So the house we are buying has been sat with 2/3rds of its backside in the hillside for the last 270 years, solid stone walls holding up the landscape. IF, and this is a big IF, we dug it out and dried its bum and put in a cuffing great big retaining wall, what effect could this have on the house in terms of the stresses and strains it would've been under and would now be released from. No foundations to speak of. 1/3rd of the house already has a retaining wall some 3 feet set back off the house. The other 2/3 increases in height (house is on a slope front to back AND left to right) of soil against the back wall from around 2 ft to 7ft along a run of approximately 40ft. Obviously a very costly job as well (though I have been unable to find out how much as of yet). If it happened - how do you shore up the bank temporarily whilst digging out and putting in the wall? Any thought? Ideas?
- Thread starter TheSpid
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88v8
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How thick are the walls?
Made of?
What's the ground?.... clay ...sand...
When digging for the retaining wall - which should have a batter on both wall and footing - the existing walls must not be undercut by a 45 degree downslope produced from the outer edge of the existing foundation (or absence thereof).
The retaining wall should have weep holes to release pore pressure.
Ivor
Made of?
What's the ground?.... clay ...sand...
When digging for the retaining wall - which should have a batter on both wall and footing - the existing walls must not be undercut by a 45 degree downslope produced from the outer edge of the existing foundation (or absence thereof).
The retaining wall should have weep holes to release pore pressure.
Ivor
Flyfisher
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Assuming there are no signs of movement then after 270 years it seems likely that everything has reached a stable equilibrium. The proposed changes seem like a quite significant change to the local conditions and could easily upset that equilibrium, depending on many factors as questioned above. I've read that even apparently 'helpful' things such as underpinning can affect the local ground conditions, leading to unexpected movements.
I can't answer your questions but I think you're right to be asking them. However, I'd say they are questions for a professional structural engineer, which should also afford some level of indemnity against any future problems.
I can't answer your questions but I think you're right to be asking them. However, I'd say they are questions for a professional structural engineer, which should also afford some level of indemnity against any future problems.
88v8 - walls are solid stone - probably 2 stone walls with a rubble middle (circa 1750) - they are around 2ft wide maybe a little more. Ground is loamy clay soil - seasonally wet and slowly permeable - struggling to understand the 45 degree thing (my bad brain, sorry) can you do an idiot guide to what that means? Many thanks for the reply.
Flyfisher - No signs of movement at all. I was thinking that I would get a structural engineer in IF we decide to go ahead - hoping to NOT have to, but will depend on how dry the walls are inside the house. Like you say, I expect that a stable equilibrium has been reached, and my fears are in changing the environment the house will become destabilised. I'm hoping lots of remedial work inside, limecrete floors instead of the concrete ones, in addition to the lime render and plaster etc will mean the back stone wall won't get damp. Looking at French drains too but seeing varying opinions on that too. Many thanks for your reply.
Flyfisher - No signs of movement at all. I was thinking that I would get a structural engineer in IF we decide to go ahead - hoping to NOT have to, but will depend on how dry the walls are inside the house. Like you say, I expect that a stable equilibrium has been reached, and my fears are in changing the environment the house will become destabilised. I'm hoping lots of remedial work inside, limecrete floors instead of the concrete ones, in addition to the lime render and plaster etc will mean the back stone wall won't get damp. Looking at French drains too but seeing varying opinions on that too. Many thanks for your reply.
88v8
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TheSpid said:
45 degree...
http://prugarinc.com/structural-terms/what-is-undercutting-of-a-footing/
Shrinkable clay. Mmmm.
Knowing they were building it against a bank, the original builders may or may not have been somewhat slaphappy in their stonework.
I had a ditch dug against our back wall which was 3ft in the ground.
Retaining wall.
French drain.
The problem we now have is that the builders of 1620ish never meant their external stonework to be exposed; leaving aside the lumpy visuals, in practical terms it doesn't shed water effectively, there are flat areas on the stones, water traps, and now four years on we have salts appearing on the inner face - the construction is two-layer + rubble, like yours - which shows that water is creeping through the wall. I suppose I need to do some benching and more extensive pointing, which will further degrade the visuals.
Hehyo.
French drain may help, permeable surface above it, so long as the water has a decent fall and somewhere to go.
https://www.google.co.uk/search?q=french+drain+section&tbm=isch&source=iu&ictx=1&fir=ll-38vxTi5lXZM%253A%252ChT8f_cG7Z5g94M%252C_&usg=___uXUUffAv2bqtNzSEKFrqJHoQc0%3D&sa=X&ved=0ahUKEwjcooSvloLaAhWsB8AKHWmACMIQ9QEIMjAB&biw=1280&bih=784#imgrc=ll-38vxTi5lXZM:
I wrapped our perforated pipe in two layers of Terram to prevent it silting up.
Does it work? Does water flow through it? I've never been out in the neighbour's field to observe the outfall while it's raining hard, so no idea!!
Ivor
Feltwell
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No one can really give you a full opinion without seeing it but here are a few pointers:-
- As has already been said, golden rule that you should not break is once you find where the bottom of the house wall is do not dig within the area that extends out at a 45 degree angle from the bottom of the wall - that is the area that is supporting your wall
- If you have enough room then the cheapest way usually to give you the space to build your new wall is to dig the soil out battered back at a 45 degree angle to the bottom of the edge of the foundations of your new wall - that is safe in nearly all circumstances - then backfill again after you've built the wall. Unsupported excavations with steeper sides can be extremely dangerous, but what you can get away with depends on your local ground conditions and how wet it is at the time. Sheer sided trenches can be dug safely with appropriate support installed from above before anyone goes into the trench, but will add considerably to your costs
- The whole trench does not have to be dug at once - a common technique if digging close to an existing building is to dig small lengths at a time and fill each with mass concrete as a foundation before moving onto the next. Makes it a slow job though.
- You don't have to build a brick or block wall - gabions can be a cheap way to give a good retaining wall that is pretty much maintenance free. Gabions are wire mesh cages that you position whilst empty and then fill with stones / rubble before wiring the lid shut, their sheer weight is what holds the earth back - low tech but very effective and normally no foundations required so you don't have to dig as deep as other options, you can stay at the same level as the bottom of your house wall - and you could then build something much lighter and non-structural in front of them to hide them if required, though they can look OK as they are with a bit of landscaping, especially if you fill them so the front face is stone to match your house with cheap rubble or stone going in behind. With your height you'd have multiple rows of gabions, single at one end and then add an extra row on top & stepped back a bit as the height increases. They are often 0.5m high cages, a 1m long cage should be about £18, to give you an idea of cost - google "Gabion Baskets" and you'll find plenty . They're galvanised but eventually the cages do rust, especially at the back, but they should last a minimum of 60 years. There are other options as well, there are a lot of proprietary modular systems for retaining walls.
- If the house walls are that thick with no sign of distress then you're unlikely to have a problem with the pressure on them being taken away, but getting a structural engineer who is experienced in old houses to both review this and look at your plans for the retaining wall would be a good idea. You may need engineer's calculations for building regs for the new wall, not sure if building regs will apply to it or not. My experience on retaining walls is from big civil engineering jobs which are regulated in a different way.
- If a solid wall then plenty of weep holes are a must as has been said, hydrostatic pressure from a water build up behind a solid wall with no or blocked weep holes is very dangerous indeed as it can lead to sudden & catastrophic wall collapse.
In my opinion French drains are a second-best option only for where having a clear gap against the wall is definitely not possible.
Hope that helps!
- As has already been said, golden rule that you should not break is once you find where the bottom of the house wall is do not dig within the area that extends out at a 45 degree angle from the bottom of the wall - that is the area that is supporting your wall
- If you have enough room then the cheapest way usually to give you the space to build your new wall is to dig the soil out battered back at a 45 degree angle to the bottom of the edge of the foundations of your new wall - that is safe in nearly all circumstances - then backfill again after you've built the wall. Unsupported excavations with steeper sides can be extremely dangerous, but what you can get away with depends on your local ground conditions and how wet it is at the time. Sheer sided trenches can be dug safely with appropriate support installed from above before anyone goes into the trench, but will add considerably to your costs
- The whole trench does not have to be dug at once - a common technique if digging close to an existing building is to dig small lengths at a time and fill each with mass concrete as a foundation before moving onto the next. Makes it a slow job though.
- You don't have to build a brick or block wall - gabions can be a cheap way to give a good retaining wall that is pretty much maintenance free. Gabions are wire mesh cages that you position whilst empty and then fill with stones / rubble before wiring the lid shut, their sheer weight is what holds the earth back - low tech but very effective and normally no foundations required so you don't have to dig as deep as other options, you can stay at the same level as the bottom of your house wall - and you could then build something much lighter and non-structural in front of them to hide them if required, though they can look OK as they are with a bit of landscaping, especially if you fill them so the front face is stone to match your house with cheap rubble or stone going in behind. With your height you'd have multiple rows of gabions, single at one end and then add an extra row on top & stepped back a bit as the height increases. They are often 0.5m high cages, a 1m long cage should be about £18, to give you an idea of cost - google "Gabion Baskets" and you'll find plenty . They're galvanised but eventually the cages do rust, especially at the back, but they should last a minimum of 60 years. There are other options as well, there are a lot of proprietary modular systems for retaining walls.
- If the house walls are that thick with no sign of distress then you're unlikely to have a problem with the pressure on them being taken away, but getting a structural engineer who is experienced in old houses to both review this and look at your plans for the retaining wall would be a good idea. You may need engineer's calculations for building regs for the new wall, not sure if building regs will apply to it or not. My experience on retaining walls is from big civil engineering jobs which are regulated in a different way.
- If a solid wall then plenty of weep holes are a must as has been said, hydrostatic pressure from a water build up behind a solid wall with no or blocked weep holes is very dangerous indeed as it can lead to sudden & catastrophic wall collapse.
In my opinion French drains are a second-best option only for where having a clear gap against the wall is definitely not possible.
Hope that helps!