loft conversion and roof carpenty


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Established Member
16 Jan 2007
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I am still at the planning stage, trying to make two bedroom in a large loft space on the second floor of my house.
I am having trouble working out how to setup the ceiling in those two rooms. maybe someone here will have a technical solution that suits me ?
Here is a sketch of one of the roof suporting frames:

and here is a top view showing where that frame currently sits (roughly 5m from the outside south wall)

finally, an artisitc impression of what it's like right now.

The idea is to have two beedrooms in that spaces that's roughly 6x8m (the bedrooms will extend from the south wall a beyond the first frame.)
I need to place some insulation material to the thickness of the underpurlins (1,2 and 3) (about 200mm), under the roof, as well as over the ceiling, as per picture:

I would also like to keep the space above the ceiling suitable for storage. so i need to fit some floorboards.

The questions i am having relates to the setup of the ceiling:
how do i fit plaster boards over the 4 to 5m span at 2.3m height ? railing is out of the question, so the best idea i have at the moment is to have three beams spanning East-West, maybe 1.2m apart, (each beam 50x150mm cross section) with a post halfway across the span resting on the concrete floor. . this post will later be inside a plaster board, when the partition wall will be installed to separate the two bedrooms.
Some plaster boards railing will hang from the 3 beams, and some floorboard will be installed on top. so far so good..but..
how to support the beams in the first place ?
Can i possibly (i dont think so) rest them on the underpurlins (the one marked 2)? that number 2 underpurlin is a little low, so a big spacer would have to be fitted to bring the ceiling height to 2.3m...but isnt that a little too much weight on the underpurlin ?

The alternative is to make three frames which would run parrallel to the existing frame, and support the beams. but this is a bit more involved and has the major inconvenience of having most of these frames sticking out of the walls. if the frames are placed right against (underneath) the underpurlin, and the plasterboard (attached to the rafters, by the way) are also just abot flush to the underpurlin, the frame obviously sticks out..

anyone with a solution to this problem ?