Level of detail: Foundation within an RPA

[Gary Prentice]

Working with a client who is trying to get planning consent where part of the foundation is within the RPA of a TPO'd tree.

 

Currently there is a structure with a similar footprint as the proposal, built on a concrete raft. Prior to this structure being built (around 2009) there was a lightweight garage with concrete raft foundation and a brick-built shed.

 

I've discussed this with the TO, who has agreed that a AMS detailing how a piled/suspended ringbeam with airspace and irrigation could be acceptable. I've also spoken to a retired senior planner who reckons that detailed drawings of the pile positions/beam construction wouldn't be required in the application, but would be a matter for building control. I've also read through the T&CPA, NPPF and the authorities local requirements, regarding what are reasonable requests for information, but the case officer appears to require detailed construction drawings from the civil engineer!

 

I've pointed the client to a recent consented application, which was very close to TPO'd trees, where the applicant submitted a one page PDF for a propriety construction 'House-raft' , which seemed 'good enough'. That application had no tree survey, AMS or AIArequirement at all?

 

The CE wants £1200 + Vat for the drawing, after I've accurately identified where all the tree roots are (underneath the existing structure)

 

Is the case officer being unreasonable in her demands?

 

 

[Paul Barton]

Yes, probably. We're finding that more planning officers are front-loading applications to require more and more information up front - which gets very expensive rather quickly for the applicants. 

 

I would have thought that in this case, particularly given the history of structures already in the RPA an indicative foundation section drawing and AMS would be enough - then use an appropriate pre-commencement condition for the rest of the detail. 

[Paul Barton]

7 minutes ago, EdwardC said:

No. Not at all. Demonstrating that the proposal can be delivered without significant harm to the TPO'd is the responsibility of the planning officer, not building control. The wellbeing of the tree is a material consideration. How many times do you see consented applications that can't be built per the permission. They therefore get built however is necessary harming the tree.

Good points Edward - but often the feasibility can be adequately demonstrated without having to produce all the specific detail drawings up front.  If, in principle, pile and a voided raft would be acceptable having done some investigations re rooting and soil, then that should be enough to demonstrate the tree should not be harmed subject to implementation via a detailed AMS. 

[Gary Prentice]

7 hours ago, Paul Barton said:

Yes, probably. We're finding that more planning officers are front-loading applications to require more and more information up front - which gets very expensive rather quickly for the applicants. 

 

I would have thought that in this case, particularly given the history of structures already in the RPA an indicative foundation section drawing and AMS would be enough - then use an appropriate pre-commencement condition for the rest of the detail. 

Thanks Paul. 

I'm inexperienced in this and have some history with the client, who is now coming to me as the only person who appears to her to be making sense.

 

I'm being asked to mediate between the CE, architect and planning and am getting a bit uncomfortable talking/helping/advising outside of my field of expertise.

[Gary Prentice]

5 hours ago, EdwardC said:

No. Not at all. Demonstrating that the proposal can be delivered without significant harm to the TPO'd is the responsibility of the planning officer, not building control. The wellbeing of the tree is a material consideration. How many times do you see consented applications that can't be built per the permission. They therefore get built however is necessary harming the tree.

Hi Edward.

 

In this particular situation,  I don't think it is a case that it can't be done without harm to the tree, or by permission, or whatever.

 

My question (lack of understanding) is more about the inequality about other applications, by other case officers, with far less requirements for details being validated and consented - and then this case officer wants the my client to spend thousands of pounds in an attempt to achieve the same goal. 

 

Theoretically, subject to the AMS explaining/demonstrating how the piling can be done within the RPA, working with the CE to redesign a beam if necessary because a significant root over 25mm dia. is come across seems reasonable. The case officer is asking that every pile position is illustrated pre-app, which would mean demolishing the existing structure, removing the existing footings and concrete raft ( to a AMS) and then undertaking an extensive and expensive root spread survey to design the foundation! Does this really seem reasonable?

 

I appreciate your point of view, I've seen it where levels don't add up, mistakes have been made by the surveyor or the planning department, shit happens! But this case is fairly straightforward - the RPA incursion is less than twenty-five percent, if the endorsed BS5837 calculation is used, and we're talking about a 100% piled foundation because there are so many rooting restrictions surrounding the tree that I can't, honestly, begin to assume where the roots are. WE're trying to demonstrate that we are considering where the roots may be but in this case it's starting to feel that the demands are unreasonable.

 

All I really asking for is a level playing field, what is reasonable? Based on previous applications, what do I tell my client? At the moment, I don't even feel that I know where the playing field is! 

 

Being new to this part of the industry, what do I do? Do I speak with the case officer, Am I speaking out of turn or what?

 

[Gary Prentice]

6 hours ago, Paul Barton said:

Good points Edward - but often the feasibility can be adequately demonstrated without having to produce all the specific detail drawings up front.  If, in principle, pile and a voided raft would be acceptable having done some investigations re rooting and soil, then that should be enough to demonstrate the tree should not be harmed subject to implementation via a detailed AMS. 

Often?

 

If, as in this situation, it is a case, that this can be demonstrated (subject to the the AMS), what can be reasonably demanded? I've had an informal discussion with the TO as to the requirements to the methodology and references to case studies and scientific literature. If he's happy, isn't he the one telling the case officer (who isn't a 'tree person) what is or isn't acceptable? Or do the planning officers feel that they know more than the arb officers, or require more?

 

ATM my client is asking me to go directly to the case officer, to meet and explain things. I'm uncomfortable with this because although I'm comfortable in my own knowledge I don't hink think the architect and civil engineer have any real grasp about trees or tree root development.

[daltontrees]

On 30/07/2017 at 10:59, Gary Prentice said:

 

 

Quote

 

 

[daltontrees]

First posting on the new website, it's mre confusing than the old one , but maybe that's just me?

 

I don't think anyone's really got to the bottom of this question yet, Gary.

 

What a Council is allowed to request to support an application is determined in a couple of ways. There are national requirements for mandatory information, but these don't affect cases like yours. There are then local requirements, and if something is requested it needs to meet 3 tests

- it needs to be on a recently published local list from the Council. The local list is prepared by the local planning authority to clarify what information is usually required for applications of a particular type, scale or location.

- it must be reasonable having regard, in particular, to the nature and scale of the proposed development; and

- it must be about a matter which it is reasonable to think will be a material consideration in the determination of the application.

 

So referring to the first one, I expect most Councils will have published some all-encompassing list of things it can ask for, but you may want to check for the area relevant to your case.

The second one is what we're discussing, and perhaps for a single house extension a very detailed engineering drawing is overkill if this can be dealt with later

The third one is the most useful test, and I imagine the LPA's thinking should be something like this....

Is the tree one that merits protection (i.e. is the rationale for TPOing it originally still valid)?

Does the proposal encroach on the root protection area per 5837?

Are there likely to be roots and a rooting environment under the encroacked part of the rpa, taking account of the current and previous use of theat land, on which the ongoing vitality of the tree depends?

Are there other areas outwith a standard circular rpa which due to the natural distribution of roots are more or equally likely to contain roots and adequate rooting environment?

Would the severing of roots at the edge of the encroachment, if properly done in accordance with 5837, likely cause infection that could result in the loss of the public amenity that the tree provides?

And only if the answers to these questions all say that the rooting is an indispensable part of the rpa, can the rpa be protected by an appropriate foundation design?

Would it suffice to grant consent subject to a condition that allows the LPA to see and approve adequate detailed design before development goes ahead?  

If not, it would probably be reasonable to require a drawing showing in principle how a foundation design would work, and to still condition consent with some stiplulation about deciding pile positions once the positions of roots are known.

 

But based on what you have said, if this drawing is required now to show how roots under an existing concrete raft, then I am inclined to think that this is unreasonable on 2 counts. Firstly the distribution of rooting volume required for the ongoing vitality of the tree  is in reality unikely to rely on near sterile soil beneath impervious concrete. Secondly, the drawings will not achieve much more than would be achieved by stating the principles of appropriate foundation design and having these put into a firmly worded planning condition.

 

All that said, if the foundation drawing is going to be needed in the fullness of time and could be obtained at this stage at the same cost as after consent, then it could be provided now if the client is comfortable that she will get consent on the principles of the proposal, such that the up-front fees aren't potentially wasted. But i suspect it won't remove the need for conditions relating to roots.

 

As for a level playing field, I am sure the LPA will manage to find some way to show why it wants drawings for this case and didn't for an ostensibly similar case nearby.

 

So, it's all about material consideration. But to save roots under an existing slab and create a void that will scarcely get water, will have unnatural gas exchange, will receive no replenishment of nutrients from decaying surface vegetation? I don't think that that is material to the ongong vitality of the tree if it is probable that other areas adjacent to the tree are, and will continue to be , providing better rooting. The usual debate, in other words, about whether circular rpas are sacrosanct. They arent to trees, and they aren't to any right-minded arboriculturist, and if a circle is needed only to humour the unimaginative and unrealistic box-ticking of a LPA, then it's not a material consideration, a refusal to provide a drawing may result in a refusal and an appeal would probably succeed. But appeals take time, and don't LPAs know how far they can push that?

[Gary Prentice]

Thanks Jules, I'll need some time to consider all of this. There's some other elements or considerations that I can't reveal in the circumstances, which are the reason the client does or doesn't want to do certain things. 

 

I have some questions in response, but I'll post them later

 

gary

[Gary Prentice]

On 31/07/2017 at 23:41, daltontrees said:

But to save roots under an existing slab and create a void that will scarcely get water, will have unnatural gas exchange, will receive no replenishment of nutrients from decaying surface vegetation?

Jules, I'm probably taking this out of context, but are you saying that where a raised foundation, with a void, is used that gas exchange is hindered? To a detrimental extent? 

 

At the moment, I'm looking at propriety irrigation methods, utilising rainwater off of the roof. Tick one box. I hadn't considered replenishment of nutrients, but most of the trees that I'm involved with in the far from natural urban environment lack that anyway. 

I can't remember reading any literature, at all, about gaseous exchange under voids, or the tolerances of different species. I wonder if species that tolerate temporary flooding are more tolerant to continuing low oxygen/high CO2 levels