PIR Insulation Boards 101: Everything You Need to Know

PIR Insulation Boards
  • Author: Fazal Umer
  • Posted On: June 1, 2023
  • Updated On: June 1, 2023

Buying insulation for your home or office can be a difficult task. And the dozens of insulation products available don’t make it easier either. Apart from traditional choices like glass wool batts and spray foam, rigid foam boards have been all the rage for the last couple of decades. So, what’s all the fuss about?

Well, here too, you have a lot to choose from. If you want exceptional thermal efficiency, high fire and moisture resistance, and boards that can be used just about anywhere, there’s no better value than PIR insulation boards. You can order them from renowned local brands in a range of thicknesses to suit your application.

What Are PIR Insulation Boards?

Short for polyisocyanurate, they are a type of thermoset polyurethane rigid foam with a closed cell structure. The material is made using a blowing agent at high heat and different additives before being cooled and formed into solid boards. These display very high thermal efficiency, good structural integrity, and, with the addition of metallic facer and backer materials, high moisture resistance.

Compared to other rigid boards, like the very similar PUR and older variants, such as XPS and EPS, these boards keep more warmth in without being as thick. Standard thicknesses range from an extra thin 25mm, good where space is tight, to extra-thick 150mm boards where there’s the need for the best possible efficiency. Sizes in between, like 60mm PIR insulation are a versatile option for different parts of a building and to good effect.

The Range to Choose From

The majority of PIR products are solid boards with thin aluminium foil bonded on either side. This prevents the buildup of moisture and enhances the structural integrity of the surrounding walls.

The boards work well for external applications as well. There is a polyisocyanurate plasterboard that is used in interior walls and roofing insulation when connected to plywood. PIR boards are put in the hollow walls of new construction projects to comply with tight restrictions regarding heat efficiency and building codes.

Various reputable UK businesses offer a selection of polyisocyanurate insulation boards, and each is made with a particular function in mind, simplifying purchasing.

Where Are They Used

Standard polyiso boards can be used throughout a building. They make excellent roof, wall, ceiling, loft, and floor materials. Older homes with uninsulated roofs typically have boards installed under the rafters, but boards installed above the rafters retain more heat.

In solid floors, they sit above or below the brickwork, and in suspended timber floors, they are used between or above the joists. Also, especially cavity walls, they function effectively in a variety of internal and external wall types.

Why Thicknesses and Sizes Matter

The thermal efficiency of an insulating product in projects depends on the material, the method of manufacture, and the thickness. Generally speaking, a rigid board will perform better the thicker it is. However, it may cost more and be restricted by the location of the boards.

Older homes may have limited space, yet even here, insulation of any kind is beneficial. Even thinner PIR boards will increase comfort and warmth without costing much, given that the UK has some of the highest rates of homes with no insulation.

Factors that determine the thickness of the boards are the level of thermal performance you’re after, the available space, and how much you’re willing to pay. To get a better picture of how boards perform, look to either lower thermal conductivity numbers or U-values (stated as Watts per Metre Kelvin (W/mK)) or related R-values (the resistance to heat flow) in metres squared Kelvin per Watt (m2K/W).

Boards optioned in 60mm PIR insulation will be more than enough for moderate uses in walls, whereas floors and roofs may need thicker boards. What’s of note is that boards can be used side by side, either in the same or different thicknesses, without compromising performance.

Most polyisocyanurate boards are in the standard building dimensions of 1200 by 2400mm, though you’ll also find them in 1200 by 1200mm or 600 by 600mm. The smaller sizes are often used in roofing insulation. Either way, the board is easy to cut to shape with simple tools, and even easier to install.

Favourable Properties and Comparison to Other Rigid Foam Boards

Not only do PIR boards have higher R-values than other insulation boards, but they also have way more than alternative materials like mineral and glass wool and spray foam. This means that to get the same level of thermal efficiency, boards can be thinner.

As mentioned, thinner boards are also cheaper, so you’ll be saving money, especially in larger projects covering a substantial area. Besides their exceptional thermal performance, these boards also excel in other key areas.

  • PIR is very durable, holds form throughout the lifetime of the building, and lends its rigidity to other building elements. Not only does it retain a lot of heat inside, but it also adds strength to the surrounding parts. The material also doesn’t shrink or rot. In addition, boards can withstand higher levels of pressure and impact, so they are good for flooring applications with high foot traffic, such as schools and hospitals. Only XPS boards have higher compressive strength but fall well short of their rated R-values.
  • It has very high flame and smoke resistance, meaning it will slow the spread of flames, and reduce the amount of smoke in the event of a fire. Some variants, with a higher isocyanate concentration also claim to be completely fire-resistant. Compared to PUR, XPS, and EPS boards, the PIR insulation board performs much better in fires, resisting melting and dripping. In this sense, it is only surpassed by newer phenolic boards but still qualifies for strict fire standards.
  • With high resistance to humidity and moisture, largely due to the closed cell structure and backing foil, PIR boards work extremely well where this can be an issue, such as external walls and roofing.
  • Despite being denser than other rigid foam boards, polyisocyanurate is very lightweight, weighing just 3.2 kilogrammes per square metre, so it is also easy to lift and handle during installation.
  • Polyiso boards are also eco-friendly, requiring less energy to produce and being recyclable. They have fewer toxic substances than their closest rivals, PUR boards, and produce considerably less waste when cut. On the green scale, they are on par with EPS and XPS boards.

Final Thoughts

The cost of these boards has substantially reduced in recent years, mainly due to the uptake of newer insulation solutions. They are now less expensive than EPS and XPS boards and more accessible than PUR variants.

Compared to all of these, though, polyisocyanurate boards have the highest thermal rating, perform better across the board, and their superior qualities make them the material of choice for a range of insulating tasks. They come in various thicknesses and sizes, and manufacturers have distinct lines for boards used in walls, floors, and roofing. When buying, go with trusted UK brands.

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Author: Fazal Umer

Fazal is a dedicated industry expert in the field of civil engineering. As an Editor at ConstructionHow, he leverages his experience as a civil engineer to enrich the readers looking to learn a thing or two in detail in the respective field. Over the years he has provided written verdicts to publications and exhibited a deep-seated value in providing informative pieces on infrastructure, construction, and design.