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Internal Wall Insulation Cost Guide

While internal wall insulation tends to be cheaper than external wall insulation, it does come with its own set of considerations. For example, it can eat into valuable floor space and changes the fabric of your home. If not installed properly, it can also cause issues such as damp and condensation. In this article, we explore the internal wall insulation cost, its pros and cons and provide tips on how to make the most of it without creating problems for your home.

Internal Wall Insulation Cost

Internal wall insulation is a popular option for homeowners looking to improve the thermal efficiency of their homes. However, it is important to note that this type of insulation is generally only recommended for certain types of homes. Solid wall homes made from solid stone or brick, usually built before the 20th century, tend to be the main candidates for this type of insulation.

What is Internal Wall Insulation?

Internal wall insulation is a method of improving the thermal performance of a property by applying insulation to the interior face of external walls. This can help to reduce heat loss and lower energy bills. There are four main methods of installation, with building a new stud wall being the most common. However, this is not always the most effective method.

It is important to note that internal wall insulation can be disruptive and require the removal and re-fixing of items such as switches, radiators, and kitchen units. Therefore, homeowners should carefully consider whether this is the best insulation solution for their home.

Creating an airtight layer is crucial, and particular care must be taken in awkward areas such as reveals and floor voids. Homeowners should seek professional advice to ensure that the installation is done correctly and efficiently.

How Much Does Internal Wall Insulation Cost?

The internal wall insulation cost varies depending on the desired finish and insulation value. It is recommended to hire an expert with experience to carry out the work. A completely finished wall has a price between £30 to £80 per square metre.

For those opting to use solid boards for internal wall insulation, there are entry-level and premium options available. An entry-level choice is the British Gypsum Gyproc TermaLine Basic. For a more premium model, the Warmline PIR Insulated Plasterboard offers premium thermal insulation.

Building a batten wall for internal thermal wall insulation is a time-consuming but not costly process. However, depending on the risk of continuing dampness in the property, it may be advisable to install a more costly metal stud wall.

There are several types of insulation suitable for a batten wall, including batts, slabs, and rolls. An environmentally-friendly choice is the Knauf Earthwool FrameTherm Roll, which is designed specifically to provide great thermal performance to external brick walls when fitted between timber studs.

Another option would be the Thermafleece Cosywool Natural Sheeps Wool Insulation, which boasts moisture regulation and excellent thermal wall insulation.

The batten wall can be topped with either insulated plasterboards or traditional insulation boards for increased heat retention. An option for insulated plasterboards is the Ecotherm Eco-Versal PIR Insulation Board, which offers great insulation and vapour control.

Another option would be the Celotex General Application Board, which are multipurpose boards manufactured from rigid polyisocyanurate.

What Building Regulations Apply for Internal Wall Insulation?

In order for a home to be compliant with Building Regulations, certain requirements must be met in terms of airtightness and heat loss. The U value of a material is the rate at which heat (in watts) is lost through each square meter of the surface, with a lower figure indicating better thermal performance.

For example, an uninsulated cavity wall typically has a U value of around 1.5W/m2, while a solid 225mm brick wall is around 1.9W/m2. A solid stone wall will range from 1.7W/m2 to 1.4W/m2, depending on thickness. Current regulations require a maximum U value of 0.3W/m2, with a more realistic target of 0.2W/m2. Achieving this U value for solid walls will require at least 100mm of rigid insulation, such as Celotex, Kingspan, or similar.

While insulation is important, improving airtightness has a greater impact on heat loss. The solid elements of the wall are naturally fairly airtight, but it is the gaps, cracks, and penetrations that can be problematic. These can occur in awkward places such as floor/ceiling voids, below the ground floor, and the first floor ceiling, as well as on accessible areas of the wall. Insulation applied to the wall can form an airtight barrier, but the benefit is reduced by up to 50% if gaps, cracks, and penetrations are not also addressed.

Overall, it is important to ensure that internal wall insulation meets the necessary U value requirements, while also improving airtightness by addressing gaps, cracks, and penetrations.

Does Internal Wall Insulation Cause Damp?

Internal wall insulation can lead to damp if not installed correctly or if the existing wall structure is not suitable for insulation. The insulation tends to keep the wall at external ambient temperature, which can cause the dew point to move towards the internal surface.

If the dew point is too close to the internal surface of the existing wall, moisture can be absorbed by the insulation and appear as damp patches on the plasterboard. To prevent damp penetration, a vapour control layer needs to be installed.

While the internal surface of an insulated wall tends to be warmer, reducing the likelihood of condensation forming, there are areas, such as where an external wall meets an internal wall, that remain cold. This can cause a distinct risk of condensation forming in those areas, typically in high-level corners. Overcoming this usually means extending the insulation to cover that cold bridge.

It is important to note that internal wall insulation can cause damp if not installed correctly or if the existing wall structure is not suitable for insulation. Therefore, it is recommended to seek professional advice before installing internal wall insulation.

How to Install Internal Wall Insulation?

Installing internal wall insulation is a complex process that requires professional expertise. It is crucial to address any dampness issues before starting the installation process. Additionally, any radiators or electricity sockets must be removed and reinstalled on top of either the solid insulation or the stud wall.

Hiring professionals to insulate the internal walls of your house can cost around £6000 to £12000 for a typical semi-detached home, according to the Royal Institute of Chartered Surveyors. However, if you have the experience and time, you can insulate a single room or one side of your house.

To attach solid boards, you can use a specialist adhesive or mechanical fixings. The gaps between the boards should be sealed with mastic and then covered with a skim of plaster. The boards should cover the entirety of the floor to ceiling to ensure the vapour barrier of the insulated plasterboards. Any gaps in insulation can cause cold bridging in your home.

If you need to build a batten wall, there are guides available online. Earthwool and Thermafleece insulations are designed to friction fit within a stud wall and securely nestle into place. For looser materials, insulation fixings are drilled into a wall and used to hold the insulation in place. Boards on top of this must be attached to the wooden studs using plasterboard nails.

Installing internal wall insulation can bring significant benefits to your property, but it is important to follow the correct procedures and seek professional help if necessary.

What Kind of Insulation Should You Use for Interior Walls?

Choosing the right type of insulation for interior walls can be a daunting task. There are several factors to consider, such as the application, cost, and eco-credentials of the product. Below are some of the most popular types of insulation for interior walls:

  • Rigid foam boards are a great option for those looking for high-quality insulation. They are thinner and take up less floor area than other options, making them ideal for small spaces. They can also incorporate a vapour barrier. However, they can be more expensive than other options and might not be as breathable.
  • Mineral wools are a widely used option and are available as semi-rigid batts or quilts. They are cost-effective and provide excellent insulation. However, they can be itchy and require protective clothing and equipment during installation.
  • Natural materials like sheep’s wool, woodfibre insulation, or cork are a good option for people interested in eco-friendly products. They provide good levels of breathability and do not release toxins. However, they can be more expensive than other options.
  • Thin insulation is ideal for floor voids, reveals, and returns. Thinner materials are needed here to ensure continuity in the insulation and eliminate cold bridges. There is a selection available, from paints like Therma-Coat Acrylic Insulating Primer to aerogels like Spacetherm.

Ultimately, the best type of insulation for interior walls will depend on your specific needs and budget. It is recommended to research and consult with a professional to determine the best solution for your home.

How to Prepare a Wall for Internal Insulation

Before installing internal insulation, it is important to address the condition of the wall’s surface and whether the wall is damp. The surface condition will determine what preparation work is needed, such as hacking off old plaster. It will also determine whether insulation can be fixed to the wall with adhesive, whether mechanical fixing will be needed, and if battening is necessary to give a flat surface.

Insulation can make a damp wall worse by reducing the temperature of the wall and by reducing or eliminating air movement across its internal surface. Therefore, it is crucial to deal with any dampness before installing insulation. There are only two ways of dealing with a damp wall: creating a stud wall with a cavity between the insulation and the existing wall, or finding the cause of the damp and eradicating it.

If the cause of the damp is rain penetration through the wall, then internal insulation would be a mistake. It might be a leaky gutter, downpipe, or overflow, which is easy to fix. Alternatively, the external ground levels may have been built up above those of the interior wall levels. In such cases, it is necessary to address the root cause of the dampness before proceeding with insulation installation.

It is important to note that rigid foam boards offer the best insulation compared to other alternatives. However, the condition of the wall’s surface and the presence of dampness will determine the appropriate insulation method.

When to Choose Insulation on the Inside?

Internal wall insulation is typically chosen as a last resort when other options like cavity wall insulation or facade insulation are not feasible due to high costs, protected facades, or restrictions because of adjacent buildings. It is often part of a house renovation, and the craftsman requires enough space to work decently, so the room has to be empty.

Internal wall insulation is a good alternative for facades that should remain untouched, for example, because of their historical value. However, it is important to consider some points of attention before choosing internal wall insulation.

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