When it comes to making your home more energy-efficient and comfortable, internal wall insulation (IWI) is one of the most impactful upgrades you can make. But with various materials and methods on the market, homeowners often wonder: what is the most efficient internal wall insulation?
In this detailed guide, we’ll break down the different types of internal wall insulation, compare their benefits and drawbacks, and help you choose the best solution based on efficiency, cost, and practicality.
Why Wall Insulation Is So Important
Insulating your walls is one of the most effective ways to reduce heat loss. This is particularly important in homes with solid walls, which were commonly built before the 1930s and lack the cavity required for cavity wall insulation.
Without proper insulation, heat escapes through the external walls, resulting in:
- Higher energy bills
- A colder, less comfortable home in winter
- Poor Building Energy Rating (BER)
- Increased carbon emissions
Installing wall insulation—whether internal or external—improves thermal performance, enhances comfort, and supports sustainable living.
What Is Internal Wall Insulation?
Internal Wall Insulation involves adding thermal insulating materials to the interior surfaces of external walls. It’s typically used in homes with solid walls or in properties where external insulation is not possible due to planning restrictions or heritage considerations.
How Does Internal Wall Insulation Work?
The insulation is applied directly onto the internal walls using a few different techniques. The process involves:
- Fixing insulation boards or wool batts to the inside of exterior walls
- Adding a vapour control layer to manage condensation risk
- Finishing with plasterboard and skim plastering
This creates a thermal barrier that slows heat transfer through the wall, reducing the need for heating and cooling.
Types of Internal Wall Insulation
Let’s take a closer look at the most commonly used materials for internal wall insulation:
1. Rigid Foam Boards (PIR, XPS, EPS)
These are some of the most efficient materials due to their high R-value per inch of thickness. Rigid boards such as polyisocyanurate (PIR) or extruded polystyrene (XPS) are applied directly to the wall or integrated into stud walls.
Pros:
- High thermal performance
- Slim profile saves interior space
- Moisture-resistant
Cons:
- Higher material cost
- Requires precise installation to avoid gaps
2. Fibreglass Batts
Fibreglass remains a go-to choice for many thanks to its affordability and availability. It’s typically used in stud walls and comes in pre-cut rolls.
Pros:
- Inexpensive
- Easy to install
- Fire-resistant
Cons:
- Can irritate skin and lungs during installation
- Doesn’t create an airtight seal
- Prone to sagging over time
3. Spray Foam Insulation
Available in open-cell and closed-cell types, spray foam expands on application to fill every crevice, creating a seamless thermal barrier.
Pros:
- Excellent air sealing
- High R-value
- Great sound insulation
Cons:
- Expensive
- Requires professional installation
- Not always suitable for older homes
4. Mineral Wool (Rock Wool)
A dense insulation with excellent acoustic and fireproof properties, mineral wool is often used in timber stud walls.
Pros:
- Non-combustible
- Good sound absorption
- Water-resistant
Cons:
- Heavier than other options
- Less thermally efficient than foam boards
5. Blown-in Cellulose
Made from recycled paper products, this eco-friendly option is commonly used in wall cavities and between studs.
Pros:
- Sustainable
- Good thermal performance
- Inexpensive
Cons:
- May settle over time
- Absorbs moisture if not properly protected
Comparing the Most Popular Insulation Types
| Insulation Type | R-Value (Per 25mm) | Cost | Airtight | DIY-Friendly | Moisture Resistance |
| Rigid Foam Boards | 6.0 – 6.5 | High | Yes | Moderate | Excellent |
| Fibreglass Batts | 2.2 – 2.7 | Low | No | High | Moderate |
| Spray Foam | 6.0 – 7.0 | Very High | Yes | No | Very Good |
| Mineral Wool | 3.0 – 3.3 | Moderate | No | Moderate | Good |
| Blown-in Cellulose | 3.2 – 3.8 | Low | Yes | Moderate | Poor (unless treated) |
What is the Most Efficient Internal Wall Insulation?
The answer depends on what you mean by efficient. Do you prioritise thermal performance, cost-effectiveness, ease of installation, or moisture resistance?
Top Pick for Energy Efficiency: Closed-cell Spray Foam
With an R-value of 6.0 or more, spray foam insulation is unbeatable for energy savings. Its airtight seal eliminates cold spots and reduces heat loss significantly. It’s ideal for high-performance builds or those with unusual wall structures.
Best Overall Performer: Rigid Foam Boards
Rigid boards offer a balance of efficiency, moisture resistance, and installation versatility. They’re thin enough to save space, yet effective enough to dramatically reduce heat loss. When installed with a vapour barrier, they’re also great for preventing condensation.
Factors to Consider When Choosing Insulation
Wall Type
Solid walls vs. cavity walls require different approaches. Solid walls often benefit from rigid boards or stud wall builds, while cavity walls may need injected or blown-in materials.
Moisture and Ventilation
Avoid materials like cellulose in damp-prone areas. Always install a vapour control layer to prevent internal condensation.
Room Usage
For bedrooms or home offices, consider soundproofing qualities in addition to thermal efficiency.
Budget and Grants
The Sustainable Energy Authority of Ireland (SEAI) provides generous grants for internal wall insulation. These are part of the Better Energy Homes scheme and are available for homes built before 2011.
Available Space
If internal space is a concern, choose high-efficiency materials that offer good insulation in thin layers, such as PIR boards.
Best Practices for Installation
Whether you’re hiring a professional or going DIY, follow these essential tips:
- Prepare your walls: Fix damp issues and clean surfaces thoroughly.
- Use vapour barriers: Especially critical in older homes to avoid trapped moisture.
- Seal all gaps: Air leakage can halve the performance of insulation.
- Consider thermal bridging: Areas like windows and corners need special attention.
- Finish with plasterboard: For a smooth, paint-ready surface.
Costs of Internal Wall Insulation in Ireland
The cost of internal wall insulation depends on:
- Type of insulation material
- Labour complexity
- Surface preparation needs
- House size and layout
Typical cost range: €80 – €130 per square metre
Other costs may include:
- Reinstating skirting boards, sockets, radiators
- Plastering and painting
- Temporary relocation of furniture
Conclusion
Internal wall insulation is a smart investment that can reduce energy consumption, improve comfort, and increase your property’s value.
With SEAI grants available, now is the perfect time to take the first step toward a warmer, more efficient home. Always work with insulation-certified professionals to ensure insulation is properly installed and meets all regulatory requirements.
If you’re in Ireland, Tamburah is a trusted expert in spray foam and wall insulation, offering eco-friendly, energy-efficient solutions tailored to your needs. Contact us today to discover how our expertise can help you save on energy costs and boost your property’s value.