top up ceiling insulation

Hey,
I'm about to embark on topping up ceiling insulation in a 1959 double brick home in Hobart Tasmania.

A few questions I have are:

I've read that I can just add new batts on top of the existing fibreglass batts rather than remove the existing batts and replacing them. If I take this approach and add R3.5 (or higher) I suspect that its likely that the batts will be higher than the rafters, is that an issue? aIf it is am I better off thinking about the blanket approach and rolling it out over the top of the rafters?

Also I'd appreciate any other tips.

Cheers,

What type of insulation is existing? Depends what type it is as to leaving in situ or not. Use R3.5 if its ok, if not and has to be removed, use R4.0
Don't use blanket insulation, you will not be able to see the ceiling joists (rafters are on the angle of the roof) and a very real danger of missing it with your foot and doing yourself a great injury as you demolish the ceiling lining.
Batts are much better, don't forget to allow a minimum of 50mm clearance around any recessed light fittings (you can get special covers with vent holes for this). It is also easier to for an electrician to alter/add electrical wiring. Use a plastic rake to push/pull the batts in the very confined area where the rafters and ceiling joists sit on top of the external walls.
While your up there, put a couple of 2pieces 300mm wide x 2.4m ply flooring strips (screwed together = 36mm thick) on top of the joists, much easier to get around the roof area that way.

thanks RW, I appreciate it.

The current insuraltion looks to me like fibreglass batts about 5cm thick. I reckon I could leave them in and put some 3.5 on top. Even if they sit higher than the ceiling joists I figure as long as I can clearly see the joists I'll be able to walk around ok?

I've also heard that you can get a more compressed batt to go around the outside of the roof where there is less clearance between rafters and joists. I guess I only need to worry about that if there isnt the 2cm space between the top of the batt and the rafter at its lowest point?

Any suggestion of the pros/cons of the different products available?

Thanks again. advice on insulation from someone that lives near cowra should be heeded I reckon! Cold there!!

The old insulation is ok to leave if its fibreglass. I used Earthwool (can get at the big green shed) and is an excellent product (used in our house).
The thicker one you refer to is acoustic insulation, is more expensive.
Doesnt mater if you have to squash the insulation up at the junction of rafter and ceiling joists because of the angle it will only be about 150 to 200mm at the most. Given the age of your house I doubt that there is any sarking under the roof tiles/cladding so it is important to make sure that the wool does not make contact with the tiles (it will wick moister onto the timber or condensation if iron. If it is iron and it is the old galvanised variety, it reacts badly with any fibre glass type insulation so just make sure you have no contact between the two.
Yes, it gets chilly at Cowra, have had a few -3 to -5 in the last week or so, the slow combustion is fantastic and lots of good quality firewood free locally :2tsup:

Hi again,

ive been up rearranging the current fiberglass R2.0 (found an old packet). Looks like when we required the house years ago the electricians just shoved it aside and didn't put it back. Raises a few questions:

can an I just put a bat over the wires going down to a standard ceiling light fitting? It's definitely not a downlight of any variety? See photo attached.

there is loads of dust on top of the current batts, a combination of a white powder insecticide (someone suggested to me it is probably permethrin, and reasonable safe) and also paint chips from the exterior of the roof, I think the roof was water or sand blasted and repainted and some of it ended up in the cavity. Should I just patch the holes, add some new earthwool batts over the top of the lot rather than removing the existing and trying to vac out the mess with a HEPA vac?

thanks!