Floor structure bathroom free span 2.4m

[justusandersson]

Deflection and durability are two sides of the same coin. Simply put, deflection is an expression of the instantaneous bending, and durability is an expression of the long-term bending. It is not enough for the floor joists to have good deflection and durability; the material that builds between the joists must also keep up.

 

[Pumabjörnen]

Yes, it's 10sqm so it's a fairly large area in this old house to heat with electricity. Also, we're installing electric heating mostly because there's not much difference in cost to add it when renovating anyway, and in the autumn and spring, before the waterborne system has started up, the bathroom floor can be warm.

The alternative is perhaps to replace the plasterboard with floor plywood and change the order.
1. Joists
2. Floor plywood
3. Routed chipboard
4. Heating pipe + plate
5. Floating with floor heating and reinforcement (min 12mm + slope)
6. Waterproofing and tiles

the build height will be similar in the end
Or go with my initial order and layers but glue-screw on 45x45 under my 45x145 beams.

but it seems there are different directives about whether it's enough to float over the heating pipe or if you should have a "dead" board on top.

If I were you, I would replace the routed 22mm chipboard with a v313-p5 moisture-resistant chipboard also 22mm, fasten the underfloor heating pipe (good idea to clip the comfort loop [electric heating] into the pipe) onto that, followed by mesh for the leveling compound and then float the floor, a minimum of 15mm over the pipe is the necessary thickness as far as I know.

Realize that this is only possible if you haven't yet bought the floor chipboard. I have at least done as above after much comparison between different industry regulations and in consultation with the manufacturer of my underfloor heating system.

Addition: of course, you lay the floor plywood first, then the chipboard.