Converting a loft conversion - SW London recommendations

[TolstoyAteMyHamster]

We have a badly converted loft - it's fine (building regs etc) in terms of all the essentials, and has a proper staircase, plumbing to the bathroom etc. but was done cheaply with no attempt to make good use of space. There's no dormer or similar - the previous owner basically just chopped the space in half and put a bedroom on one side and a weirdly huge but totally impractical bathroom on the other.

We'd like to upgrade it - probably squaring off the back to increase the amount of usable space, fit a shower room and then do some carpentry in the bedroom.

So, my questions are:

1. roughly how much should this cost? As I say the basics are (and we definitely won't move the staircase) but it will need scaffolding for the back
2. would you recommend an architect plus builder or a loft conversion company?
3. if the latter, who would you recommend? I have plenty of recommendations for the former but none for the latter. Thank you!

Are you doing a dormer or redoing the roof?
I would expect it to cost the same as a normal loft conversion unless you are only doing internal work

Probably a dormer as we really need to make some more headspace. I was hoping we would save money as the staircase/floors/plumbing/electrics are all mostly ok.

Hi, I've had to do a few projects like this on some rental properties in Wandsworth and Tooting. I would basically recommend that you contact the council to check that the property has a final certificate from building control. If yes you can make these amendments and it could cost in the region of 12-20k without obviously having seen it. If it hasn't been signed off. If all the plumbing, electrics, staircase are not being moved and you just want former windows and a proper space created then it should be straightforward. I use Clive (07966 476862) as the builder on my projects ( has architect/party wall contacts) and perhaps if they had a quick recce of the loft they could advise.

Do other properties in the street have formers? Worth checking with planning. Wandsworth often seem to want to preserve the roofline at the front via Felix.

They have various extensions at the back - some dormers, some mansards. Nothing at the front - it’s not Wandsworth but they are quite strict. We definitely have building regs sign off from the previous work; it was a delay to exchange when we bought the property and the vendor had to get the council in to get that sorted, so I have all the paperwork.

AveEldon, do you think it will be the same as an ordinary conversion? It’s got a staircase, plumbing, wiring, Velux windows at the front etc etc. I realise a lot of the cost will be the dormer but was really hoping to save a bit on the “typical cost” quotes because some of what would be needed is there already.

If it has a staircase, plumbing and the floors have had the correct strengthening for a loft conversion then it shouldn't be as expensive to build a mansard/dormer. You will need a steel to support the ridge though and that will mean PWA with your neighbours (assuming you are attached) and you will have to pay for planning permission/building regs and architects drawings and scaffolding that will cover the roof and protect the inside of the house while the work is being done. These elements all really pile on costs.

Ours was more straightforward from scratch conversion - but we used A1 lofts who I would recommend if you go down the loft company route. (We were also in SW London)