know why an existing two storey house foundation is so inadequate

How many ordinary houses have had to be under pinned because the foundations have failed under the weight of the house without any additional floors being added. Quite a few and more than enough to disprove that adding an extra floor will never overload the existing foundations.

 

[^woody^]

How many ordinary houses have had to be under pinned because the foundations have failed under the weight of the house without any additional floors being added.

If an existing two storey has such inadequate foundations for just a single extra floor (which as you may know, the extra loadings are small), then it will already be susceptable to foundation movement as the seasons change and will be at risk now.

 

[bernardgreen]

it just can't take the small amount of extra loading of an additional floor.

Is the extra loading a small amount ? Agreed the extra weight is only the weight of the new walls, flooring and occupancy of the new floor ( people, furniture, equipment etc) but it could be enough to cause problems in buildings on foundations which are just marginally strong enough for two floors

 

[^woody^]

Is the extra loading a small amount ? Agreed the extra weight is only the weight of the new walls, flooring and occupancy of the new floor ( people, furniture, equipment etc) but it could be enough to cause problems in buildings on foundations which are just marginally strong enough for two floors

The extra load is small in context of the existing loading and capacity of what's there already.

Foundations won't be 'marginally' strong enough, because as I've already started, if they were then they would have failed long ago as the building and ground went through its regular seasonal movement.

The OP could load the existing floor with furniture and that could be greater loading than that of a new floor and ceiling.

 

[tomfe]

The OP could load the existing floor with furniture and that could be greater loading than that of a new floor and ceiling.

Looks comfy!