....comments please>>>
They only really become a nightmare if you don't A) Have enough headroom in the loft at the moment and therefore have to introduce dormers etc, and B) If the floor joists aren't strong enough and you need to introduce deeper joists and/or steelwork to support the loadings, and C) If you don't have enough room on the floor below to provide a staircase that complies with the buildings regs, in terms of fire escape and protection.
If you can accommodate those things, then they are easy 
Sorry, no knowledge of firms in Yorks, as I live down south.
mmmmmm...tick the first two nightmare boxes then. 🙁
Well worth it, the best value adding of sq footage you can get IME. The building work for ours wasn't too disruptive as all the building was done from the outside, the services had to come in via the house but that was near the end. We turned a 2 bed one bathroom house into a 4 bed 2 bath for under 40K..... in London
Do it in summer though.... We had one rain storm and the tarps leaked and we got wet, would dread to think of doing it in Winter
I added C) as an edit. I don't want to put you off, as they can be a really useful way of creating more space in your house. I just want you to be aware that the costs may not be as straightforward as you think, so it's best to be aware of all the issues from the outset.
Can't recommend a firm in yorks but we had one done in our last place and it was superb. Took about a month to complete and the builders were superb. They built a stud wall on the landing where the new staircase was to go and then basically did all the work before removing the stud wall, meaning there was hardly any dust.
We've just moved and a loft conversion is definitely on the cards in the new place. Cost about 16k but we had quite a large open gallery area which opened right into the eaves of the house. It was areal feature of the property and definitely added value and made it is easier to sell.
Oh and one more thing: The architects I work for generally won't do them as the time we have to spend on them would mean that in order to make it worth our while, we would have to charge an amount that would appear to outweigh the amount of work being done.
You might just need to shop around a bit.
cheers mikey
Before you actually make a decision, it might be worth getting a Structural engineer or a building surveyor to check out your property and give you feedback on what is possible. They might even do the drawings and applications for you, which might mean that the initial survey is absorbed into the cost of the main work.
wot mikey said in first post. We did one on current house - newish 4 bed detached where 4th bedroom was tiny. sacraficed that room and a bit of the 3rd bedroom for a full size stairacse on gable wall and then huge new bedroom plus 2 big storage areas up top. We needed a new floor and all the steelwork that goes with it - not cheap but worthwhile if you are gonna use it for a good few yrs.
may I ask the ball park cost?
may I ask the ball park cost?
our building work was £25K. the steel was £4K of this. By the time we had decorated/carpeted/wardobes/furnished etc, plus tidied up the rest of the place in all about 30K. all the ceilings throughout the house needed skimmed as the plaster nails all popped from the hammering ! We used a reccomended joiner who brought in the other trades - all small/one man band type guys. very good job and a lot less than some of the quotes from bigger guys. no where near you though (Glasgow)