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”

Thank you ever so much in advance!