Loft floor insulation?

[Skiny]

I want to insulate under my loft floor, up to building regs. From what I've read, 270mm mineral wool is sufficient, but I was wonder what options are available for rigid boards instead. I don't want it to stick above the joists, because it will be in the way of the boards.

The joists are just over 200mm high, so I was wondering what alternatives are available, up to building regs?

 

[JohnD]

you can lift the flooring, put down rigid foam slabs, relay the flooring on top.

You should insulate between the joists, or cold air will blow along the void over the ceiling. Mineral wool is best for that because you can squash it to a perfect fit between the timbers, unlike rigid foam.

Rigid foam has about twice the insulating power as the same thickness of wool, but is more expensive.

If you have 200mm joists (which are unusually deep), then 200mm of quilt plus a chipboard floor will be very near as good as 270mm of wool, and I think not worth the effort of foam on top. Additional thicknesses bring diminishing returns.

 

[Skiny]

Thanks for the reply.

In a few years I'd like to have a loft conversion done, so whatever insulation I buy today, I'd like it to be up to any regulations. For that reason too, I'd rather not raise the flooring any higher.

So given board offer twice the insulation of mineral wool, could I use 100mm boards + 100mm of mineral wool, to meet/exceed regulations?

 

[JohnD]

When you convert it, you will not need insulation under the loft floor, because the loft will no longer be an unheated and uninsulated space. You will have to insulate the roof slope and knee walls instead.

 

[Skiny]

Oh!? I didn't realize that. So no regulation to say that floor will need insulating at all??

Great, explains why after hours of Googling, I couldn't find my answer

Thanks for your help.

 

[JohnD]

Leaving the mineral wool in will give a (slight) muffling of noise, though loft insulation wool is much less dense than sound reduction batts.

 

[Skiny]

With the requirements for noise insulation between floors, is there anything in particular that should be fitted between floors for this purpose?

As I say, in the future I'll do a proper loft conversion, but for now, I'd like to buy the correct product, instead of something that will have to be thrown out when the time comes.

 

[JohnD]

don't know. Try in the Building section. From my own experience, the plastered ceiling makes a big difference (as does taking it down or making holes in it, e.g. for stupid downlighters).

Old houses with thick lime plaster it is especially effective.

 

[geraldthehamster]

With the requirements for noise insulation between floors, is there anything in particular that should be fitted between floors for this purpose?

As I say, in the future I'll do a proper loft conversion, but for now, I'd like to buy the correct product, instead of something that will have to be thrown out when the time comes.

A loft conversion would normally require mineral wool insulation suspended within the floor for fire prevention purposes.

Cheers
Richard

 

[JohnD]

thanks, Richard. Would this be the dense batts? Is there a typical amount? Does "suspended" mean "not lying on the ceiling?"

 

[geraldthehamster]

thanks, Richard. Would this be the dense batts? Is there a typical amount? Does "suspended" mean "not lying on the ceiling?"

I don't know the exact requirements for material. "Suspended" means supported by chicken wire or somesuch, to prevent it falling out in the event of a conflagration.

Cheers
Richard

 

[Skiny]

Suspending mineral wool would be easy enough to do, though isn't plasterboard sufficient for fire protection?

 

[catlad]

Well there is fire rated plasterboard but most bco,s except double boarding
acoustic slabs are dense mineral wool.

 

[Skiny]

So I could just put two layers of fireproof 'Fireline' board up when I fit the ceilings, instead of messing around suspending the mineral wool insulation?