Retrospective Building Regulations vs Indemnity Insurance

Braboor

I had an exchange with the surveyor (a RICS Certified Historic Buildings Surveyor) this morning. He said there were no visible signs of subsidence & 'old rubble stone walls rarely have any formal foundation and at any prescribed depth. What you might find is a shallow foundation with the walls probably built off larger stone slabs'.

The new build was a block built cavity wall with a slate roof.

EachPenny

Braboor wrote: »

He said there were no visible signs of subsidence & 'old rubble stone walls rarely have any formal foundation and at any prescribed depth. What you might find is a shallow foundation with the walls probably built off larger stone slabs'.

The new build was a block built cavity wall with a slate roof.

This is one of the potential issues with digging trial pits to establish the depth of foundations - the hole itself may cause disturbance to the supporting mechanism.

In an ideal world you'd get a pragmatic BCO who would allow a conservative approach to be adopted. If it is assumed the foundations have no depth below topsoil and are the same width as the base of the wall then it would be possible to calculate the maximum permissible loading given a known or estimated bearing capacity of the sub-soil. It is then a case of working out the loading (and extra loading) of the walls and new structure and see whether this loading is below the maximum permissible bearing capacity - with the addition of some appropriately large factors of safety.

Assuming no depth to the foundations would mean you cannot rule out the potential for moisture related ground movement affecting the building, but it could be a way of showing the structure is 'safe' in terms of loading.

Given the age of the building and the fact several years have passed since the first floor was added then if there is no visible sign of movement it might be enough to satisfy a BCO... provided there is a willingness to take a pragmatic approach and calculations can be done to confirm the structural integrity.

If you dig trial pits and 'discover' there is no depth to the foundations, what do you do then?

The options are either to run a mile, or accept you are buying a property which may need significant additional expenditure to get it 'right'.

Does the vendor have any pictures showing the building before the first floor was added? This might be useful (necessary) to confirm what the structure (especially the roof) was like before the building work was done. If the original roof was similar to the new one, then the additional loading is effectively the weight of the (lightweight?) walls and floor plus loading from occupation - as it is a bedroom this isn't going to be excessively high.

lwhiteman88

Braboor wrote: »

I had an exchange with the surveyor (a RICS Certified Historic Buildings Surveyor) this morning. He said there were no visible signs of subsidence & 'old rubble stone walls rarely have any formal foundation and at any prescribed depth. What you might find is a shallow foundation with the walls probably built off larger stone slabs'.

The new build was a block built cavity wall with a slate roof.

I think an hour of a local engineers time at the property could be really valuable. They would be able to comment with any concerns with the foundation.

A new cavity wall above a solid masonry wall would require cavity trays, weep holes etc which again I would hope the builder would have installed.

A surveyor can advise on what is there but they're not qualified to know if the loadings are correct etc. Hence speaking with an engineer would be advisable.

Braboor

...this might give some idea of the extent of the work...

https://www.dropbox.com/s/eftun58bnoe35qj/before-after.jpg?dl=0

EachPenny

That's some substantial additional loading, especially on the gable end wall. It also looks like the roof was originally lean-to, so the load paths from the roof have changed significantly.

Another thing I would want assurance on is how the new walls were keyed onto the existing sloping walls - has this been done securely, or is the new blockwork just 'clinging' on?

Braboor

Now I'm worried. The surveyor observed a retaining wall adjacent to the extension 'is notably bowed along its length and at its mid-point vertical cracking was noted'. I'm wondering if this may be caused by subsidence in the foundations there...

https://www.dropbox.com/s/qk2c72w2hg0q4vs/retaining-wall.png?dl=0

EachPenny

Braboor wrote: »

Now I'm worried. The surveyor observed a retaining wall adjacent to the extension 'is notably bowed along its length and at its mid-point vertical cracking was noted'. I'm wondering if this may be caused by subsidence in the foundations there...

Is it the gable end wall of the house on the right and a raised garden on the left supported by the wall? If so it would be more likely that the soil in the garden is pushing the wall towards the house causing it to crack - the foundation level of the house wall would be lower.

As lwhiteman88 says, this is something you would need to discuss with an engineer to work out the best way forward. However, you'd really have to decide whether you like the house enough to take a bit of a gamble on the cost of rectification work, or on spending money for a structural engineer to investigate before you buy, or walk away.

Not an easy choice.

lincroft1710

Having seen the size of the extension I would be even more suspicious of why the vendor did not obtain BR consent. Were any plans drawn up for this extension together with a schedule of works? If so it would be a good idea to have a long hard look at them, even though there is no guarantee that the work was carried out accordingly.

System

There's somethings I would inspect myself and make a judgement on, a significant extension with no regs built onto and old wall, I'd be walking away tbh, there's too much unseen work to be confident it's been done well...