10mm holes within 50mm from top of joist

[Kaer]

Hi,

I would hopefully like to avoid all the comments i know are coming regarding why i would ever WANT to do this, as i know its way overkill, i just want to know if there are reasons why i should not do it, safety and structurally speaking.

So i am putting down 25mm plywood in all the upstairs rooms in a house i am moving in to, but i want to make the flooring “modular” and removable like panels for easy access to mvhr ducting and electricals. My over the top plan is to drive myself insane and use cross dowels.. for the whole floor.. This would involve me drilling a 6mm vertical hole around 30-40mm deep in the joist, and a 10mm hole horizontally to meet the bolts. This would need to be around 30mm down the side of the joists, but i could go further if i go for some longer bolts.

Would this combination of holes compromise the joists, if done on 400mm centers? i am medium concerned about the vertical holes where the panels join, but i should still have 35mm of joist left over with 2 “side by side” 6mm holes, and they would share the same 10mm horizontal hole with a cross dowel from either side.

This decision was made, after considering that if i used threaded inserts, i would probably go equally as insane in the process, but they have the risk of pulling out of the joist over time and shredding it on the way out, which the cross dowel wont.

I am justifying this as an okay idea in my head because if plumbers can take big notches out of a joist without houses falling down, some holes with solid bolts inside shouldnt “cave in”

I will be adding noggins every 40cm also, with joist tape along all joists and noggins for what I hope will be a very sturdy and silent floor (for home theater/bedroom)

Thank you ever so much in advance!

 

[Deleted member 174758]

You should be OK, but TBH your plan is completely OTT and to my mind just a tad bonkers - and may drive you a.bit further that way given that joists are never perfectly flat and straight and plywood can gbe a little warped, too, which will give you major alignment problems when trying to utilise furniture components desigbed forcprecision positioning and location.

It is probably just as easy to screw plywood rips down above the service runs with good quality screws, such as Spax screws (go for the Tx head ones in a 5 or 6mm shank diameter), then glue and screw the rest of the sheet materials down as normal

In reality you don't often need to lift floors in the way you are thinking, and in any case for easier access to electricals wouldn't the wiring have been better run in flexible conduits between oversize junction box "panels" (in the walls) like they do in Italy?

 

[Kaer]

When in conduit the cables are downrated, and i want to keep them open in cable tray to keep their best rating possible. Yes it is going to drive me insane, but i have 1 month to basically do 2 rooms like this, then we can move our belongings up (bristol to newcastle, so not very fun with pets also).
I want to be able to lift flooring easily for many reasons, like adding large panel lights to the living room below, adding fireproofing material down the line, adjusting the sound proofing as necessary, adding extra support under the plywood if needs be when adding a big oak bed (will be as overbuilt and over the top as this flooring plan). Running new data cables and smart home sensors as needed.

Other main reason is that if i die for whatever reason, my rather inept girlfriend who wont have much money, would be able to have maintenance done under the flooring without someone multitooling the floor up and can just bolt it back down afterwards.

Here is a model of my plan, the purple layer between the subfloor and joist/noggin is the green glue joist tape. I just dont know if that cross dowel is too close to the surface of the joist, or if i need to use 75mm bolts (45mm in the picture) to get them lower down, as right now there is only 5mm of "meat" above the dowels.

I probably wont be doing every single room like this, just the main bedroom and the pet room (so i can add more vapor barrier as needed, as my soldering/painting/chemical workshop will be right underneath them).

So yeah, i will probably be quite a bit more insane after 1 month completely alone doing this non stop, but hopefully thats the price i pay for a first floor that feels like a ground floor (fingers crossed)

 

[SFK]

The threaded cross dowels will rotate and misalign. Not an issue for furniture as you can get your hand round the back. But a nightmare when you have blocked access with your panel.

 

[Kaer]

The threaded cross dowels will rotate and misalign. Not an issue for furniture as you can get your hand round the back. But a nightmare when you have blocked access with your panel.

I have tried one out, and they are very snug, I don't see them just freely spinning around or anything, so as long as I put them in the right way up the first time they should probably stay put.
But I have weighed that up and it doesn't deter me from this unless there are structural concerns, which is my main worry

 

[cdbe]

Strange idea. I wonder how many time a standard wood screw can be driven in and out before it wears the hole and loses grip? And then a longer screw in the same hole would work, and then you could start again with a new hole a few centimeters away. I reckon you've probably got 50-100 goes but if you like your floor up once a week your gonna be in trouble in a few years.

In not sure how much strength is in those things for holding flat pack furniture together, and in my experience, they can work loose over time, and it's quite easy to strip the cheap hex heads.

Should the worst happen, I think your "widowed" girlfriend might be more appreciative of a decent life insurance policy than the benefits of an easy to remove bedroom floor.

If you're hell bent on doing it, I would want a fair bit of "meat" above the inserts - pulling down 25mm ply will require some force. You can stagger the bolts so they aren't opposite each other. As you are putting in dozens of noggins you could put the fixings in those so you don't touch the original joists.

 

[Kaer]

If you're hell bent on doing it, I would want a fair bit of "meat" above the inserts - pulling down 25mm ply will require some force. You can stagger the bolts so they aren't opposite each other. As you are putting in dozens of noggins you could put the fixings in those so you don't touch the original joists.

Would staggering definitely help? They would still be the same distance from the edge, and it's 1/4 less holes I have to drill if I can make the horizontal one a straight through
I will have to get myself a decent depth stop if I am staggering, but all the collar/grub screw type ones I have used are always the worst..

I am doing the center of the room in exterior grade ply, and the perimeter in marine grade ply, so perhaps I could screw the middle ones and bolt the perimeter for access to the cable tray around the room, it would just make ducting access a bit harder.

 

[Deleted member 174758]

Just a minor point, but how many of these were you intending to install per sheet? I generally screw down flooring on 200 to 300mm centres, which is necessary to ensure that the floor doesn't creak.

As to the other things you intend to do it is better to get all the floor up, do all the work, then close it up, rather than have the floor up and down a dozen times. Good luck trying to get tradesmen to play ball with you on this as well.

In terms of screws going in and out, @cdbe, a decent screw such as a Spax or Reisser is probably good for 20 to 30 insertions and removals (I've done 20+ a number of times), but only with larger sizes such as the 5 and 6mm - smaller screw heads tend to round out faster, I find

 

[Kaer]

Just a minor point, but how many of these were you intending to install per sheet? I generally screw down flooring on 200 to 300mm centres, which is necessary to ensure that the floor doesn't creak.

As to the other things you intend to do it is better to get all the floor up, do all the work, then close it up, rather than have the floor up and down a dozen times. Good luck trying to get tradesmen to play ball with you on this as well.

In terms of screws going in and out, @cdbe, a decent screw such as a Spax or Reisser is probably good for 20 to 30 insertions and removals (I've done 20+ a number of times), but only with larger sizes such as the 5 and 6mm - smaller screw heads tend to round out faster, I find

I was going to do it every 400, as it's 25mm ply and also on joist tape. Most everything done in this house will be by me, so until I'm dead it should just be me lifting boards, and hopefully by that time my girlfriend will be capable of using an Allen key and taking the boards up before the tradesmen get there, though I'm sure anyone doing a job would rather undo a few bolts than risk going through whatever could be underneath with a multitool.
It's a cheap house in a very "cheap" area so I just want to try my best to make the inside of the house feel as nice as possible, given we spend 99.99% of our time at home

 

[kp00110]

What about the carpet etc? Will that also be modular carpet tiles lol? You would be best in my opinion securing floor tradition way and install a thin raised access panel floor - more of an office or commercial building you are starting to build rather than anything residential!

 

[Kaer]

What about the carpet etc? Will that also be modular carpet tiles lol? You would be best in my opinion securing floor tradition way and install a thin raised access panel floor - more of an office or commercial building you are starting to build rather than anything residential!

Haha yes it will be carpet tiles, found some relatively nice ones actually, much better than they used to be. Putting a single layer of mlv down under the tiles given that it's the theater room. I'm running the electrics for downstairs inside the 1st floor as well and dropping it down to sockets, so the raised floor is needed for there too, so a raised panel floor wouldn't do.

I will admit the home won't feel traditionally homely, more like a space station with access panels everywhere, but we are more practically oriented than aesthetically.

 

[Lower]

Another vote for just using screws. I doubt you'll be able to maintain the alignment of the cross dowel nuts in the joists once you start moving around on the floor to fix them down. They'll vibrate around, end up misaligned and you'll have a nightmare trying to do them up.

If you design the floor with suitable 'hatches' for the services that are screwed down, why not just screws?

 

[big-all]

ok sideways thinking

you have say 70-80mm off material all clamped by a small round barrel with any expansion or contraction full contained and bearing on an area the size off a 5p coin
where as a screw interacts throught its length with inches off timber to grip and move in

now will your plan work faultlessly without failure or need to tighten periodically requiring carpet removal ??
well i for one dont know but suspect it will be fine but iff it fails wow what a lot off work doing it and rectifying it

 

[Kaer]

Thank you all for your replies! It has helped me a lot

I think an access hatch would be difficult, due to how i am doing the wiring, i have attached the "plans" to try and maybe show how i need to be able to access the edges of the room at minimum.

As for alignment when walking around before fully securing, i will just be placing the bolts in until i am ready to secure down the sheets to keep the dowels indexed with their holes.

I have to begin work this coming wednesday, with a 1 month time limit, so all your advice is making me think maybe i am biting off more than i can chew in this timeframe..

I will give it a go when i arrive once i get to the part where i need to do the flooring, if it doesnt work well or fast enough for a single sheet, i will switch to spax.

Unless ofc there are any structural concerns with the joists, though i think i will now try to redo this with the bolts only on the noggins.

And hey, maybe i get there and the place is a crapfest filled with notches and warped joists, then i suppose fancy flooring will be the least of my concerns