New single-storey extension near mature tree - trouble ahead?

[dwtowner]

At the back of my house I have a basic block outbuilding that I have permission to replace with a single-storey SIPs or timber-frame. There is a mature tree near the outbuilding, and the new extension will be slightly bigger, which will bring it closer to the tree. The photo below shows my existing house on the left, then the outbuilding to demolish, and a yellow tape marking where the wall of the new building will be.The property boundary is the wall where my notepad is resting.

 

My existing house is already on piles (poor ground), and a structural engineer has designed a piled foundation for the new extension which takes the tree's presence into account so I hope that building control won't raise any issues with the foundations. If a structural engineer has designed the foundations and done everything to account for the tree, can BC still object to it?

 

Are there other issues which I haven't thought of that might make it better to remove the tree as part of this work? I am really reluctant to remove the tree because it provides much needed privacy between me and my neighbour, and shade for us both, but if I'm storing up future trouble then maybe now is the time to remove it.

 

thanks,

 

 

[Conor]

Tree has to go. You can't normally dig within the root protection area, never mind against the trunk! You'll kill it. Was it on your planning drawings for removal? is it your tree on on the boundary? Did your SE not visit site / have photos?

 

 

[dwtowner]

It's my tree, right on the boundary. My neighbour acknowledges it is mine and that I can remove it if necessary.

 

The SE knows that the tree is there. They will be using a screw pile system designed for use in root protection areas, so there will no digging. As they are a professional from a reputable company, I trust their opinion. But if you think there might be a problem, then maybe BC will too, and I'm curious how that will play out as one professional opinion against another. I assume BC can ultimately override the SE?

 

 

[ProDave]

This is a case where I say just what will you achieve by moving the wall such a small distance?  A LOT of cost and effort for a small gain.

 

You have a blockwork wall seemingly not bothered by the tree (because the wall is on piles) and seemingly the wall is not bothering the tree.

 

Leave them all alone.  Clad the outside of the existing blockwork wall with external wall insulation and cladding to upgrade it, and keep the rest of it as your structure.

 

A full plan drawing of what you are trying to achieve might make more sense of why you seemingly want to demolish a wall and rebuild such a short distance away.

[saveasteading]

1 hour ago, dwtowner said:

assume BC can ultimately override the SE

No. The the BC is a generalist. He can look up the guidance on trees and foundations as we all can, but will accept an SE design.

 

Whatever foundations you choose to do, that tree will keep growing until pressing against the wall so I say it has to go if you build nearer to it.

Anyway the leaves will be a constant pain too, as will be any maintenance eg branch damage. So I'd get rid anyway.

 

We humans have a thing about expanding our territory. Do you really need that 1m2 more of house while losing access for maintenance?

What if the neighbour erects a fence?

[dwtowner]

Thanks for the advice, everyone.

 

I should have said that the outbuilding pre-dates the house and is built on a thin raft foundation which is at the wrong height to marry up to the FFL in the house. 3 of its 4 walls are in the wrong position too. It is easier to make a clean slate of it and start from a new foundation which is at the position and height I want. Even with the wall in a new position I will still have an 80cm gap between my house and the boundary, so I won't lose any access, but that was a good point.

 

[saveasteading]

Tree away.

You may still need deepish foundations though because the tree will no longer be drinking the groundwater and the roots will rot.

My pragmatic advice is to cut it down ASAP and let the ground recover.

 

It depends on the type of tree and the type of  ground.

[saveasteading]

2 hours ago, saveasteading said:

It depends on the type of tree and the type of  ground.

If you can advise on that we can add to the advice, or ask your SE.

 

Just a thought. It is an SE working for you I hope, not one working for a screw pile supplier?

With the tree gone and the winter to recover, you may only need conventional 1m strip footings.

 

[dwtowner]

Walnut tree. Underlying clay soil with high water table/springs. Sloped ground with terracing/levelling made from spoil from the original construction.

 

It's the screw pile companies own SE. The screw-pile company provide a complete solution for the foundations - design, calculations and approval for BC, install. I'll construct the building myself on top of those foundations - I've done several previously - but just want to get one company in to do everything necessary for the foundation, and I'll go from there. Is that a bad thing?

[saveasteading]

42 minutes ago, dwtowner said:

Is that a bad thing?

I can't comment on how professional they are or their product.

 

Please insist on seeing their PI insurance ASAP.

If you proceed then I would hope the the BCO reads the whole proposal to ensure that they have considered what is appropriate for the whole construction. 

I have an assumption that the company starts with sales , then moves to feasibility of their product, then proof that their product works.

An independent SE or Architect may have other matters to consider and perhaps another solution.

 

I've spoken to a few screw piles suppliers at trade exhibitions. Some are professional and understand their product and appropriate uses. Others were simply agents and were remarkably ignorant on technical matters.

 

a wanut can grow to 18m and the trunk will be wide too and reach your wall position.. Clay ground will shrink and expand a lot. so I'm guessing piles or footings will be about 2m deep, maybe more.  Or 1m if the tree is gone.

The existing house may be affected too.

My starting point is to demolish the existing building, remove the tree, use conventional concrete strip footings which any local builder can do.

Probably cheaper too, and certainly easier and cheaper to insure your house , and to sell in the future.

 

Screw piles and sips.  The result of attending a self-build exhibition by any chance?   I am NOT against either btw, just a cynic, and you have asked for opinions here.