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Insulation Board Buyer's Guide
insulation board is an all-rounder product used in almost every part of a building, whether it's roofs, walls or floors. It's a thin product that doesn't compromise on its insulation properties. The boards are faced with different materials such as paper, bitumen, glass fleece, or plasterboard, but it's more likely you will come across foil backed insulation (boards faced with aluminium foil).
Benefits of using Insulation Boards:
The obvious benefits are of course the savings on your energy bills and the impact on your quality of living. And obviously it doesn't take up as much space compared to other insulation options such as Fiberglass for instance.
From Kingspan to Celotex, all the leading brands offer a large range of insulation boards. With so many options, it can be tricky when it comes to choosing the best thermal insulation board for your project. In order to help you make the right decision, we will give you an overview of what's available on the market.
We will cover the following subjects:
- Insulation board material
- Facing options
- Where can you install an insulation board
Insulation board types
There are many types of cheap insulation board for sale. Some of the most popular types include the following:
PIR insulation board — Ideal for most applications such as floors, walls, and roofs.
Polyisocyanurate — (also referred to as PIR or Polyiso) has 50% better thermal efficiency than Polystyrene. It is more available and tends to be cheaper as well.
Rigid phenolic insulation is ideal when you need to save space without compromising on performance.
- Phenolic insulation is a rigid foam insulation board sandwiched by two flexible layers
- It is more efficient and has lower U values than the PIR boards for the same level of thickness
- It is popular in low energy design such as passive house due to its low thickness and meets the Building Regulation standards
They are generally more expensive than PIR boards of the same size. The Kingspan Kooltherm range is a good example.
Polystyrene boards - also known as Styrofoam or Aeroboard. Very rarely used nowadays as they are extremely flammable which rules them out in most applications.
Extruded polystyrene (XPS)
- Used for specialist applications
- XPS is strong when compressed under load
- This is mostly for specialist applications like in car parks and commercial floors but can be applied to more general application. You can find XPS on a plywood frame for instance.
Expanded Polystyrene(EPS) Foam Insulation
- EPS insulation board are used for specialist applications
- EPS is a good and inexpensive insulator.
- EPS insulation board are found in basement walls and areas where space isn't at a premium.
Insulation Board: Facing options
The perfect solution for internal solid wall upgrades. Directly bonded to the board, which means its also quicker to install.
A good example of insulated plasterboard is the Celotex PL4000 range.
A foil backed insulation board reflects heat back into the building and significantly improves the U-value.
Additionally, you can create an effective vapour barrier by taping the seams with insulation board tape.
Glass tissue (external wall)
This is an excellent option for reducing heat loss from your walls if you do not have cavity walls. It’s a rigid insulation board that is fitted on the exterior walls of your house. It's used behind both render and dry cladding and provides excellent thermal performance.
PIR Plywood Laminate
Plywood laminate is an insulation board bonded to plywood. It is designed for flat roof systems which will be covered with a waterproofing felt layer. It cuts down on installation time and cost and also reduces the risk of condensation.
Bituminous waterproof facing
Insulation board attached to a bituminous layer for use in warm flat roofs. It's used under torch-on, bituminous waterproofing systems. Again, it cuts down on installation time and labour costs.
Where can you install insulation boards?
- Inside walls can be insulated with plasterboard.
- For outside walls its best to use insulation board with an external-facing render
You're still getting high u-values while making the best use of the space available. Other construction costs can be reduced by using smaller fasteners and timber studs.
Insulation board are more likely to perform well over the entire life of the building as it doesn’t slump or sag over time like glass type insulation. There is no risk of gaps appearing and the boards can be easily sealed to achieve even better airtightness and thermal performance.
Solid wall insulation is labour-intensive as it covers the original brickwork. The same goes for internal wall insulation, it is advised to get a professional to install it.
Boards for the outer side of the building
There are two types of insulation board that can be fitted on external walls
- Expanded polystyrene Insulation Board (EPS Insulation board)
Boards for pitched roofs
Insulation boards are commonly used in pitched roofs. It can be used between, over or under the rafters, depending on the application.
- Joist level rigid board which is installed right above the ceiling
- Rafter level rigid board is installed below the roof
The choice of installation depends on the roof layout (warm or cold) and therefore needs careful evaluation.
At joist level, if you are intending to walk on the boards, you will need to put a layer of chipboard on the boards. This will help to divide the weight evenly along the boards and joists.
We recommend using boards which have a foil coating on one or both sides as this will help reflect the heat back in. The foil should be pointing towards you when you look at the rafters to make sure the heat is reflected back in the home.
For this, a combination of cutting tools like a fine-toothed saw, a rigid board cutter or even a Stanley knife will do the trick.
Make sure to check the measurements and get the cutting right at once to ensure there is no waste.
Boards for flat roofs
Insulation boards are the most common form of insulation in flat roofs.
Since insulation boards have great compressive strength, they are able to withstand foot traffic.
This is an important consideration in modern roofs with single-ply construction. With other materials, there is the risk of compression which could cause water to pool and the roof to leak.
They can meet or exceed current requirements without needing as much space as other forms of insulation.
Rigid insulation is easier to work with. It’s light, simple to cut and easy to handle which is important in roof applications.
As there is a lot involved to make sure it meets regulations, we recommend hiring a professional when insulating a flat roof.
Boards for floors
Floor insulation is an area often overlooked that can bring significant reductions in energy consumption.
The thermal performance of an uninsulated domestic floor is usually fairly poor. The greatest heat loss through an uninsulated floor occurs at the edges.
For suspended timber floors, installing insulation between the joists is the best solution. Using a fibrous material underneath the netting is not as practical. It would deteriorate the performance of the board, invite the risk of sagging and affect the performance too.
To insulate a suspended timber floor, you place insulation between the timber joists and under the floorboards. This is easier said than done, depending on the space below and the difficulty in removing floorboards to get in.
If, there is enough void space underneath it may be easy enough to install insulation by removing a few floorboards at the side of the room. This would allow access to the void space.
If it's a relatively new floor, the floorboards may be tongue-and-groove. If that's the case they will all have to be removed.
This is, of course, more time consuming and not very economic. So unless you need to carry out additional work that requires to remove the floor, we don't recommend that method.
Board for cavity walls
Most modern buildings have two walls. An outer wall and an inner wall with a gap in between them to stop the wind and the rain. In order to stop the heat to radiate through this gap, you need cavity wall insulation. Nowadays, all newly built properties have cavity wall insulation as part of the building process.
When cavity walls were first designed heat retention wasn’t a priority, so the vast majority of homes weren’t built with adequate insulation. If that's your case then blow-in insulation is most commonly used to insulate existing cavity walls.
With new builds you have two options when it comes to using insulation board in cavity walls:
Partial fill cavity wall insulation
Partial fill cavity wall application is an effective barrier against rain penetration. The insulation is fixated on the inner leaf to give a clear cavity. Here the door and window openings are closed with cavity closers to safeguard the cold bridging. For instance, the Celotex CW 4000 range cavity wall works in exactly the same manner.
Full fill cavity wall insulation
New innovations in insulation board such as the Celotex CF5000 range, allow the full cavity to be insulated with rigid board. They are specifically designed with a rebated edge to eliminate the passage of moisture. This maximises thermal performance without the requirement to widen the cavity.
Here's a simple video tutorial on how to cut and install insulation board
Other things to consider when choosing Insulation boards
It's all about the planning. Have your insulation delivered 2 to 3 days in advance, some manufacturers have longer lead time, so don’t wait until the last week to order. This will give you a bit of breathing space in case of unforeseen circumstances. Similarly, if you need accessories make sure to buy them in advance as well.
Always buy new boards, don't be tempted by "seconds". “Seconds” are boards that didn’t make it through the manufacturer's quality control process. It's a gamble, as some insulation board can come with air bubbles the size of your fist but you have no way of knowing just by looking at them.
That might be ok on a small project like a shed but you should definitely avoid it on a new build. Seconds can lead to problems like thermal bridging and condensation spots.
If your building contractor is supplying the insulation, check for receipts to make sure you are getting new insulation boards.
Check out the board thickness
Rigid boards are available from 20mm to 200mm. As the thickness of the board increases, so does the thermal performance. With an increment of 15mm from the last size, you can choose the one that best suits your design.
A good benchmark for the level of insulation you should be looking to achieve is 0.21 W/m2K.
However, in order to achieve that standard using the regular insulated dry-lining panels, you would require a panel 100mm thick. Including the plasterboard that is bonded to the insulation. This can be an issue in terms of losing space in rooms or in corridors/stairways.
If your walls currently have little or no insulation, you can significantly reduce heat loss with internal insulation. In this case, the wall insulation board is essential.
Get familiar with the u-value
The lower the U value, the better the heat retention in the property. For example, when using a typical rigid board of 50mm, it is equivalent to a U value of around 0.4, 100mm is equivalent to 0.25 and 150mm and thicker is a U value of 0.2 or lower.
Things to keep in mind when choosing insulation Board
Insulation boards are more expensive than Fiberglass. Sometimes up to ten times more expensive for twice the performance. They are also more easily damaged on site.