Thorfun

indeed. we specifically found a Cemfloor installer for our screeds as we really didn't want to use an Anhydrite screed due to laitance. just had the ground floor screed done this week, depth varied from 50mm - 75mm (in a few places). installer had no concerns with the depth and we now have a nice level screed to tile on to. interestingly the installer said that if tiling on to it we need to get it sanded to give the adhesive something to stick to. but I did a quick search on here and found a few threads saying that wasn't necessary at all including the very knowledgeable @nod in this thread this was one of the reasons I wanted a cement based liquid screed as I, also, didn't think sanding would be required. so I'm definitely not going to bother sanding!

Even @pocster?

we insulated outside ours

We used TSD for our basement. They’re based in Ireland (we’re not) but that didn’t bother them or us. @Bitpipe used a UK based SE for their basement but I found them a bit pricey. have an extensive read of the basement sub forum as there’s lots of info on there

sadly the house isn't finished yet so we haven't really used the blinds so i can't really comment. but i had to lower a couple yesterday to shade our new screed and they still worked. 😉 when you speak to Tim (Powell) tell him Tom from the golf club sent you his way. i won't get a kick back but he might buy me a drink after golf someday. 🤣

it's in the post

and doing a brilliant job

Thank you. I had a quick read of the link and will look into it in more detail tomorrow.

actually there are a lot more calculations that I posted above. here's a pdf for the joists in question. joist_calcs.pdf it's all Greek to me. I'm hoping someone can tell me what it all means!

and this. anyone able to make heads or tails of it?

this is from the document showing the joist design I managed to find.

The guy from the posi place said that the joist could fail if the load exceeds 200N/m2 . That sounds scary. I might have been able to find the calculations used by the TF company though so will send that off to them and see what they say. it’s a shame Flight Timber went belly up for all those that lost money with them and also as they were always really quick to respond to queries like this. I don’t have that resource anymore and so I’m left to my own devices. im not sure what the beam calculator will show as I don’t believe it’s deflection that’s the issue here as the top chord load is 2060N/m2 and we’re designed for 8mm deflection. But that’s the top chord. The bottom chord is designed for only 200N/m2

does this maths seem correct? 18lm x 0.37kg = 6.66kg / 16.32m2 = 0.41kg/m2 if so, that's nothing! and so with those maths the MF ceiling won't add any extra load i just need to figure out if i can double board with 12.5mm PB and not exceed the 200N/m2 maximum load of the bottom chord. maybe i should post this in boffins corner so all the boffins see it? otherwise it's just me and @pocster bumbling through as usual.

right, more maths required as BG technical support had finished for the day when i tried calling. according to this data sheet the GL1 channels are 0.37kg/lm. i've calculated that i will need 18lm of the stuff. the room is 16.32m2 and the GL1 channels will be spaced at 400mm centres. anyone know how to calculate the downward force imposed on the bottom chord of the posi-joists per meter squared?

SWMBO

this is an issue when the TF company no longer exists. i do have the SE calculations for the frame but would have to engage an SE to double check and that would cost money i don't have. so a decoupled timber ceiling will be my last resort to be honest.

i will try and phone Gyproc and see if they can give loading figures for the GL system.

are the tiles rated to take the weight of ceiling speakers? the frame is probably the same weight as the MF ceiling tbh. i doubt there's much in it. so the plasterboard will be the main difference

this is the TV room on the ground floor. basement comes much later. need to get the main house finished first. don't want to end up a lifer like you. 😉

it's a small room about 5m x 3m so the costs for the MF ceiling is not that high on top of what i would pay for not dropping it.

so it's still imparting a downward force on the beams above

does that grid system attach to the beams above?

so, for the dropped ceiling i guess i could look at completely decoupling the false ceiling but then that would add extra load on the TF and might cause those calculations to fail? but i'm also asking for the rest of the downstairs as all the posi-joists are designed with the 200N/m2 load on the bottom chord. so, from the way the guy was talking (although i think there might've been a bit of understandable arse covering going on) i wouldn't be able to double board anywhere.

ok, i've had some bad-ish news from the posi-joist company and i'm looking for some smart people to assist with the physics and maths and i know there are plenty on here, obviously that includes @pocster 😉. they have said that the bottom chords were designed to take a load of 200N/m2 (see @SteamyTea i got the units correct unlike some around here) and they said that a single layer of 12.5mm plasterboard is all i can put on the bottom chord of our posi-joists. they did say that as they don't have the job file which is probably now lost amongst the inaccessible files of the now defunct Flight Timber and so they cannot comment more. they are going on the details on the joist layout document that Flight sent me. so, from a quick google is seems that 200N/m2 is equal to 20.394kg/m2 and according to Gyproc their standard 12.5 wallboard is 9.7kg/m2. so, a double board of this stuff should only give a force of 19.4kg/m2, right? therefore i believe that the bottom chord should take a double board of standard 12.5mm plasterboard, right? anyone know if the above calculations are correct? and does anyone know what sort of load the MF dropped ceiling would add?

i hope not as that's my kids bedroom! 😱