A Trade's Guide to Tackle Cavity Wall Insulation Problems

21st Nov 2022 -

Cavity wall insulation (CWI) issues and defects can greatly impact building performance, creating complex challenges. This guide offers practical solutions for tackling CWI issues in new and existing structures.

We'll explore advanced techniques to prevent thermal bridging, manage moisture and the process of cavity wall insulation removal. Also, we'll discuss common cavity wall insulation problems and provide solutions to rectify these issues.

• Types of Cavity Wall Insulation
• Is Cavity Wall Insulation Worth It? How to Fix Common Problems
• How Long Does Cavity Wall Insulation Last?
• 9 Pro Tips on Removing Cavity Wall Insulation After Moisture Damage
• How Much is Cavity Wall Insulation at Building Materials Nationwide?

Types of Cavity Wall Insulation

Understanding the different types of cavity wall insulation is crucial for choosing the best solution for your project. Each type has its own set of cavity wall insulation pros and cons. Here's an overview of the most common materials. 

1. Mineral wool 

Mineral wool, made from recycled glass or rock, is a popular choice for cavity wall insulation. You'll find it's excellent at reducing heat transfer and provides good sound insulation. It's fire-resistant and eco-friendly, making it a safe and sustainable option. 

However, mineral wool can absorb moisture if exposed to water, which may reduce its effectiveness over time. Installation can be messy and it may settle over time, potentially creating gaps at the top of the cavity.

2. Expanded polystyrene (EPS) 

EPS is a lightweight, rigid foam insulation that you can easily cut to fit your cavity. It offers good thermal performance and is resistant to moisture, making it suitable for damp-prone areas. EPS is also cost-effective and has a long lifespan. 

On the downside, it's not as fire-resistant as some other options, and its production process isn't as environmentally friendly. You may need to consider additional fire protection measures when using EPS.

3. Extruded polystyrene (XPS) 

XPS is similar to EPS but with a closed-cell structure, giving you better insulation properties and higher compressive strength. It's highly water-resistant, making it ideal for areas prone to moisture. XPS maintains its insulation properties over time better than EPS. 

However, it's more expensive than EPS and has a higher environmental impact during production. Like EPS, it also requires careful consideration of fire safety measures.

4. Polyisocyanurate (PIR) 

PIR offers excellent thermal performance, allowing you to achieve high insulation levels with thinner panels. It's lightweight, moisture-resistant, and has good fire-retardant properties. PIR is suitable for both new builds and retrofits. 

The main drawbacks are its higher cavity wall insulation cost and it's not as environmentally friendly in production. You may also find it more challenging to cut and fit precisely in irregular cavities.

5. Polystyrene beads 

Polystyrene beads are small, lightweight spheres that you can easily pour into wall cavities. They offer good insulation properties and are particularly useful for hard-to-reach areas. The beads can fill irregular spaces effectively and don't absorb moisture. 

However, they may settle over time, creating gaps at the top of the cavity. There's also a risk of beads escaping if not properly contained, which can be messy and reduce insulation effectiveness.

6. Polyurethane foam 

Polyurethane foam expands when sprayed, filling gaps and cracks effectively. It provides excellent insulation and air sealing properties, reducing heat loss significantly. The foam adheres well to most surfaces and won't settle over time. 

However, it's one of the more expensive options and requires professional installation. There are also concerns about its environmental impact and potential off-gassing of chemicals during and after installation.

7. Cellulose fibre 

Made from recycled paper products, cellulose fibre is an eco-friendly option you might consider. It's treated with fire retardants and insect repellents, making it safe and durable. Cellulose provides good thermal and sound insulation. 

On the downside, it can settle over time, potentially creating gaps. It may also absorb moisture if exposed to water, which can reduce its effectiveness and potentially lead to mould growth.

8. Urea formaldehyde 

Foam Urea formaldehyde foam is injected as a liquid and expands to fill the cavity. It provides good insulation properties and can be effective in irregular spaces. The foam sets quickly and doesn't shrink or settle over time. 

However, there are concerns about formaldehyde emissions, which may cause health issues. It's also not suitable for use in very cold climates as it can become brittle and crack.

9. Reflective foil insulation 

Reflective foil insulation works by reflecting radiant heat rather than absorbing it. It's lightweight, thin, and easy to install, making it a good option for narrow cavities. The foil is resistant to moisture and doesn't degrade over time. 

However, its effectiveness can be limited in cavities where there isn't an air gap on at least one side. It may not provide as much insulation as some other materials in cold climates.

Is Cavity Wall Insulation Worth It? How to Fix Common Problems

While you're familiar with basic installation techniques, tackling cavity wall insulation issues often requires more technical solutions. Here, we outline common problems you may face with all cavity wall insulation types and approaches to resolve them effectively.

Patchy insulation

When you encounter uneven distribution of insulation, you're dealing with an issue that creates cold spots and reduces thermal efficiency. This inconsistency in heat retention leads to energy loss and potential condensation issues. 

To tackle this problem, consider using a thermal imaging-guided redistribution technique. Start by conducting a thorough scan of the affected walls to identify areas of uneven distribution. You'll need a high-resolution thermal imaging camera for this step.

Once you have pinpointed the areas, use a cavity wall insulation injection with a flexible nozzle. Target these spots with expanding foam insulation - it expands to fill gaps and voids, redistributing the existing insulation more evenly.

Damp problems

Does cavity wall insulation cause damp areas? You may find that improper installation or deterioration of the insulation allows moisture to penetrate the cavity, leading to dampness. This reduces insulation effectiveness and leads to mould growth and structural damage. 

To address dampness and moisture issues, apply a hydrophobic nano-coating. Begin by using a cavity wall endoscope (small camera) to inspect the cavity and identify moisture-prone areas. Use a hydrophobic coating using a high-pressure sprayer with an extended nozzle. 

This creates a water-repellent barrier on the insulation and cavity surfaces without affecting breathability. Ensure you choose a nano-scale hydrophobic coating solution that's compatible with the existing insulation material.

Heat escape through wall ties

When insulating a cavity wall doesn't adequately cover structural elements like wall ties, you're faced with thermal bridging. This creates pathways for heat loss, reduces overall effectiveness and can create potential condensation points. 

To solve this, consider using an aerogel-infused insulation patching technique. Start by identifying thermal bridges using a thermal imaging camera. Carefully drill small access points near the affected areas using precision drilling equipment. 

Use an applicator gun to insert aerogel-infused insulation patches around the thermal bridges. The aerogel's insulation properties will help limit heat transfer through these critical points.

Worn-out insulation

Over time, some insulation materials like cellulose and mineral wool settle, compress or degrade, losing their effectiveness. This leads to reduced thermal performance and the potential creation of voids within the cavity. 

Without completely removing and replacing the insulation, you can perform an in-situ insulation rejuvenation. Use a cavity wall inspection system (camera, moisture meter and lighting) to assess the condition of the existing insulation. 

Based on your assessment, inject a rejuvenation compound using a high-pressure injection system. It will bond with the existing insulation, restoring structure and thermal properties.

Issues with bead insulation

Polystyrene beads can settle over time, creating gaps at the top of the cavity and harming insulation effectiveness. In some cases, beads may escape through small cracks or poorly sealed areas. Moisture infiltration can cause beads to clump together. 

To tackle cavity wall insulation polystyrene beads problems, consider using a specialised vacuum system to redistribute settled beads. You can also remove and replace them entirely. Ensure all potential escape routes are properly sealed, and address any moisture issues before refilling the cavity. 

Drafts and air gaps

Air leakage allows air to circulate within the cavity, bypassing the insulation because of poor window and door sealing. This limits insulation performance and can allow moisture-laden air to enter the cavity. 

Use a targeted elastomeric sealant injection technique to address air leakage. Begin by using acoustic leak detection equipment to identify air leakage pathways. After, use a drill to create minimal access points. Inject an elastomeric sealant using precision equipment. 

How Long Does Cavity Wall Insulation Last?

Cavity wall insulation lifespan varies depending on the material used and installation quality. A key benefit of cavity wall insulation is it generally lasts for decades. Let's compare the typical lifespans of insulation materials.

Insulation Type	Average Lifespan	Factors Affecting Lifespan
Mineral Wool	25-30 years	Moisture exposure; compression
EPS	20-25 years	Moisture absorption; UV degradation if exposed
Polystyrene Beads	20-25 years	Settling; moisture infiltration
Polyurethane Foam	20-25 years	UV exposure; degradation
Cellulose Fibre	20-25 years	Moisture; settling
PIR	20-25 years	Thermal drift; moisture exposure
Urea Formaldehyde Foam	15-20 years	Shrinkage; crumbling
XPS	20-30 years	Moisture resistance; thermal drift
Reflective Foil Insulation	20-25 years	Punctures; gaps in installation; loss of reflectivity

9 Pro Tips on Removing Cavity Wall Insulation After Moisture Damage

Removing cavity wall insulation is a delicate process that requires precision to avoid compromising the wall structure. Below are 9 pro tips, from initial assessment to final inspection, that will help you navigate this task. 

1. Detailed cavity check with camera

Start by conducting a comprehensive cavity inspection using a borescope or cavity wall inspection camera. Insert this device into existing holes or, if necessary, create small access points with a drill. 

Borescope inspection provides key information about the condition of cavity wall construction, insulation type and extent of damage. By gathering data upfront, you'll be able to plan the most appropriate removal strategy and potential structural issues early. 

2. Drilling small holes for access

Calculate and mark precise points on the wall for minimal drilling using a tape measure and chalk or marker. Create small holes, typically 22-25mm in diameter, at these points using a drill with masonry bits. 

Make sure the holes are spaced to allow effective insulation removal while minimising wall damage. This approach maintains the wall's structural integrity by avoiding large-scale removal of bricks or rendering.

3. Suction removal method

Using a vacuum with HEPA filtration and long flexible hose attachments, insert the hose into the access holes you've created. Work from top to bottom of the wall, using gentle, sweeping motions to ensure thorough removal. 

You may need a step ladder to reach higher points safely. This method is highly effective for loose-fill insulations and stops dust and debris from spreading. It's also less likely to cause damage to the cavity wall structure compared to more aggressive techniques. 

4. Using air pressure to loosen material

Use an air compressor with adjustable pressure settings and appropriate nozzle attachments to introduce short air bursts into the cavity. Start with low pressure and gradually increase as needed. 

Combine this technique with vacuum cavity wall insulation extraction for best results. This helps break up compacted insulation without applying excessive force to the wall structure. It is particularly useful for areas where insulation has settled or hardened.

5. Heating to shrink certain insulations

For insulation types like expanded polystyrene beads, apply controlled heat to the wall surface using a professional-grade heat gun. Monitor the temperature carefully with a thermal imaging camera to avoid damaging the wall materials.

It causes the insulation material to shrink, making it easier to remove without aggressive action that could harm the wall. 

6. Dissolving foam insulation

When dealing with stubborn foam insulations, consider using an eco-friendly foam dissolution solvent. Inject the solvent into the cavity through the access holes using an injection pump system. 

Allow it to penetrate and break down the foam insulation before vacuum extraction to remove the dissolved material. This method effectively breaks down stubborn foam insulations without mechanical force. 

7. Shaking loose compacted insulation

Attach an adapted wall vibration tool to the wall surface at strategic points. Operate the tool in short bursts, moving regularly across the wall area. Use vibration dampeners to protect surrounding structures. 

Combine this technique with vacuum extraction for immediate removal of loosened material. Vibration helps dislodge compact insulation without applying direct force to the cavity, reducing the risk of structural damage.

8. Removing insulation in stages

Divide the wall into manageable sections, typically 1-2 metre squares, using a tape measure and chalk. Work on 1 section at a time, completing the removal process before moving to the next. It may involve a combination of the above techniques. 

This methodical approach ensures thorough removal while allowing you to maintain control over the process. Sectional removal reduces the risk of structural damage from trying to tackle too large an area at once.

9. Dealing with moisture during removal

Before and during removal, use dehumidifiers and high-powered fans to lessen moisture levels in the cavity. Monitor humidity levels throughout the process with a humidity meter. Removing moisture prevents further damage to the wall structure and makes the insulation easier to extract. It also limits the possibility of mould growth during the removal process.