We recently moved into a house which requires some insulation improvements. Cannot do much about the solid walls but the loft insulation is only one layer of +/- 100mm insulation wool. Current requirements are 270mm if I remember correctly. Since we want to keep the loft as storage for the chirstmas tree, mother-in-laws wedding gifts, etc. we cannot simply chuck another layer of wool top since the floorboards would squash it and decrease the insulation power. I wonder if one could double the wool behind the hangers and use solid insulation boards between the rafters and hanger such that internal loft area is insulated. Each insulation type is not enough but together it should be quite good and there is no need to lose the storage or to raise the loft floor. I tried to find some information if people have done this but no avail. One issue might be that there is no ventilations above the insulation wool and thus condensation might occur.
Basically this is it. Floorboards are temporary moved since we are replacing the ceiling and we removed the insulation. Other side is similar but with access to the loft of extension. I think the previous owner (well probably her ex-husband) wanted to develop the loft, judging on the walls.
Really depends how far you want to go with it and how much money? You can use rigid insulation board i.e celotex/kingspan between the rafters, maintain a 50mm air gap behind. Cutting the hipped (sloped) ones will be a little tricky though
Someone had a start and not done a bad job of it. Can see another loft conversion project coming along I would look at using thicker PIR insulation slabs in the dwarf walls.
If they are 100mm/4" rafters then use 50mm celotex in between the rafters. This is something I used in my own conversion. But would look at what future plan is with the loft, as it may change later. i.e you may want to create an extra bedroom etc. up there.
Exactly what the doctor ordered. Thank you. Thread gave me pointers to this: http://www.ybsinsulation.com/roof-insulation/pitched-roof-insulation/foil-tec-roof/ illustrating exactly what I was thinking off. I don't think there should be an issue just adding more wool behind the hangers/knee walls or what ever it is called. It is high enough for a person to stand but it is not particular large. We past the age where we migth need more than 3 bedrooms plus a man cave aka summer house/shed in the garden so I doubt we'll need an extra bedroom in the furture. Though mother-in-law is lately coming regularly so it would be nice if she stayed on a different floor then me. Money is never a problem as long you don't have to pay someone to do it.
As long as you keep the air gap along the eaves you should be ok. The YBS is very easy to install. I used this as well alongside the celotex, really is some warm stuff.
Thank you for your useful information. It might be awhile before we will be doing this. It came up since we are about to replace the ceiling in the master bedroom and the thought came up to use insulation plasterboard but they are 6x more expensive and only addresses the roof insulation in one part of the floor.
Indeed, insulated plasterboard is v expensive. PIR is a lot more expensive that rockwool type insulation but you need only about half the thickness. Hence its economical to use rockwool/earthwool where you can (e.g. 4"-6" on the first floor ceiling) and supplement that with around 50mm-70mm PIR insulation in between the rafters. Then the airtec foil insulation adds further and also acts as a vapour control layer.