Choosing ceiling insulation

There are two common types of ceiling insulation: bulk, which fits between or rolls over ceiling joists, and loose-fill, which is blown in.

Bulk insulation

Bulk ceiling insulation comes in two types - segments, which fit between the joists above your ceiling, and blankets, designed to be rolled out across the top of the ceiling and the joists.

Blankets

Blanket insulation that covers ceiling joists prevents extra heat loss through the timber joists. When you’re topping up existing insulation, it can be easier to install blanket insulation than segments because you can just roll it over the top of what’s there already. Insulation that covers ceiling joists can make it harder for a person to move around the ceiling space though.

Segments

If you install segments between joists, you need to put in higher R-value insulation to make up for the heat that gets lost through the timber - check the table of minimum recommended R-values for existing homes.

Loose-fill insulation

Loose-fill insulation is blown onto the ceiling. It can be an option if there’s not enough space in your roof to move around and install bulk insulation. Otherwise we recommend using bulk insulation (blankets or segments).

Loose-fill is not used in EECA’s insulation programme as its performance can be variable. Its safety, effectiveness and durability depend highly on the quality of the material used as well as the installer's equipment and experience. As it can settle or move around over time, the insulation can get into contact with the roof or roof underlay and cause moisture problems.

How much ceiling insulation?

How much insulation you need in your ceiling depends on how cold it gets in your area and on the thickness and condition of any existing ceiling insulation. The R-value is a measurement of the insulation's effectiveness - the higher the R-value, the more effective it is at preventing heat loss.

If you are building a new home, your insulation must meet the building code - and we recommend going much higher if you can.

Building Code - Building Performance website

Minimum recommended R-values for existing homes

The table below lists recommended minimum R-values for retrofitting ceiling insulation into existing homes. We recommend going higher if you can.

Minimum recommended R-Values for existing homesNorth Island (excluding Central Plateau)South Island and Central Plateau
Ceilings with no insulation, or up to 75mm of existing insulation  R2.9 blanket or R3.4 segment insulation R3.3 blanket or R4.0 segment insulation
Ceilings with 75-120mm of existing insulation  R1.8 blanket insulation R2.4 blanket insulation

Checklist for choosing ceiling insulation

To get a suitable, effective ceiling insulation product choose one that is:

  • intended for installation in roofs or ceilings
  • a high R-value - R-value is a measurement of the insulation's effectiveness, the higher the R-value the better
  • the right width - you need the correct width for the spacing of ceiling joists, roof trusses or rafters, if you’re going to insulate in between
  • the right thickness (particularly for skillion roofs) - you need to keep at least a 25mm gap between the insulation and the roof underlay
  • compliant with the testing Standard AS/NZS 4859.1 – so you know the product works as stated.  Look for the compliance statement on the insulation packaging.

You may also want to check:

  • performance guarantees offered by insulation manufacturers on their products
  • the manufacturer's instructions for safely and correctly handling and installing the insulation.