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Insulating Kiwi homes

Insulating Timber Floors with EXPOL – Your Questions Answered by our Technical Experts

Are you gearing up to install underfloor insulation for your home before winter arrives? If so, you’re in the right place! Welcome to our Q&A session with the technical team at EXPOL.  Whether you’re a seasoned DIY enthusiast or a first-time insulator, we’ve got you covered with answers to the most common EXPOL queries on insulating timber floors — and perhaps even a few unexpected ones. 

Why use EXPOL for insulation?

EXPOL is fantastic for insulating timber floors. It’s made of expanded polystyrene, which is mostly trapped air. Since air and polystyrene don’t transfer heat well, EXPOL does a great job of slowing down the movement of heat through your floor, keeping rooms much warmer and drier. EXPOL has engineered a range of underfloor products with high R values for excellent performance. What’s more, EXPOL won’t get moldy or degrade in damp conditions because it’s moisture-resistant and it’s very easy to install, either for a new build or under an existing floor.

Do I need insulation if I have a heat pump?

The role of insulation is to prevent the transfer of heat, so in summer it keeps the heat out and in winter it keeps it in. While a heat pump (or any other heating device) will warm the temperature of a room, good insulation will ensure that heat doesn’t quickly escape! Insulation will help you get the most efficiency out of your heating solution.

How do I know which EXPOL product to buy?

EXPOL insulation comes with different R-values. R-values are a measure of how effectively the insulation works, the higher the R-value, the greater the insulation. Depending on where in the country you live, can influence which level of insulation your home will need. New building code regulations stipulate the R-values for new builds and are a helpful guide if you are upgrading your home.

EXPOL R2.5 & EXPOL R3.1 are specifically designed to meet the Building Code changes, with R2.5 meeting the requirements for climate zones 1-3 and 3.1 meeting the requirements for climate zones 4-6. You can find your climate zone here.

How do I calculate how much insulation I’ll need for my home?

EXPOL makes this easy with our EXPOL ruler and online calculator:

  1. Determine the area (m2) of the floor space you wish to insulate. 
  2. Measure the space between joists to select the right width of EXPOL insulation. Use a tape measure or the free EXPOL ruler (available from hardware stores) to easily determine the appropriate pack size. It’s a good idea to measure multiple joists as widths can differ, and you may require more than one size.
  3. Use our EXPOL calculator and enter the floor area and joist width to find out how many packs you’ll need.
What equipment or products do I need to install EXPOL myself?

You’ll need 

  • a measuring tape or the EXPOL ruler to determine the width between joists 
  • a utility knife for cutting the EXPOL sheets to the correct size 
  • EXPOLs wireguard tape to cover any wires 
  • EXPOL push Z clips (included with each EXPOL pack)
  • Gloves, goggles, and a dust mask to protect yourself from any irritation or injury during installation

You may also need:

  • Joist saddles for new builds to position EXPOL correctly
  • A straight edge or ruler to help with cutting
  • Knee pads for comfort if working in a confined space
How long will it take?

This will depend on the size of the area you are insulating, the ease of access to the area, variation in the widths of the joists, how much cutting is required to get the right size and whether you have help or are working alone.

An average sized home can be fully insulated over a weekend – but if you don’t have that much time to spare, you can do one room at a time.

What if I can’t crawl underneath my floor?

While we have had some customers dig trenches under the house to have EXPOL installed, we appreciate that is above and beyond! We recommend insulating the areas you can access and if you ever get the chance to lift up the floor, you can insulate those areas at the same time.

If there is builders foil under the floor already, do I need to remove it before starting?

Yes, remove any builders foil or other lining before installing insulation, EXPOL should be installed directly against your flooring with no floor gap.

What do I do if there is a lot of variation in size between joists?

The EXPOL ruler is a quick and easy way to see which product you need. Simply line it up between joists and the colour coding will indicate which pack of EXPOL you require. You may need to measure more than one joist if they vary. 

Do I need to leave a gap for electrical wires?

Working around electrical wires is easy. Simply cover them with EXPOL’s wire guard which provides a physical barrier between the polystyrene and the wire. The EXPOL panels can then sit up tight against the barrier.

Will rodents chew on my insulation?

EXPOL offers no nutritional value for rodents or birds. We do not get reports of EXPOL being eaten by either birds or rodents.

What happens to my insulation during a fire?

EXPOL is protected with a fire retardant and is tested and approved for fire safety. It will not hold a flame and therefore does not burn or produce fumes.

Can I return unused product if I’ve bought too much?

If the packet is unopened, most hardware stores will receive your excess product and refund you. It’s best to check before purchasing as this may change from store to store.

We know you’ll love the difference EXPOL insulation makes to your home and we’re here to help you if you need it. Our technical team is available to answer any questions on insulating timber floors and provide support. You can contact them via the website, email or by phone (0800 86 33 73) if you have any questions, issues or feedback.


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