Hi there,
Longtime lurker could do with some opinions. I have a 1930s semi on a sloping site which has brick corbel foundations which are shallow. There is no current subsidence but after trial holes were dug, SE has recommended underpinning prior to loft extension.
I am reluctant - especially as their opinion was not given immediately while showing me the problem but after 3 other holes were dug, the boss was conferred with in private, and 2 weeks later.
They believe if the house was directly on clay, it would be fine as expected loads won’t reach the 100kn that london clay can take, but it is sitting on what is either clinker concrete (IMO and in builders opinion) or ‘black granular material’ in SE assessment. I have now opened 4 holes, two of them have very firm material under the corbels, which SE is happy is sufficient, but at the front corner of the house the material under the corbels is a bit looser. It can be flaked away if attacked from the side - looks like it is either spalling or has always been just ash and aggregate. It also looks like it may have been semi disturbed during laying of utility gas pipe years ago which runs parallel to wall. There is no indication that wall has been undermined.
SE has offered to design underpinning for a further fee. I have concerns about differential movement after partially underpinning then putting lots more weight on structure. I am also not confident that it needs to be done. The SE doesn’t seem massively experienced, the material under front corner is most definitely concrete - it is grey not black - a bit flakey but it’s been there for 100 years. I guess it was just filled with a slightly different mix.
SE feels like they are digging in behind the liability exclusion this gives them and say it is not reasonable to wait and see what happens after extension goes on. This leaves me in a bit of a conundrum -
Is spalling clinker concrete in trenches under brick corbels unusual? Does the compressive strength get compromised in this case? Should I pay a new SE for a second opinion? Or should I just take the advice I have already paid a lot for?
Any thoughts gratefully received
Longtime lurker could do with some opinions. I have a 1930s semi on a sloping site which has brick corbel foundations which are shallow. There is no current subsidence but after trial holes were dug, SE has recommended underpinning prior to loft extension.
I am reluctant - especially as their opinion was not given immediately while showing me the problem but after 3 other holes were dug, the boss was conferred with in private, and 2 weeks later.
They believe if the house was directly on clay, it would be fine as expected loads won’t reach the 100kn that london clay can take, but it is sitting on what is either clinker concrete (IMO and in builders opinion) or ‘black granular material’ in SE assessment. I have now opened 4 holes, two of them have very firm material under the corbels, which SE is happy is sufficient, but at the front corner of the house the material under the corbels is a bit looser. It can be flaked away if attacked from the side - looks like it is either spalling or has always been just ash and aggregate. It also looks like it may have been semi disturbed during laying of utility gas pipe years ago which runs parallel to wall. There is no indication that wall has been undermined.
SE has offered to design underpinning for a further fee. I have concerns about differential movement after partially underpinning then putting lots more weight on structure. I am also not confident that it needs to be done. The SE doesn’t seem massively experienced, the material under front corner is most definitely concrete - it is grey not black - a bit flakey but it’s been there for 100 years. I guess it was just filled with a slightly different mix.
SE feels like they are digging in behind the liability exclusion this gives them and say it is not reasonable to wait and see what happens after extension goes on. This leaves me in a bit of a conundrum -
Is spalling clinker concrete in trenches under brick corbels unusual? Does the compressive strength get compromised in this case? Should I pay a new SE for a second opinion? Or should I just take the advice I have already paid a lot for?
Any thoughts gratefully received