MortarThePoint

Is that the 4' sizes aren't tapered, just the 8' sides? I guess it's mainly for walls then

This is a useful resource that I have just found: Stockist Guide - Construction details. It shows other makeups for ceilings and floors. Some of the other ceilings are surprising less performant than one might expect.

No price difference in the boards really. Tapered edge is all about taping, filling and sanding the joints whereas square edge would get skimmed all over

900x1800 sheets of WallBoard (9.5mm or 12.5mm) or Fireline are £3.99/£5.80 which works out as 56% of the area for 65% of the cost. Easy handling, more screws and more joins.

Condell: 15mm SoundBloc £12.32/sheet 15mm SoundBloc F £12.94/sheet 12.5mm WallBoard TEN £8.32/sheet 12.5mm WallBoard £6.16/sheet 12.5mm FireLine £8.94/sheet 9.5mm WallBoard £6.25/sheet No brainer to step up from SoundBloc to SoundBloc F (+5%) if you are interested in sound or fire. It would be harder work to fit though. 2 layers of 9.5mm or 12.5mm WallBoard are cost comparable with SoundBloc with same or higher 'area density' and lighter but longer installation and more screws.

I thought I would record some of my research into plasterboard options and hopefully people can share their thoughts. Each manufacturer has their own equivalents, but I'll consider British Gypsum for ease. They have a useful selector here. Wallboard: 9.5/12.5/15 mm with area densities of 6.3/8.0/9.8 kg/m2. Available TE and SE. Thicker boards available as 900x2400, all available 900x1800. 12.5mm available 1200x3600!! Wallboard TEN: 12.5mm, 10kg/m2, TE only. SoundBloc: 12.5/15 mm, 10.6/12.6 kg/m2. Only TE. Minimum 1200x2400. "higher density core". Moisture resistant option (SoundBloc MR). SoundBloc F: 15mm, 14.1kg/m2, TE min., 1200x2400. " higher density noise insulating and fire performance core" F MultiBoard: 6/10/12.5 mm, 6.0/8.5/10.6 kg/m2. Only SE. Minimum 1200x2400. Fire and impact resistant. FireLine: 12.5/15 mm, 9.8/11.7 kg/m2. SE and TE. Minimum 900x1800. Fire resistant, moisture resistant option (FireLine MR) also available. Moisture Resistant: 12.5/15 mm, 8.6/10.1 kg/m2. SE only available 12.5mm 1200x2400, otherwise TE. "water repellent additives in the core", kitchens and bathrooms. DuraLine: Not Available. Highest 'area density' is 15mm SoundBloc F (14.1kg/m2). 15mm SoundBloc is around £12.30/sheet. Same supplier sells 12.5mm WallBoard for £6.77/sheet. 12.5mm Moisture Resistant is £10.90/sheet. 12.5mm FireBoard is £8.50/sheet. Solo installation and handling of 2 layers of 12.5mm WallBoard may be easier than 1 layer of SoundBloc and have a 27% higher 'area density' for 10% higher cost. I can't readily find costs for 9.5mm Wallboard, but two layers of that would have the same 'area density' as SoundBloc and be much lighter to handle. 12.5mm layers of Wallboard and Fireboard combine to make an 'area density' of 17.8kg/m2 which is 41% higher than SoundBloc for 24% higher cost.

Excuse my ignorance, but what are the main reasons to dob and dab rather than wet plaster? Does it work out cheaper or is it about using insulated plasterboard?

22mm CaberFloor states it is 15kg/m2. 18mm OSB3 will be well under. As @PeterW states it's unlikely any BCO will care though.

I've found it very hard to find density information. This link suggests Egger Protect has a density of 620kg/m3 which would give an area density of 13.6kg/m2 for 22mm thickness.

As I read it Part E does apply within a single dwelling. Table 0.1a and 0.1b set out values for 'separating' walls and floors which I presume means between dwelling units (e.g. flats) and the prevailing value for floors is around 45 dB for airborne sound. Table 0.1c sets out values within a dwelling and has a value of 40dB.

So if I understand it that document is setting out a valid substitute to the Part E "Internal floor type C".

In important consideration in all of this is Part E of building regulations: 18mm OSB3 and CaberFloor are below that 15kg/m2 requirement. I think 22mm OSB3 is also below 15kg/m2, but it is hard to find information on that. I spoke to a technical person at Norbord and they said it may have an issue there. [NOTE: normal 12.5mm wallboard plasterboard doesn't meet the 10kg/m2 requirement either]. Link to document

I expect the hydrophobic properties would stop water wicking (capillary action) out of the brickwork wherever it pools, but hopefully there are weeps there to deep with that..

It will be highly hydrophobic (like car wax makes beads of water on the surface) and so will stop liquid phase water from passing through. Capillary action is all about the contact angle of water with the sides of the capillary. If greater than 90 degrees the surface tension of the water can't pull it in to the capillary. If less than 90 degrees, the surface tension pulls the water further in. In the gas phase (i.e. water vapour) the water isn't interacting with the surface or relying on capillary action. I expect this is how a Gortex coat works as well.

The scaffold is about 400mm above the flat roof and at 11:30 last night I was putting in the last couple of screws when one jammed breaking by screwdriver bit. Couldn't get the screw out so had to grind it off, which I did this morning. Felt pretty cramped up there in the dark with only the light of my drill. Got the job 99% done though ?

Has anyone got a recommendation for something to put on the flaunching to help waterproof that. There are a couple of spots where water stands, so I'd rather get sealed. I don't know if the likes of StormDry can cope with standing water.

Well it's looking good and sturdy, but only 2/3 done as the latest batch of plywood is 2mm thicker than batch I got last year. Crazy! I started off predrilling and countersinking, but gave up on that whilst doing the first sheet as it worked well without. The second sheet though needed the countersinking as it created pushed up splinters without doing so. I wasn't worried about lack of predrilling not pulling the sheets down as I was using a screw with partial thread. 4.0 x 70mm Screw-Tite, an excellent screw IMHO. Where the firring is thicker, I'll be using a 5.0 x 100mm screw. No glue, though I would for a floor.

I like that idea. It's logical, but would it satisfy BCO etc?

Yes that's my beef really. 25mm plywood will be plenty strong enough without edge noggins, but the wisdom is to have the edge noggins so... The sheet join noggins is a different matter.

Still have to work out how to cope with the gang nails. I guess I'll jus put the noggins as close to the edge as possible but not on the gang nails.

I like this approach, but wish there was more meat to the top chord as putting 4no. 5mm screws through it doesn't feel kind. (4no. at the ends of the top chord, 2no. in other areas). It's only 35x72 timber. I'm sure I'm probably over thinking it though. The red lines below show where noggins need to be added.

I've fitted firring strips like this (exaggerated obviously :-):

I've circled here where it's going to be a pain to install noggins due to the gang nails. On the other end of the top chord there is some space. 6 noggins to install along that edge. I think the two timber sections shown at either end of the top chord in the drawing are diagonal bracing that obviously can't (and doesn't need to) be there when the sheathing is on.

It's going to be difficult as there are gang nails on the trusses at this point and the truss timber is only 72x35 on both the top chord and rafter.

I'm installing 25mm SE plywood sheets on a small area of flat roof approximately 3.5m x 1.75m in size. I'm using 47 x 50-0 firring strips under the ply to create a gentle fall. The trusses are only 35mm timber. I've laid the sheet perpendicular to the trusses. I'll be screwing the plywood down with 5x100mm screws (coungtersunk) so that the screws always pass through the firring into the truss. The end of the sheet doesn't fall on a truss so I believe I have two options: Cut it back to the centre of the truss and have the join between sheets there. I'd be happy with that if the truss timber was wider, but having a join 35mm timber feels a bit bad Add some noggins to support where the boards join. I'd make this out of 4x2 so am happy there would be room for the join. I'm inclined to go with option 2. Which of A or B would you go for? The yellow trusses are 600mm c/c. Also, should I be adding noggins between the trusses along the long edges of the plywood at the perimeter of the flat roof?