bfginger: Underfloor or ceiling?
For underfloor I would go for polyester over fibreglass. Greenstuff is polyester, Pink Batts is fibreglass. Polyester can be stapled in place but fibreglass needs straps. A cheap vapour barrier should help keep your house drier if the underfloor cavity is enclosed and has a dirt floor
The main problem with fibreglass in the ceiling is it produces abrasive dust and is an irritant to touch. Polyester is a preferable option if it's a space you're going to come in contact with. Fire risk areas are better to have fibreglass as it produces less smoke and it'll be much less likely for downlights to be rated to have polyester installed over them. If you have old torn up and heavily slumped Pink Batts they should be removed. Polyester is easier to cut to size.
Polyester insulation can be extremely overpriced in retail as the retailers prefer to sell fibreglass. The price difference should be much smaller from wholesale.
Don't go with low R values. Insulation levels are low in New Zealand compared with international norms. More like R6 is good for ceilings. Two layers might be cheaper and more effective than a single thick layer as the second layer can go over the joists and extra thick batts are a problem around edges where they're not supposed to touch the roof lining. R2.6 is the best I know of for polyester or wool-polyester underfloors.
An R value is the U value inverted. So R2.9 means U0.344 which means a 100m2 area loses 34.4watts for each degree difference on each side of the material. R2.9 of polyester may be a different mm thickness compared with R2.9 of fibreglass.
R2.9 is a minimal level of insulation for a ceiling. Greenstuf has has higher R value single layers of insulation as do their competitors.
To quote an earlier post
There are also websites you can order from like
and http://insulationwarehouse.co.nz/ .
It might be possible to order from a factory
http://www.insulpro.co.nz/ who is behind Mammoth.
http://www.greenstuf.co.nz/ Greenstuf is from Autex.
http://www.technobond.co.nz/ Ellis Fibre is in Dunedin so not much good for you. They sell on Trademe.
Terra Lana has started offering R2.6 wool-polyester underfloor
http://www.terralana.co.nz/under-floor-insulation.html Their website says products can be purchased directly from them. But they're in Christchurch.
If you DIY you need to be careful of wiring as it should be over insulation instead of under as it can burst into a fire if it isn't rated to have insulation over it. And these's the issue of falling through the ceiling ;)
Decent price, easy to handle, no itch problems and slightly higher R values for given thickness than most of the competitors I looked at the time.
(NB: 200mm thick is about the practical maximum for a lot of NZ roofs due to relatively low pitches before the insulation starts touching the underside of the roof sheeting, which you don't want because of potential moisture issues).
What was the r value for the Knauf?
Both Greenstuff and Earthwool look really good, but I'm leaning toward Earthwool. Do people have any preference?
It seems like Earthwool has more information on their website, better packaging, more variety to suit different applications.