The origin of Root Protection Areas

[daltontrees]

I have just put this on a facebook group but I am posting exactly the same thing here for anyone that's interested.

 

I believe a draft of revised BS5837 is due soon. WIth this in mind I set out to try and get to the bottom of where we got our RPR = 12 x dbh system. Turns out it has come from a single superseded publication in 1998 by Matheny and Clark which even they have moved on from. Attached is a link to my notes which systematically goes throught every calculation method in BS5837 (1980, 1991, 2005 and 2012).

I am not advocating anything in particular, but I hope as many TOs and consultants will pitch in on the revised BS from a slightly better informed position, whatever your suggestions are.

Comments public or private welcome, but don't shoot, I'm just the messenger.

HISTORY OF THE DIMENSIONS OF ROOT PROTECTION IN BS5837.pdf

[daltontrees]

Exec summary (which is not an excuse for not reading the whole thing) - BS5837 has got dumbed down over the years and then frozen in time with the 12x multiplier based on a single bit of superseded research. Meantime the rest of the world has moved on and we appear frozen in the past.

[Dan Maynard]

The ISA system seems to make a lot of sense to me, some dependency on species and age is surely a good thing.

 

Also like the earlier standard saying RPA can be shifted over a bit, that question came up a few weeks ago with a patio.

[monkeybusiness]

I don’t personally think the 12x rule is bad - it’s something that buildermorons can physically measure and it gives pretty decent protection (and is easy to police if the planners have the will to do so). The 12x rule gives a great deal of protection and future success to retained trees.

(It is also fairly straightforward to justify offsetting/manipulating the rpa if the rooting environment doesn’t fit the ‘perfect circle’ basic calculation).

I’d be concerned that if rpas end up ‘growing’ or becoming more complicated (ie more expensive) then there will be even more speculative felling than the current 5837 system forces (and it is already pretty bad!). 

Edited March 4 by monkeybusiness

[Chris at eden]

14 hours ago, Dan Maynard said:

The ISA system seems to make a lot of sense to me, some dependency on species and age is surely a good thing.

 

Also like the earlier standard saying RPA can be shifted over a bit, that question came up a few weeks ago with a patio.

The problem with the old 20% offset was that some folk were offsetting them in the direction of, and under roads to create more build space in gardens.  That doesn’t make sense as the soft garden area is likely to be ideal rooting whereas the road will be suboptimal. Some folk were reducing instead of offsetting as well.
 

The new standard does allow for changing the RPA to reflect barriers to root growth but it says deviation from the circle should be justified by the Arb.  I personally think there is some scope to offset slightly or at least there should be. 
 

I did an AMS a few weeks ago which was secured by condition, bad start I know.  The building footprint occupied less than 1% of the RPA, from memory I think it something like 0.2%. A tiny amount.  I suggested hand digging and root pruning under supervision.  My logic was that roots at this distance will not be bio-mechanical, and any fine roots can be replaced around the rest of the RPA as the build was only to the east. This was all presented in the AIA. 
 

The TO came back saying that there was a road in the opposite direction so we couldn’t offset. There isn’t, the road is to the south.  I pointed out that roots could be replaced to the north and west. He said no and insisted on pile and beam.  For 0.2%. 
 

Problem was that as the LPA had secured the info via condition, there was no scope to appeal. 
 

I am okay with the 12 x Dia but I think that it should be clarified that some offsetting could be possible if justified based on common sense as above.  I think a standard off setting of 20% is too much though without a robust justification.    
 

This is a bit off piste but one of the other things he objected to was the removal of a Cat U tree that was next to the proposed drive.  It was split at the base and hung up in the adjacent tree.  He first said that there was no justification. I pointed out that the condition was advised in the survey schedule and also in the specification of tree works in the AMS.  He then said okay you can fell it but I want a separate TPO application and it needs to be shown as retained on the TPP.  Bizarrely, he didn’t want a condition survey with the TPO app even though this is a requirement of the one app!  What is the point!  
 

Cheers 

 

Chris 

[daltontrees]

16 hours ago, monkeybusiness said:

I don’t personally think the 12x rule is bad - it’s something that buildermorons can physically measure and it gives pretty decent protection (and is easy to police if the planners have the will to do so). The 12x rule gives a great deal of protection and future success to retained trees.

(It is also fairly straightforward to justify offsetting/manipulating the rpa if the rooting environment doesn’t fit the ‘perfect circle’ basic calculation).

I’d be concerned that if rpas end up ‘growing’ or becoming more complicated (ie more expensive) then there will be even more speculative felling than the current 5837 system forces (and it is already pretty bad!). 

It takes so long to know if it works or not. I have seen limes with Kretzschmaria that I suspect have contracted it following roote severance a decade or more beforehand. The primitive 12x rule also overprotects trees compared with the ISA guidelines and underprotects for other trees especially ancient and veteran where the Ancient Tree Forum urges 15x. or drip line + 5 metres.

Personally I am not in favour of simple if it is also wrong, no matter how dumb the users are. Educating them and enforcing will save trees, using a system that underprotects won't.

Likewise if overprotection (or the perception of it) stimulates pre-emptive felling then that should be addressed ratherh than pretending that the system works and then seeing trees die in a few years.

I don't share your concerns about enforecement difficulties. Protection should be dimensioned and set out and checked on site, and after that it doesn't matter what the shape is.

It would be so much better if, when using the 12x system, we knew that it worked and why.

[daltontrees]

6 hours ago, Chris at eden said:

The problem with the old 20% offset was that some folk were offsetting them in the direction of, and under roads to create more build space in gardens.  That doesn’t make sense as the soft garden area is likely to be ideal rooting whereas the road will be suboptimal. Some folk were reducing instead of offsetting as well.
 

The new standard does allow for changing the RPA to reflect barriers to root growth but it says deviation from the circle should be justified by the Arb.  I personally think there is some scope to offset slightly or at least there should be. 
 

I did an AMS a few weeks ago which was secured by condition, bad start I know.  The building footprint occupied less than 1% of the RPA, from memory I think it something like 0.2%. A tiny amount.  I suggested hand digging and root pruning under supervision.  My logic was that roots at this distance will not be bio-mechanical, and any fine roots can be replaced around the rest of the RPA as the build was only to the east. This was all presented in the AIA. 
 

The TO came back saying that there was a road in the opposite direction so we couldn’t offset. There isn’t, the road is to the south.  I pointed out that roots could be replaced to the north and west. He said no and insisted on pile and beam.  For 0.2%. 
 

Problem was that as the LPA had secured the info via condition, there was no scope to appeal. 
 

I am okay with the 12 x Dia but I think that it should be clarified that some offsetting could be possible if justified based on common sense as above.  I think a standard off setting of 20% is too much though without a robust justification.    
 

This is a bit off piste but one of the other things he objected to was the removal of a Cat U tree that was next to the proposed drive.  It was split at the base and hung up in the adjacent tree.  He first said that there was no justification. I pointed out that the condition was advised in the survey schedule and also in the specification of tree works in the AMS.  He then said okay you can fell it but I want a separate TPO application and it needs to be shown as retained on the TPP.  Bizarrely, he didn’t want a condition survey with the TPO app even though this is a requirement of the one app!  What is the point!  
 

Cheers 

 

Chris 

I think your problem there is that the TO is stubborn and jobsworthy and maybe not too clued up on how trees actually work. I'm trying not to use a more succinct word for him. That sort of attitude just breeds resentment and encourages pre-emptive felling. I personally think that offsetting is somethimed justifiable but I like to show that there is at least 2x as much rooting available in the offset side.

 

Offsetting was stopped because people were taking the piss. Quite right.