I have searched the group via google for info on logt insulation - but can't really find an answer that fits my question.... so here goes.
Got an old house. Almost zero insulation in the loft. Planning a loft conversion in a couple of years when the barn conversion is complete (another story).
Anyway, just measured the rafters in the loft and the dims are:
2.5" wide
3" tall Space between rafters averages at approx 15.5" (some 14, some 16)
I need to put some insulation up there - but don't want to waste money by putting something down only to find it unsuitable when we come to convert.
What should I use? Kingspan/celotex? Can I cut it to fit the varying widths I'd need? If this is the best solution, how do you fit it?
Can I also ask about the loft conversion - woudl the rafters as they are support another couple of rooms - or would the whole rafter thing need upgrading (by an expert!)
The rafters are utterly unsuitable for anything more than walking around on carefully, and maybe storage of empty boxes, and will need replaced or augmented to put rooms up there.
As this is the case, the insulation is unlikely to be suitable - you may not want to insulate the two rooms off anyway as eventually you'd want the whole roof to be warm. Personally, I'd get some 150mm insulation at B&Q or wherever, and split into three 50mm layers, before laying. You should probably do some sums to see how much money you'll save in heating, and how much the insulation will cost over a couple of years.
Why not insulate the rof and then it will be ready when you install a new floor for the conversion. Kingspan/Celotex is the right route - you can cut to any shape with a saw.
But if you leave the conversion too late the new Part L will kick in and you'll need even more insulation to meet it (and it may even be impossible).
You could go with the insulate the roof option, as has been suggested. If you want to go for the more conventional approach between the ceiling joists, then use something fireproof like Rockwool since you can then re-use it later.
Upgrading yes, although you will need someone who knows what they are doing to design the stucture, implementation may not require much expertise beyond basic capentry and common sense.
You can either insulate the ceiling joists, in which case we need to know the dimensions of them, or you can turn your 'cold roof' into a 'warnm roof. which is more than just laying down some insulation stuck between the rafters.
Not sure what you are really after here.
I'd be invlined to jstslap don thick rockwool for now, and sort out a warm roof as and when you do the conversion, at which time the old insulation will get binned anyway.
If you want to start on the conversion, as it were, you should insulate the roof with Kingspan.
You will need to decide whether you are going for a ventilated area behind the insulation, or a full fill.
With a ventilation fill, you leave 50mm between the insulation and the felt. This area is then ventilated using soffit and ridge vents. You then apply as much insulation as you can (25mm in your case) and then more underneath up to 100mm total thickness (75mm). Then foil backed plasterboard over that. (You can order the insulation ready attached). This is a simple technique, but can make the roof thicker, which may be a problem for headroom, especially when you consider that the floor may need to be strengthened (i.e. made thicker).
The alternative, with no ventilation space required is just to fill the entire space within the rafters (75mm in your case) and the rest up to 100mm below (25mm in your case). This gives much more headroom. The problem is that you loss the ventilation and another method must be used to ensure that the roof timbers don't rot.
Your two alternatives for this solution:
Have no felt (old houses may have no sarking at all. The gaps between the tiles/slates provide adequete ventilation for the roof timbers). I'm not really suggesting ripping the old felt out, as it provides a useful backup when the roof covering fails and is required by building regulations.
Reroof, using breathable membrane instead of felt. This allows moisture to pass through, but still provides weather protection. Unfortunately, it needs to have all the slates/tiles removed and replaced after installation. This may be an option if you are intending the reroof anyway.
There is one other solution if reroofing anyway and you have a detached house and no problems getting planning permission. This is to install a genuine warm roof. You'd put insulation between and above the rafters. The rafters than become part of the warm climate below, protected from the cold and wet outside air. It raises the roof, which might not be aesthetically pleasing and would create an ugly mismatch on a row of terraced houses.
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