Factors to Consider when Choosing Underfloor Insulation

Regardless of whether you are choosing underfloor insulation for a new build or the renovation of an existing building, there are a few key factors to consider. These include:

• Thermal performance of the product
• Moisture resistance 
• Durability 
• Environmental impact  

In addition, with the new building regulations coming into play this month (May 2023), there are some updated regulatory factors to throw into the mix.

Thermal Performance

The thermal performance of the insulation is vital, and this is where the new regulations have focussed. The aim is to reduce the energy required to heat homes and therefore reduce environmental impact. The building code now has higher performance requirements for underfloor insulation to reduce heat loss. This change is reflected in the higher construction R-values, where the R-value is a measure of the thermal resistance of insulation, which is a material’s ability to prevent heat flow.

However, it’s not as simple as applying a new value to your new build or renovation. Depending on where in the country you are, the requirements will vary. The country is divided into 6 climate zones and each has its own requirements. There are also different requirements for floor types. Unheated slab floors require different R-values than heated slabs, and both have different requirements than suspended timber floors.

How do I know if a product will meet the code?

Previous standards required a minimum R-value of 1.3. The new minimum value is now 1.5. Anything below this will not meet the code. The maximum requirement is now an R-value of 3.0. Any product above this will exceed current requirements.

Black or White?

EXPOL’s new generation high performance insulation range has been developed with the new code in mind, providing specifiers and installers with the confidence that code compliance will be met. EXPOL R2.5 is white in colour and is ideal for timber underfloor insulation. It meets or exceeds the requirements for climate zones one to three and can be used for both retrofit applications and new floors.

For builds in colder Kiwi climates,  EXPOL R3.1 exceeds the new Building Code standards for climate zones four to six. EXPOL R3.1 is infused with graphite providing its distinct black colouring. The addition of graphite makes it up to 24% more efficient than other polystyrene panels and increases the R-value.

For concrete slab insulation, EXPOL offers Concrete Slab Edge Insulation and Under Slab Insulation, or a combination of both, to meet the new increased insulation requirements in the Building Code.

Does an increase in R-value come with an increase in thickness?

The R-value is typically calculated based on the thickness, density, and thermal conductivity of the insulation material. So it goes to reason that an increase in R-value must come with an increase in thickness. This becomes an issue when architects and specifiers are working within confined spaces, such as with concrete slab floors. EXPOL recognises the challenges this will cause for designers and installers and have engineered their new generation range to maximise density and thermal conductivity and to minimise change of thickness. 

Moisture Resistance

The choice of underfloor insulation should also consider moisture resistance. This is important for reducing dampness and mould, and also to ensure the thermal performance of the insulation. If the insulation becomes moist, it becomes less effective at slowing down the transfer of heat because water has a higher conductivity than air. Products made using expanded polystyrene (EPS) are popular due to their moisture resistance.

Compared to other insulation, EPS offers superior resistance to the ingress of water. Samples of EPS retrieved after 30 years in the ground showed less than 1% water content by volume. 

Durability

Products should be chosen for their strength, durability and ability to maintain their shape and performance over time. EXPOL underfloor insulation products are expected to maintain their performance long term and come with a 50 year warranty.

Environmental Impact

Architects and specifiers should consider the environmental impact of underfloor insulation products and should choose products that are sustainable, recyclable and have a low carbon footprint. EXPOL recognise the importance of environmental sustainability and use recycled content in over 75% of their products (by volume). Over 3200 cubic metres of polystyrene is recycled every month in EXPOLs seven recycling centres, with over 1000 cubic metres coming from household waste. In addition, with the product being produced in New Zealand, the carbon footprint due to transportation is also reduced.

If you would like more information on EXPOL’s underfloor insulation products, you can review the products on our website, or get in touch with the team on 0800 86 33 73 or tech@expol.co.nz.