Insulation for Attic Floor

Albelcro

Hi All,

Looking at getting more insulation into Attic floor. The attic floor is currently covered with aprox 10cm of blown cellulose and timber floor on top. I have 5cm thick Kooltherm insulation boards from another job that would potentially cover all the attic area. Is that a good option? Would the thickness be enough? How could I install it, on top of the blown cellulose or straight on the ceiling between the joists?

Thank you!

Sleeper12

The minimum recommended attic insulation is 300mm. 400mm is soon becoming the norm, particularly in airtight homes.

It's really up to you how far you want to go. I've just added the last 100mm to mine bringing it up to 400mm.

It's best to insulate all the way into the eaves and have vents in the roof. It's far better to insulate under the cold water tank and insulate around the tank.

whizbang

50mm Polyiso is equivalent to about 120mm of fibre insulation, but in practice it needs to be almost airtight fittting.

Just lay it on top of the existing floor, and board over the walkways; its tough enough to just use thin sheet material. In my case i used (mostly free) second hand laminate flooring.

Ideally you would also fit rigid board to the top of the wallplate, built up to almost seal in the cellulose. just need a small gap for ventilation. this way you eliminate any draught blowing through the cellulose that reduces its effectiveness.

GreeBo

https://www.boards.ie/discussion/comment/121356600#Comment_121356600

I wouldnt just stick it over the existing floor as it really depends on what the existing cellulose is doing. For example if its not tight to the wooden floor then your PIR isnt going to be doing much as there will be a breeze blowing underneath it.

I would top up the existing until you get to the tops of the joists, then use the rigid stuff and reboard over that for storage etc.

poker--addict

Any reviews on blown rockwool or cellulose? The loose fluffy stuff as opposed to the roll out. This would be for top up in a old house

GreeBo

If you are DIYing then I would favour the roll myself.

poker--addict

Ya, I won't bother DIY I think. Save a little but lose a day or two of my life. Assuming with grant the net cost isn't too bad. Attics are miserable places 😂

my query scope may have been unclear; I'm wondering how the loose cellulose stuff performs relative to roll out

Sleeper12

https://www.boards.ie/discussion/comment/121612784#Comment_121612784

Most likely cheaper without the grant. BER can cost as much as €350 at the moment. They charge an extra €30 to €100 to fill in a few lines on the grant application on top of the BER fee. All of the insulation companies are are registered for the the grant charge higher fees

TheDoc

i just finished an attic diy job yesterday. Granted I also floored mine. Best quote I got was 4500 including the grant. For just insulation was 2500.

absolute laughable quotes so said I’d do it myself. I have a pretty large attic and I paid 1000 for materials.

mismeasured somewhere. Bought ten rolls of insulation and only used six!