There is no single best insulation material for every home. The right choice depends on which part of the house you are insulating, how much room and access you have, and how damp the space is. Here is how to think it through.
Start with the part of the house
Ceilings and floors are different jobs, so the same product is not always right for both.
- Ceilings: Insulation sits in the roof space, usually on top of the ceiling lining. It needs to cover the whole area, fit neatly between and over the framing, and stay fluffy rather than compressed.
- Underfloor: Insulation sits in the subfloor space, tight up against the underside of the floor. It has to stay in place for the long term and cope with a damper environment.
Walls are a different story. Wall insulation goes in at framing stage on a new build, so if you are building, it is worth planning early. Our new build insulation covers ceiling, wall and underfloor at that stage.
What to compare
When you look at any product, these are the factors that matter.
- R-value. This is how well the product resists heat flow. It is printed on the packaging, and higher means better. If you want the basics, read understanding R-values in New Zealand insulation.
- Fit and coverage. A product that fits snugly with no gaps will outperform one that leaves spaces around framing and pipes.
- Moisture. Subfloors and some roof spaces can be damp. Think about how the space is ventilated, and whether there is bare ground underneath that needs a moisture barrier.
- Safety clearances. Around downlights, flues and wiring, insulation has to be kept back by the required distance.
- Access. A product has to be something that an installer can get into the space. That affects what is practical, and it affects the price.
- Installation quality. A good product badly fitted will not do its job. Squashed or gappy insulation loses performance.
The materials you will come across
These are general descriptions of what is on the market in New Zealand. The products we install are the Knauf ceiling batts and Mammoth underfloor insulation described in the next section.
- Glass wool batts. Common and widely used, made in a batt format that suits ceilings and between-joist spaces.
- Polyester. A fibre product, popular with people who prefer an option that is not glass. It is available in batts and underfloor blanket formats.
- Sheep’s wool. A natural fibre option, usually chosen by people who want a natural product.
- Polystyrene. A rigid board, often considered for floors because it holds its shape.
Foil insulation is worth a separate mention. Retrofitting or repairing foil underfloor insulation has been prohibited under the Building Act since 1 July 2016 because of the risk of electric shock. MBIE explains this in its Healthy Homes insulation guide. If you have old foil in your subfloor, it is worth having it assessed.
What we install
For ceilings, we install Knauf batts. For underfloor, we install Mammoth products. Here is where each one fits:
- Ceiling insulation: most ceilings take 1 to 3 hours.
- Underfloor insulation: typically 1 day for a 100m² home.
- Underfloor ground moisture barriers: for subfloors with bare ground.
- Insulfluff removal: for old loose-fill insulation that should come out before new insulation goes in.
Guide prices are $1,600 to $2,000 for a ceiling and $2,200 to $2,500 for underfloor, for a 100m² home. Your quote depends on access and materials.
Which should you choose?
In most cases the product follows the space. Once we have looked at your ceiling or subfloor, what is already there and how much room there is, the choice is usually fairly clear. Our free consultation and assessment, usually done through our online system, is the easiest way to get there. We do it in person for complicated homes, or if you ask.
If you are not sure where to start, our post on what to insulate first sets out the usual order.
Get a quote
Get a free, no-obligation quote and we aim to call you back within 48 hours. You can also call us on 027 482 0333. If you’re not satisfied, we’re not finished.