Building regs clarification needed on fire escape routes and 30min protection materials on 3 storey extension

[Shoestring]

.Hi all,

As per title I really need some help in understanding what I need to do/materials needed to comply with Building regs on fire escape routes (namely a staircase coming down from the attic onto a landing area) and 30min protection materials between floors.

 

We are mid build, with first fix elecs complete, but essentially the house is a shell.  What we have built is technically an extension, although really it is a house in its own right.  Our planning permission was for a two storey extension, & we didn't have our permitted development rights removed, so during the build we decided to install attic trusses for potential future conversion to attic, given the additional cost of attic trusses wasn't huge.  I would like to make sure all the materials we use now (on ceilings, stairwells, etc), comply with fire regs for future conversion of the loft, so it's done once and done properly.  I also want to make sure to plan the staircase to the attic has a secondary escape route because (we have an open area - play/reading areas, off the landing & directly below in the hall) and our BC officer says it would be considered "open plan" and could pose a risk in the event of a fire.  I am hoping this, will avoid us having to install a misting/sprinkler system but I have been looking into this.

 

I am a bit confused over the type of plasterboard required on ceilings, our architect has said we need two layers of Fireline board but I can't find reference to this in any building regs docs.  My dad has also just had the all clear from the same BC officer for 12.5mm plasterboard and skim (with chicken wire above holding up 100mm of rock/glass wool and finished with 22mm t&g flooring) on a loft conversation in his house.  Can anyone clarify?

 

I made provision for a staircase to the attic when we had the attic trusses designed, but didn't know at the time about the need for additional escape route.  BC officer flagged this up to us on his last visit, but did say a secondary door out into a bedroom may be acceptable. A turn in the bottom of the proposed attic stairs makes a conventional door into a bedroom a little tricky.  Does it need to be a proper door or can it be an escape hatch? Can there be a big step (400mm ish) down from staircase to bedroom? Do I need to redesign the proposed attic staircase - (which could be done, but isn't ideal, & would involve a fair bit of compromise elsewhere)? 

 

I am going to ask if we can add the attic conversation onto our Building regs plans, as it's not currently included.  Meantime we are very tight on cash and I dread doing work/ordering materials that then aren't right so any help or advice on this would be very gratefully received.