Storm damage to trees, and the damage a tree can do to buildings
Education is a wonderful thing. Unfortunately it comes to most of us after the event. Only after a car has overheated, the engine seized, and the tyres worn unevenly do we learn about tyre pressures, expansion box levels, and why an engine has a dipstick. Usually in that order with the final one being the driver! The planting of trees and their proximity to buildings is another example of this. Only when we have a storm such as ‘Doris’ on 23rd February 2017 do we begin to ask ‘What is the safe distance of trees to buildings?’ rather than ‘That’ll look nice.’
Finding a reliable answer to how safe a distance a tree should be from a building other than ‘further away than the maximum it can grow,’ is not easy. It can vary according to who you ask. Insurers are cautious and the horticultural experts are more interested in the tree than the property.
One thing that should be taken into account is what will the eventual size of the tree be? A sapling for a future 25 metre giant shouldn’t be planted only 12 metres from a building. Such a colossus is a certain bet to cause problems in the future by damaging property foundations, taking natural light from the house and garden, and when it finally needs to be removed making such a job very expensive.
In addition to the proximity to the building, consideration should also be given to the subsoil of the property. Adding trees will change the composition of the soil by taking and adding nutrients. Clay soil will contract as the roots suck moisture in and cause it to subside. The foundations on this soil will begin to move and subsequently crack. The type of tree planted is also an important factor. A willow has a massive root system that can drink up to 500 litres of water a day. Willows should therefore never be planted closer than 18 metres to a building. Birch trees on the other hand are the camels of the tree world, drinking less so allowing for much closer planting.
So what information should be taken into account?
- No one method of calculating root spread is 100% accurate!
- Trees establish 60% of their root system beyond the furthest reaches of their branches.
- Roots can extend between 1.5 and 3 times the height of the tree.
- The drip line (furthest branch away from the trunk) is only a third to a half of the distance the roots will grow
- For trees with a trunk up to 20cm wide the root growth can be up to 40 times the trunk width
So, you have a tree that was planted many years ago. ‘Doris’ the storm has come along and in its wake you are left with three issues. The first is easy to deal with, there has been no damage. The second issue can be dealt with but is more of a problem, the tree has been blown clean over, either causing damage or a problem to clear up. The final issue is more of a problem. The tree has been damaged by the storm. Is it going to cause damage to the property when it is taken down or has it already caused the damage and we can’t see it?
Foundation depths on a building changed markedly three times in the twentieth century. Before the 1950’s foundations were shallow. Up until 1978 foundations were more substantial until in that year the depth was increased again. Many trees pre-date the buildings that were built around them but more substantial foundations do not solve all the problems of a tree being moves suddenly and violently.
If an older tree has to be removed this will upset the balance of the soil and result in ground heave which is just as damaging for the building as subsidence. Before a tree is removed therefore the consequences should be looked at. In the event of a tree coming down in a storm this may be overlooked if the tree has been there since Adam was a lad. It is wise to keep a wary eye on the adjacent building until the damaged land has settled. This can take a number of years. Pollarding, a pruning system in which the upper branches of a tree are removed, so promoting a dense head of foliage and branches is one method of avoiding ground heave or lessening its effect over a number of years. This however cannot be adopted when the tree is laying on its side after having a side swipe from ‘Doris.’
By law, it is the responsibility of the tree owner to ensure that it causes no danger to neighbouring properties, even if they were built after the tree was already established. No greater example of ‘buyer beware’ will come back to bite you if you don’t take this into account when buying the property.
In short, as we look out to a garden and roadside of splintered branches, fallen boughs and twisted trunks one should satisfy oneself that this is a learning experience, and one not easily forgotten. No doubt we will forget about the lesson learned however. What should be done is that as soon as the storm settles a full tree maintenance regime should be put in place. It will save time and money and promote good practice. What will probably happen however is that it will go the same way as the service on the car. Only thought about when the knocking starts.