Large conifer stump on/near footings area

[Deejay_2]

We are about to remove a very large tree stump from our site.  The stump is/was a conifer of approx 20 m in height which was felled 2.5 yrs ago and stump killer applied at that time.  

I am attaching photos to show how near this 90 cm stump is to an old stone boundary wall and the tape on the ground shows approx where the wall of the one storey new building will sit.  The stump is encroaching where the trench will be by several cms.

My questions are:

1. Should the groundworker attempt to remove the whole stump.  Have the tree roots had time to die back.  Is this even possible.
2. The tree stump is almost touching the stone wall which we need to preserve and the digger may be unable to remove the whole root ball, so is it possible to do half and half ie remove as much as possible of the stump which lies over the footing area and then grind down the remainder as necessary.
3. Does anyone have suggestions about how to measure the depth of the trench fill foundation that might be required in a situation like this.  This proximity of a tree is not covered in the NHBC calculation table as far as I can see.  I have worked the depths out for the rest of the foundations but am "stumped" on this one.

Any help will be much appreciated. (Sorry, I could only upload one photo - I'm useless at this).

 

[saveasteading]

If no shoots have emerged from the trunk or roots then it is dead. If they do, just lop them off or spray.

 

This is tricky. Must not upset the wall. Also, ripping out the root ball might destablise lots of ground that will be under your new wall.

 

I think the whole trunk should be removed. A labourer can expose the roots, then cut them. If there is a tap root then that is a problem...perhaps just scrape with the excavator to see if it comes away.

 

OR

heave it all out (carefully for that wall) and build the foundations to below any roots.

 

You say nhbc dont cover it. That is only because the distance is zero, and so use 1m, or whatever is nearest.

 

How long has the tree been down? What does the bco say?

 

This isn't a situation of ticking a box.  You do not want the ground to heave dud to the tree removal.

[Nickfromwales]

Yup.

Needs digging out and the roots to the neighbours side cutting and leaving there.

Extra-deep fill trench where you dig down to the bottom of the root ball. Not a place to skimp on detail as you'll not ever get back in there after building. 

[Deejay_2]

Well, thank you both and I'm so glad I asked.  The tree was felled 2.5 years ago and treated with stump killer and has been covered with black plastic since.  Our neighbours are a school and behind the wall that you can see is a 1 m gap then school fence, so we won't be affecting anyone else.  

 

The BCO  didn't seem bothered about the tree stump, neither did the groundworker who just said he would try and get it out with mini digger and then if unsuccessful, would get someone to grind it down. He was concerned to be fair about the wall. 

 

We have other trees to consider, Rowan and conifer which sit in the Church grounds next door.  These are on a different elevation and the BCO said we needed 1.2 m deep trenches in a couple of areas because of these trees but didn't comment on the big tree stump.  I have been out measuring distances today and will do further calculations as to required depths/steps. 

 

As regards the large stump, I'll use the one metre distance calculation as suggested and also check on the use of clayboards and reinforcing rods down that elevation.

 

I honestly find it unbelievable just how blase the people are doing this sort of work every day - I haven't met one "professional" person so far whilst doing this project who I can honestly say I have any faith in.

 

I was in a situation some years ago where clay and trees were involved which required distance calculations, clayboards and rods and it was the Premier Warranty Surveyor that insisted on these (and upset the BCO).  No advice given beforehand by anyone to help prepare before starting work - all done on the hoof in the pouring rain with the trenches falling in.  At that time I knew nothing and wasn't aware I had to.   9 years later nothing has changed so I am trying to consider every eventuality before a start is made.

 

Thank you for your advice and any further ideas/advice would be appreciated.

 

 

[Nickfromwales]

5 minutes ago, Deejay_2 said:

I honestly find it unbelievable just how blase the people are doing this sort of work every day - I haven't met one "professional" person so far whilst doing this project who I can honestly say I have any faith in.

Welcome to Buildhub  "We'll learn you good".

[ProDave]

You won't shift that with a mini digger.  Think of the forces it is capable of withstanding when a 20M tree was attached and it was blowing a gale.  If that tree in a gale did not move the stump, a mini digger won't either.

 

I took out several very much smaller trees with my 3t digger.  It was essential to leave a good length of trunk so you had a good bit of leverage to push or pull at with the digger, and even after digging all around the base to loosen the ground it still took a lot to break the stump free.

 

I think getting someone to grind it out might be the answer.

 

Out of box thought (don't try this at home) cut some slots in with a chainsaw, soak diesel into the slots, set light to it and see if you can burn it out Roman candle style.  I accept NO responsibility if you try that, though do post the results.

[Deejay_2]

 

5 minutes ago, Nickfromwales said:

Welcome to Buildhub  "We'll learn you good".

Never a truer word spoken.  I absolutely rely on this site.

 

[Deejay_2]

Thank you.    I did wonder about the ability of the mini digger to get it out - it is a massive stump and actually looks even bigger in the flesh than on the photo.  I think if they tried to push the stump there would be a chance of the wall falling down.

 

Ok - I think I'll firstly get the advice of a stump remover company ie get their slant on things and whether a grinder will be able to remove the area of the stump that is in the way of the foundation trench, say for example slicing the stump in half.  I'm assuming a grinder leaves much of the stump in and just goes below the surface, but have never seen this done.

 

Diesel maybe ....

 

I am a bit worried now about this stump.  I will post what the grinders have to say.

Thank you again.

[nod]

2 hours ago, Nickfromwales said:

Yup.

Needs digging out and the roots to the neighbours side cutting and leaving there.

Extra-deep fill trench where you dig down to the bottom of the root ball. Not a place to skimp on detail as you'll not ever get back in there after building. 

Plus 1

A bad mistake waiting to happen 

[saveasteading]

BCOs don't tend to know much about groundworks or trees. Well, about Engineering really.

Groundworkers main asset is being prepared to get dirty and wet....no training apart from seeing bad examples.

 

It's a pine so doesn't bother the ground too much. Dead 2.5 years so 2 winters to wet the ground.

Shouldn't be a problem.

Rowan and pine would have to be close to be significant.

The easiest way to measure is on Google earth. 

[Deejay_2]

1 hour ago, saveasteading said:

BCOs don't tend to know much about groundworks or trees. Well, about Engineering really.

Groundworkers main asset is being prepared to get dirty and wet....no training apart from seeing bad examples.

 

It's a pine so doesn't bother the ground too much. Dead 2.5 years so 2 winters to wet the ground.

Shouldn't be a problem.

Rowan and pine would have to be close to be significant.

The easiest way to measure is on Google earth. 

I did measure on Google Earth and then on the ground as well. Rowan and pine not near each other.

 

I've looked at the distance calculator on the NHBC website and  the one metre distance calculation would apparently require more than a 2.5 m deep trench and therefore should be designed by an engineer. After reading this I thought I should go back to the BCO for advice but not much point if they're not qualified to give reliable advice - which has been my experience so far. 

 

It is the large Conifer stump I am concerned about and how to get around this with the footings.  Will Nick's advice above:

"Needs digging out and the roots to the neighbours side cutting and leaving there.

Extra-deep fill trench where you dig down to the bottom of the root ball."

be feasible or are we going to have to consider someting like piles.

 

I've contacted a stump remover company to see their view on removing the stump but really unsure now about the footings.

 

Thank you for everyone's time.

[Rishard]

We have similar issues with trees we have removed from the site dictating trench depths. We had a fairly basic and cost effective soil survey done with samples we provided. These provide very useful information for the behaviour of your soil. Our engineer designed the trenches based very much of the nhbc guidelines. The nhbc guidelines seem to be the measuring stick to which all bco’s use. Our bco is very well informed about trees and also soils in our local area. At the end of the day, they have to approve what you will use so its always worth discussing options with them. 

[saveasteading]

Just so I am sure. 

I'm thinking it isn't needing deep founds.

What type of pine?

What is your ground? Clay/sandy whatever?

 

Distance rowan to building and other pine

 To building.

[Nickfromwales]

If you're really pooping it, dig 50% more out from the far corner back to the near corner, where it passes "stumpy", and drop a few 3m lengths of steel re-bar in at the 33% and 66% depths of the concrete. Seriously doubt you'd have any issues, but steel is too cheap to not lob some in for belt n 3 braces  

[Gus Potter]

5 hours ago, Deejay_2 said:

Any help will be much appreciated.

Oh what an "interesting" thing you have there.

 

Good points made by all so far, make for good reading.

 

5 hours ago, Deejay_2 said:

This proximity of a tree is not covered in the NHBC

Yes, you have a special case. I'll throw a bit into the mix here and come at this from a maybe different angle, excuse the spelling and grammer please.

 

Bit of context first. Let's look at the tree and the old wall. Yes looks dead. But here are things I would like to know about it's life, the ground and the old wall.

 

1/ What kind of ground do you have, clay, compact glacial till or a post glacial material (~younger than 100 k) years.. low nutriant/ higher nutriant.. harder / easier for roots to penetrate respectively with a topping of garden nutriant rich soil. . Also you may find the roots have grown up the sides of the wall where the ground has been disturbed. Do you have sandy or gravelly type soil, chalk or thin soil with bedrock below? Reason for this is to try and determine where the secondary and tertiary roots will might be.

 

2/ Which way does the prevailing wind blow from. Trees need structural stability and will aim to grab a hold of a chunk of soil to enable them to stay stable, call that ballast. Some trees have a big tap root and that also contributes to the stability. Reason for this is to try and gather info on where the roots may be going. They may be prevelant towards you neighbours and less so on your side... good news.

 

3/ What do you know about the ground water level. Do you live up north.. more rain or down south where you get more water stress. If in a water stress area roots can be deeper.

 

4/ What can you observe in the old wall. Does it look like it has uplifted, been repointed, leaning over. Again this provides information about what impact the tree has had. The old wall will yield clues as to what effect the tree had . All good stuff to know.

 

The above is intended to allow you to understand this particular case and gather information to enable you to look at the other options.

 

Lets say that the stump falls somewhere along the side wall and not at the corner for the moment. One downside of the trench fill is that it needs a big hole that could destabalise the wall as other poster have mentioned. But what if it turns out that once we know more about the roots it turns out that we have just a potential soft spot in the ground that could settle.. as the main stump / primary roots rots away over time. As it has been dead for a good couple of years the ground has probably recovered a good bit ( swelled back up)..

 

Ok maybe settlement is the governing design factor. Let's recognise that we have a single story building (low loading) with a soft spot somewhere along the side wall but not too close to the corner. Can we just do a strip found here but make it say 250 - 300 mm thick and chuck in some 16 - 20mm diameter rebar to make a reinforced concrete beam that will span over the soft spot. Or if the roots are a bit deeper, put in a little trench fill and cast a heavier type beam to span a larger distance. This may need extra what we call steel rebar links which are much more like a reinforced concrete beam you may see in a carpark.

 

The above options may mean you can avoid deep excavation near the boundary wall and all the problems that go with that. Also in some ways you want a foundation that moves about eavenly. Trench fill can create hard spots and that causes unwanted stresses. Last, what about the existing house.. if you start digging deep founds next to that then old house may be moving up and down while your extension is anchored solid. This leads to differential movement that can be undesirable.

 

If you can get handle on these things you can put together a design that BC and all will be happy with. Once you see it all laid out you may think.. how simple is that!.. and if you think that then you probably have a good cost effective and sound solution.

 

Now if the stump is near the corner you can deploy the same concepts but here you have a cantilever found and that is more complex. How complex you need to establish and then compare with trench fill.. but the trench fill might not have to go all the way round as you can do a bit of mix and match.. the bridging and maybe trench fill running perpendicular to the boundary wall.

 

Hope this helps you a bit.

 

 

 

 

 

 

 

 

[twice round the block]

That will come out with a mini digger providing your using a ripper attachment.

If you try using a bucket to dig it out you will cause yourself all sorts of problems. 

I've just removed 26 from a walled garden plot and lots of them we're tight to the wall

[Dave Jones]

drop some steel in the trench where the stump was to give it a bit of help.

[saveasteading]

1 hour ago, Dave Jones said:

drop some steel in the trench.

Yes, £20 well spent on 2 x 10mm (or bigger) rods at mid height of a 300mm footing.

I was just imagining the finished construction, with a tree stump sitting there, rotting. It has to go, if there was anh doubt remaining.

It won't, be fun for whoever has to dig around roots and cut them , but has to be done.

 

When you have the trench dug,  you will likely have small roots sticking into it. Prune these flush with the sides so they don't stick into the concrete. 

 

Photos as you progress would be good.

[ProDave]

Our strip foundations were specified by the SE to have steel mesh, not just rods, embeded in the concrete.  No doubt that was because of the trees in close proximity.  It was neither difficult of expensive to do.

[Deejay_2]

Well, where to start.  Thank you all so much. 

 

Two detached houses were built lower down this site in 2013-2015.  The site furthest away from us eg 100 m away had medium plasticity clay and masses of it - and it was pouring with rain when the trenches were dug. I do know there was a pond in close proximity many years ago. Everything with the foundations was done retrospectively which left the trenches open longer for the elements to play havoc. No preparation was asked for or done beforehand.  Hats off to the lovely builder and the warranty inspector.

 

The other house (built first) and nearer to our house seemed to have no problem with their trenches but I think that was more because no-one asked or knew to ask.  A row of sycamores within 2 m of their footings had been totally removed 12 months before they started and I don't believe they bothered with trial holes/soil test.  The footings were approx 1 m depth.  They have a wooden suspended floor.  As far as I know, 10 years on, they have had no problems.

 

We live in South Yorkshire and I am expecting to find clay.

 

Some members will be aware of our situation ie excavating one trench to get a commencement notice before 15 June deadline for change in Bldg Regs.  The stump is on the north elevation and the trench to be dug is on the south elevation so this gives us time to sort out the stump problem.  However, we don't want to be digging a trench only to find out when we return to finish the footings that we need piles - hence why I need the stump/footings situation sorted and a plan agreed before any work is started.

 

My initial draft plan of action is:

1. Stump remover chap coming out tomorrow so I will get his opinion about removal of the stump and a quote.
2. I'll email/speak to the BCO on Tuesday and get his opinion about the stump removal and advice on footings in that area.
3. Would it be wise to pay for a foundation plan to be done by a structural engineer, then I have something to refer to and insist on. I still find some "people" taking instructions from a woman doesn't always go down well.
4. When the stump is out, could we use this as a trial hole and take the sample from there for the lab test.  We could do the same with a holly stump on the southern elevation.
5. Very happy to put reinforcing rods into the concrete and again a SE plan would help with this I would imagine.  
6. If we get to the point of digging the one full trench we are now thinking it would be wise to do the concrete fill and then cover lightly with the excavated soil.  I'm not sure how this would affect the future fills ie where it joins.  Again, the SE presumably would advise on this.

If anyone has anything further to add or suggestions on what else I should do, I would be very pleased to know.  I can't emphasise enough how much this has helped me.

 

I will post updates regularly and photos of any work done.  

 

 

 

[Nickfromwales]

8 minutes ago, Deejay_2 said:

Would it be wise to pay for a foundation plan to be done by a structural engineer,

Yes and no, as they will likely go nuts on this to cover their arses. Expense.

If it was me, I'd just dig down a bit deeper "there", buy a pair of 3600mm pre-stressed concrete lintels, and lob them in during the pour with the middle of the lintel at the centre of "operation stumpy". Treat it as a set of services that you are bridging, like a clay soil pipe and water / electric.

This has the potential to grow an unnecessary set(s) of horns £££

Reports of how the neighbours have managed fine fortifies a cheaper 'sensible' solution AFAIC.

 

8 minutes ago, Deejay_2 said:

I still find some "people" taking instructions from a woman doesn't always go down well.

Seems to work fine; when a row of builders at the pub bar at 8PM all get a text. One look and they all drink up and scarper. One assumes a woman was involved in each instance   

[saveasteading]

Some builders don't take advice from anyone. Seriously, anyone.

 

It doesn't sound complicated. You are 90% sure you will find clay. Calling it high plasticity will increase the foundation depths for trees but that is cheaper than site and lab tests.

 

I would be redesigning armed with the tree tables and bco agreement as I went along. Dig your footing as designed and check the strength at the bottom. How to, later.

This is traditional building, but you have multiple advisors on here. 99% of advice on BH is good. The other 1% just aren't agreeing with me.

Because you are being sensibly cautious we don't expect you to cut corners so can give this pragmatic advice. Ie if you weren't, we might be saying to get an SE.

In any case, your house will have normal founds, and it isn't always great to build extensions much deeper.

[Nickfromwales]

2 minutes ago, saveasteading said:

Ie if you weren't, we might be saying to get an SE.

Yup, we try to avoid providing bullets for you to then go and shoot yourself in the foot with.

The best thing done here is that you decided to start a dialogue, where the advice is impartial, but this is an internet forum and I am typing all of this from my clean, white, padded cell.

[Deejay_2]

54 minutes ago, saveasteading said:

Some builders don't take advice from anyone. Seriously, anyone.

 

It doesn't sound complicated. You are 90% sure you will find clay. Calling it high plasticity will increase the foundation depths for trees but that is cheaper than site and lab tests.

 

I would be redesigning armed with the tree tables and bco agreement as I went along. Dig your footing as designed and check the strength at the bottom. How to, later.

This is traditional building, but you have multiple advisors on here. 99% of advice on BH is good. The other 1% just aren't agreeing with me.

Because you are being sensibly cautious we don't expect you to cut corners so can give this pragmatic advice. Ie if you weren't, we might be saying to get an SE.

In any case, your house will have normal founds, and it isn't always great to build extensions much deeper.

As I mentioned earlier, if I follow the NHBC distance calculator for medium plasticity/high water requirement tree, the footings are over 2.5 m deep and would require an engineer designed foundation (the stump being right on the footing area would impact I think on at least 3 of the elevations as regards the depth of the trenches). I intend amending my foundation sketch today using the 2.5 m max depth where required). 

 

I assume engineer designed would mean piles, so if I employ a SE he may be "duty bound" to say piles are necessary because of the requirements of NHBC.

 

If I phone the BCO he may say to put reinforced bar in but I wonder what depth he would suggest for the trench eg 2.5 m?  

 

Best case scenario : 

• Remove conifer stump in total if possible.
• Soil test comes out at medium clay plasticity and we know the conifer is a high water consumer. (Test cost around £65 last time - 9 yrs ago).
• Work out trench depths required from tree distance table with 2.5 max depth where required. 
• Reinforced bars, or concrete lintels down the north elevation where the tree stump is. 
• There will be a lot of ready mixed concrete needed but at least I'll know in advance.
• Discuss above with BCO to see whether acceptable.

Does this sound OK?

[saveasteading]

3 hours ago, Deejay_2 said:

engineer designed would mean piles

No , it would mean 2.4m footings which is about 1/3 the cost of piles.

But if we (or SE or bco) discount the long dead tree then everything is shallower. I think I would discount nhbc depths for the dead tree as the ground has had 2 winters to recover.*

But I would locally take the footings below tree roots.

 

* I have done this several times, the difference being it was my decision and I was there to see the circumstances.

3 hours ago, Deejay_2 said:

and we know the conifer is a high water consumer

No it isn't. Do you know what type of conifer? Some have very little effect.