Help - worried about loft insulation

[tom1975]

Hi,

I just typed a long post which didn't save, so apologies if this is a repeat.

I live in a 4 bed terraced house (4th bed in the converted loft). The roof is less than 10 years old and has multiple air vent tiles/bricks in it.

In the remaining roof space of the unconverted loft, the floor has rockwool insulation between joists and most of the floor is boarded. This is the existing set up and no problems so far.

Anyway, after a freezing winter in the house i asked my builder to check the insulation and if necessary add more. He has added rockwool between all the rafters on the sloping ceiling and held it in place with string / wire threaded across in various places and nailed to the rafters. It's all neat and tidy and doesn't hang down.

As far as i can see, there is no gap between the rockwool and the roof (it is filled to the full depth of the rafter) and the rockwool on the sloping ceiling meets the rockwool on the floor, without a gap for ventilation.

Having read about condensation issues on this forum, and because of a number of other cock-ups the builder has made, i'm worried he's not done the loft properly.

however, he assures me that there is no problem because a) the rockwool in the rafters is not boarded up, so air can circulate through it b) it's not tightly packed in and c) the roof has air bricks/tiles.

does this sound correct to you guys? or will i have a problem come winter? sorry i'm a bit paranoid with all the other stuff that's gone on and just need to know if this sounds ok.

thanks in advance

 

[mointainwalker]

Your builder's answer shows that he doesn't understand how insulation works. Fibre wool functions by trapping air i.e. it doesn't move. Moving air is the biggest enemy of insulation because it very efficiently carries away heat.

There should be a clear void - normally 50 mm - above the ventilation which is vented to the outside to allow circulation.

 

[tom1975]

Thanks for your reply.

so is this something that must be remedied to avoid rotting and damp, or is it something that is not best practice but won't cause any harm?

if i understand you correctly, there must be a gap between the inside of the roof and the insulation - but how do you keep that gap in place when you're using rockwool? do you need to put a board or some sort of barrier on the side closest to the roof?

how would i even get the rockwool out of there and through the house without leaving dangerous particles everywhere (there's a young baby in the house).

thanks again for your help

 

[mointainwalker]

must be remedied to avoid rotting and damp, or is it something that is not best practice but won't cause any harm?

If your timber is wrapped in insulation it will suffer - but slowly. I would guess - and that is all it is - that any weakness might be 20 -30years down the line. Happy to be corrected on that.

Keeping the gap is not easy with roll insulation but would be easier with batts which is the same material stiffened with glue ( double the cost ). Many people use insulation boards for ease of fitting/ensuring free gap ( five to six times cost ).

how would i even get the rockwool out of there and through the house without leaving dangerous particles everywhere (there's a young baby in the house).

Who has told you these fibres are dangerous ? Are wool fibres from a blanket dangerous just because they are small fibres ?

I must confess that this wide-spread hysteria about any bloody thing gets on my tits . There are people posting on here showing a lump of concrete ( or using poetic licence to make my point ) a lump of wood asking " Does this contain asbestos ? "

Apoligies to the OP . It was not his fault that he touched on one of my bug-bears. However if it worries you, then wrap it in plastic and leave the wrapping in the loft. It won't migrate.

 

[tom1975]

thanks again.

the timber is not wrapped, it's left free, its the space in between that's been loosely filled.

he's told me he's going to cut it back and leave ventilation gaps at the eaves and pull the wool away from the roof so there's more of a gap. i doubt any of it would pass building reg's on a new build for what it's worth.

he's assured me it will be fine, but promised to remove it if there's any evidence of damp in the winter.

i suppose i've been warned.. i'll see what happens in 5 months.