The Ultimate Guide to Insulation Boards

Picking the perfect insulation board can be a daunting task, with a huge range of options available. In addition to standard insulation boards, there are a variety of options designed for specific uses within a building. In this guide from Building Materials Nationwide, we’ll give an overview of the different thermal insulation products available, how they can be used throughout a building, and we’ll answer some key questions about the world of insulation boards. We’ll cover specialist products for floor insulation, cavity wall insulation, loft insulation, and flat roof insulation.

What Are Insulation Boards?

Insulation boards are one of the most common forms of insulation, solid boards made from a variety of materials, designed to either conserve heat or to block sound transmission within a building. Using thorough insulation within a building, be it a house or an office, will dramatically lower energy bills and keep rooms warmer. 

Insulation boards can be made from a range of materials. PIR and PUR foam boards are both popular choices. Either made from Polyisocyanurate (PIR) or Polyurethane (PUR), these are rigid foam boards that can be used throughout a building project, and tailored for specific areas like cavity walls or warm flat roofs.

Expanded Polystyrene insulation (EPS) or Extruded Polystyrene insulation (XPS) boards are also available for use. Both polystyrene-based, XPS is extremely pressure-resistant, making it useful for floor insulation, while EPS is more affordable. You can also buy solid glass wool boards, offering strong levels of thermal insulation in a variety of settings.

Older models of insulation boards sometimes contained asbestos, but its use is illegal today. If you believe the existing boards installed within a building contain asbestos, you should engage the services of a licensed professional to examine and remove it rather than doing it yourself. Handling asbestos can be very dangerous, and should be left to trained and protected asbestos management specialists.

How to Cut Insulation Boards?

Rigid foam boards can be simply cut with a utility knife and ruler, as long as they are held on a solid surface. They can also be cut with a table saw. If using a table saw it’s important to use a mask and to ventilate your room. EPS can be cut with a knife or saw, but this will tend to leave a messy surface due to the structure of the board. A cleaner option is to use a hot wire cutter, which can produce a far cleaner and more accurate cut. XPF can be cut with a utility knife if it is too thick for a hot wire cutter. Glass wool boards are also best cut with a utility knife, using a ruler to ensure a clean and accurate separation.

What Brands Make Insulation Boards?

There are a variety of leading brands within the insulation board industry. Celotex is among the most recognised manufacturers of insulation boards, making standard plasterboards, insulated plasterboards, and boards for use throughout a house. Kingspan is the market leader for insulation and produces a range of high-quality boards suitable for various uses within a building project. Recticel produces standard insulation boards, as well as insulation boards intended for use within flat roofs or cavity walls.

We also stock a variety of other insulation board manufacturers, such as Ecotherm, Knauf, and Styline. These can be general boards or boards designed for specific applications. There are also manufacturers of sound insulation boards, built to decrease unwanted noise within a building. You’ll also find a large selection of foam boards and polystyrene insulation boards on our site.

How Can You Use Insulation Boards for Wall Insulation?

When talking about using insulation boards within a wall, we are talking about three separate things, insulating an exterior wall, an interior wall, and a stud wall.

When looking for exterior wall insulation, solid boards can be attached to your external wall using adhesive mortar. You will need to use an insulation board specifically designed for external walls, as it will need to offer water resistance. Fitting external wall panels is a specialist task, and likely beyond the abilities of a non-professional.

When looking to use insulation boards as internal wall insulation you have two options, attaching an insulated plasterboard to a solid wall, or building an internal stud wall and attaching insulation boards. To attach boards directly to the wall, you can use insulated plasterboards like British Gypsum's Thermaline Basic or Warmline’s PIR Insulated Plasterboard. These will need to be attached to your solid wall using plaster or adhesives, and held in place with extra fixings, with all joints between boards sealed. This will leave you with an insulated plasterboard wall that can be decorated.

Alternatively, you can build a timber or metal stud wall (sometimes called battening a wall) against the internal facing of your exterior wall, and insulate that. Stud walls can be filled with standard insulation boards like the Kingspan Kooltherm K112 PIR insulation board. They can then be topped with plasterboards, or even with insulated plasterboards if you are looking to maximise insulation.

For more information about sourcing and installing wall insulation, we have a series of articles on our website, covering insulating an internal wall, an external wall, and a stud wall.

View All Insulation Boards

Thermal Insulation Boards For Cavity Walls

Insulation boards are available for cavity walls on houses, and we have a wide selection available through our website. Unfortunately, these boards are only suitable for installation during the building process, as solid cavity walls would otherwise have to be removed to install them. We have a guide on our website to blown cavity insulation, the only option for those in a house with cavity walls. If you would rather insulate yourself, or your cavity walls are unsuitable, then using insulation boards on the external or internal facings of your cavity wall will offer a strong level of thermal insulation.

How Can Insulation Boards Be Used For Loft Insulation?

Within a loft, rigid insulation boards can be installed between roof joists, much like mineral wool batts or slabs. They can be simply cut to size and installed. If looking to use your loft for storage space you will need to install chipboards over the joists as loft flooring. Insulating your loft floor will give you a “cold loft”, meaning that the heat will be protected within the rest of the building but the loft will be cold. 

If looking to use your loft space as a living area you will need to insulate between or over the joists of the roof instead. You can install the boards between joists, making sure to leave a gap of 50mm between the board and your roof. Alternatively, you can attach them on top of the joists. In some cases, it may be beneficial to install both between and over the joists of your roof to fully insulate your loft. General insulation boards like Ecotherm Eco-Versal PIR boards can be used for loft and pitched roof insulation. Insulation boards can also be attached to the back of a loft hatch, to further limit heat loss.

For more information about loft insulation boards, we have an article on the costs of loft insulation.

How Can Insulation Boards Be Used in a Flat Roof?

Flat roofs contain a layer of insulation installed during the building process. This can be placed in two separate ways, either as a warm roof or a cold roof, with warm being the most common in the UK. Warm flat roofs are built with a base timber deck, topped with a vapour barrier, an insulation board, and then a waterproofing layer. Conversely, a cold flat roof has insulation boards installed between wooden joists, topped with a raised timber deck and a waterproofing layer. There are specific boards for these purposes, like the Recticel Powerdeck F for warm roofs and the Kingspan Thermaroof TR26. Insulating a flat roof, or upgrading it, is a job that will require a professional. To fully insulate a flat roof may require putting boards within the roofing system and between the joists below the deck.

How Can Insulation Boards Be Used For Ground Floor Insulation?

For a house built with a suspended wooden floor over a cavity, soft insulation like mineral wool would traditionally be used. In modern homes, there will usually be a solid concrete floor instead, which can be covered with insulation boards. There are options like the Kingspan Kooltherm K103 Floorboard, or the Dow Floormate 300A, which provides thermal insulation while still offering great strength for floors with heavy loading. Installing additional insulation boards within your ground floor will necessitate removing all flooring and installing over the base, which can be a time-consuming and costly process.

There are also underfloor heating insulation boards specifically designed for installation within underfloor heating systems, such as the Flexel Ecomax and the Ecotherm Eco-UFH. Underfloor heating insulation is a vital aspect of effective underfloor heating.

While you should check the specific instructions of your chosen insulation board before attaching it, there are a series of common ways to install insulation boards. You can use construction adhesive to attach insulation boards to wooden surfaces. A more common method would be to use screws or nails, sometimes in conjunction with adhesive.

For solid walls, your options are to attach it using dot and dab with a spray adhesive or to install it within a stud wall. For installing in a stud wall, you can simply cut boards to size and insert them snugly into the wall. You can use insulation foam to plug any gaps.

What Thickness of Thermal Insulation Board is Needed?

There are different levels of recommended thermal insulation throughout a building. This table lays out how much you should be looking to install throughout a project. In cases where one board does not adequately meet that thickness, you can use two together.

Are Insulation Boards Flammable?

All insulation in the UK must pass fire safety standards, being either fireproof or treated with a fire retardant. Insulation will still be flammable past a certain temperature, but should never contribute to a fire. You should always check the safety ratings of any insulation board you are using, as some will be unsuitable for larger buildings. There are risks with PIR and PUR foam boards of releasing toxic gases should they be combusted.

How Much Do Insulation Boards Cost?

While the costs of insulation boards designed around specific uses, such as those used for flat roofs or cavity walls, can differ, most thermal insulation boards cost between £10 and £15 per square metre. Through our website, we have a wide range of insulation boards with clear pricing. When looking for cheap insulation, we are sure to have appropriate options.