Rafterloc - should I bother?

LoTwan

My question is not should I bother with it at all, thankfully

My building is a storey & a half with 8' ceilings upstairs. In the living space I am having 100mm Rafterloc with 62.5mm insulated plasterboard under the rafters.

My query relates to the attic void. It is only about 600mm from the top of the collar tie to the ridge so the sloped roof is about 1m and the relevant part of the roof is 35 linear metres.

And now to my question... should I bother putting rafterloc between the rafters in the attic void? The money is there for the insulation itself but I imagine fitting it will be expensive simply because of the fact that access to the space is limited.

What are the benefits of insulating a ventilated rafter void?

No6

Normally you would insulate with two layers of 150mm fibreglass across the ceiling, only use rafter lock with the thermal board on the sloped ceilings directly into the habitable space, dont carry it up to the ridge, there is no point in that at all!! Check the price of replacing the rafterlock with fibreglass and increasing the depth of the insulation in the thermal board under. I have found doing U value calcs that an expensive insulation that is bridged by timber is not that much better than a cheap insulation also bridged!!but you have to keep the 50mm air ventilation, it helps dissapate moisture vapor and prevents your roof timbers from rotting.

LoTwan

It is actually the temperature in the void that I am concerned about, not the temperature of the living space. We lost our cold water in our (rental house) attic last Winter and I wanted to check if there was anything I could do along with lagging the tank and the pipes to help prevent it happening in the new building (making a warm attic is not an option at this stage).

Gulliver

Usually, it recommended that you do not insulate under the tank, but carry your insulation around and over the tank, bringing it into the heated envelope of the house. You could try to ensure that the pipes are sandwiched between the two layer of insulation that No6 suggested. This will be easier if they're plastic and not tacked down.

No6, if that is accurate about the timber bridging and cheaper/fibre insulation, I'm going to have a fit! Just spent the better part of three weeks cutting 100mm rigid insulation to fit snugly between the rafters (rafter centres were a bit funny, so the rafterloc stuff was out of the question).

Some fibreglass manufacturers have a kind of "bale" specifically for the slope, which should make leaving an air gap a whole lot easier.

As an aside, my slabber recommended to put a lighter board on the horizontal part of the ceiling due to weight and length of fixings. We have 400mm of fibre above anyway. Still going for 62.5 on the slopes.

Iwannahurl

If you have sufficient headroom already it seems unnecessary to insulate all the way up.

I did an attic conversion a while back (truss roof), but because of the lack of headroom I had the insulation and slabs extended into the peak.