Hello
I am planning to lay 22 mm slotted floor chipboards for underfloor heating in an old house (wooden joists with cc 55-ish).
I want to ensure stability and am thinking of blocking.
However, I have a 15 mm construction height allowance, so I am considering whether I can achieve the same stability by laying 15 mm plywood (instead of blocking).
Is plywood okay as a subfloor if you lay slotted floor chipboards over it?
I am planning to lay 22 mm slotted floor chipboards for underfloor heating in an old house (wooden joists with cc 55-ish).
I want to ensure stability and am thinking of blocking.
However, I have a 15 mm construction height allowance, so I am considering whether I can achieve the same stability by laying 15 mm plywood (instead of blocking).
Is plywood okay as a subfloor if you lay slotted floor chipboards over it?
It's perfectly OK to have plywood under the particle board. However, I'm considering what the right strategy is for you. The main problem in older houses (they don't have to be particularly old, by the way) is often that the floor joists have too long a span to have an acceptable deflection. You might want to consider screwing and gluing both the plywood and the particle board. What span do the joists have and what are their dimensions? Blocking solves some problems, but far from all.
The span is 6 meters at the longest, and the joist dimensions are 3x9 inches, so it feels stable at least, so I'll just lay plywood to solve stability/flex between the joists, and then skip blocking.J justusandersson said:
6 meters is way too long a span even for 3x9 inches. Both in terms of deflection and bounce. I'll try to give you a more detailed answer later in the day.
It should be clear that standards have changed over time, especially when it comes to wooden floor joists. What was acceptable in the 1930s is not acceptable today. As I see it, there is no doubt that today's requirements better reflect reality than older ones.
I would opt to screw and glue 30 mm construction plywood (the maximum size) onto the floor joists. K-plywood is significantly stiffer than chipboard and distributes point loads better over a larger area. The downside (apart from it being more expensive) is that you need to insert cross braces between the floor joists to which you can also glue and screw the longitudinal joints. These screw braces, a kind of mini-blocking, do not need to be the same height as the floor joists. 45x70 mm is sufficient.
I would opt to screw and glue 30 mm construction plywood (the maximum size) onto the floor joists. K-plywood is significantly stiffer than chipboard and distributes point loads better over a larger area. The downside (apart from it being more expensive) is that you need to insert cross braces between the floor joists to which you can also glue and screw the longitudinal joints. These screw braces, a kind of mini-blocking, do not need to be the same height as the floor joists. 45x70 mm is sufficient.