Constructing a new ceiling

I'm looking to convert what is in effect a room on our loft in to a proper working room. Currently it has no ceiling and you look up to see roof tiles.

I'd appreciate some guidance on the size of joists to use, how to attach them to the walls and any hints and tips people can give me here.

The room is 5m by 5.25 metres in size with a large wooden beam running 6.4 metres in length from (almost) one corner to the opposits one - in reality the beam is offset from the corner by 30 /60 cm (1 to 2 ft) starting and finishing on adjoining walls. Two of the walls are external and are made of stone and mortar whilst the two internal are standard hollow brick type construction.

Ideally I'd like to expose some of the beam (which is c. 30cm square).

After putting up the joists I'm planning to plasterboard and insulate with c. 200mm if insulation. The joists will not be used for walking on.

So specifically:
* what size (thickness) joists should I use?
* with the longest stretch being 5.25m, I take it is need to this size. I ask, as the largest size from the local DIY stores are 5m. I'd only have c. 2 joists of this length with all the rest being 5m or less hence could I use 5m beams finishing on some form of 'support' beam which I install?
* how far apart should joinsts be?
* how sould I attach these to the walls? Are simple metal brackets available or the like?

Thanks

Richard

Richard, I presume the building is in france?

I personally would seriously recomend you get a local chap round to take a look first, even paying him for a bit of advice if need be.

Creating rooms in roofs looks very straight forwrd, but is absolutly fraught with problems. Load/weight ratio, spans, headroom, fixings, supports etc etc.

AS a chippie with 20 yerars experience, I personally dont get involved in even the basic ones over here, unless I have a collegue who knows exactly what he's doing. I appreciate things are a bit different there, but the problems are still the same.

Oh, don't go to DIY stores you'll pay the earth for second rate timber, go to a proper timber/builders merchants, they can also get you the correct sizes you need.

If however the building is here in the Uk, dont even think about starting it until you have sought proffessional advice first.

Woody

Hi Woody - thanks for your reply. To give a bit more detail:

* yes the house is in France
* the loft is in fact not really a loft...it used to be another floor of the house and the room we are converting for some reason has the roof taken down (or it fell down....) a long time ago. As such there are no problems with weight on the floor which is exceptionally well supported by beams soooo big ...... well, you get my drift! The floor is in fact already tiled of old which we're keeping and there are two full size windows in the room in question.
* the ceiling height will be set to approximately 2.95 metres assuming we expose half of the beam. Actual room height to the roof is between 3 and 4 metres at the lowest and hightest points respectively.

In principle to me it seems fairly straight forward..... assuming I can work out how to affix the joists and ensure they are strong enough without going enormous to support plasterboard and 200mm of insulation.

Am I missing the point somewhere?

Richard

The following is an extract from our "Approved document part A". These are the suggested figures for "Normal loading conditions" in British Ceilings. Unfortunately they don't give any details for French ceilings, but I'd imagine, if they did, they'd be pretty similar.

[code:1]
MAXIMUM CLEAR SPAN OF CEILING JOISTS IN METRES

Size of ceiling Spacing between joists
joist 400mm 450mm 600mm

97 x 50 1.97 1.95 1.89
122 x 50 2.67 2.63 2.53
147 x 50 3.39 3.34 3.19
170 x 50 4.06 3.99 3.81
195 x 50 4.79 4.70 4.48
220 x 50 5.52 5.41 5.14
[/code:1]
The column for "Size of ceiling joist" refers to the cross section of the joist in mm. The figures in the other columns gives the maximum clear span in Metres (for the specified spacing of the joists).