Attic Insulation - Is More Better?

SachaJ

Living in a house built in the 1950's and the attic insulation looks older than I am. It's collapsed own to a few cm's in places so next week I'm going to lay some new Earthwool.

The area is around 63 square metres and so works out at around €178 per layer for 150mm thickness. I'm planning to put two new layers down.

Is there any real world benefit to putting a third new layer down?

Also we have one of those fold down attic stairs. Whats the best way to insulate over that?

MicktheMan

Very roughly:
% reduction of the conductive heat loss through the ceiling compared to an un-insulated ceiling :
100mm -> 89%.
200mm -> 95%
300mm -> 97%

don't forget the other type of heat loss which insulation doesn't address i.e. air leakage. Most attic hatch openings are very poor for air leakage.

Calibos

MicktheMan wrote: »

Very roughly:
% reduction of the conductive heat loss through the ceiling compared to an un-insulated ceiling :
100mm -> 89%.
200mm -> 95%
300mm -> 97%

don't forget the other type of heat loss which insulation doesn't address i.e. air leakage. Most attic hatch openings are very poor for air leakage.

Seriously?

The extra 200mm over a baseline 100mm only adds a further 8% reduction?

We've a flat with the attic over our shop that I was going to insulate soon with 300mm. Have had tenants over the last few years and currently so there was/is currently no need to use attic for storage. Hence I was going to go the full 300mm of loft roll. (100mm between ceiling joists,200mm across)

However, if what they say is true that you lose 20-25% of heat through the attic and the 100mm gets me 89% of that 20-25% but another 200mm only buys me another 8% of that 20-25%, then tbh I'll just insulate to 100mm in the attic for now as in a year or three I'll probably be moving into the flat myself whereupon I will want attic storage and will just lay down insulated loft boards across the joists over the 100mm I'll be putting in now.

ie. that extra 200mm over and above the 100mm I'm still going to put in, wouldn't save my current tenants a noticeable amount on their heating bills over and above what the 100mm will and it would just be pulled back out of the attic when I moved in, in a year or three when I need to start using it for storage and need to lay insulated loft boards.

(The ceilings are semi vaulted and thus the height of the attic is already reduced meaning that laying cross joists and a plywood floor over 300mm of loft roll reduces the available space in this attic too much. Hence why when I need to use the attic for storage myself I'd need to pull out the 200mm rolls and use foam backed loftboards instead)

Thank you for this new information. Never seen it mentioned before. Saves me time and money and hassle.