When we bought out house loft insulation had only 25 mm loft insulation thickness, with recommended 275-300 mm of fiberglass. I decided to do put some more, while also use it as an opportunity to clean up the dusty loft (no storage there).
With the current insulation in winter our second floor was colder than first floor due to roof loft heating losses. Additionally, I was encouraged by perceived saving due to improved insulation.
How to calculate economic effect from insulating your loft and any potential energy savings?
Previous insulation – 25 mm, new – 275 mm. I decided to use mineral fiberglass insulation, although if I do it again I would use more expensive natural wool. Advantages of natural wool: it absorbs condensed water and then evaporates it, traps any gases and contamination (i.e. breathes), does not loses thickness when gets wet with condensed water. Disadvantage: more expensive, perhaps more flammable.
Materials I used for the loft insulation:
Diall Loft insulation – 23 rolls - 290 GBP -3m2 per pack, coverage - 68m2.
Gardman Bubble Greenhouse Insulation - 6 rolls - 99 GBP (as a vapour barrier).
Knauf Eko Roll Loft Insulation – 14 rolls - 280 GBP – 5.5m2 per pack – coverage - 77m2.
Loft Vent Trays (plastic) – 40 pieces – 60 GBP.
Total cost: 730 GBP or 10.2 GBP/m2
Additionally, I used this as an opportunity to apply some teak oil to the joists and the roof beams, to preserve and protect them - 20 L at 160 GBP. No installer will do that for you, unless you specifically ask and pay.
All together it took 5 days ~ 7-8 hrs each or 40 hrs.
How I calculated the economic effect and return on the loft insulation: