Probably daft question about loft insulation.

[Sharpey]

Hello all.

I am planning on laying some loft insulation soon. I have bought 100mm base layer, but when it's rolled up it doesn't look 100mm to me, much thinner.

I don't think it expands as you open it, so the question I have is the 100mm a guide as to what the insulation is rated at, or is it meant to be literal, as in actually 100m thick?

Surely it's the former, because if the recommended amount is 270mm in your loft that would easily block the ventilation path on the eaves because of the height?

Thanks for any help.

 

[Lower]

It should expand to 100mm thick when unrolled. Its the air trapped in the insulation material that actually keeps the heat in, not the material itself.

 

[Sharpey]

Right OK, thanks for the response.

Hopefully it will fill out when unwrapped.

 

[John D v2.0]

if the recommended amount is 270mm in your loft that would easily block the ventilation path on the eaves because of the height?

Yes, but if your loft needs to be ventilated then you need to ensure leave a gap or put in b vents in the right places or use a thinner more powerful insulation or change the old style felt to a breathable membrane

 

[Sharpey]

Yes, but if your loft needs to be ventilated then you need to ensure leave a gap or put in b vents in the right places or use a thinner more powerful insulation or change the old style felt to a breathable membrane

Yeah I will leave a gap, I'm not insulating above 100mm anyway so it won't block.
I just want to cover some edges that aren't insulated in the hope it will stop mould growing on the bedroom ceilings.

 

[John D v2.0]

I just want to cover some edges that aren't insulated in the hope it will stop mould growing on the bedroom ceilings.

should do, good idea, even 20mm is a lot better than non from a mould point of view!

 

[foxhole]

Mould spores exist in all property , good ventilation prevents them settling , no amount of insulation prevents mould.

 

[stealthwolf]

Fluff up the insulation. After a few months of other distractions, I've started insulating the loft. I bought the Knauf 100mm "base" layer. It's very thin when you roll it out but you're meant to "fluff" it up a bit. Certainly mine expanded after I started to adjust it.

 

[Doggit]

The 100mm will expand over a few days, and the 170mm turned across the loft will do the same. Make sure you don't push the insulation down into the eaves, and that'll allow ventilation in the loft space, and stop any condensation that seeps up there causing the timbers to rot.

But if you've got mould on the bedroom ceilings, then that means that you've got inadequate ventilation in your bedroom, and the excess moisture is settling out on the cold ceiling. Once you've insulated the loft, then you'll start getting the mould behind the bed, and other areas where there isn't much air movement.