Trees and footings

Amanda Gazzola

We have started a build and the front of the house was designed around a very large/advanced Moreton Bay ash (would have to be 12-15m high). An architectural error now means that the tree is within the footprint of the house. The architect would prefer we cut the tree down but we are desperate to keep it and had the architect redesign the front entrance of the house. However even a redesign will mean the footings will still be dug within the critical root zone (they will be dug aprox 1-1.5m from the trunk on two sides). I have attached an image of the tree (tree is in top left corner of image) and the plan showing how close it is to the house/footings.

We need some serious advise. Not only is all this holding up the building but it is costing more. Can this tree survive root interference? I have had an arborist look at the problem and he feels it can be done. What are your thoughts? Cheers

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Attached Files

Amended-tree position-1.pdf (123.4 KB, 38 views)

Eric Frei

Survival vs anchorage are two different things. The tree might not die but it might blow over in years to come.

Also what will it be like in 10 years time?

Is there sufficient room for growth?

Calculations are based on DBH not tree height. There's an online calculator to assist including segments so you can see how much root system will be lost. Please visit the link below and run the numbers for us.

Online Calculator for TPZs and SRZs as per AS4970-2009

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Garry Brockley

do all three leaders connect at ground level or are there three seperate trees there?
if thats one tree you are going to have serious problems in the future a higher likelyhood of failure at basal level, i wouldn't want that over my house personally.

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redmower

Amanda
Without pre-empting the figures that are gained form the on-line calculator and the subsequent discussion.

Although I am inclined to agree with Gary in general about the risk to the residence but take comfort in the knowledge that your arborist observed on-site that you could keep the tree and build the house.

Now given your stated attachment to the tree in question I would put forward a middle-ground option. Keep the tree perhaps with selective pruning to reduce mass and weight over the asset, have the tree evaluated at a suitable frequency maybe 6 monthly in first two years then annually for a few years if all goes well. BUT in maybe five or ten years time before the risk escalates to serious the tree is managed to protect the residence (this may mean removal). In the interim you implement a planting program to develop a treescape that is more suitable to the site. In five years the new young trees can easily take over the role of this fine looking Moreton Bay ash.

Good luck with it, and I like the determination you have to preserve a fine looking tree. But whatever you do, remember to monitor this and any other trees near your house and other assets over time, maybe annually.

RM

James Taylor

Maybe you could look into using different engineering techniques to build the footings, such as using Piers instead of a slab. if you conducted some investigation into the location of the roots in the CRZ you could position the piers around them thus minimising the damage.

I would also make sure you set up as large a tree protection zone as possible around the tree to protect the roots and trunk from heavy machinery during construction. If you are going to dig in the CRZ as much work as possible should be done by hand tools and any roots which need to be cut should be done with a hand or chainsaw, excavators tend to rip and shatter the roots causing extensive damage and allowing pathogens to attack the tree.

Hopefully your Arborist will help with all these issues anyway. good luck.