Pile foundations & Tree root protection areas
Discussion
Chaps,
I've got planning permission for a 2 storey garage extension which is surrounded by a number of trees.
Planning approval is subject to the usual measures of protection of tree roots. As it turns out, three of the trees have wider stem diameters than we had realised, meaning that the root protection area is wider than the original design had allowed for. If I offset a radius around the tree, it now extends about 1m beneath the proposed extension.
A few questions,
1. I read somewhere that the root protection area does not have to be a circle. Is this correct? (i.e. could the zone be marked in a rectangle or oval shape rather than a circle? Provided that the area equates to the minimum. Say if i offset the rectangle by 1m i'd be clear of the founds and 3 sides of the tree roots are completely un-disturbed)
2. 20% tolerance for tree root protection. I've only ever seen this related to a single isolated tree in the middle of a field. I'm guessing in a fairly densely populated area the RPA needs to be calculated to the full shibang so I won't be able to knock 20% off the area?
3. If I need to work on a circular RPA would piled foundations be permitted within the Root protection zone? I'm assuming they will cause less disturbance than a deep trench foundation. As strip foundations would need to be 2.7m deep, Piles are actually the cheaper option on this project, so will have an engineer design piles regardless.
Just to add none of the trees have a TPO.
Advice would be greatly appreciated.
Thanks!
I've got planning permission for a 2 storey garage extension which is surrounded by a number of trees.
Planning approval is subject to the usual measures of protection of tree roots. As it turns out, three of the trees have wider stem diameters than we had realised, meaning that the root protection area is wider than the original design had allowed for. If I offset a radius around the tree, it now extends about 1m beneath the proposed extension.
A few questions,
1. I read somewhere that the root protection area does not have to be a circle. Is this correct? (i.e. could the zone be marked in a rectangle or oval shape rather than a circle? Provided that the area equates to the minimum. Say if i offset the rectangle by 1m i'd be clear of the founds and 3 sides of the tree roots are completely un-disturbed)
2. 20% tolerance for tree root protection. I've only ever seen this related to a single isolated tree in the middle of a field. I'm guessing in a fairly densely populated area the RPA needs to be calculated to the full shibang so I won't be able to knock 20% off the area?
3. If I need to work on a circular RPA would piled foundations be permitted within the Root protection zone? I'm assuming they will cause less disturbance than a deep trench foundation. As strip foundations would need to be 2.7m deep, Piles are actually the cheaper option on this project, so will have an engineer design piles regardless.
Just to add none of the trees have a TPO.
Advice would be greatly appreciated.
Thanks!
Most trees and roots I have worked near with tpo's have the roots marked out as being underneath the crown, e.g if all branches are right over to west side that is where the roots will be. Most ecologists seem to use this rather than girth of trunk.'would that help? If so get an ecologist to do a report.
Not sure on legalities if no tpo.
2.7 m founds - u sure the engineer didn't hear 20 story extension? Sounds v deep, maybe poor ground where u are?
Not sure on legalities if no tpo.
2.7 m founds - u sure the engineer didn't hear 20 story extension? Sounds v deep, maybe poor ground where u are?
cqueen said:
Good document that , saved it for issue to conbtractors where working within close proximity of trees.torqueofthedevil said:
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2.7 m founds - u sure the engineer didn't hear 20 story extension? Sounds v deep, maybe poor ground where u are?
Our foundations for a modest extension were 2.64 metres deep to get below thw adjoining sewer. (Hopefully that lump of concrete will help to hold up the corner of the house). 2.7 m founds - u sure the engineer didn't hear 20 story extension? Sounds v deep, maybe poor ground where u are?
It's the same with tree roots deep foundations solve potential problems
Thanks for the replies.
Re: depth of foundations, this is to do with shrinkage and expansion. The ground is medium clay with a large poplar, sycamore, ash and apple near by. Approx. 600mm trunk dia and 5m away from the extension. None of the foliage spreads over the extension. Local guidelines and building control ask for 2.5m foundations due to heave, but as I mentioned, piles are cheaper (around 30% less) for this particular build.
Looking at things I think it will just be a case of providing above ground protection for the RPA during construction as there aren't any TPO's.
The planners have actually been quite relaxed about it all, but I would want to avoid losing any of the trees as they are very well established and in good condition. So my question was more a case of wondering if keeping the trees would have knock on implications.
Good little link that thanks.
Re: depth of foundations, this is to do with shrinkage and expansion. The ground is medium clay with a large poplar, sycamore, ash and apple near by. Approx. 600mm trunk dia and 5m away from the extension. None of the foliage spreads over the extension. Local guidelines and building control ask for 2.5m foundations due to heave, but as I mentioned, piles are cheaper (around 30% less) for this particular build.
Looking at things I think it will just be a case of providing above ground protection for the RPA during construction as there aren't any TPO's.
The planners have actually been quite relaxed about it all, but I would want to avoid losing any of the trees as they are very well established and in good condition. So my question was more a case of wondering if keeping the trees would have knock on implications.
Good little link that thanks.
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