Rear extension questions

Madthinker

Hi all,

I am considering making an offer for this detached bungalow in London.  The value in the property for me is the potential to extend at the rear (as shown in the photos).  However, I need to know what I'm letting myself in for.  Some questions I'd appreciate any help with.

1 - My reading of permitted development rights is that for a detached house it is permitted to go up to 8m extension to the rear?  Does this also apply to bungalows?  Have I read this right?  Note that even with an 8m rear extension, no part of the property will be within 2m of the boundary.

2 - What would be the best roof design?  My wife wants another pitched roof for the extension, parallel to the existing.  However, this would mean a 'valley' of water.  Is this practical over this sort of distance (total length approx 16m).  Will we be forever having draining problems/pooling?

3 - What other design would be appropriate?  I want high ceilings too.  My thought is that the roof could gently slope outwards, with large pitched skylights to provide the space and light.  The ceilings are c2.45m high inside.  Is the edge of the roof high enough already for this to work without the ceilings being too low, given the gradient needed?  If it is too low, would it be practical to reduce the pitch of the edge of the current roof from a few tiles in?

4 - Million dollar question (but hopefully not answer).  How much would this cost?  I see indicative quotes per square metre, but these don't typically indicate what would be included, and I'm also hoping the cost per square metre is lower for a larger area due to the reduced marginal work (unit area per unit wall reduces).  What would I roughly be looking at for something along these lines:
 - 16m x 6m
 - Flat roof (gently sloping outwards) roof, with 2 large pitched skylights
 - ceiling-floor windows for about 5m, including sliding doors.
 - electrics, plumbing for kitchen (but not the fitting of the kitchen)
- flooring, painting / surfacing of interior
- a couple of internal partition walls.
- in general, to a good quality finish, but nothing unnecessarily  high-spec.

5 - The access to the property is slightly difficult.  I can get  my Duster down the drive easily, but apparently ambulances have trouble.  Will this cause a problem for the builders?

6 - Is there anything else I should be aware of / any advice?

Thanks for any help

Albermarle

 16m x 6m

Can you just confirm that is correct? as at nearly 100 M2 it is similar floor space as you would get in many smaller two storey houses, so a very big extension.

Madthinker

Yes - that is correct.

From a practical point of view, I don't see a problem, save for how the roof would drain away.  The bungalow is on a big patch of land, so wouldn't encroach too much on the garden. Aside from the neighbour to one side (who isn't very close), the boundary of the plot is the rear boundary other properties back gardens.

From a planning permission point of view, it does to me appear to be covered under permitted development.  

So, it would be big, but I can't see why not.  But please do let me know if you think I've missed anything.

Madthinker

I should add/clarify - there is a rule under permitted development, that requires the extension to be no more than 50% of the footprint of the original property.  The property is 7m deep, so I think the maximum rear extension under permitted development is just over 3.5m (very slightly higher potentially because the front has a porch which I think would be part of the original footprint).

That said, I don't see on what grounds a full planning application could be rejected.  The extension would barely be visible to other properties.

TELLIT01

The flat roofed section to the left on the photograph is probably an extension, so it's possible that part of the PD size has already been taken up by that.  I would suggest having a conversation with the planners.

grumpy_codger

It always baffles me why people chose a flat roof where a normal pitched roof is an easy option (although more expensive).

TELLIT01

In the situation of the photo posted on this thread, a pitched roof may have covered the window in the end elevation of the existing building.

grumpy_codger

Yes, but it's a small window and can be replaced with a Velux one if needed.

DevilDamo

1. Yes, but it only applies to the original/as-built house.

2. No issues with a box/valley gutter. The devil is in the detail and workmanship.

3. You could see if a shallower pitched lean-to roof would work but also making sure the additional volume complies with the PD requirements.

4. It will not be less than £230k. If you need a more firmed up cost, then you will require drawings, details and calculations.

5. Not at all. Access restrictions will be taken into account when obtaining quotes.

6. Don’t be too hung up on trying to meet the PD requirements (on the assumption the property benefits from them).

Madthinker

Thanks - that's a good point re: the garage.

On the one hand, if the garage was part of the original building, then it would seem odd not to extend the pitched roof and put the loft window at the end.  On the other hand, does the continuous brickwork not indicate that it was all built together?

What's the best bet for getting a definitive answer for the original (or 1948) footprint?  I guess the title deeds will show this?

DevilDamo

Pulling out that side gable would require Planning.

The Council will or should have information on the original building.