Topic: Insulating an existing ceiling

Insulating an existing ceiling 

I have a badly designed/insulated roof/ceiling for which I would please like some advice on insulating.

Firstly I will try to describe the existing ceiling:
* From inside the house I have exposed beams measuring 45x190 at 1m centres.
* Above these beams is a Gib-board type material
* Above the Gib board are batterns of variable size (maybe 50x25 ??? laid at right angles to the inside beams.
* Attached to the batterns is a metal roof that slopes towards the centre of the building.
* There is a "thin" layer of insulation between the gib and the tin, some fluff that has blown around (and perhaps out) over the years.

What I plan to do:

1) inside the house run batterns (75x25) at right angles to the beams.
2) insulate between the batterns and the gib board with something appropriate (I think it was suggested I use R3.6 pink batts measuring 180cm)
3) attach gib board to the batterns
4) add cornice
5) plaster and paint

So my questions are:

is this a good idea?
it will create a sealed air space, should I be drilling large holes in the existing GIB so as to allow for air flow?
I can remove the outer tin roof, it seems to be "clipped" on I removed a strip one to look inside but I would rather not unless this is really recommended.

Thanks

Re: Insulating an existing ceiling 

Womble

A sealed airspace is exactly what insulation requires to function. Air flow reduces the performance of insulation significantly.
And if insulation is permanentlly exposed to atmospheric conditions it deterates and gets ripped apart by wind. This is a major (widely denied)dilemma in NZ standard roof and ceiling design.
A vapour barrier/check between the new insulation and the new gib is probably the right solution.
Talk to the guys at pro clima ( and no I am not involved with them !!!)

Re: Insulating an existing ceiling 

You are right - because the existing gib is painted on the inside it will seal the new space below, limiting the amount of drying towards the roof - a potential problem if moisture can migrate into the cavity through cracks and joins.

So I think you are right that you need to drill or create holes in the upper gib, exposing some of the insulation below. And whilst you could stick a small amount of vapour transport membrane across these holes, I suspect this is probably not necessary in your case.

As an additional idea. You could fit a thin layer of polystyrene between your new lower battens. This will create additional insulation plus thermal break across the existing upper beams. Bonus!


My opinion - for air barriers, you can go the extra mile in your case by applying extra caulking where necessary. You are aiming to create an effective seal at joints and boundaries. Intello membrane won't be necessary, if you seal your joints well (as either happens by default or with extra attention). In your case New celing paint + good cauking = effective air barrier.
I think intello would be more appropriate on a new build or complete room strip out. (Others may disagree.)

Good luck

Re: Insulating an existing ceiling 

If you go down the way with the holes you will need to run a breathable air barrier over it.
Remember moving air over insulation is a no no.

Re: Insulating an existing ceiling 

What spacing between holes and what size holes?

I was thinking 100mm holes at 1000mm intervals?

Also how should I attach the membrane? Glue? Specifically what glue or product would be best?

Re: Insulating an existing ceiling 

I recommend you talk to the guys at proclima.co.nz
They will be able to help with a solution and perhaps the required products.