Unsure how to replace and insulate upstairs sub floor

[leem2837]

Hi,

I've got two bedrooms in an extension where the flooring is really botched and falling to bits. It's a mish-mash of bits of chipboard with various bits chipped and broken, so I want to replace the whole thing properly.

So my first question is, should I replace with subfloor-grade chipboard again? Not sure what's a realistic alternative other than T&G floorboards. Is this actually any better?

Also, what's the best way to insulate under this floor? I've heard from some sources (can't remember where, somewhere online) that you shouldn't really insulate upper floors, only the ground floor. If I do insulate, what should I use - just loft insulation? If so, how do I suspend it beneath the flooring to keep a void for air flow and electrical / heating pipes?

Thanks...

 

[kbdiy]

There is no reason to insulate between ground and 1st floor at all. So long as the loft is well insulated you should be able balance the heat to make all rooms comfortable. You should be aiming to insulate the entire envelope, not areas within it.

 

[leem2837]

Thanks for that. I've realised I missed a fairly vital bit of info from my question...

The rooms are both above a garage, so there's no heating or insulation below these rooms. One of them is partly above a garage (a former box room of a 1930s semi, extended to make it wider, therefore over the top of the front of a garage) and the other completely so.

So I agree with what you're saying, but effectively 1.5 of these two rooms are "ground floor" for insulation purposes.

 

[tony1851]

Depending on the perimeter/area of these rooms, you would probably be looking at filling most of the void with glass wool supported off chicken wire stapled to the sides of the joists, though leave a suitable gap for wiring.
Ensure the garage ceiling is min 30 mins fire resistance (usually one thickness of fireline board + skim).

 

[leem2837]

Thanks Tony.

Hadn't thought of chicken wire. I read somewhere about using wooden strips to keep the insulation near the joists too, but chicken wire would certainly be cheaper.

What should I use to replace the sub-floor too? Some people say chipboard floor panels are terrible, but not convinced T&G floorboards won't warp either.

Either way it'll be covered with either laminate or carpet, so I just want a subfloor that's as stable as possible.

 

[tony1851]

You're probably better with 22 thick t&g chipboard if using laminate.

 

[jabuzzard]

There is no reason to insulate between ground and 1st floor at all. So long as the loft is well insulated you should be able balance the heat to make all rooms comfortable. You should be aiming to insulate the entire envelope, not areas within it.

That is not strictly true. For example in my house without insulation between the lounge and the bedroom above when the lounge hits 20-21°C the bedroom would be ~23°C. Fairly basic thermodynamics really.

By sticking some insulation under the floorboards of the bedroom, I can have the lounge at 20-21°C and the bedroom at 18-19°C.

It's the same misguided thinking that says there is no point insulating central heating pipes between floors.