Loads of builder's waste under subfloor - is this really common?

[a twig]

I’d suggest finding less “helpful” friends

 

[Lacan07]

Your situation doesn't appear to be as bad as this guy -> https://jack-kelly.com/insulating_our_victorian_living_room
Rotting joists, unsupported load bearing wall, and failed damp proof "treatment".

If you have the entire floor up, use the opportunity to get some insulation under there.

Fair play to that guy, what a lot of work he's put in but why is he insulating the walls with PIR on batons?

 

[Lacan07]

Insulation is the plan.

A friend of mine has just thrown in a comment that I could really do without, which is that I may not want to have all the waste removed as it could cause the external walls to end up acting as small retaining walls. Haven't had a chance to clarify what they mean (and they do have qualifications that makes me pause to think twice about what they've said). There is no talk of excavating anything here, simply removing what's been dumped to reinstate the original. Really confused that this would suggest the waste is having some kind of structural effect now.

I think most people would be confused with that suggestion

 

[info_45]

I need to speak to them but I think it might have been because I described the subfloor as 2 feet deep, so potentially they are imagining 2 feet deep against the base of the external wall. Although in the centre of the room the waste might not be far off 2 feet, thats only against the sleeper walls. Its shallower around the edges, and right by the external back wall I can just about see the bare earth beneath, so much less here. Even if it was deeper, its not compacted or anything its just tipped material, so still struck me as an odd thing to say.

 

[stuart45]

I think most people would be confused with that suggestion

I'm confused if it came from an engineer. Older houses often had crawl spaces of 2 or 3ft below floor level, but the floor was usually a fair bit higher than the external ground level. It needed to be to allow for the air bricks.
The amount of earth being retained was usually only about 12inches or less.
A cavity wall filled with concrete, or a 9inch wall will easily take that, especially with the weight of the house on top.
Foundations in the cellars of houses in the USA sometimes fail through hydrostatic pressure when built with 8inch hollow blocks, but they are retaining a lot more earth.

 

[fernicarry]

Your situation doesn't appear to be as bad as this guy

Most shocking thing about that blog is how cheap materials were in 2010!!

I removed lots of debris from under the floor of the back room. Rotten wood and plaster, lots of bits of linoleum, old electrical bits. No where near as much as you are dealing with but it feels good to know it’s all tidied up and airflow is unrestricted. I also insulated between the joists. All done from below without lifting the floor.

If I ever had a phobia of confined spaces, or heights for that matter, this house has cured me.

 

[info_45]

I managed to catch up with them. The seemed to be saying that even unconsolidated material could have some passive resistance (my terminology may be wrong in relaying this) and that there is no way of knowing what the ‘original’ internal ground level was i.e. is someone has deliberately raised the level for some reason. So removing waste near the foundations – if there are any foundations to speak of – has a risk of impacting the wall in some way. The key final point was that the difference between external and internal ground levels should be kept no greater than about 45cm.

It is the case that I can’t know with certainty what the original ground level was inside. I’ve tried counting bricks from some photos and relating them to the airbrick height outside and, as you’ve suggested Stuart45, the difference isn’t actually just the depth of the subfloor. With the waste still in-situ its very difficult to know exactly what the level is though.

It seems very obvious to me that this has all been dumped in a thoughtless manner and is not intended to provide any benefit whatsoever. The contractors are just being instructed to remove the waste and I would have thought that what is waste rather than what is soil would be fairly obvious so they shouldn’t accidentally dig under any foundations. I can make this clear to them again. By getting an asbestos contractor to treat this has though there could be something hazardous, it does mean that the room will be sealed off and a builder can’t be in there checking things.

I’m not trained in this at all, but I still can’t get my head how, if 50 houses on the street don’t have waste chucked under the floor and are fine then why does removing the waste from the 1 house that does suddenly make things risky.

 

[a twig]

Agree - I stand by my earlier comment of finding friends who are less “helpful”

All you are doing is removing some lazily dumped rubble not excavating a mini basement - it will be fine

 

[stuart45]

Agree - I stand by my earlier comment of finding friends who are less “helpful”

All you are doing is removing some lazily dumped rubble not excavating a mini basement - it will be fine

I'd agree with a twig. You need a minimum of 150mm clear space below the bottom of the joists, although 300mm is better. Hard-core piled up in mainly the centre isn't going to add anything much to the wall's stability. It's only when people start digging out well below the footing courses that there can be issues.

 

[Lacan07]

I managed to catch up with them. The seemed to be saying that even unconsolidated material could have some passive resistance (my terminology may be wrong in relaying this) and that there is no way of knowing what the ‘original’ internal ground level was i.e. is someone has deliberately raised the level for some reason. So removing waste near the foundations – if there are any foundations to speak of – has a risk of impacting the wall in some way. The key final point was that the difference between external and internal ground levels should be kept no greater than about 45cm.

It is the case that I can’t know with certainty what the original ground level was inside. I’ve tried counting bricks from some photos and relating them to the airbrick height outside and, as you’ve suggested Stuart45, the difference isn’t actually just the depth of the subfloor. With the waste still in-situ its very difficult to know exactly what the level is though.

It seems very obvious to me that this has all been dumped in a thoughtless manner and is not intended to provide any benefit whatsoever. The contractors are just being instructed to remove the waste and I would have thought that what is waste rather than what is soil would be fairly obvious so they shouldn’t accidentally dig under any foundations. I can make this clear to them again. By getting an asbestos contractor to treat this has though there could be something hazardous, it does mean that the room will be sealed off and a builder can’t be in there checking things.

I’m not trained in this at all, but I still can’t get my head how, if 50 houses on the street don’t have waste chucked under the floor and are fine then why does removing the waste from the 1 house that does suddenly make things risky.

Waste under an internal floor provides no structural integrity.