Beeny Prog Comment

[TheScullster]

Hi all

How are you finding the new Beeny prog? Last week's wound me up big style, can't even remember the topics. A half hour program extended to 1 hour by endless repetition of what the problems were and how to solve them (with further repeated and emphasised info after every ad break). Maybe I was more distracted by the woman herself last night, but the format seemed marginally less irritating. There was also the business about core drilling to find suitable foundation-supporting substrate. Surely inadequate ground bearing is something the BCO should have picked up at time of build. I've frequently heard people complaining about having to dig mega foundations for a single skin garage due to instruction from BCO. Maybe they are only recently (last 10-20 years) taking their responsibilities seriously. Why is there no accountability on the part of BCO for lack of this sort of control? Surely their mandate is to ensure a safe/stable structure?

Phil

[The Natural Philosopher]

Depends how long ago the thing was done.

[js.b1]

Most BCO are obsessive about foundations due to experience a) when it goes wrong b) why it went wrong c) how much it costs to put right later d) how someone will cut corners if they can and foundations is one place historically they did. However there is no legal liability attached to any inspections & certificates at all.

The problem was the area was a former stream, with firm clay some 6 metres down. The leaking drain would not have helped water saturation, over a couple of years that could have been a substantial volume of water. The original foundations were ok, the ground may have been drier before the couple of years of leaking water.

[TheScullster]

"js.b1" wrote

Most BCO are obsessive about foundations due to experience a) when it goes wrong b) why it went wrong c) how much it costs to put right later d) how someone will cut corners if they can and foundations is one place historically they did. However there is no legal liability attached to any inspections & certificates at all.

The problem was the area was a former stream, with firm clay some 6 metres down. The leaking drain would not have helped water saturation, over a couple of years that could have been a substantial volume of water. The original foundations were ok, the ground may have been drier before the couple of years of leaking water.

Your response reminded me of a comment made somewhere in the program about the perils of building foundations on top of clay due to movement. I always thought that clay was a pretty good support medium for foundations provided that there aren't streams running through it (in the absence of a handily sited granite slab that is).

[js.b1]

Clay is except it obviously expands & contracts with the weather. As I recall, in summer evaporation tends to make areas sink, in winter frost heave tends to make areas rise. This variation is fine if the area under the foundations is all the same - but very often it does not "move as one". With very shallow foundations they can fracture and extensions can begin to fall away from (as last night) or jack against the house. Lime mortar absorbed a lot of this movement in the past, cement mortar is fine for very solid foundations.

One solution was a thick concrete slab raft & keel with rebar, the idea being it can tolerate pretty much anything. That said in 2009 and

1981 winters I recall the frost heave caused the main beam spanning the back of the house to "ring" the floor, the beam "rang" and the floor jiggled. Not a lot, but I was sat on it at the time. The stresses from frost heave are immense - the garage doors were pushed by frost-heave lifting 3x2 up into the 1/4" L-angle lintel and buckled it at both ends. Improving drainage in that area this year.

Clay is not a "consistent material" in many cases. You can have sink holes, sandy contours, sandstone further down, and thus the opportunity for underground streams is simply immense. This house is on a hill of sandstone and has natural springs all over it, it is however stable - when it is not you need piles or houses can walk down a hill (not often, but landslip is one reason why piles are a good development over rafts).

I have a suspicion piles are cheaper overall than a good raft (say

3-4ft thick) simply re labour vs concrete, concrete has fairly risen in price. Shale and soap waste are pretty crap to build on, you need to go very deep indeed and I think piles have replaced rafts for that reason in most areas. Single story extensions tend to need beefier foundations because there is a common "lets add another on top because we are fed up repairing the flat roof". 3M roofing membranes and Firestone EPDM are often overlooked.

[TheScullster]

"js.b1" wrote

Clay is except it obviously expands & contracts with the weather. As I recall, in summer evaporation tends to make areas sink, in winter frost heave tends to make areas rise. This variation is fine if the area under the foundations is all the same - but very often it does not "move as one". With very shallow foundations they can fracture and extensions can begin to fall away from (as last night) or jack against the house. Lime mortar absorbed a lot of this movement in the past, cement mortar is fine for very solid foundations.

One solution was a thick concrete slab raft & keel with rebar, the idea being it can tolerate pretty much anything. That said in 2009 and

1981 winters I recall the frost heave caused the main beam spanning the back of the house to "ring" the floor, the beam "rang" and the floor jiggled. Not a lot, but I was sat on it at the time. The stresses from frost heave are immense - the garage doors were pushed by frost-heave lifting 3x2 up into the 1/4" L-angle lintel and buckled it at both ends. Improving drainage in that area this year.

Clay is not a "consistent material" in many cases. You can have sink holes, sandy contours, sandstone further down, and thus the opportunity for underground streams is simply immense. This house is on a hill of sandstone and has natural springs all over it, it is however stable - when it is not you need piles or houses can walk down a hill (not often, but landslip is one reason why piles are a good development over rafts).

I have a suspicion piles are cheaper overall than a good raft (say

3-4ft thick) simply re labour vs concrete, concrete has fairly risen in price. Shale and soap waste are pretty crap to build on, you need to go very deep indeed and I think piles have replaced rafts for that reason in most areas. Single story extensions tend to need beefier foundations because there is a common "lets add another on top because we are fed up repairing the flat roof". 3M roofing membranes and Firestone EPDM are often overlooked.

Thanks js.b1

Our house is built on (what I think was described as) boulder clay. Although we get some local standing water at the back of the house, being at the top of the hill the 2007 floods didn't cause any significant issues (despite living on the outskirts of Hull, one of the worst affected cities). So hopefully, ground swell/shrinkage due to water take-up/release should be minimal.

Phil

[The Natural Philosopher]

clay moves a lot.

especially when it gets wetter or drier.

Its probably the WORST foundation material.

Rock being best.

BCO insisted I go pretty deep, until he was sure I was in more or less 'wet all the time' clay, and well below tree root level.

We threw in rebar as well and lined the trench before pouring with poly slabs to take any lateral movement.

[The Natural Philosopher]

I used strip foundations and suspended floor of concrete. Piles would have been similar cost to strip. At least strip can be ripped out fast with a digger, and poured fast too.

Don't want a slab floor on clay if possible. Or rest it on polystyrene and rebar it so its strong in itself, and the poly takes the heave.

[dennis]

The original foundations were piled. They should be OK. The extension also needs to be piled.

I wonder why they bought a house which had big cracks and problems that a survey should have thrown up.

[dennis]

Or trees or anything else that changes the soil wetness like rain.

[dennis]

If you pile you still need to fill between the piles, it is effectively a raft on top of piles.

My house has a huge raft under it. The edges are at least five feet thick and have as much steel in them as a bridge has, no its not an exaggeration. Its really odd as the other houses on the estate that are a different design have strip foundations only the ones like mine are built on rafts.

They also had an odd way of building.. they used an earth mover to take six foot off the site, built the rafts and then filled it back in.

My neighbour, who has just retired from being the head of building control, reckons they just purchased a batch of standard foundations from a ground works company and used them up.

[js.b1]

I think they use a ring. Which basically means what you may save on concrete you eat up in rebar & labour associated with it.

Rafts can be very thick, going to be a right P.I.T.A. if you have to get a new underground water pipe in. Then again BES do a surface entry (looks like a mini meter box coming out of the ground stuffed with closed cell insulation and bricks the CW main in further up, might even allow an external stopcock which would be rather nice).

Actually I think that is how they did these in 1949 - you do several at once.

It may be different ground re stream somewhere and a simple way of doing it.

[dennis]

Fortunately they put a piece of soil pipe in and ran the water pipe in through that.

[Hugo Nebula]

Just watched it on 4OD.

Firstly, is it known whether it was ever inspected by Building Control? Unauthorised works are not uncommon.

If it had been inspected by a BCO, I would have expected the surveyor to have at least had the foundations excavated to 1m deep. If the ground had still been soft clay, carry on digging. By the time they got to 2m, I would have been suggesting they get hold of an engineer and/or pile it.

I've been in Building Control for 20 years, and for all that time, a foundation in clay soil would have needed to be at least 1m deep in the south-east. The guidance of foundation depth is largely produced by the NHBC, who care more about insurance liability than structural stability. Generally after major droughts (and claims), their guidance has tended to require deeper foundations, and the last update was AFAIK after 1984.

Building Control can be held liable, but only for health & safety matters. Economic loss isn't covered, so in the case of this extension, the underpinning couldn't be claimed for, as the extension wasn't about to actually fall down. The leaking drain might have been, if it had been caused by the controlled work, not a later unauthorised bodge job.

It's the responsibility of the person carrying out the work to ensure a safe & stable structure. Building Control's duty (mandate) is to ensure that the Building Regulations requiring it are enforced within their district. If you drive a car with bald tyres, it's not the police's fault, it's yours.

[Hugo Nebula]

Solid bedrock, yes. Shelf of rock sitting on top of glacial clay, no. One of my patches had a thin crust of rock no more than a few x100mm of loose limestone boulders over clay a couple of x100mm below the ground. I'd turn up and the builders would have scraped away the soil to the top of the rock. I would then be called all the names under the sun when I told them to keep on digging. The next day I'd be there and the top layer had come up like paving stones to reveal a band of clay on top of the bedrock. Local knowledge is a wonderful thing, and something lacking with Approved Inspectors covering several hundred square miles.

Sand is probably the best foundation material. Good bearing pressure, but easy digging. However the builders who went to Sunday School didn't seem to like it. I'd get a phone call, "I've dug down over a metre into sand and I haven't hit any clay yet, what do I do?" "STOP!"

[The Natural Philosopher]

[Dave Liquorice]

Unless you are in an earthquake zone, sand and other lose sediments "liquify" when shaken by an earth quake. Two main effects, the shaking is amplified and the building sinks, probably unevenly, into the liquified ground.

Solid bedrock is what you want...

[Man at B&Q]

On Aug 18, 11:47=A0am, "TheScullsterbut the format

You must be desperate, Shae isn't keeping at all well.

MBQ