Can any of you guys tell me what is involved with loft conversions?. I know you need planning permission and possibly buidling regs, but just exactly what is involved with the woodwork side of it, Roof trusses, stairs, joists etc. and how about the windows in the roof?. Would appresiate any info you can give. Is it a DIY project or do you have to have a reputable joiner/builder to do the work?.  ???

There are a number of criterea that need to be met in relation to a loft conversion the foremost one as far as building control are concerned is the fire regs. You will need to provide half hour fire protection to ceilings by overboarding (first floor) or fire retardent insulation between joists hung on chicken wire, (though might not get away with that theese days) you will need an enclosed fire checked stairwell with fire doors possibly self closers on doors below attic.
There must be an accessable top hung roof light at low level for means of escape.
Floor joist will need upgrading and need to bear on internal walls, you can not glue and screw to existing but straddle the existing joist with probably 7 or 8x2.
triple R or Kingspan insulation between rafters leaving a two inch air gap between underside of roof covering and insulation, under no circumstances use rockwool type insulation.
You will probably need an engineers report for the plan submitted in regards to the proposed joist layout, all in all there are alot of rules to abide by.... however if you are turning the attic into what you might term a hobbies room, sewing room, utillity room etc etc then you do not need planning peremission as long as it wiil not be a habbitable space, therefor you can convert as you see fit and what you do with it is your business  

malee,
         i noticed you mentioned  roof trusses .Modern trusses  rely on the way they are made  for their strength.They can not be cut to provide space in a attic
I  rescently read a newspaper article about a man ,who done this  in  a housing assocation house  that he was living in.
Apparently  he is was not very happy with the £30,000 they estimated  it would cost repair his handy work

greg,
      I do understand that all things are possible .Unfortunetly  they are not always viable.The cost would be very high.  

Surprising as it may sound it is invariably cheaper to take a trussed roof off in full and cut in a traditional roof, then reinstate tiles rather than attempting to convert from the inside. On a traditional cut roof there is no stress on the original rafter so even 4x2 need no alterations other than additional 2x1 or 2x2 tacked to the underside so as to gain the depth for in between rafter insulation. In short a trussed roof is a financial no no. steels are often a requirement on longer spans hence an engineers spec though often enough you can get by with timber trimmers or double trimmers on shorter runs.

Expensive job warm roofs!