Thorfun

wonderful summary and spot on, thank you. M12 x 160mm coach screws is set in stone (or timber i guess would be more accurate! 🤣) the decision about whether to cut out the finished floor, use some form of steel pipe spacer, or replace the underlay with a solid material is still in discussion with SWMBO. i'm leaning towards cutting the finished floor out and fixing directly to the 22m chipboard flooring and then simply caulking any gap between the channel and the floor but i'm still mulling it over. i will also consider a couple of brackets at the top of the straight run for a little additional support against wobbling. thank you so much to everyone's thoughts and assistance so far. it is, as always, invaluable and i may not always use the suggestions but i do appreciate the differing opinions and solutions to a problem.

so, there's no timber up the wall on the nearest run to attach anything to. i could use some heavy duty plasterboard fixings to assist with a glass bracket holding the glass but that would only really help with wobble i guess. i'm aware i can cut out the plasterboard and put timbers but would rather not go through that disruption to the decoration if at all possible. the balustrade is designed to not have the side support afaik.

measurements added

not sure. i will cross that bridge if/when i get to it. one thing on my side is that one of the sections is an L-shape so will have the other 'leg' to assist in resistance.

but the finished flooring is like a 3mm layer of hardwood. the rest is softwood ply. i wonder if i could, as was previously suggested, change the underlay under the channel to 5mm ply.

oh. sorry for my misunderstanding of the issue here and it's a shame you won't contribute further. i'm now interested in how the threaded bar would differ in rotation and aluminium hardness compared to the coach screws?

this is an interesting idea indeed. but anyone have a calculation as to the pull out resistance that this will have? I'm looking to replicate the manufacturers testing and ensuring that there is a 10kN pull-out resistance at the moment, at least that's the current thinking.

they tested using FISCHER FAZ 11 12/10 fixings in to concrete and from the spec sheet of those it was determined I need fixings with a 10kN pull out resistance. which led to the M12 x 160mm coach screw decision. indeed. it was an ingenious solution but I just don't know if it was the right one. especially considering @markc's explanation of the forces involved when using the spacers.

it's a possibility but if the coach screws will do the job then I'd rather do that. but this will be kept in the recesses of my brain as a potential option.

the best reason I've read so far to fix to the solid surface. thank you.

they do. just in to concrete. it's "not tested in to timber" seems to be the stock answer and so they cannot advise. simply not possible now. well, it is but it'll involve way too much upheaval at such a late stage in the build I don't want to do it. plus the frameless balustrade has already been bought and we don't have the money to get it re-done. 😞 yeah, that's what my builder mate says too. I told him about my engineer mate's suggestion of coring through to the timbers and using steel pipe as a spacer and he was a bit sceptical. said things along the line of "he's thinking like an engineer" which wasn't a slur but more that it's a different way of approaching the issue. I'm sure both ways will work and it would come down to whether I trust science or experience!

Not seen @Gus Potteron here for a while. Would be great to get his input. Don’t suppose you have a link to that previous thread do you?

Thanks, but way too late as it’s all sitting in the house ready to be installed.

ok. I sent the information to a friend who's a civil engineer and he sent me the following table which I believe is for the fixings the manufacturer used for their testing the manufacturer states that their tests were performed with FISCHER FAZ 11 12/10 fixings and my engineer friend stated that if I can get timber fixings that have a 10kN pull out I'm all good. he then said so I'll be looking for TIMco din571 or equivalent M12 x 150mm coach screws! I asked him about the floating floor and he said which sounds like an interesting idea and also mitigates the concern my builder mate has about the floating floor. although I would have to buy some steel pipe! I hate to tag you @Gus Potter but I'm going to anyway (sorry!). are you able to cast your eye over the above and see if you agree with the findings please? and any other recommendations before I put this to bed and get on with doing some work?

5mm yes. the screw just fits through.

14mm. 3mm veneer and 11mm ply (approx). I'm not sure from your answer if the crushing is a good thing! it doesn't sound it to me and it sounds like there might be a slope as the underlay and flooring is crushed? yes. do these photos help?

thanks all so far for the responses. another thing if I may. we have 14mm engineered wood flooring on that landing fitted with an underlay (so floating). my builder mate said he was concerned about fixing through the floating 'thin' layer and down into the chipboard and subsequent timbers and I should cut the finished floor out and fix directly to the chipboard and through. that seems to make sense to me but I'm struggling to understand the reasoning behind it as surely the fixing will then go down in to the timbers anyway so why does it matter if there's a thin floating floor between the profile and the solid timber? any of you knowledgable folk care to shed some light on that one please?

was 100% going to pilot hole. this is interesting. I was planning on using washers simply because the hole for the fixing is quite wide and I thought washers would reduce the risk of the screw head going through. didn't know about using them to spread load! thanks. tbh, I don't remember how they fixed it sorry. and I don't see any specific photos of how it was done.

we wanted the clean aesthetics from the landing so as to not interfere with the view up and through.

That’d do it and if I’d thought of it 6 months ago before plasterboard and plastering I might have done just that!

If I’m too worried then I’ll see how much an SE will charge to do the calculations. It’s just frustrating that manufacturers don’t test. Don’t suppose any SEs on here would be willing to do some calculations?

No balustrade suppliers I can find seem to certify for timber, they only test in concrete. 😢

I do have some 160mm M12 coach screws left over from fitting our external brise soleil. I was originally going to use those but the chippie said probably excessive and had potential concerns about the amount in to the wood and structural integrity of the timbers. But I was thinking 160mm is only just over 50% of the depth so still plenty of depth below them.

Here’s how it is with the 22mm chipboard flooring

Additional information: red lines show where the channels will be and the timbers they’re going in to.