Attic insulation

funkey_monkey

I want to increase insulation in the attic of our 70's bungalow. It currently has mineral wool only between the joists. Can I place insulation boards on top of the joists or must I stick with the same type of insulation?

Padre_Pio

You can, but it's probably cheaper and easier to add more wool across the joists.

Is there a reason you want to go for the boards?

funkey_monkey

No. I thought it might be easier to just put the flooring boards back down on top of them and maybe would have a better u-value for same depth.

Padre_Pio

Yes your right, you just need to make sure there's no air gap between the wool and the board, while trying not to squash the wool too much.

Those click in flooring boards are expensive, you can use half inch ply instead. The rigid PIR gives a decent backing to it, and screws into the joist stop it flexing.

Biker1

https://www.boards.ie/discussion/2058354103/attic-insulation

If you use mineral wool in the majority of the area and use 150mm EPS backed plywood for the area you need for storage. Cheapest option.

funkey_monkey

https://www.boards.ie/discussion/comment/122208890#Comment_122208890

The attic is already floored with chipboard so I have to lift it first and then put it down on top of the raised insulation.

I thought I could get away with thinner insulation board and just set the chip board on top. Otherwise I'll have to use those risers and the mineral wool which would require a lot more work to secure and tidy up the edges.

whizbang

You wont have to lift the existing flooring; it wont make any difference to the insulation value, and saves a lot of work. But you need some sort of rigid boarding over the PIR board .

funkey_monkey

https://www.boards.ie/discussion/comment/122486141#Comment_122486141

Can I mix insulation types? It is mineral wool used as the insulation. Could I just put PIR Board over this in the eaves and leave like that. Only flooring over the main part of the attic floor?

https://www.boards.ie/discussion/comment/122487137#Comment_122487137

This sort of approach is not going to work unless you compromise your eves ventilation. The eves ventilation is simply wicking away the heat trapped in the roof space rendering your added insulation redundant.

Has to be on top of the existing insulation and you absolutely have to maintain eves ventilation otherwise you will get significant loft condensation.

funkey_monkey

https://www.boards.ie/discussion/comment/122487160#Comment_122487160

So best going with the same type on top? The inspector said there should be insulation across the top of the joists as well. Currently just insulation between them

https://www.boards.ie/discussion/comment/122487189#Comment_122487189

Yes cross wise to what's already there. Also not a bad idea to introduce a vapour barrier which will slow down draft wicking of heat.

funkey_monkey

https://www.boards.ie/discussion/comment/122487306#Comment_122487306

Vapour barrier on top presumably?

I'm going to leave to pay that is floored untouched.

The floor on the existing insulation should do a good job of stoping draft wash as it's called, so just adding on top of that should be adequate.

If theres no physical barrier on top it's worth adding.

MicktheMan

I wouldn't advise introducing any type of vapour barrier on top of the insulation layer.

whizbang

Rigid board insulation is sufficient to reduce or stop draft wash, but remember then the edges of the ceiling between the refters are open to the eaves. In a pitched roof, there can be a significant pressure difference on a windy day to cause a noticable draft through the eaves, and up in through the fibre insulation.

Ideally close off these ends also, allowing only a small ventilation gap.

greasepalm

On a few bedrooms i got lads to fit warm boards to the ceiling as attic can be a curse as it has spray foam on tiles and partial floor on the joists.

Room is warm in the Winter and cold rad .

1 Sheet and 1 blanket to keep warm on bed.

Hot sleeper.