We live in a detached house in the South of England. We would like to install insulation between our rafters to improve the insulation of our house - so it becomes a "warm loft". We are not doing a loft conversion but would like to use the loft for storage. There is already fibreglass insulation on the floor of the loft.
Our reasons for wanting to insulate between the rafters are:
- Improve the overall energy efficiency of the house, so that the house is warmer in winter and cooler in summer
- The loft height is limited, so would ideally not want to raise the loft floor to install more fibreglass
- Protect any stored items from extremes of heat or cold
- We may choose to later move the hot water tank into the loft, so it would be good to minimise heat losses from that.
We have 100mm rafters, so to maintain a 50mm air gap, we were thinking of installing 50mm of PIR between the rafters. Then to further increase the insulation, attach 25mm battens to the rafters to create another air gap and then staple multifoil insulation to it.
My question is around ventilation. We plan to add vents in the soffits - which should help ventilate the gap between the PIR and the roof membrane. And maybe some vents in the roof ridge.
The superquilt multifoil insulation instructs you to ensure that all the joints are properly sealed with aluminium tape - to prevent heat escaping.
Does the main internal loft space also need ventilating? How how do you ventilate without also loosing all the heat?