Another loft insulation question...

[Mottie]

We had our loft insulated about 25 years ago along with cavity wall insulation under some scheme or another. I forget what thickness the loft insulation was but it protruded above the 4X2 joists. Possibly 6 or 8”? Anyway, not long after that I boarded out my loft which required compressing whatever insulation I did have, down to the thickness of the joists - 4”. We did this because we needed to use the loft as a storage area.

Will I have been getting near enough the same thermal qualities with it squished to 4” compared to what it was? It’s bloody cold up there and we do get frost settling on the tiles when cold (apart from the area directly above the boiler which is fitted in the loft) - it was certainly cold enough one year to freeze the unlagged portion of pipe going to the cold water storage tank when we had one. If not, will it be worth the expense of unboarding the loft, adding extenders, more insulation and then reboarding or will 4” of insulation, 19mm ply plus a layer of 30 years of 'stuff' be enough?

 

[Notch7]

Loft insulation needs to retain its natural thickness. If you squash it, you reduce its insulation qualities by a significant amount.

The point of loft insulation at joist level is of course to stop heat getting up into the loft area -so if your loft is very cold, its doing its job quite well -which I presume is what you are saying.

 

[Mottie]

Yeah. It’s bloody freezing so I suppose I should leave it at that.

 

[John D v2.0]

It's heat loss that matters, not how hot it is in the loft. The loft has no insulation around it presumably so any heat that did escape would leave very quickly.
In reality adding more insulation would save money but floor insulation does more to increase comfort but less money saving.
If you're using the middle for storage, treat that as a small cost and just add another layer around the edges of the roof.