Filling a suspended floor - Will the filled in weight impact the adjoining wall?

[seekingadvice001]

We're in the planning stages of a home renovation and would like to install wet underfloor heating in our kitchen area and in the hallway.

We're fairly inexperienced and have a few questions related to filling in a suspended floor that we would appreciate your opinion on. The full context and the questions are below. Hope you can forgive the basic questions.

Please also see the attached image - it labels each area in question and should provide clarity on the layout.

CONTEXT:

• The issue is that the hallway floor is currently suspended (around 5.5ft deep) and the the kitchen floor is solid. We've had a builder opinion that filling in the suspended hallway floor might impact the adjoining wall (the wall between the lounge and the hallway) due to the weight of the new material against the wall (it's a 4 inch wide wall).
• The builder suggested we fill the floor on both sides of the wall (fill the lounge floor and fill the hallway floor) so that there is equal pressure on both sides of the wall.
• We've also had an opinion from a second builder who thinks it isn't an issue - and that we could add an additional 4 inch wall in the ground for support if we were concerned.
• This second builder showed us that the wall between the solid kitchen floor and the lounge floor is also 4inches wide (same width as the wall next to the suspended floor). His view was that the solid kitchen floor should give assurance that it isn't an issue (because the kitchen floor is against the same width wall as the suspended floor is). The house is unoccupied and bare at the moment so the builder was free to dig a little into the kitchen floor to demonstrate the floor was also against a 4inch wall.

QUESTIONS:

• What are your thoughts on filling in the suspended hallway floor - will the new weight impact the adjoining wall?
• The lounge is next to a party wall. If we chose to fill in the lounge's suspended floor, would we require permission from our neighbour (as they share the party wall which we may be impacting)?
• We will need to dig the kitchen floor before installing underfloor heating. The second builder suggested that we could use the dug-up underfloor from the kitchen to fill up the bottom of the hallway's suspended floor (e.g. underfloor from kitchen goes into suspended floor -> is compacted -> then hardcore/membrane/concrete/screed layed on top). Is this advised - to use the kitchen underfloor (mostly dirt) as the bottom layer when filling in the suspended floor?

Thank you.

 

[John D v2.0]

my thoughts (I'm not an expert)
seems like a lot of expense, why not repair and insulate the hall floor as needed and fit suitable UFH for suspended floor?
You're going to struggle to infill 1.7m unless you get a steamroller in! as made up ground is liable to settle too much. If you planned to concrete fill , then the wall would be safer in the long term, as concrete will shrink slightly as it cures and dries out.

 

[JohnD]

I can't see what you hope to gain by pouring concrete to replace a wooden floor.

Have you got a damp problem? Often caused by the old pipe running under the hall leaking due to age.

 

[Notch7]

generally it is not recommended to use more than 450mm of backfill material as a base for a floor slab.

I would be wondering why the kitchen floor is solid and resting against a 4” wall.


Your better option is to put the underfloor heating in aluminium platens or put the underfloor pipe work in between the joists then screed over. Bear in mind you might need to increase joists strength to do this.

 

[seekingadvice001]

I would be wondering why the kitchen floor is solid and resting against a 4” wall.

Right. I was going to cancel the plan to fill the floor due to the work involved and the chance of the ground settling - but now I'm wondering what to do about this. We've just bought the house so not familiar with this part of its history but this solid-floor-against-4inches must have been laid during the original construction.

Do you think laying a solid floor in the lounge would combat the risk of the kitchen solid floor being against a 4inch wall?

What are my options?
- Leave it as it is
- Re-enforce the wall somehow
- Fill the lounge floor

generally it is not recommended to use more than 450mm of backfill material as a base for a floor slab.

I would be wondering why the kitchen floor is solid and resting against a 4” wall.


Your better option is to put the underfloor heating in aluminium platens or put the underfloor pipe work in between the joists then screed over. Bear in mind you might need to increase joists strength to do this.

What if we were to use only 450mm of backfill - followed by the below layers:
- hardcore in layers of 1ft and then compact
- building sand of 1inch
- membrane
- concrete of 5-6inches
- 50mm celetex insulation
- liquid screed

Would above reduce chances of settlement or would it not make a difference?
Would compacting so much layers have an effect on our walls (due to the vibrations)?

I can't see what you hope to gain by pouring concrete to replace a wooden floor.

Have you got a damp problem? Often caused by the old pipe running under the hall leaking due to age.

No damp problem. We wanted UFH and thought it worked best with a solid floor. This was before realising how deep the suspended floor was and before realising the 4inch wall issue.

 

[JohnD]

What are my options?
- Leave it as it is

Yes, forget about filling it. Lots of cost and effort for no discernible benefit.

 

[John D v2.0]

What if we were to use only 450mm of backfill - followed by the below layers:
- hardcore in layers of 1ft and then compact

Hardcore is backfill, and also you can't compact it in layers of a foot, more like 4 inches.
I think you need to get this specified properly to avoid a very expensive mistake, rather than guessing and relying on randoms on the internet

 

[Notch7]

Right. I was going to cancel the plan to fill the floor due to the work involved and the chance of the ground settling - but now I'm wondering what to do about this. We've just bought the house so not familiar with this part of its history but this solid-floor-against-4inches must have been laid during the original construction

I’m guessing your house is on the side of a hill.

If that’s the original structure, there is more going on than you can see, there may have been a cellar or something, who knows.

What did it say on the survey?

 

[jks7492]

Guessing the floor to your lounge is suspended timber - are you sure the kitchen floor isn't also suspended but just with a suspended concrete slab?

5.5ft is too much really to be backfilling to form a ground bearing slab - with new houses anything above 600mm of fill below a slab and you'd be expected to use a suspended floor.

You can get underfloor heating systems specifically designed for retrofitting to existing timber suspended floors - have a look at Continal underfloor heating.