Flat conversion - Suspended ceiling.

[Roofer]

If you go the timber joist route it would be far better to have joist hangers in the walls rather than bearing on a batten, neater as well

 

[Monsoon]

145x47 C16 @ 400c/c with a dead loading of 0.6kN/m2 can span 3.9m, as i said before thats with 0 live load. Your whole idea will be a little springy and your looking at about 6-10mm deflection in places, but thats within acceptable limits (just) and there is no live loading to create cracks.
A less flexible option would be 170x47 members @ 400 centres (also will get passed by building regs easier).

But surely deflection should only be a issue when you apply a live load?Even if it was slightly springy, no one will have access to the void so it would matter if it was a little springy as long as it didn't sag (or whatever the structural term is for that)

BTW I appeciate the replies and suggestion.

Monsoon.

 

[Monsoon]

If you go the timber joist route it would be far better to have joist hangers in the walls rather than bearing on a batten, neater as well

I will certainly consider the joist hangers as an alternative to the batten - cheers.

BTW. Roofer, Do you have experience of installing both framing systems, wood and metal? .... Could you hazard a guess at the cost of both systems in terms of materials and labour(timewise)?

 

[Roofer]

I don't have any direct experience of either systems but IMO the metal framing would be a lot faster and cheaper

 

[Static]

But surely deflection should only be a issue when you apply a live load?Even if it was slightly springy, no one will have access to the void so it would matter if it was a little springy as long as it didn't sag (or whatever the structural term is for that)

Springy as in each 3.9m long member will deflect(sag) by 10mm from straight on dead load alone. Springy as in vibration may cause cracking of the plaster from say a slamming door. Go for the 170dp joists they will only deflect by 7mm, or even 195dp members with 5mm.

 

[jbonding]

I don't have any direct experience of either systems but IMO the metal framing would be a lot faster and cheaper

i would agree its alot faster the cost may be similar but the amount of waste is a lot less. i would say if you know how to do it it would be done five times quicker or more, than doing it in timber. also its probably atleast a tenth lighter

 

[Monsoon]

I don't have any direct experience of either systems but IMO the metal framing would be a lot faster and cheaper

i would agree its alot faster the cost may be similar but the amount of waste is a lot less. i would say if you know how to do it it would be done five times quicker or more, than doing it in timber. also its probably atleast a tenth lighter

The numbers are starting to come in now.

Metal frame (inc a double layer of 12.5mm plasterboard). £12 per m2
Timber frame (inc a double layer of 12.5mm plasterboard). £6 per m2.

Note:This price increases by approx £1 per m2 if I go for the thicker joists.

So the timber frame works out at half the cost of a metal frame(material only). The metal frame cost is only based on a single quote, so I have no idea how competitive this figure is.

 

[Monsoon]

I don't have any direct experience of either systems but IMO the metal framing would be a lot faster and cheaper

i would agree its alot faster the cost may be similar but the amount of waste is a lot less. i would say if you know how to do it it would be done five times quicker or more, than doing it in timber. also its probably atleast a tenth lighter

Sorry I dont follow your reasoning.

Why will I create a lot of waste? Based on the above drawing I've calculated I need.

22 X 4m lengths of 145 X 47 C16 @ £1.50 per m2 = £132
1 X 6.5m Timber I Beam @ £4.00 per m = £26
36 sheets of 2.4 X 1.2 plasterboard @ 3.50ea = £126
48 joist hangers @ £20

Total £304

 

[Static]

My timber size was based on 400mm centres, so your looking at 17 joists per side, 34 total.

 

[Monsoon]

My timber size was based on 400mm centres, so your looking at 17 joists per side, 34 total.

I think 175 X 50 would be the most appropriate for a 3900mm span but I dont see why I need them at 400mm centres.

600mm centres according to the software on the net gives a deflection of still just over 5mm well within the 12mm limit.

Here's a link to the software( under downloads).
http://www.jji-joists.co.uk/

Design Results. SI = 2.221
______________________________________________________________________________
Type : SJoist Placement: Floor (Intermediate)
Joist : C16 Width: 50mm Depth: 175mm
Span : 3900mm Spacing: 600mm Plies: 1
Girder: No K8 = 1.10 Max.Def. = Span * 0.003 or 12mm
______________________________________________________________________________
Loads.
Standard: No Load
Imposed 0.000 (kN) Dead 0.000 (kN)
Uniform :LV Imposed 0.000 (kN) Dead 0.600 (kN) Start 0 End 3900
______________________________________________________________________________
Reactions (Long )
Shear (kN) 0.684 @ 0mm Max 4.299 CSI 16% (All)
Bearing (kN) 0.702 @ 0mm Max 9.350 CSI 8% (All)
Bending (kNm) 0.650 @ 1950mm Max 1.579 CSI 41% (All)
Deflection (mm) 5.132 @ 1950mm Max 11.400 CSI 45% (All)
Support 0 @ 0mm (Left Width 100 Blocks No ) = 0.702 ( 0.702)kN (All)
Support 1 @ 3900mm (Right Width 100 Blocks No ) = 0.702 ( 0.702)kN (All)
______________________________________________________________________________
End of Design Results.

 

[jbonding]

I don't have any direct experience of either systems but IMO the metal framing would be a lot faster and cheaper

i would agree its alot faster the cost may be similar but the amount of waste is a lot less. i would say if you know how to do it it would be done five times quicker or more, than doing it in timber. also its probably atleast a tenth lighter

Sorry I dont follow your reasoning.

Why will I create a lot of waste? Based on the above drawing I've calculated I need.

22 X 4m lengths of 145 X 47 C16 @ £1.50 per m2 = £132
1 X 6.5m Timber I Beam @ £4.00 per m = £26
36 sheets of 2.4 X 1.2 plasterboard @ 3.50ea = £126
48 joist hangers @ £20

Total £304

where from?

 

[Monsoon]

I don't have any direct experience of either systems but IMO the metal framing would be a lot faster and cheaper

i would agree its alot faster the cost may be similar but the amount of waste is a lot less. i would say if you know how to do it it would be done five times quicker or more, than doing it in timber. also its probably atleast a tenth lighter

Sorry I dont follow your reasoning.

Why will I create a lot of waste? Based on the above drawing I've calculated I need.

22 X 4m lengths of 145 X 47 C16 @ £1.50 per m2 = £132
1 X 6.5m Timber I Beam @ £4.00 per m = £26
36 sheets of 2.4 X 1.2 plasterboard @ 3.50ea = £126
48 joist hangers @ £20

Total £304

where from?

http://www.selco-bm.com/EDLP_1.asp

 

[Static]

http://www.jji-joists.co.uk/ software is for TJI style joists not standard timber thus your going to get a better design. 170x47 C16 joists at 600 centres gives you just under 10mm deflection, at 400 centres that drops to 6mm.
Your better off going for 170x47 joists at 400mm centres, as they can be proved to building regs without calcs.

 

[Monsoon]

http://www.jji-joists.co.uk/ software is for TJI style joists not standard timber

Not true - It has two options and one of them is for solid timber which I selected when entering the figures.

Which tables/How are you calculating your figures?

I appreciate it's only a few more joists going the 400mm route but based on the figures I have it would just add extra to the work/cost.

Design Results. SI = 2.221
______________________________________________________________________________
Type : SJoist Placement: Floor (Intermediate)
Joist : C16 Width: 50mm Depth: 175mm Span : 3900mm Spacing: 600mm Plies: 1
Girder: No K8 = 1.10 Max.Def. = Span * 0.003 or 12mm
______________________________________________________________________________
Loads.
Standard: No Load
Imposed 0.000 (kN) Dead 0.000 (kN)
Uniform :LV Imposed 0.000 (kN) Dead 0.600 (kN) Start 0 End 3900
______________________________________________________________________________
Reactions (Long )
Shear (kN) 0.684 @ 0mm Max 4.299 CSI 16% (All)
Bearing (kN) 0.702 @ 0mm Max 9.350 CSI 8% (All)
Bending (kNm) 0.650 @ 1950mm Max 1.579 CSI 41% (All)
Deflection (mm) 5.132 @ 1950mm Max 11.400 CSI 45% (All)
Support 0 @ 0mm (Left Width 100 Blocks No ) = 0.702 ( 0.702)kN (All)
Support 1 @ 3900mm (Right Width 100 Blocks No ) = 0.702 ( 0.702)kN (All)
______________________________________________________________________________
End of Design Results.

 

[Static]

Ok,
Im calculating the members from BS5268.
Ok didnt really want to get too technical but can: Ive looked at the results more in depth now and can see what asumptions it has made, firstly 50x175 timber is a metric planned size and your are more than likely to get 47x170 metric sized sawn softwood C16 grade.

Thus the SI is incorrect and should be 1924cm4 (1.924), also it has assumed that this is a flooring and has taken the mean modulus of elasticity i would only assume that if i know ply or floor boards were going on top and the whole area will act as a composite floor which it wont (cant rely on plasterboard for stiffening). Anyways the upshot is that the actual calculated deflection at 600mm centres is 10.70mm with an allowable delfection of 11.70mm (which your computer programme rounds up to 12).

Im not saying it will fail, just saying its a little tight on design, unless you plan on screwing down some boarding i would just add a few extra members. Also the 47x170 is stated in building regs part A - TRADA tables for ceiling joists at 400c/c to span 4m thus you can refer Building Control to those tables if they ask.