Underfloor Insulation
Underfloor Insulation for Warmer Floors and More Energy Efficient Homes.
DIY friendly, easy to install, available in four R-values
Expol Timber Underfloor Insulation
A warmer, drier and healthier home
Expol Timber Underfloor Insulation is specifically engineered for New Zealand's climate and building conditions, designed to stop heat loss through timber floors and create a warmer, healthier home all year round. Suitable for both DIY installation and professionals, the Expol range includes retrofit solutions for existing homes and options for new builds that meet current Building Code requirements.
Our R1.4 White and R1.8 Black panels are ideal for retrofit installations where homeowners want immediate comfort improvements and lower heating bills — without major construction. For new homes, our high-performance R2.5 and R3.1 panels are engineered to meet and exceed the current Building Code H1 energy efficiency standards.
Sustainable, Smart and Built for New Zealand Homes
Expol Timber Underfloor Insulation is designed with sustainability at its core. Expol R1.4 and R2.5 contains recycled content and is 100% recyclable at end of life, helping reduce waste and support better environmental outcomes for our communities.
Through our nationwide recycling and Expol Take-Back Programme, we ensure polystyrene is responsibly collected and reused — reinforcing our commitment to a circular manufacturing process and a cleaner, greener New Zealand.
Want to learn more about how Expol is leading the way in responsible manufacturing and recycling? Click here to explore our sustainability programme.
Click here to view the Masterspec document
Expol Underfloor Insulation Product Range
Choose the right underfloor insulation solution for your specific R-value requirements
R1.4 Timber Underfloor Insulation
A cost-effective insulation solution for improving the warmth and comfort of existing homes.
R1.8 Timber Underfloor Insulation
Designed for homeowners wanting greater thermal performance in retrofit applications.
Note: Do not store in direct sunlight.
R2.5 Timber Underfloor Insulation
Engineered to meet the current Building Code for new homes. Recyclable, 50-year product warranty.
R3.1 Timber Underfloor Insulation
Our highest-performing underfloor option for new builds. 24% better than R2.5.
Note: Do not store in direct sunlight.
Did You Know? Small Changes Make a Big Difference
Underfloor insulation is one of the most effective home improvements you can make
20% Heat Loss Prevention
Up to 20% of heat is lost through uninsulated floors in timber homes.
Year-Round Comfort
Proper insulation makes your home warmer in winter and noticeably cooler in summer.
Healthier Home
Insulation supports drier, healthier indoor environments with less condensation and mould.
Energy Savings
Lower heat loss means reduced energy use and long-term cost savings.
Consistent Temperatures
A well-insulated floor helps your home maintain consistent temperatures, meaning less reliance on heating and cooling systems.
Whether you're renovating, upgrading a home or building new — underfloor insulation is one of the most effective ways to improve comfort and lower energy costs.
Expol Underfloor Range
Choose the right R-value for your specific requirements and building code compliance
R-Grade Comparison
1200mm in length, 60mm and 100mm thick in four standard widths 360, 410, 470, 560.
| R-Value | Thermal Conductivity | Density | Recycled Content | Thickness |
|---|---|---|---|---|
R1.4 | K-Value 0.043 | 12 kg/m³ | 30% | 60mm |
R1.8 | K-Value 0.032 | 18 kg/m³ | 0% | 60mm |
R2.5 | K-Value 0.043 | 12 kg/m³ | 30% | 100mm |
R3.1 | K-Value 0.032 | 18 kg/m³ | 0% | 100mm |
Product Options & Sizes
All panels are 1200mm long. Choose the width that matches your joist spacing.
R1.4 White & R1.8 Black UnderFloor Insulation
Dimensions (mm)
| Thickness | Length | Width | p/bag | m² coverage |
|---|---|---|---|---|
| 60 | 1200 | 360 | 12 | 5.18 |
| 60 | 1200 | 410 | 11 | 5.41 |
| 60 | 1200 | 470 | 10 | 5.64 |
| 60 | 1200 | 560 | 9 | 6.05 |
R2.5 White & R3.1 Black UnderFloor Insulation
Dimensions (mm)
| Thickness | Length | Width | p/bag | m² coverage |
|---|---|---|---|---|
| 100 | 1200 | 360 | 7 | 3.02 |
| 100 | 1200 | 410 | 6 | 2.95 |
| 100 | 1200 | 470 | 6 | 3.38 |
| 100 | 1200 | 560 | 5 | 3.36 |
Installation & System Components
INSTALLING EXPOL TIMBER UNDERFLOOR INSULATION
Looks like you are about to take the next step to creating a healthier home environment. That's great news for you and your family.
Whether you are choosing to have EXPOL professionally installed or going it alone, you will not go past EXPOL Underfloor Insulation.
To assist you, we've developed an easy step guide – follow it and you can't go wrong.
Don't forget to pick up your EXPOL Underfloor Insulation DIY Ruler from your store. Use it to measure the underfloor joist sizes, so you can purchase the correct panels for your DIY Insulation project.
Step 1 – Measure
- Place your EXPOL Underfloor Installation DIY Ruler against one side of the joist. The opposite joist will fall within one of our 4 panel sizes. Joist sizes can vary, so be sure to measure more than one.
- You may need a few different panel sizes to complete the job.
Step 2 – Trim the edge
- If the panel is too wide, simply slice down the appropriate concertina edge, leaving the panel approximately 5mm over sized to ensure a firm fit.
Step 3 – Existing Floor Fixings (R1.4 + R1.8 & R2.5 + R3.1)
- Slide the panel between the joists. The concertina designed cuts will ensure a tight fit. The panel should be pushed up hard against the bottom of your floor leaving no air gap.
- A minimum gap of 200mm must be left around metal heating flues, OA rated recessed down lights and ceiling exhaust fans, and a 50mm gap is required around brick/concrete chimneys.
Step 3a – Existing Floor Clips
- EXPOL Z Clips are a push fit – no nails bracket to squeeze between the panel and the joist.
- They are to be positioned diagonally in opposite corners under the panel.
- Set these 200mm in from the end of the panel.
Step 3b – New Floor Fixings (R2.5 + R3.1 Underfloor)
- Before floorboards or flooring sheets are installed.
- Fix two EXPOL Joist Saddles diagonally in opposite corners of the space approx 200mm from the end of the joists. Simply slide the saddles over the joist, nail the saddle into the top of joist if required.
- Joist saddles ensure the panel will stay in place once the floorboards or flooring sheets are installed.
Step 3c – New Floor Fixings (R1.4 + R1.8 Underfloor)
- Before floorboards or flooring sheets are installed.
- Fix two 60mm Galvanized Nails diagonally in opposite corners of the space approx 200mm from the end of the joists, 60mm from the top of the joist.
- The nails will ensure the panel will stay in place once the floorboards or flooring sheets are installed.
Step 3d – New Floors
- Simply place the panel on top of the EXPOL Joist Saddles or nails.
- The panel should sit flush with the top of the joist to ensure there is no air gap.
Step 4 – Electrical
- For cables that come into DIRECT contact with EXPOL Underfloor Panels, place EXPOL Wireguard around the wires before installation.
- Do not use a staple gun to fix the Wireguard.
- Take extra care when working around electrical wiring.
Step 5 – Pipes & Plumbing
- For obstacles such as pipes and plumbing, use your sharp knife to cut the panel and notch around the difficult areas.
- For future maintenance, leave 100mm clearance around pipes and plumbing.
Slide 1 of 10: Introduction
Technical Data
| Properties | EXPOL R1.4 UNDERFLOOR INSULATION | EXPOL R1.8 UNDERFLOOR INSULATION | EXPOL R2.5 UNDERFLOOR INSULATION | EXPOL R3.1 UNDERFLOOR INSULATION |
|---|---|---|---|---|
| Material | Expanded Polystyrene | |||
| - | with Graphite | - | with Graphite | |
| Density | 12 kg / m³ | 18 kg / m³ | 12 kg / m³ | 18 kg / m³ |
| Sheet Size | 1200 mm x 360 mm | 1200 mm x 410 mm 1200 mm x 470 mm | 1200 mm x 560 mm | |||
Key Features & Benefits
BRANZ tested and certified (R2.5)
Independently tested and verified for quality standards
Lightweight and easy to handle
Simple installation for DIY or professional use
Cuts easily with knife or saw
Perfect sizing with standard tools
Fits standard joist spacings
Designed for New Zealand building standards
Non-toxic and safe to handle
Safe for installers and building occupants
Why Choose EXPOL Premium?
Superior Thermal Performance
Excellent R-values from R1.4 to R3.1 for optimal energy efficiency
Moisture Resistant
Closed-cell structure prevents moisture absorption and mold growth
Easy Installation
Lightweight and easy to cut, perfect for DIY or professional installation
Trusted by New Zealand builders for over 45+ years
Underfloor Insulation FAQs
Answers from the EXPOL technical team on choosing, sizing and installing underfloor insulation in New Zealand homes.
Is underfloor insulation worth it, and what difference does it make?
Yes. A suspended timber floor without insulation is one of the largest sources of heat loss in a New Zealand home, and cold floors are one of the most noticeable comfort problems. Insulating between the joists keeps warmth in the living space, makes floors feel warmer underfoot and reduces the energy needed to heat the home. Because EXPOL panels are rigid EPS they hold their performance for the life of the floor rather than sagging over time.
What R-value do I need for underfloor insulation in New Zealand?
It depends on whether you are retrofitting or building new, and on your climate zone under NZ Building Code H1/AS1. Consents issued from 1 May 2023 must meet the updated requirements for new builds, which means R2.5 or R3.1 depending on your zone. For retrofitting an existing home, R1.4 is a cost-effective improvement and R1.8 delivers higher thermal performance. Check the current H1/AS1 schedule or ask your builder or installer to confirm what your project requires.
What is the difference between the white and black panels (R1.4 vs R1.8, R2.5 vs R3.1)?
The black panels incorporate graphite during manufacturing, which makes them more thermally efficient at the same thickness — R1.8 Black is around 30% more efficient than R1.4 White, and R3.1 Black is around 24% more efficient than R2.5 White. The white panels suit normal New Zealand suburban and rural conditions and contain 25% recycled content; the black panels are the better choice for extremely cold, windy or exposed sites. All are recyclable and carry a 50 year product warranty.
How much underfloor insulation do I need, and what size should I buy?
Measure the clear span between your floor joists and choose the matching panel width — widths often vary across a home, so measure in several places. Panels come in 360mm, 410mm, 470mm and 560mm widths and are 1200mm long; R1.4 and R1.8 are 60mm thick and R2.5 and R3.1 are 100mm thick. Then use the EXPOL calculator with your floor area and joist width to work out how many packs you need.
How do you install underfloor insulation yourself?
EXPOL underfloor insulation is designed for DIY installation in any home with accessible subfloor space, with no need to lift the floor. Work along each joist bay, push the panel up hard against the underside of the floor — no air gap is required, in line with NZS 4246 — and secure it with the push-fit clips included in every pack. You will need a tape measure or the free EXPOL ruler, a heavy duty utility knife with a slide-out blade for cutting, and EXPOL WireGuard for any electrical cables. Gloves, goggles, a dust mask and knee pads are recommended. An average home with good access can usually be completed over a weekend.
What if my joist spacings don't match the standard panel sizes?
The panels have flexi-cut edges that compress 1mm to 2mm to suit varying joist spacings. If a panel is slightly too wide, trim it to size with a utility knife. If a bay is wider than the panel, cut a strip from another panel and insert it alongside to fill the gap.
How do I insulate around electrical cables and plumbing?
Electrical cables must always have a barrier between the wiring and the polystyrene, because plasticiser in the cable's plastic casing reacts with EPS. Use EXPOL WireGuard — 50mm is included in every pack — or another suitable barrier such as duct or insulation tape. This is a chemical reaction, not a fire risk: at worst the cable may feel slightly sticky where the two have touched. Around plumbing, leave a 100mm serviceable gap.
Do I need to remove existing building foil first?
Follow the EXPOL installation guidelines for your specific situation. In many retrofits the insulation is fitted directly against the underside of the floor, but where existing foil or subfloor lining is present, check the installation document or ask a professional installer whether it needs to be removed or can stay in place.
Will it absorb moisture, sag, grow mould or attract rodents?
No. EPS underfloor insulation is moisture resistant and inert, so it performs well even in damp subfloors and will not rot, sag or support mould growth. It offers no nutritive value to rodents, although it is not rodent proof.
Is EXPOL underfloor insulation fire safe and BRANZ appraised?
It is manufactured with a fire retardant additive and tested to AS/NZS 1530.3, achieving a spread of flame index of 0 and a smoke developed index of 5, so it will not sustain a flame. EXPOL R2.5 UnderFloor Insulation also holds a BRANZ Appraisal.
Is there a warranty, and where can I buy it?
EXPOL expanded polystyrene underfloor insulation carries a 50 year product warranty when installed in accordance with EXPOL installation instructions. It is available nationwide from Mitre 10, Bunnings, Carters, PlaceMakers, ITM, BuildLink, Timber World and other independent hardware and building supply stores.