brambles, roots, water absorption and damage

G_M

I have some cracks in my garage wall. A builder blames the bushes and wants to remove them and drill out the trunks at quite a cost.
Structural engineer suggests a different cause and ignored the bushes, though the builder has pointed out a valid-sounding reason why the SE is wrong - I can go into detail if folks are interested - but my question is whether these types of bushes DO suck out moisture from the ground in sufficient quantity to cause damage?

Davesnave

Is there supposed to be a picture GM? I can't see it; just a box.


Brambles don't have especially high moisture requirements, but their roots can become very large and persistent. Getting rid of them chemically is possible, if rather slow, but killing top growth back to the root and keeping them small is easy and would immediately reduce water take-up.


They'll be going semi-dormant soon anyway.

coffeehound

If you open the placeholder in a new tab it says something like 'file too large for server'

Is it a massive image?


Edit - nope it's the URL that is too long

G_M

yes 62KB but I've reduced it (with some difficulty). It's now 5KB so the forum accepts the post, but does not show the picture. Will keep trying (for a bit!)


Not sure why looking at the 'box' info it links to Lunapic. That's the software I used to reduce the size but I saved it to my desktop and copied from there to here.

G_M

Davesnave

Those look like more than brambles, but it's still what looks like quite a young hedge and not particularly threatening.

This is a difficult one. Behind where I'm sitting now is a hedge, roughly 2m from the building. It looks small, but when the leaves fall, the trunks of old elms are revealed, up to 0.5m in diameter. The only reason the hedge survives is because it's been laid and it's kept trimmed, so the Dutch elm beetle leaves it alone. Any trunk allowed to grow naturally to around 5 or 6m will be attacked and eventually killed by the beetle. I've proved it.

I don't worry about that hedge, although I know its root system goes much further than 2m. I've hit thick roots 4m from the hedge many times, but I think the house foundations are up to resisting them, since it's a modern building with a good foundation depth. There's no sign of cracking.

A garage could be different. The foundations might be quite shallow, or it could even be built on a raft of concrete which would be easy to undermine. Even so, those bushes don't look substantial enough to cause a problem.

But the short answer is, "I don't know!"


What does the SE think?

Grenage

I would be surprised if those bushes were the cause of cracks in the garage wall. Maybe if it was heavy clay it would have more of an impact, but even then.

G_M

SE discounted them as the cause, but did suggest consuting an arborist about them and a tree at the rear.

As a first step I've arranged to get them cut back drastically - if nothing else it will tidy things up and improve the view. Then will decide on the remedial action needed for the garage. Builder No. 2 next week.....

Thanks for your thoughts.

DaftyDuck

That looks partly like a retaining wall on the drive, so soil level would be higher on the other side? That may change the equation, as pressure of root, moisture and soil will be on the wall, not the foundations.

If the hedge were kept well-trimmed, and soil levels were equal, I would not be concerned. I would, if soil is higher and hedge remained at that size or ongrowing.

G_M

DaftyDuck wrote: »

That looks partly like a retaining wall on the drive, so soil level would be higher on the other side? That may change the equation, as pressure of root, moisture and soil will be on the wall, not the foundations.

If the hedge were kept well-trimmed, and soil levels were equal, I would not be concerned. I would, if soil is higher and hedge remained at that size or ongrowing.

Yes. The field on the right is at a higher level. The SE has identified this as the primary cause - failed French Drain beside garage wall and pressure from sloping bank.

But builder has pointed out the side wall with the crack appears to be perfectly vertical ie there is no inward movement of the lower part, suggesting (to him) that the lower half of the wall has dropped vertically slightly, rather than being pushed inwards.

(I knew I'd end up having to explain - time to move to my natural home : the property forum?).

My plan is belt and braces:

* to dig out along the base of the wall and insert some form of barrier to prevent further pressure from the field above
* to drastically cut back the hedge

Question is, will hard pruning reduce the extent of the roots and/or reduce the moisture take-up? Or is the builder right that I need to

" Hire a stump grinder tree remover. Cut all the little trees on the right deep to their roots, when facing the garage front door, take rubbish away"

(hence posting here rather than back home).

DaftyDuck

Hard pruning will not, in itself, reduce root spread that's already there. Roots are also more likely to result in heave, not subsidence, especially with the higher soil level. If the wall has dropped, my guess - and it's as wild as that hedge - is that it's water run-off from the field. Many hedge lines followed old ditches, which followed streamlets in times far gone, for obvious reasons.

Either way, if you have access to that hedge (do check your deeds and, remember, borders aren't hedges... I learned that somewhere...) trimming it hard will be no bad thing, and digging down to below wall level and putting in a drain, all worth doing.

I do not believe grinding the stumps would serve any purpose whatsoever, other than lightening your pockets.

You could achieve the same emptying and have As much fun with tools by getting a bloke in with a drainage auger. Several notes a few metres deeper than the foundations, fill with vertical field drainage pipe, no more water problems. Bigger toy than stump grinder, generally cheaper to do, though!

Just noticed, in front of garage, on drive, it looks like it has sunk somewhat. Roots wouldn't do that in a single patch. If it's puddle-shaped, it's reflecting a subterranean puddle! It would be moderately easy to dig it up and look, but I would bet it would be fearsomely wet after rain.

I'd strengthen my bet: 80% water run-off from field, 10% roots, 10% just no foundations worth having. Unless you had it built, that is!