Concrete patio on top of edge of floating slab foundation - causing damage?

grassylawn

Bungalow is about 90 sq metre. Ground behind slopes down slightly. A concrete patio is installed on top of the of the foundation against the rear wall, cut into the slope with a retaining wall. It is about 60 sq metres and runs about two thirds the width of the house.

I'm aware that it was a bad idea to install the patio on top of the slab because of it shouldn't be as high against the house. I plan to get a french drain installed along the wall to improve any issues with damp that could be caused.

The patio is divided into two areas and each side slopes slughtly to the side into aco drains.

My greater concern is whether it might damage thr foundation. I noticed thin cracks in the surface of the slab that I think are new. There are also thin cracks in the plaster inside that I think are new as well. I found there was a condensation issue in the attic that I thonk might have caused them though?

So my questions are 1. - is this something I should be worried about and 2 - if yes, then what can I do about it?

Calahonda52

so the floating slab extended out beyond the wall of the house and the patio was built on part on it?

How much is the overlap?
where is the DPC in the wall?
what is the floor level relative to the top of the patio
If you are concerned about the weight of the patio on the floating slab, then just get a big water cooled con saw and cut it along the line of the floating slab

grassylawn

Calahonda52 wrote: »

so the floating slab extended out beyond the wall of the house and the patio was built on part on it?

How much is the overlap?
where is the DPC in the wall?
what is the floor level relative to the top of the patio
If you are concerned about the weight of the patio on the floating slab, then just get a big water cooled con saw and cut it along the line of the floating slab

Yes the floating slab extends out about two meteres from the wall of the house and the patio is on top of it.

The overlap is about two metres, with the patio touching the house wall.
DPC = damp-proof course? Not sure, there is external wall insulation that makes it hard to judge. The bottom of the EWI is in line with the floor.
patio is level with the floor of the house.

Do you mean to remove the part of the patio on top of the slab? Or just spearate it from the rest and leave it in place?

The waste pipes from the house are under the patio, possibly laid in the same concrete. Do you think there would be a risk of damage to them via uneven settling if the patio was disconnected from the slab..?

grassylawn

There are at least two cracks. One of them is on the opposite side of the house perpendicular to the wall. It lines up with the edge of the patio on the other side of the house. There is a concrete ramp covering the same spot on the side with the patio.

The other is at an angle and connects to the corner of the house past the edge of the patio at the back. It about parallel to where a drainage pipe was laid under the concrete.

blackbox

grassylawn wrote: »

Yes the floating slab extends out about two meteres from the wall of the house and the patio is on top of it.

The overlap is about two metres, with the patio touching the house wall.
DPC = damp-proof course? Not sure, there is external wall insulation that makes it hard to judge. The bottom of the EWI is in line with the floor.
patio is level with the floor of the house.

Do you mean to remove the part of the patio on top of the slab? Or just spearate it from the rest and leave it in place?

The waste pipes from the house are under the patio, possibly laid in the same concrete. Do you think there would be a risk of damage to them via uneven settling if the patio was disconnected from the slab..?

Did you build it yourself? It is very unlikely that a builder extended the foundation 2m beyond the house. More likely he put in a separate concrete path that is not load bearing.

grassylawn

blackbox wrote: »

Did you build it yourself? It is very unlikely that a builder extended the foundation 2m beyond the house. More likely he put in a separate concrete path that is not load bearing.

No I didn't build the house or the patio, and I don't know much about construction.

The house was built in about 1979. The patio was built about a year ago.

grassylawn

The concrete that I took to be the foundation slab comes out about a metre at the sides and front of the house, it is only at the back that it is about two metres. It looks like there was a thin layer put on top of the original concrete at the back at some point, before the patio.

Would the foundation be likely to come out one metre, or is it all most likely to be just a path?

Calahonda52

blackbox wrote: »

Did you build it yourself? It is very unlikely that a builder extended the foundation 2m beyond the house. More likely he put in a separate concrete path that is not load bearing.

Now with the more detail this looks like what you have