How to top up your roof insulation

Before doing anything else, you’ll need to get into your roof space. Most homes have a manhole access point. Often tucked away in a hallway or cupboard ceiling. Set up a sturdy ladder and gear up with safety equipment including gloves, a long-sleeved shirt, a dust mask, and eye protection. A headlamp or torch will help keep things visible and your hands free while you move around.

Once you’re up there, only step on the joists which are the timber beams running across the space. The plasterboard in between isn’t designed to hold your weight and could give way. Take care to avoid disturbing any existing cabling, ducting, or materials while you inspect the area.

Take a moment to assess what insulation you’re working with. In older properties, it’s not uncommon to find very little insulation, or materials that have seen better days. You might spot batts, which are firm, rectangle-shaped pieces laid neatly between the joists. Alternatively, you could come across loose-fill insulation, which looks like soft, fluffy fibres sprayed or scattered over the ceiling.

If it’s loose-fill and you’re unsure what type it is or how it was installed, it’s best to leave it undisturbed. Some materials used in the past can pose health risks, so if there’s any uncertainty, it’s a good idea to call in a qualified professional.

Once you know what you’re dealing with, you can decide how to top it up. Sticking with the same insulation type makes the job easier and helps avoid uneven coverage. Not sure what product matches up? Take a quick photo and head in-store. A team member can help you find the right fit and recommend options based on your region.

In most New Zealand's climates, roof insulation with an R-value between R4.0 and R6.0 is a solid choice. R-values measure how well the material resists heat flow, so, the higher the number, the better the performance.

When you’re ready to install insulation, start at the spot furthest from your manhole. That way, you won’t be stepping on areas you've already insulated and you’ll avoid making extra trips back and forth.

Gently place the batts between the ceiling joists. If you're adding a second layer, lay those batts across the top of the first. Make sure each one sits flush against the next, without being compressed. Insulation needs its loft to work properly, so don’t push or squash it into place.

As you lay insulation, be mindful of things like ceiling lights, fans, vents, and any electrical wiring. Batts should be kept at least 100mm away from fittings that produce heat unless those fittings are rated safe for insulation contact (IC-rated). If in doubt, check the product label or speak with a licensed electrician.

To get a clean fit around edges or obstacles, use a sharp utility knife and a straightedge to trim the batts. Always cut on a flat surface and use gloves for protection. Thermal covers can also be installed over lights or transformers to create a safe barrier where needed.

Learn how to insulate your walls.