Installing underfloor insulation: Everything you need to know

April 20, 2018 at 1:15 PM

Temperatures have dropped dramatically over the past week, giving us all a timely reminder that colder weather is on its way! If you’re thinking about winter-proofing your home, installing underfloor insulation is an important consideration. 

In this article, we tackle a few of the common questions we’re asked by homeowners who are considering installing underfloor insulation.

What is R Value and why is it important in underfloor insulation?

R-value is a measure of thermal resistance for materials (such as insulation) and assemblies of materials (such as walls and floors). 

The higher the R-value, the better the thermal performance and heat retention of the material or assembly, and the slower the heat loss. 

To meet building regulations, it’s important to ensure the R value of the underfloor insulation product you use is correct. EXPOL’s premium polystyrene underfloor insulation meets New Zealand’s required building regulation R Values, and is available in two grades – see the next section for more detail.

REMEMBER – The R-value of a product is only maintained if it’s kept in its original condition. EXPOL insulation can never sag or reduce in size and will always maintain its rated R-value. Be carful to avoid cheaper products that do deteriorate with age.

Which EXPOL underfloor insulation product is right for you?

EXPOL R1.4 White Premium UnderFloor Insulation is the ideal solution for most New Zealand suburban environments, as well as rural areas that do not experience extreme temperatures. 

Water resistant, durable and backed by a 50 year warranty, EXPOL R1.4 UnderFloor Insulation is also manufactured using 25% recycled content, making it an environmentally-friendly choice.

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EXPOL R1.8 Black UnderFloor Insulation is infused with graphite, making it up to 30% more efficient than other polystyrene underfloor insulation panels. With an R-value of R1.8, it is ideal for extremely cold temperatures and windy environments.

More about our EXPOL1.4 and R1.8 underfloor insulation products:

• As well as being fire-retardant and water-resistant, EXPOL polystyrene underfloor insulation is non-allergenic.

• Unlike ‘batts’ type products, polystyrene underfloor insulation won’t absorb water or sag over time, meaning you won’t end up having to replace it after a few years.

• It is designed to be super quick and easy to install, with colour-coded packs in a range of joist widths from 560, 470, 410, 360.

• Custom-designed ‘I’ brackets  make it simple to install in existing floors and special joist saddles ensure installation under new floors is just as easy.

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What’s does EXPOL underfloor insulation cost?

An average-sized New Zealand home is around 100 square metres  and the cost of EXPOL R1.4 White Premium polystyrene underfloor insulation is approximately $11 per square metre (note – underfloor insulation cost will vary per retailer).

That makes the cost of insulating an average home around $1,100*. As an easy-to-fit insulation product, EXPOL also makes DIY a breeze – saving you money on installation. 

If you’re living in the South Island, you may want to consider our 30% more efficient EXPOL R1.8 Black Premium polystyrene insulation to ensure your home remains toasty even in the worst winters. For this type of underfloor insulation cost is a little higher (about $14 per square metre), meaning that the investment to insulate an average-sized home would be about $1,400*.

*Excludes Installation

How much EXPOL underfloor insulation will you need for your home

EXPOL underfloor insultation comes in 4 different width to fit between the joists, each pack contains the following:

EXPOL 360    1200 X 360 X 60MM    12 Panels per pack    Covers 5.18m2

EXPOL 410    1200 X 410 X 60MM    11 Panels per pack    Covers 5.41m2

EXPOL 470    1200 X 470 X 60MM    10 Panels per pack    Covers 5.64m2

EXPOL 360    1200 X 360 X 60MM     9 Panels per pack     Covers 6.06m2

If you’re wondering how many packs you’ll need, just check out our handy underfloor insulation calculator. You can use the results to determine how much your home’s underfloor insulation cost. 

How do I know which width I need?

• Simply measure the space between your joists with a tape measure, or call into your local EXPOL stockist who can give you an EXPOL Joist Ruler to measure the space between your joists and get the right pack sizes. 

• Make sure you measure the internal width between the joists, and sample a number of joists as widths can vary where alterations have been done.

• Always order a pack with a slightly larger width than the space available - the concertina cuts on the side of the panels mean you get a snug fit or  you can easily cut panels down to fit between joists.

Where can I buy EXPOL Premium UnderFloor Insulation?

EXPOL is available nationwide in all major hardware outlets. Find your nearest stockist.

Got a question we haven’t covered? 

Having supplied premium polystyrene underfloor insulation to New Zealand homeowners and landlords for more than 30 years, we know a thing or two about how to best warm up Kiwi homes. Our team is expert in the art of creating healthy, dry homes and they’re happy to answer any questions you might have. You can call us on 0800 86 33 73 or email us at 


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