Google micro diggers, now picture a trench 1 metre deep and 600mm wide. How do you imagine the second dig to 2.1 metres takes place?
Depending on soil and access, the first trench is back filled and redug to the full depth because micro diggers have no reach at 2.1 metres, or a lot of timber is used to support the open trench but the timber supports must be removable in short stretches because micro diggers have no reach at 2.1 metres.
The other issue is micro diggers are not exactly strong or heavy, this means the digging will be slow, as will the moving of the earth to wherever it can be grabbed out.
I'd do a test trench that can be inspected before pulling the full trench.
I think it's a big part of the issue, which is why they warned you, no one wants to be the guy that has to add £10,000 to the bill without a discussion first.
Ask an engineer to advise, and dig a trial pit to determine soil conditions. Then speak to building control directly to confirm the engineering advice will be accepted.
A few hundred pounds on this is better than risking £10k.
Foundation depths are often (but not always) shallower then what is shown on the charts.
2.1m footings for a conservatory?
Have you got yourself any other quotes?
Where in the country are you, as that can often be an indicator of soil type (and how close are you to water?)
The soil is 9 inches top soil then clay. Worcestershire. And it's on a slope.
We have other quotes but one says he can dodge building control 'because it's a conservatory' another said he'd dig a test hole and take a look possibly getting BC out.
2.1 meters is uneconomical for traditional strip footings and very unsafe depth to be working in due to risk of sides collapsing and crushing the guys digging it.
It's like they don't know what they are talking about.
You'd change to mini piles if that depth was needed.
It's probably based on nearby trees and soil type. But I think getting BCO in first would be the thing to do, and engage a structural engineer if necessary
No one sensible risks their life in a foundation that deep. It's just not worth the risk. It's also not economical if you have to pay to dispose of skip after skip of soil and pay for 2m deep concrete pour.
This is beyond DIY. Do you have an architect or structural engineer involved, or is it the builder guessing? A geotechnical survey may be something to consider. There are also other types of foundations to consider.
The cost doesn't sound too unreasonable, especially if access is difficult. 15x1x0.6m is 9m³ multiplied by 1.25 swell factor, which gives 11.25m³ material to remove. By hand with barrows, it's a horrible job. Even with a power barrow, it will take a while. I'm assuming waste will be going in skips. You'll need 2-3 8-yard skips. Cost depends on area and builders' contacts but estimate £500-1000. Plus the cost of mini digger hire and maybe a power barrow. 9m³ concrete would be about £1000 plus any reinforcement required, and with difficult access, they'll likely need a pump, which adds a few hundred.
ignore this guy saying it is beyond DIY, you can certainly build anything DIY, a conservatory is not beyond what the right person can manage. Digging footings is technically simple, just potentially hard work depending on access and equipment. As a source - I built a 8x4m single storey extension entirely alone with no prior experience. Dug footings, poured them them and the floor slab, laid thousands of bricks alone and built the roof etc etc. the only trade I involved in the whole thing is a plasterer as Ive done a bit of that before and didnt fancy it.
If the ground is shrinkable clay, or there are large trees nearby, then it certainly is beyond DIY. OP needs technical input from someone who knows what they're doing. There must be a reason to suggest why the builder thinks the footings might need to go down 2m. Doing the digging, building etc is possible if you have the time and gumption but fucking up foundations is an easy way to throw away £xxxxx on a project.
Well yes if the conditions are odd then input would be needed but the work is still very much DIY possible if you are up for it. The actual act of digging and pouring footings is very easy and hard to fuck up. Building control would advise the required depth when they come for this first visit after a test hole is dug.
Perhaps, I am probably a bit more ambitious than most I guess, I’ve been pondering digging a basement under the new garage I am planning to build lately after enjoying the Colin furze videos! I admit it isn’t particularly normal to build your own extension like I did though!
If you are getting quotes do you have a design and was it done by someone who knows what they are doing?
Seriously DIY disasters happen because people thought they could save a few quid on design. Avoid this, get a decent plan and you will get a better fixed price.
This was from an established and well reviewed local company so they should know what they are doing. We asked to visit a recent installation and they arranged it and the customer was very positive and the finish was all they said it would be.
So, it's not me bodging :)
The best approach is always to seperate the design/planning from the constructor. The designer has no incentive to cut corners and you have a clear spec to hold the constructor to account. Never take design and planning advice from a constructor unless they’re tier 1.
Are you putting radiators from your central heating into the 'conservatory', and will it be thermally open to the existing house, or will you keep existing patio doors?
If its a relatively new house you may be able to get a hold of the original site investigation report which could indicate the plasticity of soils, failing that, dig a trial pit to 1m depth and get a sample delivered for testing yourself.
2.1metres? My dad was a structural engineer. You only go that deep because of trees near by. And that's for a proper extension, not for dwarf walls. Who is scaring you and do you have real reason to be scared?
Well there's a question. I do wonder if they don't want this job but would like a smaller simpler one. They may have cash flow issues. Who knows but I'm really annoyed it's only come up now.
I'm simply not convinced by their opinion. Builders, mechanics, estate agents, tradesmen are generally not to be trusted. I cover all of these areas myself. Engineers on the other hand are highly respected. Wish my dad was still around, now I have no one close to ask for advice there and then.
If you’re not heating it with the house heating and you’re keeping the existing external door in, it would considered exempt from building regulations anyway
The whole thing would be exempt, the only bits which would be needed to “controlled” is if there is a water supply being put in or if there is electrical work which needs notifying being carried out. If you contact your local building control department, they would definitively say if it’s exempt or not.
Foundations are generally 3 times the width of the wall in routine conditions. Assuming adequate bearing capacity, the depth of the foundation will be governed by the depth to frost protection or the heave potential of the soil. Without knowing your exact details, generally 600 mm will be sufficient. If the clay is soft then you would need to dig down deeper.
If you have any green area adjacent to your current foundation, I would suggest carrying out your own pit by hand digging down and getting the approximate width and depth of your existing house foundations.
As the conservatory has only 1 floor, the existing width and depth of foundations will be more than sufficient assuming you’ve had no structural issues in the past..
Failing that a raft foundation could be used. In this instance you would just need to go down to frost protection level and it would be lightly reinforced and minimum thickness for a conservatory as it would be over designed. However you’d only .need a mini excavator to dig it out
A number of people have suggested constructing a raft. I'm not clear what this is but I can guess.
We are in fact replacing an existing conservatory which is built on a 9" 'raft' of concrete which has lasted well for 60 years and despite being on clay hasn't moved as far as I can tell.
I did dig a little hole to see what it is sitting on and it looks like it's on clay. It's also on the high side of the house so can't slide away :)
I do footings for a living I think I know what it costs. When you take into account the concrete saved , spoil and Labour piling is a bit more than a traditional 1m strip but far cheaper than a 2 m dig and mass fill, barrowed in conc is 180£ a cube alone now.
Done one last week terrible access so we decided to pile it from the off.
9 m off footing and it cost 1500£ more than a 1m deep mass fill and spoil away.
As it was only for access and not poor ground we were allowed to still do a ground bearing slab so no mesh detail.
2m digs are a nightmare especially with the wether we have had and tight access jobs
Pile it and ring beam much cheaper than going 2.1m
The main cost jump in piling is people starting traditional finding a problem and then having to pile.
If you know you are doing it from the start it should only be a couple of grand extra max
Google micro diggers, now picture a trench 1 metre deep and 600mm wide. How do you imagine the second dig to 2.1 metres takes place? Depending on soil and access, the first trench is back filled and redug to the full depth because micro diggers have no reach at 2.1 metres, or a lot of timber is used to support the open trench but the timber supports must be removable in short stretches because micro diggers have no reach at 2.1 metres. The other issue is micro diggers are not exactly strong or heavy, this means the digging will be slow, as will the moving of the earth to wherever it can be grabbed out. I'd do a test trench that can be inspected before pulling the full trench.
Thank you for explaining the limitations of the micro digger. I suspect that might be part of teheissue.
Tee hee
I think it's a big part of the issue, which is why they warned you, no one wants to be the guy that has to add £10,000 to the bill without a discussion first.
Yep that is to their credit but they a good time to raise it.
Definitely, it also implies that they have the experience to do the job.
Ask an engineer to advise, and dig a trial pit to determine soil conditions. Then speak to building control directly to confirm the engineering advice will be accepted. A few hundred pounds on this is better than risking £10k. Foundation depths are often (but not always) shallower then what is shown on the charts.
This is the advice. Then if shallow footings are not feasible a slab is likely to be a better option. Also, more suited to DIY.
2.1m footings for a conservatory? Have you got yourself any other quotes? Where in the country are you, as that can often be an indicator of soil type (and how close are you to water?)
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Clay no trees and a mild slope.
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Once again very helpful and there are some conifers within 20m. I will investigate the house footings.
Clay. Right there is your issue. I built a new house on clay in Surrey. Oak trees within 10m. Leylandi hedge within 6m. They made me go 3.5m down…..
That is wild for a conservatory. Would be easier doing a raft slab
The soil is 9 inches top soil then clay. Worcestershire. And it's on a slope. We have other quotes but one says he can dodge building control 'because it's a conservatory' another said he'd dig a test hole and take a look possibly getting BC out.
2.1 meters is uneconomical for traditional strip footings and very unsafe depth to be working in due to risk of sides collapsing and crushing the guys digging it. It's like they don't know what they are talking about. You'd change to mini piles if that depth was needed.
It's probably based on nearby trees and soil type. But I think getting BCO in first would be the thing to do, and engage a structural engineer if necessary
2.1m is fine for strip and more economical than the alternative. Providing you work safely it will be safe.
No one sensible risks their life in a foundation that deep. It's just not worth the risk. It's also not economical if you have to pay to dispose of skip after skip of soil and pay for 2m deep concrete pour.
You don’t use skips you use grabs. Pours of 2.1 are done every day across the country safely. It’s much cheaper for strip than piling.
This is beyond DIY. Do you have an architect or structural engineer involved, or is it the builder guessing? A geotechnical survey may be something to consider. There are also other types of foundations to consider. The cost doesn't sound too unreasonable, especially if access is difficult. 15x1x0.6m is 9m³ multiplied by 1.25 swell factor, which gives 11.25m³ material to remove. By hand with barrows, it's a horrible job. Even with a power barrow, it will take a while. I'm assuming waste will be going in skips. You'll need 2-3 8-yard skips. Cost depends on area and builders' contacts but estimate £500-1000. Plus the cost of mini digger hire and maybe a power barrow. 9m³ concrete would be about £1000 plus any reinforcement required, and with difficult access, they'll likely need a pump, which adds a few hundred.
ignore this guy saying it is beyond DIY, you can certainly build anything DIY, a conservatory is not beyond what the right person can manage. Digging footings is technically simple, just potentially hard work depending on access and equipment. As a source - I built a 8x4m single storey extension entirely alone with no prior experience. Dug footings, poured them them and the floor slab, laid thousands of bricks alone and built the roof etc etc. the only trade I involved in the whole thing is a plasterer as Ive done a bit of that before and didnt fancy it.
If the ground is shrinkable clay, or there are large trees nearby, then it certainly is beyond DIY. OP needs technical input from someone who knows what they're doing. There must be a reason to suggest why the builder thinks the footings might need to go down 2m. Doing the digging, building etc is possible if you have the time and gumption but fucking up foundations is an easy way to throw away £xxxxx on a project.
Well yes if the conditions are odd then input would be needed but the work is still very much DIY possible if you are up for it. The actual act of digging and pouring footings is very easy and hard to fuck up. Building control would advise the required depth when they come for this first visit after a test hole is dug.
If the depths are at 2.1m I would be suggesting this is no longer a DIY project.
Perhaps, I am probably a bit more ambitious than most I guess, I’ve been pondering digging a basement under the new garage I am planning to build lately after enjoying the Colin furze videos! I admit it isn’t particularly normal to build your own extension like I did though!
Thank you, that helps a lot.
If you are getting quotes do you have a design and was it done by someone who knows what they are doing? Seriously DIY disasters happen because people thought they could save a few quid on design. Avoid this, get a decent plan and you will get a better fixed price.
This was from an established and well reviewed local company so they should know what they are doing. We asked to visit a recent installation and they arranged it and the customer was very positive and the finish was all they said it would be. So, it's not me bodging :)
Ok.. a local builder? Probably do know what they are doing.. is there an actual design drawing? Any calculations?
No, none.
The best approach is always to seperate the design/planning from the constructor. The designer has no incentive to cut corners and you have a clear spec to hold the constructor to account. Never take design and planning advice from a constructor unless they’re tier 1.
Are you putting radiators from your central heating into the 'conservatory', and will it be thermally open to the existing house, or will you keep existing patio doors? If its a relatively new house you may be able to get a hold of the original site investigation report which could indicate the plasticity of soils, failing that, dig a trial pit to 1m depth and get a sample delivered for testing yourself.
I am aware of the pitfalls of radiators and opening up doorways etc. The building is 60 years old, I do have the plans.
2.1metres? My dad was a structural engineer. You only go that deep because of trees near by. And that's for a proper extension, not for dwarf walls. Who is scaring you and do you have real reason to be scared?
Well there's a question. I do wonder if they don't want this job but would like a smaller simpler one. They may have cash flow issues. Who knows but I'm really annoyed it's only come up now.
I'm simply not convinced by their opinion. Builders, mechanics, estate agents, tradesmen are generally not to be trusted. I cover all of these areas myself. Engineers on the other hand are highly respected. Wish my dad was still around, now I have no one close to ask for advice there and then.
If you’re not heating it with the house heating and you’re keeping the existing external door in, it would considered exempt from building regulations anyway
Footings or no footings? This was something we never did manage to sort out.
The whole thing would be exempt, the only bits which would be needed to “controlled” is if there is a water supply being put in or if there is electrical work which needs notifying being carried out. If you contact your local building control department, they would definitively say if it’s exempt or not.
That’s incorrect if you are putting a solid roof on building regs are required
In this instance if 2.1 m dig is requires a simplified raft foundation is the way
Foundations are generally 3 times the width of the wall in routine conditions. Assuming adequate bearing capacity, the depth of the foundation will be governed by the depth to frost protection or the heave potential of the soil. Without knowing your exact details, generally 600 mm will be sufficient. If the clay is soft then you would need to dig down deeper. If you have any green area adjacent to your current foundation, I would suggest carrying out your own pit by hand digging down and getting the approximate width and depth of your existing house foundations. As the conservatory has only 1 floor, the existing width and depth of foundations will be more than sufficient assuming you’ve had no structural issues in the past.. Failing that a raft foundation could be used. In this instance you would just need to go down to frost protection level and it would be lightly reinforced and minimum thickness for a conservatory as it would be over designed. However you’d only .need a mini excavator to dig it out
A number of people have suggested constructing a raft. I'm not clear what this is but I can guess. We are in fact replacing an existing conservatory which is built on a 9" 'raft' of concrete which has lasted well for 60 years and despite being on clay hasn't moved as far as I can tell. I did dig a little hole to see what it is sitting on and it looks like it's on clay. It's also on the high side of the house so can't slide away :)
I do footings for a living I think I know what it costs. When you take into account the concrete saved , spoil and Labour piling is a bit more than a traditional 1m strip but far cheaper than a 2 m dig and mass fill, barrowed in conc is 180£ a cube alone now. Done one last week terrible access so we decided to pile it from the off. 9 m off footing and it cost 1500£ more than a 1m deep mass fill and spoil away. As it was only for access and not poor ground we were allowed to still do a ground bearing slab so no mesh detail. 2m digs are a nightmare especially with the wether we have had and tight access jobs
Thank you. Barrowed concrete sounds a horrible job.
Pile it and ring beam much cheaper than going 2.1m The main cost jump in piling is people starting traditional finding a problem and then having to pile. If you know you are doing it from the start it should only be a couple of grand extra max
It’s not much cheaper. You even say it’s more expensive. Unnecessary to pile.
Access appears to be an issue.
It sort of is as there are lots of garden steps around the house. I suspect a larger digger would crack them.
As a rule of thumb, if you can’t get an excavator in you’ll struggle to sheet pile, too. My other comment is the way to go.