Loft conversion - what percentage of downstairs space will be used?

[WorkingBling]

I know, it's a "how long is a piece of string" question, but we are considering doing a loft conversion. I'm going to get some builders in soon to give us some thoughts but while I'm dreaming and fantasizing thinking about things, I'm trying to work out what's doable. The roof is very sloped which I understand is good. But is there a rough calculation of how much floor space you'll get up there based on how much space you have below?

I dream of a large bedroom, with sitting/babyfeeding area and ensuite bathroom and lots of built in storage

You will get all the space your main roof covers below- 100%. However most people build cupboards into the eaves for storage. These typically seem to be around 5ft deep. Assume the rest of the room will be useable space and your staircase. Look at houses on your street that have already been converted-- you can look at floor plans on right move via current listings or via the sold properties section for inspiration. I also got some layout inspiration looking at applications that had been made on the planning portal for properties in my area. Even though you can do a loft without planning a lot of people get a certificate of lawfulness and that application requires achitect drawings so you can see what other people with houses like yours have done.

Good luck

Thanks. What counts as the main roof? Do you mean there will be the same amount of space as there is downstairs minus staircase? In which case, Whoo hoo!!

What is the shape of your house and when was it built? It will be easier for me to explain it if I have a better idea but roughly speaking the answer to your question is yes :)

Nothing to add except .

Actually no there won't be. You lose a good five foot all around at least for the pitch of the roof, then a chunk for the staircase, then you need a lobby in front of the door which takes up another chunk. So in my house which is about 8m long or so, my loft conversion is only 5m deep (probably could have squeezed another metre out of the depth to be fair, but I prefer a neat dormer) and it's only 3m deep in front of the door and a really odd shape (sort of a U shape around the stairwell, with an en suite taking one arm of the U and a weird alcove in the eaves taking the other and the usable space being the bottom of the U). We do have a large en suite, but we're squeezing our bedroom furniture into it, as there aren't that many usable walls by the time you include the pitched wall (in front of which we're having built in chests of drawers), the big window on the dormer (radiator in front of it) and having to put the bed against a wall. Basically we've ended up building a sort of walk in (if you crouch) cupboard for all my clothes and shoes in the corner of the roof space not taken up by stairs or en suite and the one usable wall has our bedhead, small wardrobe and dressing table against it. That's it. I too had fondly imagined putting my nursing chair in there. That's not going to happen. It looked massive on the plans too.

I mentioned 5ft for eaves storage and the stairs in my original post. However, if you do a dormer the rest of the loft space becomes bedroom space. So the floor below is 25 ft long by 16 ft wide, you'll end up with a room that is 20ft long by 16ft wide plus 5 feet of loft storage. How you position the stairs (there are lots of options) will determine how much space they eat into the room. In reality it doesn't have to be a lot. You can allocate the remaining space between bedroom / bathroom / closets etc as you then see fit. It's all about what your personal needs are.

Here is a good example for a typical Victorian-semi with a dormer extension. It also needed a hip-to gable but that's not always necessary to create the same space.

planningonline.southwark.gov.uk/DocsOnline/Documents/211991_1.pdf

As you can see the loft space created is the same size as the floor below and has been carved into a bathroom, storage and bedroom space. This is a very efficient way to do your stairs as well.

It also depends how many sides of your roof slope. Our house is a semi and the roof slopes on 3 sides - my neighbour's roof just slopes front to back so they have more usable space (and a vertical exterior wall to put proper windows on)

Oh and do you have chimneys? Depending on where they are located, they might restrict how you can use the space as well.

But in our loft conversion we actually lose more than five foot - there's no way we could build on storage all the way to the front. So we lose about five foot and then have storage in front of that starting from 50cm high. You also lose the depth of the chimney breast and a lot of planning officers don't really like the dormer to go all the way to the back of the house, so you lose a few feet there. You can build out and create a gable end if you don't have one, which helps, but if you have a typical 3 bed semi which isnt halls adjoining, you have the stairs in the middle or lose part of a first floor bedroom. Which rather eats into your space.

Yes, it very much depends on the style of house. 30s semis and Victorian Semis are the easiest to covert without losing lots of space typically and you can typically do a hip to gable and dormer under permitted development to maximise the useable space.

The OPs best bet is look at the floor plans of houses that have been converted on her street on rightmove and look up applications for loft conversions on her street on her councils website. That will give her the best idea of what is likely to be feasible for her home and the various permutations that are feasible.

Thanks all. I had a look on right move and my county council site as suggested. Looks like the hip to gable extension is popular around here.

Ours is a 50's semi. Standard layout of front room going through to a diner looking out the back and a kitchen ?looking out back). 2 good size bedrooms over the lounge / dining room and a small 3rd bedroom over the front door/ hall.

Roughly it looks like house is 5.3 metres wide and 6.5 metres long. Sorry, don't do feet but I guess that means we could get roughly 4m by 5 upstairs?

I'd recommend checking out some resources online when it comes to costs. we went with central london lofts and they just told us what costs we were looking at when we got in touch with them, and they had a brochure to check out and a few blog posts that outlined potential costs. just leave it to the professionals i say, since you don't want to mess up any measurements and get misquoted

Do you know what head height you have? Ours is a 30s semi - similar layout to yours and don't have sufficient head height - we'd have to lower the ceilings in the bedrooms. Yes the other 30s semis starting 2 houses further up the road are all okay. I think it's difficult for anyone to give you a realistic estimate of how much usable space you'd get - get a loft company round to talk it through.