Increasing loft insulation-is it worth it?

Yorky

In a new house with 250mm of loft insulation,is it worth upgrading the insulation to 300,350 or 400mm of insulation? It would cost €350 for 150mm of insulation to upgrade it to 400mm. I plan to sell the house in eight years-is it worth it to upgrade and if so to what depth?

Thanks in advance for any replies.

Reyman

The U value of 250mm of glass fibre is 0.16W/m2/deg C. For 400mm it's 0.10W/m2/deg C. I.E. You reduce heat loss through it by 33%.
This ignores the joists which complicate the calculation.

It's your choice but you're losing very little heat through 250mm at present and I wouldn't be bothered.
You also have to consider the effect on pipes, tank etc up in the attic of cooling it even further

Yorky

Thanks for your reply. With regard to the tank and pipes, they are all lagged and the insulation removed beneath the tank and enclosed so any heat rising is channeled to the underside of the tank.

Would you still not bother?

tampopo

Yeah, I'd love to add extra insulation in the attic. It's an old house and the existing lagging is collapsed quite flat. What stops me is how do I raise the height of the joists to compensate for the increased depth of insulation???

buy some lengths of 2x1 and screw several on top of the other????

10-10-20

I'm not able to do the calculations on this, but don't forget that the walls loose heat too, and in Ireland's climate, too much insulation in the attic will become a waste after ~300mm.

jdpl28

I put up a load of 2x4's in the attic, perpendicular to the joists, and layed an extra 100mm between them. Then put flooring on top. I'm sure you could get 2x8's if you looked. You could put ridgid insualtion on top of the flooring if you like, but it's very expensive for the U value.

Reyman

10-10-20 wrote:

I'm not able to do the calculations on this, but don't forget that the walls loose heat too, and in Ireland's climate, too much insulation in the attic will become a waste after ~300mm.

I agree on this point. You're really not going in overall heat loss beacuse you'll find your windows and walls are wasting 85% of the heat at present.

That's why I wouldn't bother --plus it's one of the most awful jobs you can take on - laying glass fibre rolls

311

The more the better ,it will stop your energy bills going through the roof

Yorky

I agree on this point. You're really not going in overall heat loss beacuse you'll find your windows and walls are wasting 85% of the heat at present.

That's why I wouldn't bother --plus it's one of the most awful jobs you can take on - laying glass fibre rolls

Well, I had 250mm but with settlement it is now more like 225mm so how about putting an extra 100mm layer on to bring it up to 325mm?