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BEST FLOOR INSULATION*
The temperature of a non-insulated floor can vary between 8-10c. Adding just 100mm of insulation can significantly change floor temperature up to 18-20 degrees. This means we could create a physical barrier to both the heat and cold side. In this article we will focus on some basic insulation options, their costs and the most popular thicknesses used to insulate the floor. Further in this article, you can read which insulation is best - boards or rolls.
TABLE OF CONTENTS
- BEST FLOOR INSULATION
- FLOOR INSULATION OPTIONS
- FLOOR INSULATION COST
- FLOOR INSULATION THICKNESS
- FLOOR INSULATION BOARDS
- FLOOR INSULATION UNDER CONCRETE
- FLOOR INSULATION ROLL
- FLOOR INSULATION SLABS
- FLOOR INSULATION 100mm
FLOOR INSULATION OPTIONS
Depending on your specific floor build up and situation, you may need solid boards or loose laid rolls. While roll insulation is usually a cheaper and faster option to fit, boards are definitely more convenient to install. However, in terms of acoustic properties they don’t perform anywhere near as good as insulation rolls. Unlike high dense rock wool rolls, they are light in weight which means they are not a good sound absorber. However, taking into account their low thermal conductivity ranging from 0.018 to 0.031W/mk, we can save a lot of space. For instance, 50mm phenolic boards such Kingspan K103 are considered to be one of the best rigid, closed-cell structure materials for floor insulation at present being up to 50% more effective than other common insulation materials such as expanded or extruded polystyrene.
When building or renovating a floor they are really 3 main kinds of insulation options you are going to have to choose from:
- Rolls - Ursa, Isover, Rockwool, Knauf, Superglass
- Slabs - Rockwool RWA45, RW3, RW5, Knauf RS45, RS60 and RS100,
- Rigid foam panels such as Phenolic foam (PF), Polyisocyanurate known as Polyiso (PIR), Expanded Polystyrene (EPS) and Extruded Polystyrene (XPS) - often called Styrofoam.
Read everything about insulation rigid boards here.
Read everything about insulation phenolic boards here
Read everything about insulation polystyrene here
Read everything about insulation rolls here
Read everything about insulation slabs here
FLOOR INSULATION COST
The amount of money you spend on floor insulation can vary greatly depending on the type, so it's important to know what you're getting before you buy. Here, we bring you a complete comparison of floor insulation costs.
Remember - the total floor insulation cost has two parts. The cost of materials and the cost of installation. As of 2023, the average cost for suspended floor insulation is £165 per m2. That includes the 100mm Kingspan K103 board and installation cost. In fact, phenolic boards such as Kingspan K103 will likely be the most expensive of all the rigid foam insulation options available on the UK market.
On the other hand, PIR insulation boards combine thermal efficiency with an economical price point, although the slightly better thermal performance of phenolic foam may justify the increased cost if depth in the floor construction is at a premium.
However, EPS leads the other floor insulation products when it comes to R-value per £ because manufacturing costs of EPS are generally lower compared to other insulating materials like PIR or Phenolic Boards.
As for the price, XPS polystyrene is cheaper than Phenolic boards but more expensive than EPS polystyrene.
Floor insulation rolls work out cheaper therefore they become the most favoured option from all of available insulation types. Floor insulation rolls normally cost around £25-27 per roll.
Naturally, costs will vary depending on the size of the room and the type of floor. As far as home improvement jobs go, this one is relatively reasonable regarding pricing. Prices depend on whether you do it yourself or get the professionals in.
Having a timber floor insulated professionally, including filling the gaps between the floorboards and around the skirting, depends on the size and shape of the room and the insulation material used, but typically costs as of 2023 around £960.
The cost of insulating a concrete floor can vary greatly, especially if the concrete is removed or additional works are done, but costs will probably start around £1,450.
According to the Energy Saving Trust you could save between £40-£65 per month on your energy bill through good floor insulation.
If you are looking for the cheapest place for floor insulation, an online insulation shop is the way to go. It is because products come to you directly from the manufacturer without involving middlemen
FLOOR INSULATION THICKNESS
The building regulations require that floors achieve minimum thermal performance U-values and this affects the amount of insulation required. Achieving a U-value of 0.25 W/m2K or less would require at least 70mm of Phenolic high-performance foam insulation called Kingspan® K103, 150mm of Knauf® or Rockwool® Mineral Wool and 200mm of EPS100 polystyrene. In the case of PIR Rigid Insulation Boards, thickness of 100mm is normally used. In terms of XPS boards such as Soprema SL or STS, 50mm thickness is sufficient for the floor insulation.
If you are concern about compressive strength of the floor insulation material, you should consider buying XPS extruded polystyrene board with the highest compressive strength ranging from 300kPa to 800kPa, followed by PIR rigid insulation boards (150kPa) manufactured either by Kingspan, Celotex, Xtratherm, Iko-Enertherm, Ecotherm or Recticel GP.
The most popular thicknesses for insulating floors are 50mm, 75mm, 100mm and 150mm. Thinner insulation boards, ranging from 12mm to 50mm are offered by Celotex, Xtratherm, IKO Enertherm, Ecotherm and Kingspan. PIR insulation boards are available in a range of thicknesses such as 12mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, 55mm, 60mm, 65mm, 70mm, 75mm, 80mm, 90mm, 100mm, 110mm, 120mm, 125mm, 130mm, 140mm, 150mm, 165mm, 180mm and 200mm.
FLOOR INSULATION BOARDS
When it comes to floor insulation boards you have got 5 options to choose from:
- Phenolic foam (PF) | 2400mm x 1200mm (8’ x 4’) size
Phenolic board is a top shelf panel that can be used to insulate floors in both new build and refurbishment of residential, commercial and industrial buildings. As a part of Kooltherm range, Kingspan K103 Floorboard offers fibre-free rigid thermoset phenolic core with thermal conductivity of just 0.018 W/mK across all thicknesses. In fact, K103 is a premium product in terms of floor insulation.
Product has been developed by Kingspan as a premium floor insulation board, providing high performing insulation with a thinner material than was possible before. K103 Kooltherm can be used on both solid concrete and suspending floors. Kingspan is followed by Xtratherm brand with SR/UF Safe-R Phenolic Floor Insulation Board. Xtratherm phenolic board offers thermal conductivity of 0.020W/mK and compressive strength of 150 (kPa).
Phenolic floor boards are the most expensive but also most productive type of insulation panels. Boards are mainly intended for investors who want to achieve the standard of an energy-saving or passive house. Panels have a slightly higher R-value and a slightly thinner profile than PIR boards due to the manufacturing process. While PIR offers the lambda value of 0.022 W/mK, phenolic closed cell foam offers 0.018W/mK. In fact, that is only 10% better than PIR.
Phenolic foams are produced with densities in the range up to 160 kg/m³. The exceptionally low thermal conductivity of closed cell phenolic foam boards means that appropriate insulation efficiency can be achieved with the thinnest possible material.
PRICE (m2): 100mm - £38
SIZE: 2400mm x 1200mm (8' x 4') (2.88m2)
THERMAL CONDUCTIVITY (λ–value): 0.018 W/mk
COMPRESSIVE STRENGTH: 120kPa-160kPa
ADVANTAGES: highest fire rating among many organic insulation materials, highly resistant to water penetration, resist attack by mould and microbial growth, thinnest possible insulation board.
DISADVANTAGES: most expensive, causes pipework corrosion when it gets wet, easily crushes when walked on.
- PIR insulation board, short for PolyIsocyanuRate (PIR) | 2400mm x 1200mm (8’ x 4’) size
PIR board is one of the most capable and valuable heat resistant materials used in UK constructions that can be used to insulate floors for energy conservation. Its rigid core is usually sandwiched between two aluminium foil facings that are high performance, thus creating a tough, hard wearing yet lightweight insulation board.
The major advantage of PIR compared to other insulation materials is the insulation value. The Lambda value of PIR is situated between 0.021 to 0.032 W/mK. This means that PIR offers superior insulation with the same thickness.
PIR insulation board is often associated with market leader Celotex company as they began producing rigid polyisocyanurate foam as first. In fact, Celotex invented the thinnest thickness of PIR insulation measuring only 12mm. Many PIR insulation brands, such as Celotex, Xtratherm, Kingspan or Recticel come with a grid marked on, which can act as a guide to help ensure the thermal insulation board is cut in a straight line.
Depending of thickness and brand, rigid insulation boards come in multiple name options, including Celotex GA4000, Celotex TB4000, Celotex XR4000, Xtratherm Thin-R, Kingspan TF70, Kingspan TP10, Kingspan TW55, Recticel Eurothane GP, Quinntherm, EcoTherm EcoVersal, IKO Enertherm ALU and Ballytherm PIR.
PRICE (m2): 100mm – £23
SIZE: 2400mm x 1200mm (8' x 4') (2.88m2)
THERMAL CONDUCTIVITY (λ–value): 0.022 W/mk
COMPRESSIVE STRENGTH: 120kPa
ADVANTAGES: wide applicability, provided with a vapour barrier on both sides, not corrosive to metal over time.
DISADVANTAGES: needs a nice, tight fit (for more information on how to cut PIR insulation click here).
- Expanded polystyrene called EPS | 2400mm x 1200mm (8’ x 4’) |1000 x 500 |1200 x 600 size
This product is a budget-friendly material because it has a high percentage of trapped air inside which makes it an excellent premier insulator. However, unlike XPS insulation boards, EPS panels have partially closed cells which may retain water and reduce its thermal properties.
EPS board requires slightly thicker levels to achieve the same thermal performance as PIR or Phenolic board. For example, while a project may call for 120mm of white EPS, the same thermal performance can be achieved with 70mm of PIR. On the other hand EPS polystyrene is said to be slightly easier to work with when cut. For more information on how to cut styrofoam click here.
Either Jabfloor or Kay-Metzeler range of insulation boards have been manufactured specifically for use with flooring. While EPS70 polystyrene is used to insulate floors between joists, EPS 100 is recommended to use under concrete, because it is a much denser material offering 100kPA compressive strength.
PRICE (m2): 100mm - £19
SIZE: 2400 x 1200, 1000 x 500, 1200 x 600
THERMAL CONDUCTIVITY (λ–value): 0.038 W/mk
COMPRESSIVE STRENGTH: 70kPa
ADVANTAGES: 100% recyclable, cheap to buy, easy to cut.
DISADVANTAGES: can attract ants and termites, fire class-E-F.
- XPS (EXtruded PolyStyrene) foam called ‘polyfoam floorboard’ or ‘styrofoam blue board’ 1250 x 600, 1265 x 615, 1200 x 600 size
XPS is a fully closed cell, high density, upgraded extrusion skin panel designed especially for floor applications. Chemically it’s made up of the same as EPS polystyrene but rather than being formed into droplets and then expanded, it is foamed up. Just like EPS, XPS is made of 98% air and just 2 % plastic.
XPS board has no thermal drift or loss of R-Value over time. It remains waterproof over the decades. XPS polystyrene has excellent compressive strength reaching 300-500 kPa which means it can easily cope with different flooring loads in different grades. Due to this fact, XPS is regularly used in applications where it is going to be under some strain, such as car park decks. For more information on differences between EPS and XPS click here.
XPS is typically supplied as blue, pink, green or yellow coloured boards. XPS is made by Styrofoam and Dow Company, green XPS called GreenGuard is made by Kingspan and yellow XPS is made by Soprema. While they are all the same, the colour helps distinguish manufacturing companies on job sites.
There are a few main manufacturers offering XPS products. While Soprema offers an SL version with compressive strength of 300kPa, Kingspan with its Greenguard GG offers either 300kPa, 500kPa or 700kPa. On other hand Polyfoam offers square edged xps standard board that has a middle class compressive strength of 200kPa.
PRICE (m2): 100mm - £26
SIZE: 1250 x 600, 1265 x 615, 1200 x 600
THERMAL CONDUCTIVITY (λ–value): 035 W/mk
COMPRESSIVE STRENGTH: 300kPa
ADVANTAGES: can withstand over 1000 freeze/thaw cycles, excellent compressive strength, below DPC level application.
DISADVANTAGES: can attract ants and termites, breaks easily, fairly expensive product.
FLOOR INSULATION UNDER CONCRETE
Cordek have created a wide range of Cellcore HX Plus void formers with an extra added insulation. This two in one solution is designed for use beneath reinforced concrete floor slabs to protect against the potential effects of ground heave with the additional Filcor EPS100 insulation layer protected by a ultra thin polypropylene sheet on top. HX Plus under slab is a combination product. In fact, it has a range of cellular legs with different depths of insulation glued onto the top of those cellular legs dependent upon the target U-value that you need to hit. It incorporates an integral layer of EPS insulation available in various thicknesses to meet thermal performance requirements. HX Plus is made in 25mm increments, which means insulation material ( Filcor ) is added.
PRICE (m2): 100mm - £36.50
SIZE: 2400mm x 1200mm (8' x 4') (2.88m2)
THERMAL CONDUCTIVITY (λ–value): 0.033 (W/mK)
COMPRESSIVE STRENGTH:
Safe load: 13 kN/m2 / Fail load: 18 kN/m2
ADVANTAGES: 2 in 1 product, easy to cut, straightforward installation, BBA certified.
DISADVANTAGES: fairly expensive product, custom product-long lead time (7-10 working days)
FLOOR INSULATION ROLL
Floor insulation roll is designed to help to retain heat in your floor. Floor insulation rolls are 1200mm wide and ready-cut to produce three, 400mm centre wide rolls, or two, 600mm wide rolls and manufactured to a minimum density of 10kg/m3 meeting the requirements outlined within related Building Regulations. It means you have no offcuts. The rolls are both lightweight and non-combustible (with an A1 Euroclass rating), with average thermal conductivity of 0.044 W/mK. This means they offer the worst thermal factor (the lower the better).
However, floor insulation rolls are easier to install correctly than other insulants such as PIR rigid insulation boards because they adapt to any slight imperfections in the substrate and knit together, eliminating any air gaps.
For more information on how to cut insulation roll insulation click here
Installing floor insulation rolls is a relatively easy task for the homeowner, as well as a great way to save on your heating bills. Common floor roll layers are: 100mm, 150mm, 170mm or 200mm.
Most popular floor roll turned out to be the 100mm Knauf Earthwool Combi-Cut 44 followed by 100mm ISOVER Spacesaver Glass Mineral Wool. Floor insulation rolls are available in various thicknesses covering 11m2, 15m2, 15.6m2, 24m2. Range of floor rolls features products from industry-leading manufacturers such as Isover, Knauf, Ursa, Terra, Rockwool or Superglass. The rolls of floor insulation you can buy come in lots of seemingly random thicknesses, for example 50mm, 60mm, 75mm, 80mm, 100mm, 120mm, 150mm and 170mm.
FLOOR INSULATION SLABS
Floor insulation slabs are essential to any noise reduction project and can be used to insulate floors especially. In fact, floor slabs allow any moisture to dry omnidirectionally - in other words both ways. These slabs are non-combustible, with a class ‘O’ fire rating and can be friction fit. Generally speaking, acoustic slabs can be divided into 2 main categories named as a mineral wool slab and stone wool slab. Different ingredients are used in the production of these acoustic slabs. While stone wool slab is made of basalt - volcanic rock (stone), mineral wool slab is made of glass cullet together with quartz sand. Both types of slabs come from well-known brands such as KNAUF® and ROCKWOOL®.
Floor insulation slabs start at a minimum density of 45kg/m³ up to 140kg/m³ and are manufactured to a higher density than other forms of insulation, unlike thermal insulation which is lower in density and supplied in rolls. When you normally use rolls for walls, slabs are normally for floors.
Floor slab range is available in a variety of thicknesses and densities. All slabs are 1200mm x 600mm. They also came with a range of densities and this is how compacted the slab is (not the weight). The range in density is kg/m³ from 45, 60, 80 100 & 140. It’s the density that marks out this type of soundproof floor insulation from other types of insulation. The easiest way to understand which one to choose would be to assume the higher the density, the better the overall level of soundproofing. It is recommended to use for the the floor 60kg/m³ option as this offers the best sound insulation for the money spent.
Common thickness: 25mm, 30mm, 50mm, 75mm, and 100mm
PRICE (m2): 100mm - £15/m2
SIZE: 1200mm x 600mm
THERMAL CONDUCTIVITY (λ–value): 0.035W/mK
ADVANTAGES: non-combustible material, excellent sound absorption characteristics, available in a wide range of densities, easy to cut.
DISADVANTAGES: fairly expensive product, unfaced material.
FLOOR INSULATION 100mm
The minimum required dimension of floor joists in the UK is 97mm x 50mm and 122mm x 50mm if the span is no more than 2.48m. This is the main reason why 100mm size is known as the most popular when it comes to insulating floors. Due to the fact that it is not much, the best variant to isolate the floor at this particular height would be the phenolic board called Kingspan K103 or Xtratherm SR/UF Safe-R. Second option to insulate a floor is either the Rockwool RWA45, RW3, RW5 or Knauf RS45, RS60 and RS100 slab. However, for unknown reasons, 100mm PIR boards are most often used to insulate the floor between the joists. Perhaps it has to do with its relatively low price compared to the products mentioned above. This insulation product it’s been around for so long and is widely available from most building merchants such as Screwfix, B&Q or Wickes.
The 100mm XPS or EPS polystyrene is less often used to insulate suspended floors as it may attract ants and termites. So once again, 100m phenolic foam board or Rockwool RWA45 is the product to go when insulating the floor between joists.
Related articles:
Difference between EPS and XPS polystyrene boards
An exceptional performance of rigid phenolic foam
Feel the difference with XPS boards
12mm Celotex TB4012 vs 15mm Xtratherm Thin-r
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