Garage has sunk in one corner - advice

[^woody^]

You do need to confirm that there are no drain leaks, and to do that you need to CCTV all drains near the garage - it is very important to check all nearby drains. For this you will need to trace all drains and confirm where all the drains are, and trace them from every down pipe and gully and soil stack connections on both houses. There might not be any soak-a-ways, but the only way to tell is to check were all the rainwater pipes are running.

The CCTV company will produce a plan showing the condition of all drains and their locations/depths within both of the gardens.

Also check the garage to see where the roof run-off is going. If the roof is on a slant and all the rain is running down that wall, then the ground will be saturated, and if sand or loose fill, then liable to compact.

Holly is on the list of potentially problematic shrubs, and can dry out soil within a 5m radius. But its just a possibility at this stage

Potentially, there could be a local pocket of poor ground under that wall. It might be an idea to dig a hole at the four corners to check the foundation depth and whether the ground is any different at each corner. If you get an engineer involved, then that's what he would do, and also take some soil core samples along the wall.

Its very important to find out the cause before even thinking of a remedy. Ground can move back and walls lift once moisture is stabilised, underpinning is commonly thought of, or ground grout injectionis possible. But no-one will suggest a remedy without knowing the cause. It may be that once the cause is known, if no more movement is anticipated, then the door can be re-aligned and the roof levelled up to avoid costly foundation work.

You need to get that CCTV survey re-done before you can move on. A local engineer might be able to give you some more definite advice from a site visit, but he will most certainly advise drain and ground reports.

 

[fRAiLtY]

Hi Woody,

I've just realised that I've missed out probably one of the most important points about this issue, as this thread was initially posted before I found out.

Next door, the right hand side in that picture, 10 years after it was built (originally in 1977), was demolished and the ground laid flat for almost a year. Then in late 1987 it was rebuilt to the original plans. Apparently, this area was farm land and where next door was built was a deep mass grave for diseased poultry. The farmer allegedly filled the ground back in so on the face of it nothing looked awry. Then, presumably as the carcassed decomposed the ground began to shift and that property sank. Apparently the damage was severe enough to demolish and rebuild after a period of the area being left fallow.

To put "area" into context, there are 5 properties on that side of the cul-de-sac, all detached and this sits in the middle of 2, so the width of the plot is probably 30ft or so. I've attached a picture below to show what I mean. The property that was rebuilt is circled in red, and mine is arrowed.

Interestingly, the blue circle is the house that backs onto ours, a copy if you like, just mirrored so their garage is inline with ours. From our conservatory you can clearly see their garage has leaned the same way. No cracks at all and they aren't even aware of it (as we spoke and they never mentioned theirs leaning) but it's definitely leaning the same direction as ours, away from the properties. I have "assumed" that we have caught the edge of this pit that was dug and that's caused both garages to lean that way, although no other houses in the area seem to have been affected, just the garages and nextdoor. I've spoke to plenty of people in the area who all corroborate the main points of the story and next door told us "some tests" were done on the surrounding area presumably to check the rest of the estate wasn't about to be swallowed up also. I'm taking relative comfort in the fact this was nearly 30 years ago and no other problems with actual dwellings have been reported or noted, just these 2 garages are leaning that way.

I'm trying to avoid going near the insurance company as at the end of the day, it is just a garage and as long as it doesn't effect the dwelling I'm relatively happy. That said, I'd like it to be resolved.

Do you think given this information it's still worth double checking the drains incase it's a red herring/coincidence about next door? I was very disappointed nothing about this serious incident turned up on our surveys but then was told as it didn't effect our property it's unlikely to, which I don't know to be true or not. I'd also love to find these "tests" that were done whilst the plot laid fallow but God knows where or if I'd ever find that and whether it would be available in the public domain.

Sorry for the long post, I just thought you should have all the information that had come to light since the original posting.

Once again, thanks for your replies.

 

[^woody^]

Made up ground is one of the common reasons for foundation movement. It would be determined by core samples which would be part of the investigation process along with drain CCTV.

 

[Himaginn]

If you do seek advice/assistance from your insurance and there is an effect when you come to sell, assuming the cause of the subsidence is this previous animal carcass pit, then a simple, cheap indemnity insurance policy for the prospective buyers will facilitate the sale.

 

[theprinceofdarkness]

the elephant in the room (or the cow in the pit) is the size of this animal grave yard , it could be 3m deep and many metres across, say 5 by 5. This means that you have to go down to this depth before you have solved the problem. I like the idea of the concrete pump, but it could just last for a few years as the pit continues to collapse, then you have to get through this hunk of concrete to get to solid ground. I think I would have a word with them to see what sort of life guarantee they offer.
Frank

 

[fRAiLtY]

If you do seek advice/assistance from your insurance and there is an effect when you come to sell, assuming the cause of the subsidence is this previous animal carcass pit, then a simple, cheap indemnity insurance policy for the prospective buyers will facilitate the sale.

I'm trying to avoid the insurance if possible, for the very reason you say. There may come a time where it's unavoidable then no doubt the property will be relatively worthless which is my biggest fear.

the elephant in the room (or the cow in the pit) is the size of this animal grave yard , it could be 3m deep and many metres across, say 5 by 5. This means that you have to go down to this depth before you have solved the problem. I like the idea of the concrete pump, but it could just last for a few years as the pit continues to collapse, then you have to get through this hunk of concrete to get to solid ground. I think I would have a word with them to see what sort of life guarantee they offer.
Frank

Yes this is unknown and probably will remain so. The current inhabitants of nextdoor who in effect bought it "new" in 1987 after it was rebuilt tell me their property is now on 20ft piles. I'm hoping the garage can be shored up and made good for a relatively small amount of money in comparison.