New Garage - Probably Permitted Development… Some Questions

[LightningMat]

paulrockliffe said:

LightningMat said:

No there are no pipes, drains, or anything else like that in that area (I checked in the paperwork from when we bought the house).

Just quoting this for your build thread.........

Dammit... Did I just Jinx myself??

[LightningMat]

Equus said:

GT911 said:

The calculation for the radius of the RPA is 12 times the diameter of the stem at breast height, up to a maximum of 15 metres radius.

... or if they are multi-stemmed trees, it's based on the square root of the sum of each individual stem squared (for up to 5 stems) or the square root of the mean stem diameter squared (for more than 5 stems).

That's to make sure your building doesn't harm the tree.

So, I went and measured a few of the trees today... as luck (?!) would have it, the largest of the trees is in fact a multi-stem tree, with two large stems that split off from each other about half a meter above ground level...

I ran the maths, but wanted to check I got this right (calculated numbers below are rounded to 3dp):

Stem 1 = 2.23m Circumference (therefore 0.710m Diameter)
Stem 2 = 1.93m Circumference (therefore 0.614m Diameter)

Squaring these two Diameters:
Stem 1 = 0.504
Stem 2 = 0.377

Added together = 0.881

and then Square root = 0.939

x 12 for an RPA of = 11.265m

Is that all correct (did I understand correctly on the squaring and square rooting process)?

All the other trees are between 0.3m and 0.6m Diameter, so max calculated RPA of around 8m for any of the others.

That would mean I would need to move the plan over and forward by around 3m from where I had originally thought…

[LightningMat]

However, one thought, the existing garage is already in that area (i.e. around 8m away from this multi-stem tree) - Would that have any material impact? i.e. the fact that the foundations already in place are 3m into the RPA for this particular tree, and has been there for many years, I'm thinking (but I may be wrong… it has been known!) that there would be very little risk of impact by replacing and expanding (the expansion would be away from the tree line)?

Or to ask a slightly different question, not that this is what I want to do, but out of interest - Could I knock it down and rebuild to same spec? Or in the process of removing the old, would the new still need to abide by the RPA rule?

[Equus]

LightningMat said:

RPA of = 11.265m

Yes, your calculations look right to me.

LightningMat said:

However, one thought, the existing garage is already in that area (i.e. around 8m away from this multi-stem tree) - Would that have any material impact? ...

Potentially, yes.

BS5837-2012 said:

Any deviation in the RPA from the original circular plot should take account of the following factors whilst still providing adequate protection for
the root system:
a) the morphology and disposition of the roots, when influenced by past or existing site conditions (e.g. the presence of roads, structures and
underground apparatus),
b) topography and drainage;
c) the soil type and structure;
d) the likely tolerance of the tree to root disturbance or damage, based on factors such as species, age, condition and past management.

... but that would take you into the realms, I would suggest, of stuff that you're not qualified to assess. You'd need a qualified arboriculturalist to make such judgements and agree them with the LPA Tree Officer.

Edited by Equus on Tuesday 20th April 22:20

[GT911]

LightningMat said:

However, one thought, the existing garage is already in that area (i.e. around 8m away from this multi-stem tree) - Would that have any material impact? i.e. the fact that the foundations already in place are 3m into the RPA for this particular tree, and has been there for many years, I'm thinking (but I may be wrong… it has been known!) that there would be very little risk of impact by replacing and expanding (the expansion would be away from the tree line)?

Or to ask a slightly different question, not that this is what I want to do, but out of interest - Could I knock it down and rebuild to same spec? Or in the process of removing the old, would the new still need to abide by the RPA rule?

If the entirety of the foundations in the RPAs are existing and you intend to reuse them, then this should help significantly.
The majority of roots are in the first 600 mm of the ground, so it is likely they will have diverted on coming up against the existing foundations, but there is always the chance they have damaged the foundations, depending on the species.
What species of trees are you dealing with?
If you want to replace the existing foundations and you don't intend to change the incursion into the RPAs from what is already there, it most likely will just need a supervised hand dig and replacement of the foundations, the supervision is done by your appointed arboriculturalist.
As an aside, there are solutions for new build over RPAs that a reasonable Tree Officer will be happy with, particularly if the incursion is not too significant.
These are usually some sort of above-root raft that is supported using smallish diameter piling, helical piling is quite good for this sort of thing.
However you wish to proceed, you do need to get an arboriculturalist to properly assess the situation.

[LightningMat]

GT911 said:

If the entirety of the foundations in the RPAs are existing and you intend to reuse them, then this should help significantly.
The majority of roots are in the first 600 mm of the ground, so it is likely they will have diverted on coming up against the existing foundations, but there is always the chance they have damaged the foundations, depending on the species.
What species of trees are you dealing with?

No idea of the species, there are several different ones - Does bring up a concern though about potential damage to new foundations, even outside of the RPAs... Something to get more details from an Arboriculturalist on then...

GT911 said:

If you want to replace the existing foundations and you don't intend to change the incursion into the RPAs from what is already there, it most likely will just need a supervised hand dig and replacement of the foundations, the supervision is done by your appointed arboriculturalist.
As an aside, there are solutions for new build over RPAs that a reasonable Tree Officer will be happy with, particularly if the incursion is not too significant.
These are usually some sort of above-root raft that is supported using smallish diameter piling, helical piling is quite good for this sort of thing.
However you wish to proceed, you do need to get an arboriculturalist to properly assess the situation.

Helpful things to consider, thanks.

Equus said:

... but that would take you into the realms, I would suggest, of stuff that you're not qualified to assess. You'd need a qualified arboriculturalist to make such judgements and agree them with the LPA Tree Officer.

Oh, without question, I agree wholeheartedly I am well out of my comfort zone, but nonetheless, all the helpful feedback from everyone is appreciated!

Time to find a decent arboriculturalist...