Adding extra loft insulation beyond 270mm

[Pingouin]

Hi everyone.
My house built in 1972 had fibreglass insulation between the battens, I guess 100mm.
The previous elderly owner then used the government scheme to top it up to, I believe, 270mm. They also did cavity insulation. So currently, I can't see the battens, but I checked that they didn't block the ventilation around the heaves.
I see on Gumtree someone local selling few rolls of 100mm thick fibreglass. Would it be a good idea to buy this cheap and lay it on top?

Reasons for it:
- Cheap at £40 for 5 rolls, which would be just about enough to do my whole attic while not blocking ventilation.
- Energy saving?

Reasons against it:
- Need to make sure I don't impede ventilation.
- Need to make sure I don't step off the battens while laying 5 rolls!
- Energy savings negligible since most of my heat loss would be through the loft hatch that I only plug with 100mm of polystyrene.
- Lazy!

Thanks for any input!

[steviejoiner74]

Don't waste your money or time mate,you'll save about 10p a year

[big-all]

laws off diminishing returns lets assume you loose say £100 a year
first 50mm you will save perhaps 70% of waste so save 70 waste 30
next 50mm will again save say 70% but now off 30 so 21 save 9 lost
next 50mm will again save say 70% but now off 9 so 6.30 saved 2.70 lost
next 50mm will again save say 70% but now off 2.70 1.89 saved 90p lost
next 50mm will again save say 70% but now off 90p 63p saved 27p lost
you now at this stage add another layer and as said about 10p

[Pingouin]

Ok, thanks guys.
But then that would mean that my great great great grand children would see it amortised

[caravan72]

Ok, thanks guys.
But then that would mean that my great great great grand children would see it amortised

Eh!, you will not gain anything noticable from adding to what you have! you could look at your heating controls and you might get your fuel cheaper from another supplier.

[big-all]

Ok, thanks guys.
But then that would mean that my great great great grand children would see it amortised

Eh!, you will not gain anything noticable from adding to what you have! you could look at your heating controls and you might get your fuel cheaper from another supplier.

it eventually gets to the stage where the energy /cost to make' transport ' install dammage to the enviroment are far greater than what is saved
you also have to work out you loose valuable space so your building has to be perhaps 5% bigger to give you the same useable space

its worth the effort where you have far colder climates where the saving will be perhaps 5 times as much

[steviejoiner74]

Ok, thanks guys.
But then that would mean that my great great great grand children would see it amortised

Eh!, you will not gain anything noticable from adding to what you have! you could look at your heating controls and you might get your fuel cheaper from another supplier.

it eventually gets to the stage where the energy /cost to make' transport ' install are far greater than what is saved
you also have to work out you loose valuable space so your building has to be perhaps 5% bigger to give you the same useable space

its worth the effort where you have far colder climates where the saving will be perhaps 5 times as much

Agreed! New homes will go overkill to save the homeowner potential costs.
20 years ago 100mm was the norm,its treble that now in a loft in Scotland.
Rigid insulation is also the norm externally here now,the next step is sprayfoam like they have in Canada and the Baltic states. This is however in timber frame construction which is the norm in Scotland and is rarely used in England.