Attic Insulation

rob555mark

Hi, the attic in my house has insulation in between the attic floor rafters but not in the roof rafters if that makes any sense. I have two & three layers of insulation (moy yellow fibre glass stuff) down, do I also need some in the roof rafters or have I enough as it is? I was also wondering about the water tank, I have a single layer of insulation under it but the tank is risen up by about 10 inches from insulation, safe to leave it alone or remove?

Thanks.

slimjimmc

There's no need to insulate the rafters so long as you have plenty of insulation on the ceiling, 300mm of glass fibre is currently considered the minimum thickness you should have but you could boost this if you wish.
In fact insulating the ceiling is more effective than insulating the rafters because it has a much smaller surface area and keeps the heat closer to where you want it , i.e. in the rooms below. There's little heat/cost benefit to be gained by insulating the rafters too.

Regarding the water tank, first thing you should do is remove all insulation underneath it. You should never insulate under the cold storage tank as you need some warmth rising from below to help reduce the risk of it freezing. Insulate the tank well on all other sides and the top, an easy way to do this is make a good fitting box from polystyrene or insulating board (you could drape a bit of glass fibre over the box too if you like), you want that rising heat to stay in the tank instead of disappearing into the attic space.
And don't forget the pipes, all exposed pipes should be lagged in foam pipe lagging if they are not already under the glass fibre.

Sparkpea

in the really cold winter nights put a 100w bulb in the loft and leave it on near the water tank, heat is the only thing to stop the tank freezing. either that or leave the trap door open slightly. yes your heat will escape up there but works the same way.

gsxr1

they say we are in for a colder winter than last year. I have a load of fiberglass round the tank in my gaff already. The thought of a burst pipe in the attic is a nightmare.

rob555mark

Thanks lads, forgot to ask another stupid question but I have the insulation between the rafters, all my wiring running across them with a roll of insulation ran out like a carpet on top, no problems keeping wiring wraped up like that?

Sparkpea

unfortunately it doesnt matter how much fibreglass is in the attic when it comes to burst pipes that only keeps the heat out of the attic but its only heat that helps stop burst pipes.

all the bursts I repaired in attics in Jan 2010 where well lagged and insulated but still burst

slimjimmc

rob555mark wrote: »

Thanks lads, forgot to ask another stupid question but I have the insulation between the rafters, all my wiring running across them with a roll of insulation ran out like a carpet on top, no problems keeping wiring wraped up like that?

I think you mean between the joists (rafters are the timbers in the roof slope), and no it's not ideal to have your wiring buried under layers of insulation.

It shouldn't pose a problem with cables carrying light loads but there may be a risk of overheating if a cable is carrying a load close to its max rating for a prolonged time.
It's a good idea to ensure that cables carrying heavy loads such as electric showers, immersions, ovens, washing machine, tumble drier, etc are left in free air or up-rated with a heavier gauge wiring.

JOSman

How thick should the insulation between the joists be? I'm going to do this soon and need to know what to buy.

Thanks

gsxr1

at least 300mm.

150 inbetween joists and a blanket of 150 across the other way.

RKQ

slimjimmc wrote: »

Regarding the water tank, first thing you should do is remove all insulation underneath it. You should never insulate under the cold storage tank as you need some warmth rising from below to help reduce the risk of it freezing. Insulate the tank well on all other sides and the top, ..... all exposed pipes should be lagged in foam pipe lagging if they are not already under the glass fibre.

100% agree. Insulate sides & lid only.