Under Floor Insulation Materials - Your Options for Underfloor Insulation
- Jan 18
- 5 min read
Installing underfloor insulation is a great way to improve your property's energy efficiency. Doing so helps reduce cold coming from your under floor crawl space, reduce damp rising from below the floor and stop draughts between old floorboards.
However, there are many products and insulation materials that can be used to insulate under your home. Often it's hard to know which will provide the best results for you. What is the best underfloor insulation? What underfloor R value should you aim for? How to insulate underfloor crawl spaces?
Let's go through the options we commonly use on Waiheke Island to help our clients!
Expol Underfloor Insulation
Expol is a polystyrene insulation product, that comes in sheets at 1.2m long. It is ridged and comes in widths to match most standard floor joist spacing.
When is expol the best option? When underfloor joists are standard sizes and spaced at standard measurements apart. Because Expol underfloor insulation is ridged, the width matters as every alteration takes time to cut and makes install more complex and take longer.
Specifications of Expol Underfloor Polystyrene Sheets
Standard widths of the boards are: 360mm, 410mm, 470mm, 560mm.
Expol underfloor insulation has four board options with different insulation R value rating: R1.4, R1.8, R2.5 and R3.1.
The thickness of the R1.4 and R1.8 sheets is 60mm, and will fit in between almost all floor joists. This makes them a great retrofit option.
The R2.5 and R3.1 sheets are 100mm thick, making them ideal for new build. However if joists are deep enough these can also be used in retro fit underfloor insulation jobs.
Expol Underfloor Insulation Pros and Cons
Expol is a great choice, but there are some things to keep in mind when choosing this product. Here are some pros and cons in our opinion:
Expol Underfloor Insulation Pros
Clean finish that is aesthetically pleasing and keeps the crawl space tidy.
No gaps between boards and the joists making a near air tight finish.
Can be upgraded in the future with additional sheets.
Expol Underfloor Insulation Cons
Expensive to transport, as the sheets are not compressible expol products can take up alot of space in the trucks and freight costs increase.
Takes a longer time to install than some other products, meaning install costs can be more expensive.
Requires consistent joist spacing for the best and fastest results.
Choosing your Expol Underfloor Insulation Product
So you have determined expol is the way you want to go, great choice! Which of the four options should you go with?
Keep in mind, the install time and price will stay fairly consistent no matter which R value you choose. This means the higher R value you get, the better the deal really is.
To achieve Healthy Homes Standards for your rental, any of these options will suffice. However we often encourage upgrading to R1.8 as you likely won't upgrade the underfloor insulation again, so it's worth getting a bit more for your money for the future.
When it comes to New Build, R2.5 is the minimum on Waiheke Island. So you want at least the R2.5 sheets. Again, do it once and do it right, we encourage your to upgrade to the R3.1.
Mammoth Blanket Insulation
Mammoth blanket insulation is a quick and effective to install underfloor insulation product. It is made of polyester long runs, and is installed by stapling the edges to the joists. Because of the way the product is designed, it can be installed even where joist spacing is irregular.
When are Mammoth Underfloor Blankets the best option? When the install is tricky or not standard, if floor joists are old and crooked mammoth can still be installed well without taking extra time (or extra costs!)
Specifications of Mammoth Underfloor Insulation Blankets
Mammoth blankets are made to be oversized, allowing a fold down of a few centimeters to allow stapling. Our team can help you select the best sie for your application.
Standard blanket insulation widths: 450mm, 510mm, 600mm, 650mm.
R values of mammoth insulation underfloor blankets: R1.5, R1.8, R2.0.
The nominal thickness of R1.5 blankets is marked as 100mm, while the R1.8 and R2.0 are 115mm.
Mammoth Underfloor Blanket Pros and Cons
Pros of Mammoth Underfloor Insulation Blankets
Easy to install when the floor and floor joists are not standard.
Affordable insulation option.
Less mess when installing and less offcuts.
Cons of Mammoth Underfloor Insulation Blankets
A professional should always install blanket insulation, as it takes more care than polystyrene sheets or sections.
The R value max is R2.0 for this product, which makes it not suitable for most New Build applications.
The finish is not as clean as other options, with folded edges visible.
Can not be moved into areas the installer can not access (if the ground is too close to floor joists)
Choosing Mammoth Blanket Options
Mammoth blanket is great to meet Healthy Homes Standards for your rental property. It's also a good affordable option for your own home if your budget is restrictive. However the low R value of the product makes it not suitable for new build.
Your budget will determine which R value you go for. However we would always recommend the highest R value you can afford.
Mammoth Section Insulation
Mammoth Underfloor Insulation Sections are the cream of the cream, the premium underfloor insulation option. These sections fit snug between the floor joists and offer a high R value and a clean finish leaving no gaps or doubts.
Clients who have gone for this product often comment how it makes the crawl space or underfloor feel instantly clean and tidy, and deadens sounds going through the floor.
Specifications of Mammoth Underfloor Sections
Mammoth underfloor sections are 20mm oversized to allow a snug friction fit that means they stay in place and do not move.
Standard sections widths are: 370mm, 425mm, 475mm, 580mm.
However the R3.2 option only comes in 370mm and 425mm.
The R values of Mammoth Underfloor Sections are high: R1.9, R2.8, R3.2, R3.4, double layer R3.8.
R1.9 depth is 90mm, R2.8 and R3.2 and R3.4 is 140mm, and double layer R3.8 is 180mm.
Mammoth Underfloor Sections Pros and Cons
Mammoth Underfloor Section Pros
Quick and effective install.
Very high R values for premium results.
Clean appearance and long lasting.
Fills joist spacing leaving a flat finish, especially if looking at lining.
Mammoth Underfloor Section Cons
The most expensive underfloor insulation option we offer.
Needs consistent joist spacing, otherwise installation takes extremely long.
Thick, needing deep joists for most R value options.
Choosing Mammoth Underfloor Sections as your Underfloor Insulation
Mammoth underfloor sections are a brilliant option, perfect for new build under floor insulation with its high R value and clean finish. It is a great option for retro fit as well, so long as the joist spacing is standard to the width of the product.
If you're looking for the premium underfloor product we supply and install, this is the one for you!
Conclusions
Hopefully you have a much better idea of your underfloor options! If you're still not sure or you're ready to go ahead, get in touch now for a chat about the next phases.
If you're interested in the pricing and how much your project will likely cost, the price per m2 for these products is posted on our "underfloor" page on the website.
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