Frequently Asked Questions

What is MAXRaft?

MAXRaft slabs are insulated under and around the edge of the slab. Utilising our patented MAXEdge perimeter insulation, MAXRaft has a product for almost any situation anywhere in NZ to meet the requirements of the building code.

Is MAXRaft a New Zealand made product?

Yes, all our EPS insulation is manufactured within NZ and delivered from the closest factory to site. 

Do MAXRaft slabs meet the new building code update May 2023?

Yes! All MAXRaft designs meet and exceed the requirements of the building code changes effective May 2023. See more about the performance of our product range here and try out our Product Finder to find the right slab for your project.

What is the R-value of a MAXRaft slab?

Because all floors are different the R value varies, but a typical MAXRaft® foundation design will range between R1.5 and R5.25 depending on the slab type and area/perimeter ratio.  See more about the performance here.

Or try out R-value Calculator.

Who provides the Engineering design?

As a part of our package, MAXRaft has it's own fully qualified engineers who can provide a site specific engineering design. Alternatively if you would like to use your own engineer then we can work in with you to ensure a smooth design process. You can also design it yourself using Specifi.

Can I install the product myself?

Yes. Supply only is a great and common option among builders and slab contractors.  Our products are simple to install and pre-cut to minimise waste and make the process efficient onsite.  You can also check out our list of installers here.

Can MAXRaft be used in conjunction with underfloor heating?

Yes, they are a perfect match. Because the MAXRaft® is fully insulated underfloor heating works extremely well as our slab edge insulation will prevent heat loss around the perimeter of the slab.  We have seen efficiencies of 30 – 40% when UF heating is used in conjunction with a fully insulated MAXRaft slab.

Under the requirements of the new building code MAXSlab is ideal for good ground when UF heating is specified and on soft ground MAXRaft Plus+.

Why should I choose MAXRaft?

You can change your windows, you can replace your carpet, you can buy a new kitchen...

You can't change your foundation.

MAXRaft® is a great choice for any home.  MAXRaft® acts as the thermostat for your home which means the temperature doesn't fluctuate as much as other floors. This constant temperature reduces the susceptibility of your home to mould growth and assists in providing a warm and healthy living environment.

What kind of technical support does MAXRaft provide?

We supply a full onsite guide to builders and owners, architects and engineers, which supports the site specific PS1.  You can also contact us directly on 0800 629 7238 or email

Can I have a MAXRaft with 90mm Frame?

Yes. MAXRaft is suitable with 90mm frames or wider frames and has been BRANZ approved.  When used with 90mm frames MAXRaft will recommend specific bolt fixings to ensure requirements are met. This is not necessary if the frames are 140mm +.

How is MAXRaft installed?

MAXRaft® is available in two ways; either as supply of the MAXRaft insulation only OR as a fully installed slab system by MAXRaft's installers. MAXRaft® has a comprehensive Onsite Guide and with guidance from the MAXRaft® team any full trained builder can install a MAXRaft system.   

How do I protect the perimeter insulation after the concrete pour?

There are a few different options for coating the outside edge of MAXRaft® from a Hard Edge to a Plaster finish. Please see our MAXEdge Finishing page.

We also now offer a pre-coated option that simply requires painting during the build process.  Contact us to find out more about this product.

Do I have to use a specific concrete supplier?

No.  MAXRaft products are not attached to any particular concrete manufacturer so you can choose who you prefer.  However, as our slabs are always fully engineered, it is important to check that the correct concrete mix is supplied to comply with the engineers documents.

What sets MAXRaft apart from similar building methods?

  1. Warmer, healthier and more energy efficient homes.
  2. Products to suit all climate zones and scenarios
  3. Increased thermal efficiency & higher R-values.
  4. Pre-cut factory made insulation to reduce onsite waste.

What is the width of the MAXRaft perimeter insulation?

The standard MAXEdge perimeter insulation detail shows a taper that goes from 50mm to 15mm at the top.  This detail is used when MAXRaft is constructed with 90mm frame.  For frames that are 140mm+ the standard taper is 50-40mm, however we can also remove the taper altogether to give you additional insulation if preferred.

Can MAXRaft be installed anywhere?

Yes.  MAXRaft® is available nationwide and can be custom engineered to work on almost any site.  MAXRaft has systems that are suitable for good and soft ground including TC2 and piled sites.  MAXRaft is not generally suitable for TC3 land unless the ground can be remediated to TC2.

How do I go about ordering a MAXRaft floor?

Simply email a full set of your plans along with a Geotech report (if applicable) to  We can produce a quote for you within 3 business days.  Following acceptance of the quote the engineering will be completed (if required) and once consent is issued we generally require 3-4 weeks notice to be onsite.

How environmentally friendly is MAXRaft?

Known for its highly efficient insulating properties, Expanded Polystyrene (EPS) has long been a leading choice in the industry for energy efficient homes. Plastics New Zealand has designated EPS as compatible with the environment as a result of its insulation ability. The waste produced in the MAXRaft® production process is recycled and turned back into new EPS insulation.

All MAXRaft slabs are designed using a software system so that there is minimal waste onsite with pre-cut factory made components therefore reducing waste.

How long does it take to install a MAXRaft slab?

For a standard 200m² house on good ground we would allow approximate 5-7 days to start and pour the slab. 

If we already have consent for a standard slab can we change to a MAXRaft design?

Yes, we will supply an engineered foundation package and you will simply have to fill out a variation to your building consent.

How does MAXRaft perform in an earthquake?

All MAXRaft slabs require site specific engineering design and are generally designed to be floating to minimise the risk of seismic damage.

How does MAXRaft perform with a polished concrete floor?

Excellently. Because the MAXRaft® isn’t tied to ground, the concrete will shrink when curing resulting in a stronger slab.  You can never guarantee a slab will not crack, however please ask us for tips on how you can minimise the risk.