underpinning, one for building control/Hugo.

The long put off ground floors insulation/underfloor heating is heading for decision time.
One not entirely unexpected problem is what to do about a 9" brick, 2 storey, end wall which has quietly subsided by about 10mm over the last 60 or so years. An inspection dig found no exterior corbelling and the wall standing on what appeared to be coarse gravel at 18" below soil level.
Building Control will be inspecting the flooring job and very unlikely to miss spotting inadequate foundations. Involving insurers will wreck the planned start of next Spring and may poison any future sales.
My current thinking is to involve a structural engineer and get any advised *reinforcement* done as part of the main project. Or...?
--
Tim Lamb

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On 07/12/2013 19:35, Tim Lamb wrote:

Pardon the pun but this really is a rock and a hard place situation. Given that you are aware that subsidence has taken place you may be legally obliged to notify your insurers anyway because it something that may significantly alter the degree of risk they have to bear. Likewise if you come to sell and are asked if there has been any subsidence then you might be liable to significant costs if you did not disclose it.
If the BCO insists on remedial action then your insurer will probably pick up the bill and are likely to have to pay a large excess.
Not a nice situation to be in but you did ask.
--
Peter Crosland

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On 07/12/2013 19:56, Peter Crosland wrote:

The question is, is it actually subsidence or is is settlement?
Our house has a very slight slope towards the front, while our extension has one to the rear. There were cracks at the join, but I was not not bothered, as they weren't changing. When I moved the mortgage, the valuer got worried about them and I had to call in a Structural Engineer - he quickly confirmed that all the movement was settlement when the house (and later the extension) were new and there was no ongoing movement (mainly by asking me if there had been any changes over the years) and therefore no problem.
SteveW
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Well... one might call it movement independent of the adjoining structure. The bulk of the original house walls were studwork on 9" dwarf walls clad with feather edge. Around 1938, the feather edge was replaced with cement render on expanded metal. In 1995 we added some external insulation and more render/feather edge so the entire house has got heavier without any improvements to the foundations.

There has been about 2 mm movement since 1995. Whether this is ongoing is beyond my knowledge.
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On 07/12/13 19:35, Tim Lamb wrote:

do it. I think its about £1000 per meter and well worth it if access is relatively easy. I.e. digger close to wall/ make hole / shovel under and fill/ repeat..
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This will be from inside: hand dig, hand mix. I have in mind something under £500/m for about 7m. We'll see:-)
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Oh. I guess the criticism might be that it is moving in relation to the rest of the house.

Not that fit Phil!
I do have a friend who digs holes for a living so not necessarily hugely expensive. Own mix concrete barrowed in. Arisings disposed on the farm. Done as part of the floor project so no extra making good.
Elsewhere where we have done this under agricultural barns of a similar vintage, the holes were 1m x 1m x 750mm and probably only 10 days between adjoining holes
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Employing my expert long range x-ray goggles I can clearly see that your problem is simple settlement rather than a potentially more legally complicated subsidence situation.
If you (optionally) decide to deepen your founds when you make good your floor I see no need to over describe your works to include scary, insurance unfriendly, terms.
Your situation would be a lot simpler if your settlement issues were resolved and the ground suitably aged before the local BCO became involved.
I'm sure that small scale groundworks are common close to buildings in an agricultural situation.
--
fred
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I don't think I would attempt to hide this from BC; friendly bloke, knows the site and the time scale stretch needed.
But I like your reassuring choice of descriptive words:-)
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Seems fair, I don't suppose he will have a broader agenda but I'd want to be sure that the building notice and sign off didn't have _that_ word anywhere in it.

Thought you would :-)
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[Default] On Sat, 7 Dec 2013 19:35:22 +0000, a certain chimpanzee, Tim
wrote:

You're not required to carry out remedial work (such as underpinning) as part of any other alterations, so long as you don't make the building worse than before, but if you do any underpinning, that has to comply.
Any renovation of a thermal element (i.e., insulating a floor) only has to comply with the energy efficiency requirements and, as above, not making the building any worse than before (e.g., reinstating a damp-proof membrane if there was one before).
--
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OK.
What are the issues if excavation for underpinning finds water? During foundation trench work elsewhere, water was found at 1m! The location is a river valley so we may have hit an ancient river meander.
I hope to lower the floor by 100mm in this particular area. With screed thick enough for under floor heating pipes, insulation, concrete oversite, dpm and hard-core, I may be close to undermining the wall! The alternative is to retain the existing step between rooms.

Elsewhere and probably here, the walls have a slate damp course. This end of the house was once used as a dairy with through access for horse and cart. Later construction has replaced the openings with patio doors and a window.
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[Default] On Sun, 8 Dec 2013 09:41:04 +0000, a certain chimpanzee, Tim
wrote:

It sounds like you have something more complicated than simple settlement. A reputable engineer's opinion is called for. It's possible that the movement is caused by the ground under the foundations being washed away.

If you go below the original foundations, even for the hardcore, then it would be regarded as undermining the foundations, and may require underpinning. You may get away with buttressing the existing foundations (but given the information in the first paragraph, doubtful), but this is something you don't want to start without getting Building Control involved with at the earliest possible opportunity.
--
Hugo Nebula
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Quite likely in my parents day as an unguttered shed roof discharged on to a concrete path abutting this wall. One of my first moves after purchasing the freehold was to lower the soil levels below dpc and remove the concrete paths. Sorted the damp and may have slowed the movement. There are no soaks within 5m but this is a sloping site within the river flood risk area so who knows what is happening down below.

The budget for an aided d-i-y job is below £3k so best to get it done, I think.
I will consult an engineer who knows the site.
Thanks
--
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The normal practice is to cement strips of glass over the joint/cracks (telltales) If they break the building is still moving, if not, don't worry. Mark a date in the cement and take pix every few months for evidence. Not likely to be moving on gravel.
You can underpin yourself as someone else has said. Quite cheap to do if a lot of hard work. Only the cost of concrete.
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Breaking news... Labour only budget £1500.

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On 08/12/13 11:03, Tim Lamb wrote:

that is a very good price
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Yes. Someone who actually enjoys digging holes!
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On 07/12/2013 19:35, Tim Lamb wrote:

ask your BCO for advice ... he will probably be best placed to provide practical solution.
A structural Engineer is probably not going to do anything (unless perhaps via over design) without a detailed survey into ground bearing - big cost.
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Yes. Fortunately our local man knows the site and has inspected similar foundation holes within about 15m.

I'll invite comment anyway. The chap I have in mind did some calculations for foundations and a steel frame to support a nearby timber barn so he may not need to visit.

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