how much are you allowed to extend an existing house?

[MizZan]

We're considering buying a small 3 BR semi (only about 800 sq ft) with the idea of extending it quite substantially to the side and back. Overall we would want to extend to basically double the square footage, over two floors.

I know there are planning restrictions of some kind on how much you can extend an existing house, but does anyone know what these typically are? Is there a rule of thumb at all? Does it depend on the size of the plot of land, or the size of the existing house? In our town I have certainly seen houses extended to fill most of their given plot of land, but I've also heard of other cases where planning to extend further was refused (on the basis that a house had already been extended "to the maximum").

the house is not in a conservation area or anything - it's a very ordinary 1930s semi with a medium sized (for a town) garden.

anyone know? I'd hate to buy it and then find out we couldn't build out as much as we hope to. thanks!

Your council probably has a website where you can browse planning permissions. Not in detail, but enought to see what sort of things are generally passed and what are refused. Also what proportion of applications are refused. In our council's website this info is presented as an interactive map, so you can see at a glance where there are or have been planning applications, and in what sort of areas, rather than have to trawl through a list.

Our council tends to be fairly sympathetic to substantial extensions, houses often seem to double in size. It's been ages since I looked at the website, but IIRC there's no restriction on maximum increase, only on whether it is suitable for the house and the area.

on this matter, and sorry to jump on, does anyone know about extention and parking? we want to add an extra bedroom on, but have been told by an architect that we would have to show we had an offstreet parking space for four cars (because we will have four bedrooms).

any idea?

We are extending our house and we've doubled the size of the original house, although we have knocked down the original garage which sort of offsets the square footage.

We looked at the guidelines and designed our house with them in mind, we spoke to the planning department before we applied to see what they thought of our design and when we applied we attached a long letter saying how we had taken the guidelines into consideration. For example:

Even with the proposed extension, there will be room for off road parking for 3-4 cars.

The roof pitch on the ext would be the same as the original house.

The extension would be rendered (the original house is brick) so it was obvious to distinguish between old and new.

We were leaving x amount of room between the ext and the boundry.

We weren't putting windows and doors into aspects that don't have them already.

If I were you, I'd take some photos and make an appt with someone in the planning department to get their opinion.

The biggest problem is they are guidelines, so they are open to interpretation.

The laws of 'Permitted Planning' rights changed at the end of last year and you should be able to find them on your local council's website in the plannning section.

They now allow for more scope but that is only if the allowance hasn't already been used. It definately doesn't allow for doubling the space though!

I think parking depends on your local council. Again I'd check - get it from the main source before you get carried away.

In our area (South Bucks) it's quite hard to turn a 3 bed into a four/five as so many people have done it, that on some roads there is a ban because the 3 bed housing stock is diminishing. Look around on the road and see what others have done and maybe find out when they did it. It's much easier to extend out of the back so it's not visible from the front.

If you can't see anything else that has set a precendent then I'd be very cautious. Persoanlly I'd phone up the planning - or drop by - they usually give you an idea.

They do make you laugh, if three bedroom housing stock is diminishing it's because nobody wants it surely, can they not keep up with peoples needs ?
However I have never understood the need for spare rooms.

I think part of the guidelines that cover us state that you can't take more than half the back garden, that you need to retain access to the back garden or show that you can get to the back without going through a habitable room such as a lounge etc.