How to deal with subsidence of badly converted porch

Laukei

Hello! We bought a 1960s-built house last year where the previous owner had (some decades prior) put up a wall around the original house's open flat-roof porch and stuck an angled roof on top to create an enclosed porch.

Fast forward to this summer and the porch's wall started breaking up. We had a builder look at it and they suggested the original concrete base, designed to hold just the weight of the original lightweight roof via support poles, was probably not replaced with proper depth foundations, causing it to drop in the dry weather. There's no evidence of wider issues with the rest of the house.

I'm not sure what's the best way to deal with this. It seems like getting buildings insurance involved would at best cause claims of the house subsiding and the significant issues that causes with reselling/insurance/mortgages. If we got the porch underpinned without the insurer being involved we'd still have to declare we've had it done for reselling/insurance/remortgaging I think, causing the same problems.

Someone suggested we get the porch removed and fully rebuilt with proper foundations on the basis it's not really subsidence of a correctly built conversion, but a poor workmanship issue, which I guess makes sense to me.

Does anyone have any insights or advice for this? Thanks!

Section62

Laukei said:

Someone suggested we get the porch removed and fully rebuilt with proper foundations....

This^.  Decide you'd really like to replace the shabby old porch with something a bit more weather resistant, especially with energy bills going up as they are.

Just be careful you apply for planning consent and/or building control approval as necessary.

gwynlas

Rather than replace as is would you benefit from a larger porch where you could include storage for coats and shoes? Otherwise you could demolish what is there if original intact under neath.

stuart45

gwynlas said:

Rather than replace as is would you benefit from a larger porch where you could include storage for coats and shoes? Otherwise you could demolish what is there if original intact under neath.

That's what I did for my daughter. She said it's been a Godsend as.she.lives in a small house and can fit all the shoes, some coats, push chair etc.

Ectophile

I had that problem with a dodgy DIY porch that came with the house.

I decided that I did not want the insurance company involved.  If they think my house suffers from subsidance, then my premuims will rocket for years to come.  The house itself is fine.  It's the poor foundations on the porch that's the problem.

In the end, I paid a moonlighting builder to knock it down and build a new one, on evenings and weekends.

Unfortunately, even the new one is moving.  Though it's not actually cracking up yet.  It's very difficult of you've got the sort of ground that moves with the seasons.

Section62

Ectophile said:

Unfortunately, even the new one is moving.  Though it's not actually cracking up yet.  It's very difficult of you've got the sort of ground that moves with the seasons.

There's two different approaches that would help with this.

The first is to ensure the two structures are tied together - e.g. the footings of the porch need to be dowelled into the house foundations with the new matching the existing as closely as possible. The walls should then be constructed either toothed in or with heavy duty starters.

The second approach is to accept there will be movement and design to allow it.  Have movement joints between the old and new construction such that seasonal movement doesn't cause cracking.

The problem with the average builder being asked to build a basic porch is they build somewhere between the two - that there is some connection between the structures, but not sufficient to stop differential movement.