Is It Better To Insulate Walls From Outside Or Inside?

Whether to insulate walls from the outside or inside has been a persistent inquiry among homeowners and builders alike.  This dilemma stems from the desire to enhance energy efficiency while considering cost-effectiveness and structural integrity.

In this article, we will dive into the merits and drawbacks of both approaches. The goal is to provide clarity and guidance for those facing this decision.

Understanding Exterior Wall Insulation

Exterior wall insulation is the process of adding insulation to the outside walls of your home or structure. This method is often used in new construction projects or when renovating the exterior facade. Common exterior insulation materials include rigid foam boards, mineral wool, and insulating concrete forms (ICFs).

One big benefit of exterior wall insulation is that it stops heat from escaping through the structure’s framework. This also helps prevent moisture from building up inside the walls which reduces the chances of mould or damage.

Exterior insulation can make the building look nicer too by providing a smooth surface for adding siding or other finishes. 

Exploring Interior Wall Insulation

Interior wall insulation involves adding insulation material to the inside of your home’s walls. This approach is generally more cost-effective and easier to install compared to exterior insulation. 

One of the main advantages of interior insulation is that it does not require any disruption to the exterior finishes of your home which makes it a convenient option for existing homes.

Interior insulation can be made from various materials like fibreglass batts, cellulose, or spray foam. These materials are readily available and relatively inexpensive that contribute to the overall cost-effectiveness of interior insulation.

Factors to Consider When Choosing Insulation Location

When deciding whether to insulate your walls from the outside or inside, there are several factors to consider:

  1. Climate and Weather Conditions – In cold climates, exterior insulation is often preferred as it helps prevent condensation within the wall assembly and reduces thermal bridging. In warm climates, interior insulation may be a more suitable option, as it helps keep the living spaces cooler.
  1. Building construction type – For new construction projects, exterior insulation is generally easier to install and can provide a continuous insulation layer. For existing buildings, interior insulation may be more practical, especially if the exterior siding or cladding is in good condition.
  1. Energy efficiency goals – If you want to achieve maximum energy efficiency and reduce thermal bridging, exterior insulation is typically the better choice. However, interior insulation can still provide significant energy savings, especially if combined with other energy-efficient measures.
  1. Future Renovation Plans – Youl to consider how the insulation location may impact those plans if you anticipate future renovations or additions to your home. Exterior insulation may be more suitable if you plan to expand the living space, while interior insulation may be preferable if you intend to keep the exterior finishes intact.
  1. Budget and cost considerations – While exterior insulation often has higher upfront costs, it may provide better long-term energy savings and a higher return on investment. Interior insulation is generally more cost-effective in the short term but may not be as energy-efficient as exterior insulation.
  1. Moisture control and ventilation requirements – Exterior insulation can help prevent moisture condensation within the wall assembly, while interior insulation may require additional vapour barriers and ventilation measures to manage moisture effectively.
  1. Aesthetic preferences – Exterior insulation can improve the overall appearance of a building by creating a smooth, uniform surface for siding or other finishes. Interior insulation may impact the look and feel of interior spaces, especially if it reduces the wall cavity depth.

Cost Comparison: Exterior vs. Interior Wall Insulation

The costs associated with exterior and interior wall insulation can vary significantly depending on several factors:

Material costs

Exterior insulation materials like rigid foam boards and mineral wool tend to be more expensive than interior insulation materials like fibreglass batts or cellulose.

However, exterior insulation may require less material overall as it can provide a continuous insulation layer without the need for additional framing or stud cavities.

Labour costs

Exterior insulation installation typically requires more specialised labour and equipment, such as scaffolding or boom lifts, which can increase labour costss though grants are available.

Interior insulation installation may be more straightforward, especially for DIY projects or smaller renovations.

Long-term energy savings and payback periods

Exterior insulation often has higher upfront costs but it can provide better long-term energy savings due to its continuous insulation layer and reduced thermal bridging.

The energy savings from interior insulation may be lower, however, the initial investment is typically more affordable that results in a shorter payback period.

The question of whether it’s cheaper to insulate from the inside or outside depends on weighing the higher initial costs of exterior insulation against the potentially greater energy savings over time.

In some cases, combining both approaches or implementing additional energy-efficient measures may be the most cost-effective solution in the long run.


Choosing between exterior and interior wall insulation is a decision that requires careful consideration of different elements. The decision should be based on a comprehensive evaluation of your specific project requirements and priorities.

The key is having patience and keeping the long-term benefits in mind. You will enjoy a cosy, efficient home for generations to come With the right insulation system properly installed.

Consult with us! We can help you make an informed choice and ensure proper installation for optimal performance and long-term energy savings.

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