18th Nov 2022 -

As a construction professional, you understand the critical role external wall insulation (EWI) has in improving energy efficiency. This article delves into the advanced techniques and best practices for external wall insulation projects.

What Homes Need External Wall Insulation?

Identifying the right homes for external insulation can significantly enhance energy efficiency and reduce heating expenses. As a builder, understanding which properties benefit most from this upgrade is crucial for providing value to your clients.

Choosing suitable building types

External wall insulation is particularly beneficial for older homes with solid walls, which often lack adequate insulation. These properties, typically built before the 1920s, can experience significant heat loss through their walls. By adding external insulation, you can dramatically improve their thermal performance.

Properties lacking cavity wall insulation or those with poorly insulated cavity walls are also prime candidates for external insulation. Additionally, buildings with poor energy efficiency ratings can see substantial improvements. External insulation can help these structures achieve better energy performance certificates, increasing their value and appeal.

Climate and environmental factors

The local climate plays an important role in determining the need for external wall insulation. You should consider factors such as average temperatures, exposure to wind and rain, and temperature variations throughout the year. 

Homes in colder, wetter areas typically benefit more from external wall insulation. In these climates, the insulation helps prevent heat loss and reduces heating costs. You'll find that clients in these regions often see a faster return on their investment. 

However, even in milder climates, external insulation offers benefits by maintaining a more consistent indoor temperature year-round.

What External Insulation Boards Should Be Used for EWI?

A construction worker wearing a red polo shirt and grey cap holding exterior wall insulation outside against a brick house.

When you're planning an external wall insulation project, choosing the right insulation boards is crucial. Your selection will significantly impact the building's energy efficiency, fire resistance and moisture control. Understanding the characteristics of different insulation materials will help you make the best choice for your specific project requirements.

Polyisocyanurate (PIR)

PIR insulation boards are widely used in EWI applications, particularly for homes requiring high thermal performance. These boards offer excellent insulation properties, allowing you to achieve the desired U-value with a thinner overall wall construction. 

These boards benefit from their high thermal resistance and fire-retardant properties, making them suitable for a wide range of building types. However, you should be aware that PIR boards are more expensive than some alternatives and may require additional fire protection.

Expanded Polystyrene (EPS)

EPS insulation boards are a popular choice for EWI systems, especially in residential properties. You'll find that EPS boards offer good thermal performance at a lower external insulation cost compared to PIR. They're also lightweight and easy to install.

Also, EPS boards are also moisture-resistant and durable, ensuring long-term performance. However, you should note that EPS has a lower fire resistance rating than some other options, which may limit its use in certain building types or heights.

Extruded Polystyrene (XPS)

XPS insulation boards are particularly well-suited for buildings in areas with high moisture exposure. You'll appreciate XPS for its excellent water resistance and high compressive strength. This makes it ideal for below-grade applications or areas prone to flooding. 

XPS boards also maintain their insulation properties well over time, even when exposed to moisture. However, like EPS, XPS has lower fire resistance compared to some alternatives, and it's generally more expensive than EPS.

Mineral Wool

Mineral wool insulation boards are an excellent choice when fire resistance is a top priority. You'll find that mineral wool offers superior fire performance, as it's non-combustible and doesn't contribute to flame spread. These boards also provide good sound insulation, which can be beneficial in noisy environments. 

Mineral wool is vapour-permeable, allowing your walls to breathe and reducing the risk of moisture buildup. However, you should be aware that mineral wool boards typically have a lower thermal performance compared to plastic foam insulations. They require thicker installations to achieve the same U-value.

For more information, take a look at our guide on why you should choose external wall insulation for homes.

6 Advanced Techniques for Pros on How to Insulate External Walls

A construction worker wearing a blue hard hat, red plaid shirt and orange work gloves working on exterior wall insulation installation holding a tool for air sealing.

Adopting the below 6 advanced techniques to ensure optimal performance of external wall insulation. They boost the insulation's effectiveness and durability of the building envelope. Let’s explore these techniques in detail. 

1. Reducing thermal bridges 

Thermal bridges are a significant source of heat loss and condensation issues. An effective approach is using continuous insulation boards with integrated fastening systems. These boards limit the need for mechanical fasteners that potentially create thermal bridges.
Also, you can introduce insulated angle profiles and proprietary connection details at window and door openings and roof-wall interfaces. This reduces thermal bridging and improves the overall thermal performance. 

2. Choose the best fasteners

Mechanical fasteners like screws and anchors are essential for securing external wall insulation. However, as outlined above, improper use may compromise the insulation's performance. 

For external stud wall insulation, use specialised fasteners with improved thermal properties. These may include fasteners with larger heads or integrated washers to distribute the load more evenly and reduce thermal bridging. 

Carefully plan the placement and spacing of fasteners to limit the number required while still maintaining the necessary load-bearing capacity. 

3. Boosting airtightness 

Ensuring the airtightness of the building envelope is crucial for energy efficiency and indoor air quality. Use specialised tapes (butyl rubber, acrylic adhesive, EPDM), sealants and membranes to create a continuous air barrier. 

These products are compatible with both stud wall and external wall insulation on cavity wall applications. This includes carefully sealing all joints, gaps and penetrations to eliminate air leakage paths. 

Consider high-performance, vapour-permeable air barriers that allow the wall to breathe while still providing effective airtightness and moisture control.

4. Smart drainage solutions

Effective drainage is key for the long-term durability of cavity wall external wall insulation systems. Introduce specialised drainage channels, weep holes and ventilation systems to ensure the proper management of moisture and prevent water intrusion.
These integrated drainage solutions can extend the lifespan of the insulation and protect the building structure from water-related damage. Pay attention to integrating these features to ensure they function properly without compromising thermal performance. 

5. Add vapour barriers 

Proper moisture management affects the longevity and performance of both external stud wall and cavity wall external wall insulation systems. Advanced techniques involve the integration of high-performance vapour barriers or retarders into the wall assembly. 

These specialised membranes effectively control the movement of water vapour, preventing condensation within the wall cavity. Consider vapour-permeable membranes that allow the wall to breathe while providing moisture control. This reduces moisture-related risks.

6. Building insulation layers

To further improve thermal performance, you can explore layered insulation assemblies. This involves combining different insulation materials, such as rigid foam boards and flexible batt insulation, to create a multi-layer system. 

The integration of these layers boosts the overall thermal resistance, addresses thermal bridging and provides added benefits like fire resistance. 

Top Pro Tips on How to Integrate External Solid Wall Insulation & Building Systems

A construction worker wearing a red jacket, hat and white trousers and long sleeve shirt fitting exterior wall insulation on the outside of a house next to a window opening with scaffolding.

When integrating various building components and external wall insulation, there are top tips to ensure the best performance. Below are top tips for you to consider throughout the process.

Design smart penetrations

Instead of cutting holes through the insulation, plan and design smart penetrations for HVAC ducts, electrical conduits and plumbing lines. This may involve the use of specialised grommets, collars or prefabricated openings that maintain the insulation. 

Add insulated sleeves

Create thermal breaks by installing insulated sleeves around any building system penetrations that pass through the exterior wall assembly. This reduces thermal bridges and preserves the overall thermal efficiency of the building envelope, even with varying insulation thicknesses.

Advanced sealing techniques

Go beyond basic caulking to air-seal all building system penetrations. Use specialised tapes, gaskets and high-performance sealants that can create a durable, airtight barrier around these transition points.

Design for accessibility

When integrating building systems with external wall insulation, consider the long-term maintenance and potential future upgrades. Introduce design layouts that allow easy access to these systems without compromising the insulation system's integrity.

Seamless door & window integration

Plan the integration of windows, doors and other systems with the insulation to maintain continuous thermal and air barriers. This involves using specialised jamb extensions, sill flashings, and other techniques accounting for the specific external wall insulation thickness.

What Are the Challenges With Insulation for External Walls and Retrofitting?

You may face several key challenges with retrofitting external wall insulation. Dive deeper into understanding and addressing these issues to ensure your projects are successful. 

1. Restricted access to wall cavities

A key challenge is limited access to the wall cavities, especially in older buildings with complex wall structures. Traditional insulation methods that require extensive wall openings may be difficult to introduce in these scenarios. 

To overcome this, consider using spray foam insulation or vacuum-insulated panels. They can be applied without substantial wall modifications, providing a seamless integration into the existing construction. 

Additionally, explore flexible insulation materials that can be inserted through small openings, allowing you to insulate hard-to-reach areas.

2. Thermal bridging at structural elements

As mentioned previously, thermal bridging can significantly reduce the overall effectiveness of the insulation system. Be careful with areas like window and door frames, corners and wall-to-floor junctions - these are common thermal bridging points. 

Introduce materials such as aerogel or phase-change materials (PCMs) which have superior thermal performance and can effectively mitigate heat loss. To minimise thermal bridges, use thermally broken components at key connections and plan the insulation layout carefully before installation.

3. Moisture management issues

Proper moisture management prevents issues like mould, rot and structural damage. When retrofitting external wall insulation, ensure the insulation materials are vapour-permeable to maintain a healthy indoor environment. 

Consider vapour control layers and add mechanical ventilation systems like heat recovery ventilators (HRVs) to regulate moisture levels. Additionally, introduce drainage and air gaps within the wall assembly to allow for proper moisture drainage and drying.

4. Structural integrity considerations

Retrofitting external wall insulation may impact the structural integrity of the building, particularly in older constructions. Carefully assess and compare the existing wall and load-bearing expectations before and after external wall insulation. This is to make sure additional insulation weight can be safely accommodated.

Consult with structural engineers to design appropriate modifications to maintain stability. Addressing the potential disadvantages of external wall insulation and retrofitting is crucial to ensure long-term success.

How Much is External Wall Insulation at Building Materials Nationwide?

The cost of external wall insulation depends on your specific requirements. We source our insulation from trusted manufacturers like Knauf, Kingspan and Rockwool, ensuring superb thermal performance and value for money. 

Call us to learn more about how we can help. By shopping with us, you can be confident you're getting the best external wall insulation cost available.

We also offer the opportunity for you to open a trade account with us. This allows you to streamline ordering and receive personalised support from your trade account manager. By opening a trade account, you can efficiently source the external wall insulation materials you need at competitive trade prices.

If you're a construction professional in need of external wall insulation, look no further than Building Materials Nationwide. Browse our selection, open a trade account and transform your jobs with the best external wall insulation. 







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