MortarThePoint

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?

That's a great price. I was paying £1.153 each in June last year down near Cambridge. As soon as I had a quote from one BM, the job was known and I got the same price form others.

Even with the top alternative insulation below, it may be difficult to get the space below airtight if not achieved by the ceiling.

I'm trying to understand resilient bar installation. For it to have any acoustic benefit, it is essential to avoid short circuits like a screw going through the plasterboard, resilient bar and into the joist above. It's all about isolating the mass of the ceiling from the joist. "Where Resilient Bar is being used for ceilings the bars are fixed at right angles to the underside of the joists as close to the perimeter of the room as possible without touching the walls" (link) In the video below they use a silicone type sealant at the board edges, but it doesn't look very convincing from an airtightness perspective. I will have areas above the ceiling near walls that are exterior vented. I have some questions that anyone who has considered this before will likely have worked out: Airtightness: How best to airtight the ceiling at its edges with the wall? This could be done at joist level, so maybe I need a membrane above the resilient bars. Wet plaster: Can we just wet plaster into the ceiling corner and is short circuiting the ceiling to the wall is less of an issue? Plaster cracking: Will the plaster crack at ceiling corners as it is possible the ceiling may shift relative to the walls slightly?

Probably, but if the formaldehyde concentration being higher near the floor is true, then it's a consideration for anyone who is interested in the formaldehyde part of this thread so I thought I'd share it.

Saw this and thought it may interest this discussion if someone comes here. I don't know mch about MVHR, but the height of room extraction may be a factor. https://www.novofibre.com/health/indoor-aqi.php

As an example, my copy of SPON's has 7.0N Hemelite @15.51/m2 and 3.5N Hemelite @ 15.76/m2, so 7.0N cheaper than 3.5N.

3.6N feels a bit on the low side to me for load bearing. Has the Structural Engineer specified 3.6N? There may not be much of a price difference between 7.3N and 3.6N. There was a point in time when I had 4 types of 100mm block on site (7.3N Stranlite, 7.3N Stranlite paint grade, 7.3N Fibolite, and 10.4N Stranlite). I wouldn't do it again that way. Structural Engineer hadn't called for anything more than 7.3N for 100mm blocks so wasn't critical.

D'oh! Too late for that unfortunately.

Mounting the plasterboard on Resilient Bar (or Resilient Channel as the US call it) could be a useful approach. It reduces my centres to 400mm or 450mm and also helps reduce sound transmission: I think this may be based on two layers of plasterboard, but one would still give benefit. https://onlineinsulation-sales.com/resilient-bar-rb1-45mm-x-16mm-x-30m-138-p.asp

Don't know what I was thinking, it should be called 'Site Club'

I could start a new 'Gym Club'. The rules of which would be: Don't talk about Gym Club Carry these 15mm plasterboards through this cunningly devised assault course

The nog-tastic approach has the option of reduce size boards (1800x900) but I expect they are probably expensive compared to the normal sized board

Would I want this for fire resistance as well? I think 3 storeys requires 30 minutes and on 600mm joist centres the table below says 15mm if using Wallboard. That said, the White Book where that table comes from has lots of different and somewhat confusing tables. I'm going to get bored of carrying heavy sheets of plasterboard through the scaffolding.

I wasn't clear in my original post. I was planning to use 12.5mm plasterboard, but wondered if the plasterer's concerns were based on experiences from when plasterboard was more often 9.5mm. Would stepping up to 15mm, from 12.5mm, negate the concern and give a good stiff ceiling? It's the first floor ceiling and we have attic trusses above with living space. The service gap could be handy for running pipes and electrical cables, but I can route those OK near the eaves on top of the trusses I think.