Insulating inbetween loft floor joist before boarding?

[diycooper]

I am going to be boarding my loft out, before I do this I want to insulate in between the joists. The joist are only 75mm thick, what is a alternative insulation to use apart from lagging as this would not be adequate due to the joist size and boarding ?

Would 75mm boards of polystyrene be ok cut to fit snug between the joist then board be ok ?

I remember seeing one on a diy tv program where you pour it in the joists, can anyone tell me what this insulation is called.

thanks in advance

 

[mointainwalker]

apart from lagging as this would not be adequate due to the joist size and boarding ?

Would not be adequate for what ?

 

[diycooper]

What I ment by adequate was would not be suitable for the job as I am boarding the loft and the lagging would get squashed between the joists decreasing its R value.

 

[ladylola]

If you are boarding out for anything other than light storage you may get problems with only 75mm joists.
Better to run timbers at 90* to these joists to increase the effective depth of them and also increase your insulatable space.

 

[mointainwalker]

Firstly ladylola makes a good point, but if you want to insulate the loft as it is then :

1) Cover the ceiling in a poly-sheet to act as a vapour barrier taping the joints.
2) Fill between the joists with what you like. Fibre-wool is cheaper than polystyrene and has the same insulation value.

If you have water-tanks up there, do not insulate underneath them.

Do not block the eaves with the insulation so you still have good ventilation in the loft.

The fibre-wool is not going to be squashed because it's the same height as the joists and even if you buy 100 and it is squashed to 75 mm. you still get insulation value of 75 mm..

Loose -fill materials are ???? ( forget name ) , made of shredded newspaper or loose polystyrene beads. Both will cost you a lot more than the fibre-wool.

 

[ladylola]

Loose -fill materials are ???? ( forget name ) , made of shredded newspaper or loose polystyrene beads..

Probably the term you are looking for is vermiculite at least for the polystrene beads. My parents had this insulation in their roof space and we were constantly sweeping it up in the bedrooms

 

[mointainwalker]

Hi ladyl.

No , the name i wanted for the paper is "Warmcell" and I did mean poly pellets. Vermiculite is a light, non-flammable type of rock which would insulate but cost even more

The mess was another reason I wouldn't recommend loose-fill materials.