Void/hole in soil under suspended timber floor and close to wall that has clearly subsided.

[TBreezy]

I have lifted my floorboards to find a hole in the soil underneath the floor. It goes very deep - I couldn't reach the end. There are two channels both running away and slightly parallel to the walls.

This corner of the house has clearly subsided in the past but a very long time ago - looks at the space about the french doors in the first picture.

Also the soil is damp where the subjoist meets wall and the subjoist is rotten.

Broadly I see my options as

A) NUCLEAR OPTION:
- Remove the joists, sub joists and bricks.
- underpin the wall by digging out and filling 1x1m sections with concrete.
- Rebuild the entire floor

B) Quick and cheap: fill all the voids with concrete and then repair all the joists and subjoists and properly waterproof them.

C) pay a structural engineer to tell me to do A.... Or potentially something smarter.

ANy help appreciated!

 

[aockenden]

How rotten are the sub-joists? Are they like proper mush along the whole length, or just a few bad spots here and there?

 

[TBreezy]

How rotten are the sub-joists? Are they like proper mush along the whole length, or just a few bad spots here and there?

Yeah pretty mushy - but only up to the third joist then it's fine

 

[TBreezy]

To be honest more worried about the hole as easy to rebuild the joists.

 

[lizziecupcakes]

Hi there you have such a lovely room there and cornices are lovely.

I would personally redo that area properly, so option A, but i think it would be worth understanding that hole. I wonder if water is getting in from the other side of it. You could pass something that’s several meters long down there and see of you hit a bottom. Something like a drainage camera might be useful, but where to get that from apart from hiring someone out

I would really wamt to investigate that hole before filling it.

If joists etc are rotten, definitely replace in the meantime.

About the subsidence: I really do think it’s best to get the professionals in as they’ll know how deep to go for long-term stability.

 

[lizziecupcakes]

Also, I note a drain right outside the french doors. Does water get in that into the void of the house? Maybe that is failing and causing the rot, rather than the hole. You could test that drain if you haven’t already.

The void beneath the suspended floors is quite shallow so I wonder if it gets enough air/ventilation in there. Maybe you could consider adding a ventilation block on the wall to that side as you rebuild it too

 

[TBreezy]

Thanks for the reply. So will go into a bit more detail as I have done some exploration and removed some of the joists already so I could get access to the hole.

Basically the hole goes into three separate tunnels each of which ran about a metre and then came to a dead end. But they don't go anywhere near the footings.

I am going to remove the whole floor and fully excavate the holes to double check that they dead end and to see if there are any others. I will rebuild the whole floor from scratch now anyway so I don't need to worry about repairing joists.

The house has sunk in that corner but the surveyor and everyone who has come to look at it said that happened a long time ago and it doesn't look like it's moved in a long time.

I did a full drain survey when we moved in and the drain was cracked in that corner with the run off from the roof created a small void underneath that corner. The drain guys filled the void with concrete and replaced the whole drain system so that there are no leaks. I am monitoring a single crack about that french door using a telltale on the outside and I have had no movement in 6 months and the crack is 3/4mm wide currently.

I have read that concrete under pinning can cause other issues so now not going to try and underpin the corner. My plan is now to dig out the footings where it has clearly subsided and check there are no voids and make sure the footing is on solid ground before I decide what to do.

I will excavate the holes and fill them up with soil although don't think they will affect the house structure as they are more than 50cm away from the walls.

 

[lizziecupcakes]

I wonder if it’s a sink hole of some kind? But it does llook almost perfectly round, so probably a manmade hole. Maybe a previous owner was testing the ground for something and just left it??