Formula to compensate TPZ

[Boa07]

I agree. New AS draft standard (DR AS 2870) for residential slabs and footings is out for comment and they suggest getting rid of trees (or planting no trees and shrubs on most residential lots) rather than figuring out that at some stage they may get planted ... I say screw piers for all reactive soils ... screw the cost ... screw the footings rather than screwing with the trees.


That's right ... not a single relevant arboricultural text. Perhaps engineers should go about and do their job properly (screw piers) and let us go about doing ours

Thanks for the heads up....this is quite ridiculous I feel a long and unpleasant letter coming on...and not just to the draft committee...if we don't get organised and fast we will find ourselves behind the root barrier on this one and we'll regret it for a VERY long time.

 

[Boa07]

On closer reading of the draft....yes it does have the absurd bibliography from the 1970's and 80's....however it also states within Appendix CH that

This practice note has been written in consultation with senior members of teh arboricultural (ISAA) [missed a C there I suspect????] and housing geotechnical industry (FFSA) and provides guidance to reduce the risk of foundation movement and better footing designs in the proximity of trees
CH5 Alternative Design Mehtods p154

It also makes specific reference to 15yrs of experience from SA supporting the approach taken within the standard, (Design of Buildings for Tree Drying of the Soil p150)

I am going to have to put time aside (which I do not have right now) to carefully read through the document, there appear to be some very odd descriptions of root growth and variations in water demand based on factors including tree height.

In the mean time I strongly suggest any Aussies reading this advise their own state professional bodies of the draft DR AS2870 and have them review it for comment.

 

[Corymbia]

Not quite there

Ignoring all the technical issues, the anthropomorphising etc there is one significant underlying fault to the standard.

What the standard seems to be saying is that engineers can specify a standard that may result in the footing or slab failing if there is a leaking pipe or if someone plants shrubs or trees to close to the house (too close being one or two house lots away.

One must ask the question "Why shouldn't engineers design the structure to deal with what should be an inevitable event?" (- most people plant a tree on their lot). The issue is not just limited to the owner of the structure but impacts on adjacent property owners and existing trees.

It would be like designing a roof that may leak if we got one inch of rain in an hour. No one would tolerate that yet here we are writing a standard that acknowledges that when subjected to a probable event the standard will produce a product that is likely to fail? Pity help us all.