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We're kicking around extending and changing the layout of our house. One option is a new second storey bedroom on top of the 20 year old single storey extension.
We've been told by neighbours that the previous owner built it with an idea of adding the second storey, so foundation and walls were built with this in mind.
It's timber frame and block. There's currently no access into the roof space, however one option is to add a hatch and get up there to look.
How can I find out?
If you're building on top of something I'd be more concerned with what's underneath.
We hired a guy with a digger to dig a hole ~1m deep next to our external walls to see what kind of foundations we had, and a structural engineer to confirm that they were non-existant and therefore effectively useless. It would explain why it appears that wall has collapsed and been rebuilt some point in the last 150 years or so.
There should be building warrant drawings for the extension extant in your local council building control department.
Some councils have started digitising them but there should certainly be paper copies.
Getting a hold of them might prove challenging these days as most BC departments are all working from home.
The other option is the destructive / disruptive one.
Dig down to expose the foundations / lift floors / borescope through walls.
You almost certainly have to expose the existing footings - Building Control will want that and so will your structural engineer. Drawings won't be any good as thats no proof of what was actually built!
Add a hatch. Any investigation work would require an intrusive survey, so just make good with a small inspection hatch.
I would just did down to find out, why make it any more complicated?
Well building regs have moved on over the last 20 years. My house is mid 90's build and we had a single storey extension built about 5 years ago. The foundations for the single storey extension were designed as for a 2 storey construction as per current building regs - I guess assuming at some point in the future someone might want to extend vertically as you might. When the build was happening the foundations for the extension were significantly deeper than those for the house, so that goes to show how the building regs have changed in the last 20 years. So if it is a 20 year old extension and even if it was built back then with foundations capable of supporting 2 storey's then I suspect they wont conform to todays regulations or requirements. Not sure what that means in terms of what you're looking to do and if there is any alleviation in cases such as yours? Your architect or structural engineer should be able to advise.
You almost certainly have to expose the existing footings – Building Control will want that and so will your structural engineer. Drawings won’t be any good as thats no proof of what was actually built!
Are you sure? I can understand that with regards mass produced houses on a large housing estate, but for an extension there should be several points through the build where a bod from the council comes along to inspect the build and ensure it is being constructed according to plans and code. That's what happened in the case of my build. Not sure if there are any changes to the design for whatever reason that they are recorded particularly well as deviations from the original plan so might not avoid the need for exploratory work ultimately, but for a recent extension build then inspections should have occurred through the build.
We do this a lot in my job (Engineering geologist working at a company with building sureyors as well). We would typically do some hand dug pits to uncover the existing foundations, sketch and CAD up for review by your structural engineer.
Depending on the state of the foundations and how much extra load the extension is going to impose we might also do some deeper investigations, shallow boreholes and penetration testing etc etc.
We joke that foundations pits either uncover terrifyingly shallow / non existant foundations or absolutely insane deep Victorian brick shennanigans. No middle ground ha
I do like the deep stepped brick foundations which you can find for older buildings. Can appreciate the work that went into them more than a huge usually messy concrete footing.
I've had to dig a foundation inspection hole to alter a 10 year old conservatory from dwarf wall to a proper single storey extension. It's about 1m deep so hopefully meets the current regs.
It's a 1970's house, with 1980's and 2000 extensions...
If we do this, the 1980's room will be bulldozed as it's utter crap....
You almost certainly have to expose the existing footings – Building Control will want that and so will your structural engineer. Drawings won’t be any good as thats no proof of what was actually built!
Whilst I wasn't building on an extension (I was removing an internal wall - which there was some debate about its structuralness!). Building Control provided copies of the original warrant from when the house was built, structural engineer then used them to write a letter saying that 3/4 of the wall was not structural and could be removed. Warrant granted. I think the structural engineer did suggest assuming it was structural when removing it and calling him if anything we found didn't match the plans. I don't remember the cost being as high as £107. It was pre-covid and quite quick. It was both quicker and cheaper than the structural engineer doing physical investigations. Usually you have copies of the building warrant (but perhaps not all the associated drawings) in with the house deeds etc when buying / selling - certainly you'd expect that with extensions the solicitors confirmed they were legal. You may need a structural engineer to understand the drawings because they probably don't say "I've made this bit stronger in case I build upwards in the future".
Guy we used (who is a friend of a friend): based in Perth but will definitely travel to Dunblane https://www.3slimited.co.uk/
Access your local authority planning website. Ours is free
I found the planning permission details and drawings that the previous owner submitted for the garage back in '86.
As above, it may not have been necessarily built to the drawing spec,but it should give you a rough idea, based on how detailed the drawings are.
No idea about the foundations, but do your numbers carefully before you commit to remodelling your existing place. Given the cost and availability of decent trades seriously consider just moving.
Since 1992, applications for building warrants (in Scotland) have had to be supported by a design certificate from a Chartered Engineer. I would imagine that should be available, and if the calculations aren't included you might be able to get them from the Engineer.