Accessible roof attics (where someone can crawl through) can be insulated with Blanket/ Batting/Board or Loosefill/Sprayed types of insulation.
Inaccessible roof cavities are those with no access after construction and can only be insulated with blanket/batting or board materials when the roof or linings aren’t present.
Blanket/Batting or Board Materials
Blankets/Batting for roof attics are made from Glasswool, Polyester, Polystyrene, Sheep Wool/Polyester blend or Sheep Wool and detailed information is available in the Tech Data page. Most blankets/batting will exceed the Gib 2010 Site Guide maximum loading of 3kg/m2 for unsupported insulation on Gibboard ceilings, once they exceed R5.0
These should always have the a first layer installed tightly between and to the top of the ceiling joists or batten and a second, layer of Battenblocker installed at right angles either between ceiling battens or over joists, so all gaps, joints and framing timber is covered.
Otherwise assume the installed insulation total R- value ( installed ) will be 45% less than what is written on the bale.
Do not drape blanket/batting over the ceiling joists, as the resulting small air cavity alongside each joist will usually be vented and reduce overall performance by around 30%.
Any airgaps left around recessed lights or flues must be sealed down to the ceiling lining. Otherwise asume the Total R-value installed is reduced by 25%.
Polystyrene must have all edges and joints sealed with extruded sealant and be separated from all electric cables.
Granulated and Loose Fill Materials
These materials are blown or sprayed into accessible roof attics.
All granulated or loose fill material must be installed by weight and not thickness, at the density specified in material R-value tests. Otherwise, the Total R-value (installed) will be significantly less and the product will settle over time.
Granulated mineral wool materials are made from consistent raw materials.
Qmulus mineral wool will not exceed the Gib 2010 Site Guide maximum loading of 3kg/m2 for unsupported insulation on Gibboard ceilings, until R10.0/595mm, so is suitable for most gibboard of plaster ceilings.
Rockwool mineral wool will ” exceed the Gib 2010 Site Guide maximum loading at greater than R1.9/75mm, so should not be used or most gibboard or plaster ceilings, unless separately supported.
Cellulose (macerated paper) loose fill is made from waste newspaper and dry powder chemicals.
Cellulose loose fill will exceed the Gib 2010 Site Guide maximum loading at greater than R1.9/65mm, so should not be used on most gibboard or plaster ceilings, unless separately supported.
Sheep wool loose fill is made from low grade wools, waste carpet or clothing and various chemicals.
Loose fill made from waste can have variable performance, due to variable raw material. Moisture absorbent loose fill (Cellulose or sheep wool) used in high winter humidity locations (most of N.Z except the central plateau & central Otago) will exhibit significant Total R-value (installed) reductions in winter.