Visti

That is not a bad shout at all. I think I'll go with that. Mind some clarifications? - what grade and thickness of plywood did you use? - How'd you fix it to the beams? They did yes, but I'm not convinced on that as a finished floor, and I really don't want to have to double up. Plus they are not the most cost effective solution!

We're putting in a mezzanine with 6x2' beams (planed square edged) and looking to do the flooring as easily as possible. Any suggestions where I only have to install one later of board for a decent combined structural and finish floor? Or is T&G chipboard the most cost effective way to go, but with what on top?

You can see what we did to strengthen existing joists, though additional static load bearing capacity isn't the same as deflection under dynamic loads such as walking: ,

253mm is standard height for pozi joists, and the majority are 600mm centres. Also, joists longer than 4m are possible, as you can see in some of the early SE calcs for our frame. Comes at the cost of a lot of deflection though as bending moments get worse the longer the beam. We had those PZ2 joists rotated 90 degrees to shorten them down to 3.6m for more robustness.

If it is a simply supported beam (at each end) and uniformally loaded (weight distributed evenly across it's length), then yes the centre will be the point of max deflection. If it is a cantilever, it'll be the unsupported end that'll experience the most. If you have stud walls or a large weight focused at one point, then the max deflection will depend on the result of all the bending moments.

Good news is that there is a very cheap resoution after all! And far less technically challenging. Rather than ~£1.5k on flitch beams, Nicks idea of reinforcing the joists beneath the partitioning wall is a green light. It requires some specialist material rather than plywood, but a 45mm thick Kerto S beam affixed with ESCR screws to each joists will reinforce them enough according to our engineer. Only about £200 after delivery fees.

@Nickfromwales suggested the same as you @ProDave in turning the partitioning wall into a beam effectively with the use of OSB and glue/nails. He also suggested reinforcing the sides of the existing posi joists the same way so that they can better support the partitioning wall. I will be going back to the SE today to see how much improvement that would be! Not a bad idea either! That'll avoid the need to worry about the partitioning stud wall and the joists beneath all together Possibly, but not getting a straight answer from them at this time! Yup, afraid one loses an order of magnitude more than one might expect 39kg/m2 isn't much at all to play with when domestic regs require ~60kg dead load plus the 150kg improsed.

Problem isn't the partitioning wall, but the joists below. They were supposed to engineer in tolerance to support a wall holding up the mezzanines, but failed to do so. That means the joists supporting the partitioning wall can only support 0.55kN/m. That equates to 0.39kN/m2... not very much I am going to see if I can add in suspension cables from the ridge beam to take some of the rest of the load...

We're adding some additional elements to our building and are trying to spec out the size of the flitch beams that'll be needed for the job. It is a 5.8m span between the ends of the beams (in blue), with the partitioning wall only able to transfer about 0.39kN/m2 down to the pozi joists below. Domestic floors are required to support a dead load of 0.6kN/m2, and imposed load of 1.5kN/m2... but is that overkill for a storage mezzanine? Anyone dealt with something similar?

Yup, it is a learning curve!

Got it from GH Supplies together with a larger batch of goods. Buying it on its own wouldn't be cost effective I don't think. I'll likely go with Pete's suggestion

Got a Fermacell spatula, but may get another as my sister used it to scrape off the joint stick before I could tell her otherwise. "Tough going it was..." Yeah, no kidding!

Not tried the FST. Got the big buckets, so going to wait until there's a large area to do so it won't go off (don't even know if it does!)

Another lesson learned, another part of the self build experience. As they say, it gets sorted in the end! I now go by the mantra "If it can go wrong, it will go wrong"... Except the first part is irrelevant, it will always go wrong! ?

I admit it doesn't leave a lot of tolerance to hide those errors. But 10-15mm?! Damed that stud work sounds like a right nightmare. I've taken to using a mallet to get the noggings into line and in the worst case a plane to shave just a bit off to ensure the bord sits flush with the stud. I also am sanding the joints following joint filler with an orbital sander. First 50 then 80 grain. More work, but the finish feels good. Also found box cutouts are easiest with a 10mm steel drill bit into each corner, and a jigsaw with the Makita B-50 bit to connect the dots. Cuts like butter. Struggling with a multi tool at all... Anyone found some decent blades that'll work on th stuff?

Hi from Bicester, all the best in your new build!

They go by the name Archital now (https://archital.co.uk/). Having used them for the cost of near £5k for all our ventilated cavity cills, roof trims and cappings, I personally suggest that you avoid them unless absolutely desperate. Took two and a half months for a quote. Almost impossible to get on the phone or get an email reply. Never deliver on verbal or written promises and rarely deliver on time. Fail to follow your designs, or will outright change them without informing you. They'll ignore actual on site measures taken by you, and even by themselves. They won't account for tolerances so what will fit in their workshop doesn't when you're 8 meters up on a 4 meter gable. They'll say that shoddy welds are acceptable, and if it leaks it is your fault for it being damaged somehow. They'll take shortcuts to rush a job the 2nd time rather than just getting it right. They'll refuse a refund when you want out, and then two months later they'll say they will refund you since the work isn't profitable any more and leave you hanging. I've spent as much again on my scaffolding due to their delays and mismanagement. Find someone else for your own sake.

The cladco ones come with an anti condensation coating on the back for an extra £2/m or so. Can't speak for how effective it is, but given how cheap the material is in the first place relative to other options I'd rather be safe than sorry... Only downside is all the waste I have cannot be recycled as pure steel.

We got the BAZ washers without realising, and they are quite large compared. Wish we'd known before hand, but it is all installed now and god knows I ain't going back and revisiting that!

Nothing in the building regs that I know of. Ask them to quote the Reg part and paragraph and you'll get a clear message as to whether it is needed or not

Vinyl is cheaper if you DIY it for certain (£30-60/m2 depending on where you get it), though we found that if you've got to pay for surface treatment and installation on top you're actually only about £5/m2 away from a resin or microcrete option at ~80/m2. Check out Flexcrete if interested. We found the labour for the glued panels about £18/m2 for installation, and another £18/m2 if you need to prep the underlying surface.

Why not 75mm in a 89mm stud? As long as the mineral wool isn't compressed it should be fine.

@Tom's Barn the battens were all fixed through the external timber marine board and external membrane down to the joists themselves, both vertical and cross battens. Any other way is asking for trouble. That results in 50mm clearance between the sheet and the board which allows it to ventilate and try if you get any condensation on the underside. WeYou don't want to fully block the passage of air under the sheets for this reason. We got our sheets treated on the backside with an anti-condensation layer to help avoid that anyway. Cladco, the steel sheet supplier has some decent installation manuals on their website. Highly recommend. See my post below in how not to install corrugated sheeting. Very DIYable, wouldn't pay a roofer to do it next time when I do the car port. I'd recommend listening to @Cpd's posts as they are very helpful. My own tips are: - get the domestic screws and caps, we didn't know there were options and the commercial ones are quite obvious, even with caps. - you only need to cut sheets down to length. Don't cut along the length of you can avoid it. For windows, one sheet each side and then shorter sheets above and below, don't cut out the corner for the sheet to wrap around. Looks horrid. - use the right tool to cut the sheets (nibbler) and it is a breeze. Don't be and idiot and try with a recip saw... Very very bad cuts. - plan the spacing of your fixings ahead of time. It is really obvious if they aren't aligned or regular - don't trust trades when they claim they can do a job. Check their references, give them the supplier instructions, walk it through with them, check up on them, inspect the work as they go, get a paper trail via email... - ... Or just DIY this. Low skilled job provided flashings are in place along the edges of the sheets

Am considering a similar setup and wondering whether it could be easier with Fermacell given you don't need the bead or skim... Hummm

It is likely to be quite OTT, but I am very keen on acoustic solutions as I wake up with the slightest sound. I am even considering a layer between the two sheets of plasterboard to reduce transmission further