BS5837 Adjusted RPA

[jacquemontii]

With regard to section 4.6.2 of BS5837, it is my view that the circular RPA for these sycamores should be adjusted (see attached photo). In this instance the trees are off site (the site is in the car park above) and the trees are located at least 1m below the retaining wall and the level of the site. I think it is unlikely that any roots growing under the footing of the retaining wall would be well established below the surface of the car park above? Surely the majority of roots will be in the garden below in the more favourable rooting conditions? What does anyone else think? Not sure how I can prove this either way without the aid of a mini digger, so can anyone point to any literature which deals with rooting characteristics in this kind of situation?

[Jon Heuch]

With regard to section 4.6.2 of BS5837, it is my view that the circular RPA for these sycamores should be adjusted (see attached photo). In this instance the trees are off site (the site is in the car park above) and the trees are located at least 1m below the retaining wall and the level of the site. I think it is unlikely that any roots growing under the footing of the retaining wall would be well established below the surface of the car park above? Surely the majority of roots will be in the garden below in the more favourable rooting conditions? What does anyone else think? Not sure how I can prove this either way without the aid of a mini digger, so can anyone point to any literature which deals with rooting characteristics in this kind of situation?

 

Ha ha ha!

 

Without knowing the relative ages of car park and trees (and associated excavations) and without having some information on the depth of any footings of a retaining wall I would say anything is possible in these circumstances - there could be big roots under the carpark; there could be nothing.

 

There is a tree in a big city near me that has cost the local council a lot of money. There is a long established two-way tarmac road between said tree and building. It might be reasonable to assume no roots under the road but a large root has turned up to the extent that direct damage is reported. What the tree is feeding on is anybodies guess but I would steer clear from saying there are no roots without some evidence

[kevinjohnsonmbe]

What are they looking to do? Remove the carpark retaining wall and install a new building? Surely that's just crying out for later drama if the trees remain in situ?? Is it a different land owner at the wall face or the same?

[Gary Prentice]

Maybe time for some exploratory digging!

[jacquemontii]

The retaining wall (which is at least 1m high, although it doesn't look it in the photo) will remain in place and the trees are outside the site ownership. Excavations for a new house are proposed approximately 4m from the wall within the existing car park.

 

I would estimate the trees are approximately 30 to 40 years old and it is thought that the wall pre-dates the trees. The footing depth of the existing retaining wall is unknown at this stage.

 

My thoughts are that the roots are unlikely to be established below the compacted surface of the existing car park within the site, and that the likely distribution of roots will be located within the more favourable soil conditions in the gardens below.

[daltontrees]

The retaining wall (which is at least 1m high, although it doesn't look it in the photo) will remain in place and the trees are outside the site ownership. Excavations for a new house are proposed approximately 4m from the wall within the existing car park.

 

I would estimate the trees are approximately 30 to 40 years old and it is thought that the wall pre-dates the trees. The footing depth of the existing retaining wall is unknown at this stage.

 

My thoughts are that the roots are unlikely to be established below the compacted surface of the existing car park within the site, and that the likely distribution of roots will be located within the more favourable soil conditions in the gardens below.

 

This comes up againa and again, especially on UKTC. There is a borad consensus that there is no hard scientific evidence about rooting distribution in situations like this.

 

5837ers seem a little obsessed with avoiding damage to roots, but what 5837 really says is that you need to establish what volume of soil is needed for teh ongoing vitality of a tree. SO it's as important to establish where it will get support, nutrints, water etc. as where it gets the m from at present. Now obviously if all the roots are on one side and the only soli that will be available after developmentis on the other side, it would be nuts to sever allt the roots and expect the tree to move into the soil. So initially matching the future requirement to the current distribution is of fundamental importance.

 

I'd say if that wall is of any sort of age the three will not be deriving significant benefit from material under the car park but will be deriving important tensile support on that side. The rooting distribution will probably be in all other respects strongly asymmetrical downslope and if so that's the area to safeguard for water and nutrients.

 

If you can get a hold of Tree Roots in the Built Environment, it will ask every question you would eventually ask yourself, but not for want of trying the authors will leave you realising that there is no proof. Without a lottery win to squander on investigations anyway.

[kevinjohnsonmbe]

This comes up againa and again, especially on UKTC. There is a borad consensus that there is no hard scientific evidence about rooting distribution in situations like this.

 

 

 

5837ers seem a little obsessed with avoiding damage to roots, but what 5837 really says is that you need to establish what volume of soil is needed for teh ongoing vitality of a tree. SO it's as important to establish where it will get support, nutrints, water etc. as where it gets the m from at present. Now obviously if all the roots are on one side and the only soli that will be available after developmentis on the other side, it would be nuts to sever allt the roots and expect the tree to move into the soil. So initially matching the future requirement to the current distribution is of fundamental importance.

 

 

 

I'd say if that wall is of any sort of age the three will not be deriving significant benefit from material under the car park but will be deriving important tensile support on that side. The rooting distribution will probably be in all other respects strongly asymmetrical downslope and if so that's the area to safeguard for water and nutrients.

 

 

 

If you can get a hold of Tree Roots in the Built Environment, it will ask every question you would eventually ask yourself, but not for want of trying the authors will leave you realising that there is no proof. Without a lottery win to squander on investigations anyway.

 

 

That makes a lot of sense.

 

But, in this apparent situation, it would be impossible for the prospective developer to safeguard the "un-owned" area of rooting no?

 

Can't be done so, surely, the tree can't be safeguarded.

 

So unless the neighbour removes the tree - with or without inducement - the tree can't be safeguarded.

 

So, if the neighbour wants to keep the tree, the development proposal can't be approved?

 

All questions and thinking aloud!!

 

Also, wondering, what sort of footing would be required to support anything more than a shed on that sort of made-up ground?? Unless the lower level is excavated rather than the higher level being made-up??

[daltontrees]

So, if the neighbour wants to keep the tree, the development proposal can't be approved?

 

 

If the developer has not secured rights to work offsite, there is no new threat to the tree from development. So th development could be approved.

 

But more generally, it can't be assumed that the Council would look for these trees to be retained. At this stage the 5837 survey might just be needed to inform the designers and planners. It's rare and arguably wrong for conditions of consent to relate to things on ground not within the appication site anyway. Council'd probably have to TPO the trees.

[Gary Prentice]

That makes a lot of sense.

 

 

 

Also, wondering, what sort of footing would be required to support anything more than a shed on that sort of made-up ground?? Unless the lower level is excavated rather than the higher level being made-up??

 

Piled. I've heard of some incredible depths being necessary on some sites to hit solid ground.

[daltontrees]

Piled. I've heard of some incredible depths being necessary on some sites to hit solid ground.

 

I was the developer on a site in the highlands of scotland, we drove piles to 9 metres. About 50 of them. Inside an existing building. You wonder if you're ever going to hit anything solid. It's an expensive open-ended business.

 

But statistically low chance of hitting a major root with a pile.