Trees!

[patp]

Well, we have had the earth scraped off the site prior to digging the actual footings. It has given us the idea of the size and shape of the building. 

 

Next came the bother over the trees. There are some Sycamore trees on the site's Southern boundary and a hawthorn hedge. Now most people know that you have to be careful with trees close to houses but do you know why? It is not, as I thought, that the roots would creep under the house and cause problems. it is because they suck up moisture and, therefore, dry out the land underneath the foundations which can cause cracking and subsidence. Some trees are worse than others. We all know about Willows. The Sycamores are close enough to cause such problems. They also cast a lot of shade and will shed a lot of leaves. Also, they are shallow rooted and so could, in high winds, fall on the house. We decided to enlist Farmer Mark next door to remove them. If you have ever tried to dig up a hawthorn then you will know what a job we had. An ordinary JCB was not man enough! He had to bring his 12 ton massive beast. It was a shame but, we thought, necessary for all the reasons given above.

 

I was in constant email contact with the Building Control Officer about the coming works and the tree problem. He was advising that we dig deeper where the trees were and pour more concrete into the footings. Over the weekend we decided, for all the above reasons, to dig them all out (about five massive Sycamores and four hawthorns) but could not notify him of our decision until the deed was done. He now informs us that removing large trees and hedges can cause the land to become suddenly wetter which brings different kinds of problems! He has scheduled a site visit for tomorrow to discuss our options.
I still think we made the right decision but I might change my mind tomorrow when he delivers his verdict. Eeeek!

[Mr Punter]

If you are on shrinkable clay, removal of trees that would have an impact on foundations is often something to do before you even apply for planning. Even small young trees are calculated at full maturity.

 

Most of the warranty providers do a foundation depth calculator.

 

Because your BCO has seen the trees before removal he may want deeper foundations and some Clayshield heave prevention on the inside face.

[PeterW]

It’s the same answer - depending on soil type you dig deeper. I went 1500mm in places next to a sycamore and we found no roots at all and this is on sand and gravel. 

 

You may also get asked to go beam and block to leave a void, or use clayboard that allows ground deformation if it is anything other than a free draining subsoil. 

[patp]

It is chalky clay. The BCO has not seen the plot as we have owned it for over 30 years and knew its history (farmland).

Sycamores are shallow rooted and take up a medium amount of water. Hawthorn are very, very deep rooted! As soon as I heard that Sycamores are shallow rooted I went into panic mode about them falling on the bungalow.

[nod]

Similar answer to above I’m afraid

 

We have multiple lines of ash trees 

Shallow rooted medium amounts of water On Clay also

My first thoughts where to chop them down

But our SE explained that it would have the opposite effect and advised foundations at 1.8 and clay board around the perimeter to cope with the heave 

[ProDave]

Interesting discussion.

 

We have at least 2 types of Willow, Goat and Pussey.  Most people seem to think they spell disaster.  I guess our foundations are a metre and a half or more down, having stripped over half a metre of top soil then dug the strip foundations.

 

The SE and BC were happy, the only stipulation from the SE (having witnessed me dig some test pits) was the foundations must be down into the "sandy clay" sub soil.

 

At that depth here it is always wet (bottom of the valley next to a burn)  I can't see it ever drying at that depth.  And that was well below any sign of any roots even small ones.

 

Most of our trees are right on the edge of the burn. No prizes for guessing where most of their roots go and where they get most of their water from.

 

We will be thinning them out, but only gradually and not felling any completely, just thinning and reducing their bulk.

[Oz07]

@ProDave don't forget you've got a suspended ground floor with void which helps

I understood some sycamores to be strong rooted. I built within 7m of a London plane. 1.5m deep. 1m of clayboard never had any problems and was a lovely tree

[patp]

There is no shortage of trees in the vicinity. Just across the track to us is a copse of mature mixed trees including Oak, Ash, Sycamore etc. There is a mature hedge bordering the Western boundary and a lovely Silver Birch a short distance from the Eastern boundary.

 

Once I heard that Sycamores were shallow rooted I had to deal with them. Imagine every time there was a "strong wind warning" I would be in fear of one of them toppling onto the bungalow.

 

BCO has mentioned Clay Board and Block and Beam in our chats but will see what he thinks when he comes.

[patp]

Thanks so much for all the above replies.

 

BCO has been and has advised a 1.6m foundation trench along the side nearest to the site of the now removed trees. He has also said that we may need to use clayboard. 

Most interestingly he has said that he would, if he were building a house, always use a beam and block floor. As the foundations have not been dug out yet he is not saying that is what we have to do but nevertheless I am keen to listen to his expert advice. What do others think? Is there a big cost difference? Will we need someone expert in the field of do groundworkers generally know about them?

[PeterW]

1 hour ago, patp said:

nevertheless I am keen to listen to his expert advice

 

I would caution here ....

 

Whilst your BCO is signing off your build, they aren’t experts in construction (ask @JSHarris about this...)

 

Is this private or Council BCO ..? You need to meet the Building Regulations and there are lots of options how to do that, some just have a set way of doing things. 

 

If you’ve got to go to 1.6m, and use ClayBoard then seriously consider an insulated slab for the whole build as it is borderline cost at those sorts of depths. 

[Jeremy Harris]

25 minutes ago, PeterW said:

 

I would caution here ....

 

Whilst your BCO is signing off your build, they aren’t experts in construction (ask @JSHarris about this...)

 

Is this private or Council BCO ..? You need to meet the Building Regulations and there are lots of options how to do that, some just have a set way of doing things. 

 

If you’ve got to go to 1.6m, and use ClayBoard then seriously consider an insulated slab for the whole build as it is borderline cost at those sorts of depths. 

 

I had to deal with an old school building inspector who came in right at the end of our build.  His first comment was that he'd never have accepted our passive slab, as he didn't like the fact that the house was sat on EPS.  Thankfully that bit had already been signed off, but it does seem that inspectors can be both opinionated and ill-informed.

[Ferdinand]

But reserve your own judgement.

 

You are the one with balls in the slot machine.

[Oz07]

Bco's like beam and block because it's simple to understand. Everything is bearing on the walls which sit on the foundation. 

 

Some are not open minded enough to see the benefits of other methods 

[patp]

Our, private, BCO is on holiday and so his colleague is coming out on Monday. 

 

Would it be worth while just running our problems by this BCO to see what his opinion is?

 

I have to say that, re reading, our BCO's email, he did say that he would look at the ground near where the trees were, to see if it was desiccated, before making any recommendations on beam and block or slab. He had not seen anything other than the scraped off soil on his first visit. Our, very experienced, digger driver says the soil (chalky clay) is excellent in the, tree free, part he was digging before the water main discovery caused him to pause.

 

The 1.6m depth is only for one side of the build (where the tree line was). We know nothing about insulated slabs @PeterW . Are they the ones used in a passiv system?

[patp]

The senior BCO seems to think that a slab will be fine if that is the way we want to go.

 

What is an insulated slab please? 

[Jeremy Harris]

10 minutes ago, patp said:

The senior BCO seems to think that a slab will be fine if that is the way we want to go.

 

What is an insulated slab please? 

 

There's some photos of our passive insulated slab going down here (they are all much of a muchness in the way they are laid):  http://www.mayfly.eu/2013/10/part-sixteen-fun-and-games-in-the-mud/

[patp]

Very interesting @JSHarris!

[Gone West]

1 hour ago, patp said:

What is an insulated slab please? 

More insulated slab laying.

 

 

[gc100]

So trees have striked again!

 

BCO come out today to have a look at our foundations, and due to close proximity to trees around the property has said we need to go down to 2meters instead of .75 as spec'd from the structural engineer. 

 

That to me seems a lot for a single story timber build. I release the risk is the chalk/clay ground to raise and lower in the season changes but 2 meters!!! The such a large amount of concrete to pour and we are trying to avoid concrete in this build for environmental reasons. Even worse he says we might need to cut down a small oak that is nearby which I really don't want to do. 

 

And then to add insult to injury the electricity board call me to tell me where they are connecting me, they have discovered asbestos on the ground and I will have to pay for the extra cost dealing with it even though it belongs to someone else.....!!

 

[joe90]

5 minutes ago, gc100 said:

BCO come out today to have a look at our foundations, and due to close proximity to trees around the property has said we need to go down to 2meters instead of .75 as spec'd from the structural engineer. 

 

Question, does the BCO out rank the structural engineer? Structural engineer will have insurance, will the BCO?

[patp]

Sorry to hear this @gc100. One minute the trees are a problem if you leave them standing the next minute they are a problem if you take them out!

 

@joe90 we did not use a structural engineer. Would it be cost effective, do you think, to do so if they start requiring deep foundations etc.

[redtop]

we had to have a SE due to using pile foundations, he did all the calcs and the BCO really had no choice but accept them; he didn't question them mind but he seemed more than happy as we had used a SE

[gc100]

On 17/10/2019 at 14:50, joe90 said:

 

Question, does the BCO out rank the structural engineer? Structural engineer will have insurance, will the BCO?

 

I think ultimately BC have the say. However in this case they said they are happy to do whatever the structural engineer said so as long as they had it in writing before completion. In the end the engineer came out and made several measurements and we ended up with various depths for the foundations. We went from 11 m3 of concrete needed to 37m3 !! All done and laid now. They also had to add clay boards on the inside of the foundations.