Level of detail: Foundation within an RPA

[daltontrees]

I recall being at the AA conference a few years ago in Exeter and listening to a really interesting presentation from arborists representing a municipality in Sweded. Names escape me right now, but the whole thing made perfect sense to me. The presentation was about civil engineering structures in streets that were designed to provide good rooting environment for street trees. For anyone who has been at  a club or concert where carbon dioxide is used to create a ground layer of fog, it's obvious as any chemist knows that CO2 is denser than air, and hugs the ground. What the presentation said was that the structures weree being designed to copy what hapens in nature, allowing for rises and then drops in ground water levels to push CO2 to the surface where it could be vented away, and then draw oxygen down. Cutting a long story short, and taking it that it is good to have CO2 pushed to the surface in this way and removed by air movements, it seems imperative that voids beneath buildings that are being used as part of the rooting environment must be vented, and effectively so, or else roots will be partly or wholly asphyxiated.  The occasional existence of root in unventilated voids doesn't mean that these environments are productive rooting environments, the roots may be getting by, but cannot possibly be as productive as rooting out in the open. An unvented void will just push CO2 up to or near the surface, then pull it back down when ground water levels drop again.

 

Bear in mind CO2 is an unwanted by-product of root respiration and, unlike with in leaves where some CO2 can be re-used in photosynthesis, a build-up will result in poisoning (asphyxiation) of roots.

 

I'll get on to nutrient replacement after I've had my dinner.   

[kevinjohnsonmbe]

On 31 July 2017 at 23:41, daltontrees said:

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?

Was a great post that!  Meant to say that earlier!!

[Gary Prentice]

1 hour ago, daltontrees said:

it seems imperative that voids beneath buildings that are being used as part of the rooting environment must be vented,

I don't know why, but I was assuming that they were generally pretty much open enough, to allow a free flow of air. This is where my lack of construction knowledge will catch me out.

 

I've been a bit confused as some of the literature that I've been looking at for suspended ring beams shows impermeable surfaces over the existing ground levels. Piling for reasons other than tree roots?

 

Just found this on a quick search and assume that it would be the minimum specification for air flow if those are airbricks/vents in the exterior wall connecting via the wall cavity to the air void below.

 

 

Really liking this new attachment method

Edited August 3, 2017 by Gary Prentice

[Gary Prentice]

Found a solution

[daltontrees]

PIling to avoid tree roots is about the least likely reason for piling. It's generally an expensive solution compared to strip or raft foundations. So I would expect a lot of standard piling details to include oversite concrete because roots are not a consideration.

 

The detail you have found seems to have airbrick-type vents just below floor level. Normally subfloor ventilation is to remove humidity, but the way that detail is drawn would not promote air movement across the solum and might not on its own be adequate to remove CO2.

 

If you're going to go to the over-the-top expense of piling to protect roots, it would be a good idea to make sure the roots are not then asphyxiated, otherewise it's been a waste of time and money. And roots.

Edited August 5, 2017 by daltontrees

[daltontrees]

Here's the first part of that Swedish presentation. I can send the rest to anyone that wants it, but it's A BIG file.

 

3 separate mentions of the need to remove poisonous CO2.

wed_05_Bjorn_Embren-The_Stockholm_Solution pt1.pdf

[Gary Prentice]

On 03/08/2017 at 20:25, Gary Prentice said:

At the moment, I'm looking at propriety irrigation methods, utilising rainwater off of the roof.

Is there any propriety irrigation methods for under-void watering, using rainwater off of the roof? Anyone

 

 

I've been searching the websites in the expectation that I would find something similar to tree pit watering systems suitable for this, but to no avail. Is there anything available that anyone has specified (and had accepted) or is it the case of adapting something else to suit?

[daltontrees]

I don't imagine it needs to be much more complicated than this...

 

https://www.guttermate.co.uk/irrigation/porous-pipe-ring-irrigation-kit-977.html

 

Well, connection from gutter to water butt, and then to this network of porous pipes. This seems nice and simple because it need only be staked onto the solum, and because it sprinkles rather than puts water directly into the ground the roots will not choke the pipes. Looks like coverage of about 7m x 7m. It would be common sense to match the collection area (roof) to distribution area.

 

That said, I've never tried something like this before. Do you think it would work?

[Gary Prentice]

I don't see why not. I found this http://www.rainwaterirrigation.co.uk/ last night, option 2 does away with the Water butt, but I wonder how difficult it would be to balance the system, to make sure some areas didn't get over-watered and others under. 

 

 

This jobs interesting, with the number of issues to overcome and explain.

[daltontrees]

13 hours ago, Gary Prentice said:

I don't see why not. I found this http://www.rainwaterirrigation.co.uk/ last night, option 2 does away with the Water butt, but I wonder how difficult it would be to balance the system, to make sure some areas didn't get over-watered and others under. 

 

 

This jobs interesting, with the number of issues to overcome and explain.

Yes that would do away with the water butt,  but would only work I think if carefully set up so tha the flow holes are all at the same level, requiring brackets on (in your case) the inside face of the wall. It's main attraction might be as a means of getting rid of water off a roof to avoid putting it into surfacfe drains, raher than as an irrigation system, as it might over-irrigate anyway.

 

I think the system I spotted is a bit better beacause it's easy to fit and just requires a flexible hose connection to it. But it requires water pressure (tap or water butt). If butt is not an option, I can still see how it can be done but can't see a product that does it (it would involve using a length of downpipe as the waterbutt).

 

You'd think that there would be a product for this by now...