INTERNAL WALL INSULATION   

Internal wall insulation is an economic and alternative way to insulate solid masonry wall with inner insulation designed to increase the thermal performance and improve its airtightness. Most often it requires the use of PIR rigid boards, phenolic boards or rock wool roll. The thickness of insulation needed to insulate the wall internally strongly depends on the specific U-value that you want to achieve. A lower figure means better thermal performance. Current Building Regulations require a maximum U-value of 0.3W/m2 for existing buildings (0.16W/m2 for new buildings). Achieving that U-value for solid walls will mean installing at least 120mm of Kingspan, Xtratherm or Celotex rigid insulation. However, Kingspan Kooltherm® K118 is the most commonly used insulating material that meets current U-value requirements with just 50mm (62.5mm) thickness. Since is only 50mm thick it is a top-class three-in-one product for internal wall insulation used as mechanically fixed and adhesively bonded 'dot and dab' insulated plasterboard. The Kingspan Kooltherm K-range comprises the thinnest commonly used insulation products for any specific U-value. With a fibre-free rigid thermoset phenolic core, and a thermal conductivity of 0.018 - 0.023 W/mK, these are the most thermally efficient insulation products commonly used in internal wall applications. There are many other popular UK products such as Knauf EPS Thermal Laminate or Gyproc ThermaLine Basic Insulated Plasterboard. However meeting specified U-value requirements won’t be possible with such materials as it is low cost product based on EPS core designed only for single walls. For instance, if you insulating less than 50% of the room. All other internal insulation products would require bulkier product to be used: 120mm Celotex PIR, 150mm of Knauf® or Rockwool® Mineral Wool and 200mm of EPS100 polystyrene. It is worth to mention insulation called 10mm Sempatap Thermal Wallpaper. This type of insulation became extremely popular in the UK due to their unique ultra-thin thickness properties. Internal insulation will straightforwardly absorb sound waves and reduce vibration due to its density. Because of that, it promotes comfort and privacy, protecting people from ‘outside-to-inside’ noise such as traffic, and ‘inside-to-inside’ noise from neighbouring dwellings. If you insulate more than 50% of the internal walls of the room you need Building Regulation approval. If you live in a house with no cavity walls it is not recommended to use such insulation as it may get you damp problems. If your house was built after the 1920s, it is likely to have cavity walls.
Internal wall insulation is 50% cheaper than external wall insulation but unfortunately less effective, potentially more problematic and more disruptive. It needs careful planning as it more likely causes damp problems.
Also you should expect to lose at least 100mm on each wall when insulating interior walls. The thickness of internal wall insulation varies. You can expect it to be anywhere from 62.5mm to 200mm. 

IS INTERNAL WALL INSULATION WORTH IT?

Colloquially speaking if you don't have any other options to insulate your solid wall, an internal wall insulation system is the way to go, the more so as its cost is much lower. The major advantage of internal insulation compared to other insulation methods is nothing but the insulation cost. Regardless of the manufacturer, internal wall insulation will add physical thickness to the wall, most evident at the reveals and eaves, and also will keep the wall at external ambient temperature and thereby draw the dew point towards the internal surface. To help prevent damp penetration, a vapour control layer will need to be installed. It may also disrupt things inside your property in the way that any refurbishment would, so you won't be able to easily live in the house during the work. On the other hand the internal surface of an insulated wall will be warmer. Installing internal wall insulation is better than doing nothing, for sure. You have better payback than external wall insulation, which possibly makes it worthwhile overcoming mentioned problems. Moreover, internal wall insulation grants are available as part of the Government’s Energy Company Obligation (ECO). The scheme provides grants for home owners and private renters who would otherwise be unable to afford to insulate their homes. Grants are paid for by energy companies and the scheme aims to reduce fuel poverty while also reducing carbon emissions. 

INTERNAL WALL INSULATION COST

The costs given here are given in good faith as an indicative guide only and should be used with understanding. Insulationgo Limited cannot accept any liability for any budget produced using these figures.

The actual cost of internal wall insulation will vary according to the type of insulation specified. You should expect to pay anything between £10/m2 to £45/m2 and £130/m2 when a new stud wall is built. In terms of m2 coverage cost internal insulation can be classified in particular order:

• Fibreglass Insulation - £2.96/m²
  
• Rockwool Insulation -  £10.51/m²
• Insulated Plasterboard – polystyrene core (Gyproc ThermaLine Basic, Knauf EPS Thermal Laminate ) -  £16.31/m²
• PIR core Insulated Plasterboard - £18.78/m²
• Sempatap Thermal Wallpaper - £22.80/m²
• Phenolic core Insulated Plasterboards  - £41.16/m²

But when it comes to performance the list takes the following form:

• Phenolic Boards Insulation - Thermal Conductivity of 0.018W/mK
  
• PIR Rigid Insulation Boards - Thermal Conductivity of 0.022W/mK
• Rock wool Insulation - Thermal Conductivity of 0.035W/mK
• Fibreglass Insulation - Thermal Conductivity of 0.044W/mK
• Sempatap thermal wallpaper - Thermal Conductivity of 0.194W/mK

TYPES OF INTERNAL WALL INSULATION

Depending on the available space and your budget you can choose between 6 types of internal wall insulation.
 
1. PHENOLIC INSULATED PLASTERBOARD

Phenolic insulation bonded to plasterboard is a premium performance, factory-bonded wallboard to a fibre-free rigid thermoset phenolic core insulant. It provides a level of performance that is unrivalled in the world of rigid thermoset insulation materials with a thermal conductivity of just 0.018 W/mK across all thicknesses. Manufactured with a blowing agent that has zero ODP and low GWP, it is an insulated plasterboard for mechanically fixed and adhesively bonded insulated dry-lining. Provides internal dry lining and insulation in just one fixing operation, giving faster completion times. Boards provide exceptional thermal performance for both new build and refurbishment projects. Can be plastered with either Thistle Board Finish or Thistle MultiFinish plaster. All boards are easily applicable measuring 2400mm x 1200mm. Depending on the design, you can choose from various brands. All of the brands offer a variety of sizes and thicknesses. Kingspan Kooltherm K118 and its alternative Xtratherm Safe-R SR/TB insulated boards are the most effective type of rigid phenolic insulation boards currently available in the UK.

Products:

Kingspan® offers Kooltherm K118 Insulated Plasterboard

Xtratherm SR/TB-MF Safe-R Insulated Plasterboard

Cost: £35.42/m² (ex VAT) 62.5mm, £25/m² installation
Disadvantages: expensive to buy, causes pipework corrosion.

2. THIN THERMAL WALLPAPER

Sempatap Thermal solid wall insulation is a 10mm thick roll of insulation manufactured from latex foam that’s faced with a coated woven fiberglass layer. It’s been used in many applications by local housing authorities, private landlords and homeowners to minimise their energy bill and improve the thermal performance of their home. Sempatap thermal has been tested by numerous organisations including the National Physical Laboratory whose results showed that it will reduce the ‘u’ value (coldness) of a wall by nearly 30%. Sempatap thermal not only has outstanding thermal performance but can also be used as acoustic insulation on walls and ceilings. It is easy and quick to install and the economic solution for insulating your home to reduce heat loss and lower your heating bills. It is applied much like wallpaper. Since it’s only 10mm thick there’s no need to fiddle with extending services. On a standard solid 9 inch brick wall, Sempatap Thermal can make the wall up to 30% more efficient offering thermal resistance of 0.194W/mK

Product:

Sempatap Thermal Wallpaper

Cost: £22.80/m2 (ex VAT) 10mm, £16/m² installation
Disadvantages: expensive to buy

3. PIR INSULATED PLASTERBOARDS

PIR insulation bonded to plasterboard is a high performance, easy to install polyisocyanurate insulation board, laminated to a piece of 12.5mm or 9.5mm tapered edge plasterboard. These insulated plasterboards also incorporate an integral vapour control layer, which helps to reduce the risk of condensation. Moreover, it provides a continuous layer of thermal insulation across studs in timber frame walls removing the ‘thermal shorts’ that occur at the framing which can reduce the insulation value of a conventional wall by up to 20%. Designed to achieve excellent thermal u-value where minimal cavity is required giving buildings continued thermal efficiency throughout their life span. In terms of thermal conductivity, panels can be classified as a middle class product offering 0.022W/mk. They are easy to handle and quick to install. All boards are easily applicable measuring 2400mm x 1200mm. Boards can be fixed with plasterboard screws or even adhesive, making it an easier option. The thermal laminates boards are suitable for direct bonding ('dot and dab') and mechanically fixed installation techniques. Therefore it has been incredibly popular due to installation time and cost. The ability to install quickly is a huge advantage. This 2 in 1 product brings a whole host of benefits to your home. Starting from low labour costs to low heating bills. Future costs will be kept down due to the energy efficiency of Thermal Plasterboard. In fact, 72.5mm Celotex PIR core insulated plasterboard turned out to be a great alternative to phenolic core 62.5mm Kingspan Kooltherm K118. 

Products:

Xtratherm XT/TL Insulated Plasterboard Thermal Liner

Xtratherm XT/TL-MR Insulated Plasterboard Moisture Resistant Thermal Liner

Celotex PL4000 Insulated Plasterboard PIR Thermal Laminate

Xtratherm XT/TL-MF Thermal Liner Mech Fix Insulated Panel

Cost: £24.15/m² (ex VAT) 62.5mm, £16/m² installation
Disadvantages: expensive to buy

4. EPS INSULATED PLASTERBOARD

EPS insulated plasterboard so called "Thermal laminate" or "Thermal basic" is a combination of a 9.5mm gypsum based wallboard, strongly bonded to expanded polystyrene (EPS) insulant that can be used internally in new build and refurbishment projects requiring a basic thermal upgrade. These types of panels are often associated with the brands such as British Gypsum, Knauf or Warmline. All brands offer thinnest insulated plasterboard as thin as 22mm thick and offer certified thermal conductivity of 0.038W/mK. Those types of insulation are no doubt the best available options in the UK. They are quick and easy to install measuring in length 2400mm and 1200mm in width. Omitting all the details it can be said that they were all designed to be a simple and effective way to improve the thermal efficiency in both walls and roof applications.

Products:

Gyproc ThermaLine Basic Insulated Plasterboard BG

Knauf EPS Thermal Laminate Insulation Board

Cost: £16.31/m² (ex VAT) 40mm, £16/m² installation
Disadvantages: suitable only where the basic level of performance is required

5. FIBREGLASS INTERNAL WALL INSULATION ROLL

Fibreglass insulation is essentially an insulating material that is built into your internal side of your wall. Glass wool is one of the most popular insulation used to insulate walls internally. It is probably the most common and non-combustible type of insulation used to insulate a wall from inside, however it’s itchy and gets everywhere with very little effort. If the insulation gets wet, you will need to replace it a soon as possible. To get decent thermal performance, you need a lot of insulation rolls which can quickly eat into your room space. However, it is the cheapest and most favoured option. This is one of the most popular types of insulation, mainly due to the fact it’s been around for so long and is widely available from most building merchants such as Screwfix, B&Q or Wickes. Being lightweight, it has a good thermal conductivity of 0.044 W/mK. 

Products:

Knauf Earthwool Insulation Roll 44 Combi Cut

URSA 10 Diverso Insulation Roll

Superglass APR Multi Acoustic Partition Insulation Roll

Cost: £2.96/m² (ex VAT) 100mm, £16/m² installation
Disadvantages: irritating during installation, takes a lot of space.

6. ROCKWOOL INTERNAL WALL INSULATION

Rockwool wall insulation is manufactured in sheets that are pre-cut to fit between wall timber frame construction. Boards will boost thermal performance and improve acoustics. Slabs are provided in sizes that are easily transportable and good for handling measuring 1200mm x 600mm. Rockwool and Knauf are main players in the UK market. General-purpose rock wool insulation boards such as RWA45, RW5 or RW3 are perfect for internal wall applications. Range slabs include the following thicknesses:
25mm ǀ 30mm ǀ 40mm ǀ 50mm ǀ 60mm ǀ 75mm ǀ 90mm ǀ 100mm 

Products:

RWA45 Rockwool Insulation Slab

RW5 Rockwool Insulation Slab

Rocksilk RS45 Knauf Insulation Building Slab

Knauf Rocksilk Flexible Insulation Slab

Terrawool TW50 Insulation Slab

Cost: £10.51/m² (ex VAT) 100mm, £19/m² installation
Disadvantages: irritating during installation, if any moisture settles in the insulation fabric it will eventually rot.

INTERNAL WALL INSULATION INSTALLATION

There are 4 basic methods of installing internal wall insulation. The most commonly used method is the insulated plasterboard Dot & Dab method. The installation process involves nothing but plasterboard adhesive. There are no physical holes left after this installation. Sheet stays originally flat with the paper coating intact. This method uses either British Gypsum Adhesive or Knauf Plasterboard Adhesive. Generally speaking, Dot & Dab methods tend to be 3 times faster to install as it takes between three and six hours to set, which means you could carry out jointing or skimming the same day. In contrast, plaster takes two to three days to dry. Second technique of fixing insulated plasterboard is called the standard timber method. In this particular situation, you should always mechanically fix wooden battens and screw the plasterboard to battens. This technique requires plasterboard screws, plasterboard wall plugs or other fixings in order to be ready to finish.
Metal frame is also considered to be one of the quickest options to insulate your internal walls. It is built to form a partition wall, offering flexibility to the layout of the space. Steel frame method offer strength and longevity that insulated plasterboard can’t compare with. Insulating the frame and particularly over the frame as well as between the joints stops thermal transfer. This makes the building more comfortable and energy efficient for the occupants.
There is also another method that has been in use in the UK and Europe for years. In fact, has been successfully installed in 1,000’s of flats and houses by Local Authorities, Housing Associations, private Landlords and homeowners. This remarkable thermal insulation is called 10mm Sempatap Thermal Wallpaper. Thermal wallpaper works by slowing down the rate at which cold walls soak up heat energy. Consequently, it insulates rooms considerably faster, in many cases increasing warm-up times by 65%. Thanks to its thickness, expertly blended material and advanced aerospace technology, this warmth is easily maintained even in the harshest weather conditions.

Related articles:

Does internal wall insulation make any sense? 

In search of the thinnest insulation.

5 Benefits of Insulated Plasterboard.

Debunking the top 3 myths about vapour barriers and foam rigid insulation

How to choose the right Kingspan insulation board for construction?

Rigid insulation board bonded to plasterboard. How does it sound?

Thinnest Insulation Solution for Londoners.

Cheaper alternative/equivalent to Kingspan insulation

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How to Dot & Dab thermal wall insulation boards. Kingspan K118, Xtratherm XT/TL.

What is U-value? What’s it all about?

Quality Phenolic foam boards.

What is Mineral Wool?

How to cut a PIR insulation board?

Spray foam insulation – is it really that good?

Video credit:https://www.youtube.com/watch?v=fHX0QOV4e8U