Large tree stumps where house will be on the plot- foundation help

[Jane W]

Apologies for the long post....We are almost ready to exchange contracts on a plot of land in a conservation area which has a couple of garages on there(to be demolished). The house we plan to build (approx 150m2 over 2 floors) will fit fairly tightly on the plot allowing for just enough parking space to the front and not much more than a postage stamp sized garden to the rear - but big enough for us! We have a couple of  trees (plum and holly) at the back which may mean we need to adapt our foundations according to the labc calculator due to clay soil being highly likely(no soil tests done yet though). At the front there is a row of leylandi and a couple of large tree stumps which I hadn't considered. One of these stumps will be directly where the side wall of the house is planned and I've  suddenly thought that they will probably also affect the foundations. Obviously the stumps will need to be removed but then what? What about the roots coming off these stumps...do they also have to be removed and to what depth and radius? How might these affect the foundations. I've had a ballpark estimate done for the build and I've attached a photo of the foundation estimate. I think these did not account for trees or stumps but did assume clay soil.

So the thing I'm struggling with are the potential costs of all of this. Is there an easy way to calculate extra costs? I'm thinking that in the costing the allowance is for 1.2m deep trench foundations. Do I just add 50% if we need 1.8m trench or double it for 2.4m, or are there other costs or complications associated with the extra depth eg reinforcement.

Could they prevent us removing a Leylandi or two with it being a conservation area and could the stumps prevent us from building what we planned? May be it's just a bit of panic before we take the plunge...

[Roundtuit]

I'd guess that the only complication will be the size of the hole created by the stump removal, and the additional cost of shuttering for the foundations. If these are old stumps and rotten then additional work might be minimal. Even if they're relatively 'new' I can't see it being a a show-stopper.  Removing trees in a conservation area is likely to require consent, but Leylandii is unlikely to pose a problem if you follow due process.

[saveasteading]

1 hour ago, Jane W said:

Do I just add 50% if we need 1.8m trench or double it for 2.4m,

NO. It is less than twice the work. But twice the earth has to go somewhere else. The concrete quantity depends on the design. the deep trench may need shoring for safety.

So it is more expensive for sure.  How much? well, technical estimating  was my job for decades and I still don't know without knowing all your details.

 

The tree trunks and roots will rot and leave voids.

The leylandii wont be too much trouble and perhaps the bottom of the trunk can be left in place and bridged over.

 

If the bigger trunks can be carefully removed then there is still a hole, and any replacement fill will be harder/ softer than the existing. It needs onsite expertise. The less ground id displaced, the better.

 

 

 

[Conor]

What are the planning conditions regarding the trees? Assume you have to fence off the root protection area? Digging out old stumps is not an issue. An extra cube of concrete. 

 

We made life simple by applying to remove all trees within the construction area and plant replacements in other parts of the site. But sounds like you've a tight site. Your site layout drawing would be usefu.

[Jane W]

Thankyou @saveasteading, @Roundtuit and @Conor for your thoughts.

Will the species of tree stump make a difference?  I thought I should ask what type of trees the stumps were and how long ago they were felled.

It is being sold with outline planning, all matters reserved and  vague in terms of building detail. The building shown on the application plan is to the right side of the plot,  smaller (about half the footprint we would like ideally) and fairly uncontentious.

The estimator then drew a plan to estimate from which is scant and overall actually slightly bigger than we are opting for, but the way our planned house will sit on the plot is similar except that the front of the build (the garage in the illustration) will not jut out as close to the front boundary as shown but the lounge will be be extended just over half a meter towards the front, right at the side of the leylandii. I've  very 'untechnically' added the trees in green (conifers at the front, plum and holly at the back), and the stumps in orange.

[Post and beam]

My proposed build is in a conservation area, in North Hertfordshire. All trees are protected by default in such an area. But we asked in writing for permission to remove a 65' leylandii. Because its a non natural species the planning department were glad to see it go. And, i guess glad that someone other than them paid for it to go.

Take away message, no one cares about Leylandii

[Jane W]

Thanks, that's good to hear. Hopefully removing a couple closest to where we're hoping to build will be possible.

[Alan Ambrose]

You may be able to see on google street view (the dated images) when they were removed. Also you might be able to gauge the size/age of tree from the stump diameter. I have a couple to go also, and I think it’ll take a sizeable digger to remove them.

[saveasteading]

Leylandii have minimal effect on foundations, and the roots aren't huge or intrusive. I would consider ignoring them other than digging through them, and reinforce the footing there.

[Jilly]

You are right about last minutes panic: be aware that self building can do this to you! It’s all new and emotionally laden.
Have a contingency fund, this might happen frequently.  Perhaps save money perhaps by living on site if you can?
I came rushing here each time I spotted something that worried me or I didn’t understand, and it was like having 10 good friends giving me advice (with a few conflicting opinions of course). 
Your structural engineer will likely make final decisions about foundations and some of it is up for discussion. 

[joe90]

It may be that your BC officer will advise what you need to do (saving you the cost of an SE).

[Nick Laslett]

1 hour ago, Alan Ambrose said:

You may be able to see on google street view (the dated images) when they were removed.

Great suggestion.  Another option is the Google Earth app specifically on PC/Mac, this allows you to see many more satellite images going back 30 years. You have to download the app to be able to do this, it is not available in the web version. 
 

https://support.google.com/earth/community-guide/256123000/versions-of-google-earth-desktop-web-mobile?hl=en

[Jane W]

@Jilly thanks, I  have already found the support, advice and expertise offered here to be amazing and we've not even got around to purchasing the plot yet! I also like those conflicting opinions. It encourages discussion and helps to consider options from different angles and see how different experienced people approach things. All so very helpful for a newbie!

The site is tight so I don't think there would be room for a caravan until the shell is up. Its certainly something we would look at if its possible when we're at that stage though.

We have reduced the size and some finishes to ensure we have some contingency but it's so worrying when the budget is absolute to know how costs can spiral. I think there may be many sleepless nights ahead!

[Jane W]

31 minutes ago, joe90 said:

It may be that your BC officer will advise what you need to do (saving you the cost of an SE).

That would be good. Presumably that would not  be a LA BC officer?

[Jane W]

6 minutes ago, Nick Laslett said:

Great suggestion.  Another option is the Google Earth app specifically on PC/Mac, this allows you to see many more satellite images going back 30 years. You have to download the app to be able to do this, it is not available in the web version. 
 

https://support.google.com/earth/community-guide/256123000/versions-of-google-earth-desktop-web-mobile?hl=en

Great idea I'll have a look at maps and earth see what comes up

[joe90]

3 minutes ago, Jane W said:

finishes to ensure we have some contingency

It’s often said here (by me and others) that kitchens, lighting etc can be bought cheap and replaced at a later date rather than compromise on insulation etc that’s permanent and good as they are near the end of the build.

[Jane W]

1 hour ago, Alan Ambrose said:

You may be able to see on google street view (the dated images) when they were removed. Also you might be able to gauge the size/age of tree from the stump diameter. I have a couple to go also, and I think it’ll take a sizeable digger to remove them.

Yes good ideas. I think it's always the cost implications, there's always a solution, but how much does each solution through the build add to the cost.   

[joe90]

3 minutes ago, Jane W said:

That would be good. Presumably that would not  be a LA BC officer?

Mine did, (but I had no trees) he just knew the area and said “this deep and this wide” if you don’t ask you won’t know. On a previous renovation we came across a soft section of trench and the local BC officer just asked for a couple of rebar lengths over the area. 

[Jane W]

1 minute ago, joe90 said:

Mine did, (but I had no trees) he just knew the area and said “this deep and this wide” if you don’t ask you won’t know. On a previous renovation we came across a soft section of trench and the local BC officer just asked for a couple of rebar lengths over the area. 

Good to know thanks

[Blooda]

We had ours designed by SE, as we had removed trees, tree remained and we are on clay.  Original take off was 29M³   .

By the time we had taken into account

   Stumps we found,

   Smoothing out steps,

   BCO wanting more in some areas, as we found small routes, 

   Chimney and porch details too tight so we had to cut more,

   Lack of 750mm bucket. [bank holiday, in lockdown]

 

We ended up with 64m² 

The ground worker was on daywork and cost plus for the concrete, So I was not ripped off, but could have easily been.  

   

 

[Jane W]

23 hours ago, Nick Laslett said:

Great suggestion.  Another option is the Google Earth app specifically on PC/Mac, this allows you to see many more satellite images going back 30 years. You have to download the app to be able to do this, it is not available in the web version. 
 

https://support.google.com/earth/community-guide/256123000/versions-of-google-earth-desktop-web-mobile?hl=en

I have looked at Google maps and Google earth and it appears that one was felled in 2020, the other one which didn't look healthy, was felled in 2018. As there hasn't been any mention of tree species, am I correct in thinking that this doesn't have any effect or bearing once a tree has been felled?

On 11/06/2024 at 08:05, Alan Ambrose said:

You may be able to see on google street view (the dated images) when they were removed. Also you might be able to gauge the size/age of tree from the stump diameter. I have a couple to go also, and I think it’ll take a sizeable digger to remove them.

Yes good ideas. I think it's always the cost implications, there's always a solution, but how much does each solution through the build add to the cost.   

[Jane W]

Expand  

I have looked at Google maps and Google earth and it appears that one was felled in 2020, the other one which didn't look healthy, was felled in 2018. As there hasn't been any mention of tree species, am I correct in thinking that this doesn't have any effect or bearing once a tree has been felled?

[Mr Punter]

Not strictly on topic but it appears that you are building right up to the boundary on the left.  Do you have consent from the adjacent owner to erect scaffolding and possibly construct foundations on their land?

[G and J]

1 minute ago, Mr Punter said:

Not strictly on topic but it appears that you are building right up to the boundary on the left.  Do you have consent from the adjacent owner to erect scaffolding and possibly construct foundations on their land?

Oh no! Party Wall Agreement! We need these on both sides!

[Jane W]

5 hours ago, Mr Punter said:

Not strictly on topic but it appears that you are building right up to the boundary on the left.  Do you have consent from the adjacent owner to erect scaffolding and possibly construct foundations on their land?

No we don't.  The hopeful drawing allows 50mm in from the boundary which I think may be the minimum, but please let me know if this is incorrect. It is a parish council car park on that side of the plot. The drawing was more for reference although we are hoping to build as far up to that boundary as we can (but without lots of complications!)