Anyone built on top of a one storey back addition?

[alice]

has anyone done this/ or knows whether this could be done as part of the 10% allowed without planning permission. grateful for any wisdom

[alice]

Is it that rare? Would I have to knock single storey down and build a 2 storey? Or is there another way?

[red devil]

Not sure what you mean by 10%. Permitted Development rights for rear extensions to a house are governed by distance/height not % volume.

You are not allowed to exceed 50% of the house's original curtlige.

If an existing extension extends more than 3m beyond the original rear wall of a detached house, then you cannot build a second storey under PD (see page 19 of this guide to PD rights)... http://www.planningportal.gov.uk/uploads/100806_PDforhouseholders_TechnicalGuidance.pdf

I couldn't see an example for a semi or terraced house, which tends to suggest Full Planning Permission would be required in such cases, but that's something you can easily confirm with a phonecall/email to Southwark planners...best to get what they say confirmed in writing.

If you went down the FPP route, you should first ascertain whether the foundations of your single storey extension are strong enough to support the additional load of a second storey. A structural engineer can do this for you. My guess is that they wouldn't be, and a lot of additional steelwork to carry the additional load would be required, which might seriously impact on your budget...

[Jeremy]

Well people build a third storey over the rear addition all the time, as part of a loft conversion. So common sense should dictate that building a second storey over the rear addition is OK.

But common sense does not always prevail....

[MissMadMoo]

I very much doubt you would be able to build without planning.

There are so many factors which need to be taken into account.

You would be well advised to engage an Architect if you have not already.

[bornagain]

We didn't build on top of an existing but we did build a 2 storey rear extension. We managed to sneak it in within permitted development (can't remember all the figures, it was nearly 10 years ago).

I do remember that there were rules then about maximum height you can build near neighbouring walls (poss min of 2m from boundary?) Our house is not a standard ED terrace so we had enough room.

One thing to consider is your neighbour's reaction - our totally legit extension didn't go down well with our neighbour. Soured relations for years, only just thawing.

Good luck

[red devil]

bornagain Wrote:

-------------------------------------------------------

> We didn't build on top of an existing but we did

> build a 2 storey rear extension. We managed to

> sneak it in within permitted development (can't

> remember all the figures, it was nearly 10 years

> ago).

The old volume PD rights were superceded by the current distance/height parameters in Oct 2008, so your extension would've got through on volume allowance, from memory around 40-50m3 depending on type of house. The current PD rights still retain a volume limit for works to roofs though...

[AbDabs]

Jeremy Wrote:

-------------------------------------------------------

> Well people build a third storey over the rear

> addition all the time, as part of a loft

> conversion. So common sense should dictate that

> building a second storey over the rear addition is

> OK.

>

> But common sense does not always prevail....

Er, not sure that's common sense. When you add a third storey to an existing two storey you are increasing the load on the footings by 50%. When you add a second storey to a single storey building then you are increasing the load by 100%. So it depends on the factor of safety used in the load bearing of the original footings.

[red devil]

That's assuming the second/third storey is of a similar construction to the ground floor. For instance, you could build a lightweight timber framed box on top of a heavier traditional brick block.

But you're right about having a factor of safety, so one should always get an SE to look at the structural consequences, especially with the unstable ground conditions of London clay...

[Jeremy]

AbDabs - I was referring to what the planning dept might consider acceptable, not necessarily what is structurally sound. Also... your load % is probably off, given that these extensions tend to be timber frame clad with tiles.

[AbDabs]

Sorry Jeremy, misinterpreted your post. And yes, the extra loading of an additional floor wouldn't be a simple multiple of the original for a variety of reasons (bedrooms less the kitchens), although that may also depend on the new roof structure.

[alice]

thank you so many brilliant ideas and comments - so much to consider - need to do more research. i like the idea of a lightweight maybe wood and glass box. First step will be to ring up planning