What Thickness Of Insulation Should I Use for External Wall Insulation?

External wall insulation is a great way to improve the thermal performance of a building. It reduces the amount of heat lost through the walls, increasing comfort and saving money on fuel bills.

There are many different materials used in external wall insulation systems. Each material has its own characteristics and can be installed in different thicknesses to suit your needs or budget.

In this article, I will discuss the different products available, their thicknesses and how they can be used to insulate your home.

Introduction

External wall insulation is a great way to improve the thermal performance of a building. It reduces the amount of heat lost through the walls, increasing comfort and saving money on fuel bills.

There are many different materials used in external wall insulation systems. Each material has its own characteristics and can be installed in different thicknesses to suit your needs or budget.

In this article, I will discuss the different products available, their thicknesses and how they can be used to insulate your home.

Before discussing the various insulation materials used in external wall insulation, it is important to have a basic understanding of what external walls are and what they do.

External walls are usually made of brick, concrete or blockwork and form the outer face of your home. They provide protection against weather conditions such as wind, rain and snow. External wall insulation will help keep your home warm in winter and cool in summer by preventing heat from escaping through gaps around windows and doors or from other parts of the building like garages or sheds attached to it.

Insulation Types and Thicknesses

There are three main types of insulation used within the construction industry.  These are EPS, Mineral Fibre and Phenolic Foam.  Each has a different insulation value depending on their thickness and are suitable for different types of construction.

EPS or (Expanded Polystyrene Insulation) boards are a grey polystyrene board which are used predominately in the residential market where homes are only around 2 storeys.  They have a good thermal insulation quality and are lightweight and easy to install.

Mineral Fibre is a rigid insulation board similar to loft insulation.  The boards will need to be thicker to gain the same thermal insulation qualities as EPS but these are great for multi-occupancy properties and properties over 2 storeys due to it’s A-rated fire rating.

Phenolic Foam is a rigid board that has a high thermal insulation quality which is great when you need to achieve the right u-value but don’t have the thickness available.  When applied correctly these really do perform well for residential properties.

For a typical single brick 2 storey home that requires insulating on the outside of their home you will be looking at the following insulation thicknesses;

EPS – 90mm

Mineral Fibre – 110mm

Phenolic Foam – 60mm

Importantly, it is important when considering your project that you are aware of whether or not it falls under a retrofit or refurbishment. For example, if you are insulating an existing property or building but your current structure has been altered in some way (which is common) then this would be considered as a refurbishment and therefore would require any alterations to meet current standards. If however you have built a new house with no alterations made then your project will fall under ‘retrofit’ requirements.  This is important when needing to register your project with for building regulations.

Insulation thickness is essential, but it's not the only factor to consider.

The thickness of insulation is certainly an important factor, but it's not the only one to consider.

Other factors include:

Airtightness - this is how well your home is sealed against air leaks. If you have poor airtightness, then you will have draughts and gaps in floors, walls and ceilings which can cause major heat loss from your home.

Ventilation - if there’s no ventilation in a room or if there are blocked vents then this can lead to condensation forming on the inside of windows and walls (which can rot wood). Also, damp conditions may encourage mould growth on surfaces such as plasterboard sheets or tiles which could make them unsafe for living in.

Different wall structures might need different types of insulation.

The type of wall structure you have will affect how well your insulation performs. External wall insulation can be used in:

  • timber frame walls
  • brick or stone walls
  • concrete walls
  • steel framed walls (the steel will conduct heat)
  • wooden framed walls with timber studs and plasterboard lath (the timber studs aren’t good at conducting heat but the plasterboard is.

Your local installer and manufacturer will help you decide on the right insulation for your home so always consult a specialist when costing out your project.

Choose external insulation based on your existing structure and how much you want to spend.

Before you can decide what thickness of external insulation you need, there are some other factors to consider.

  • What type of structure do you have?
  • What is your budget?
  • What is the U-value of your existing insulation?

When deciding if External Wall Insulation is right for you or to install internal wall insulation look at the full costs as well as the impact this will have you and your family whilst this is being installed.  Other works may need to be done to ensure that everything is working including the moving of electrics, plumbing, lights, alarms, satellite dishes and anything else that is fastened to the walls.

Also look at the post costs.  What savings will you make in your energy bills, how this will impact your family and of course your environmental impact.  I would also suggest that the curb appeal on your home and your resale value are to be considered when thinking of completing these works.

Conclusion

In this article, I have listed the different thicknesses of external wall insulation and their respective thermal performance. The choice of insulation thickness should be based on a number of factors that include the existing structure, budget and the anticipated heat loss. Not all external wall insulation systems are the same, so it's important to consider a variety of options before making your decision.  Talk to your local installer or a manufacturer who will appoint a certified installer to talk to you.

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