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
Blankets
Blanket insulation that covers ceiling joists prevents 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 below.
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.
For rental homes, insulation must meet the Residential Tenancies (Smoke Alarms and Insulation) Regulations 2016.
Insulation regulations for rental homes - Tenancy Services website
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 homes | North Island (excluding Central Plateau) | South Island and Central Plateau |
|---|---|---|
| Ceilings with no insulation, or up to 70mm of existing insulation | R2.9 blanket or R3.4 segment insulation | R3.3 blanket or R4.0 segment insulation |
| Ceilings with 70-120mm 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.
