If you’re planning to extend your home, it’s worth considering whether you should carry out energy upgrades at the same time. Combining a house extension with a home energy retrofit can be one of the most practical ways to improve your property’s comfort, energy efficiency and overall functionality.

Many homeowners across Ireland are choosing to renovate and extend their existing properties rather than move house. However, while an extension creates valuable additional living space, it doesn’t necessarily address problems such as poor insulation, draughty windows, outdated heating systems or high energy bills in the original property.

The good news is that you can retrofit a house while building an extension, and in many cases, completing both projects together makes financial and practical sense.

At House2Home, we specialise in home energy upgrades, extensions and renovations, helping homeowners create warmer, more comfortable and energy-efficient homes.

Why Combine a House Extension with an Energy Retrofit?

Building an extension and retrofitting your home are often treated as two separate projects. However, combining them can offer several advantages.

1. Reduce Overall Disruption

Major renovation projects can involve significant disruption, particularly when replacing heating systems, upgrading insulation or carrying out structural alterations.

If you’re already planning an extension, completing energy upgrades during the same construction period can reduce the need for additional building work later.

For example, if you’re extending your kitchen and need to alter the existing plumbing or heating system, it may be an ideal opportunity to upgrade your heating throughout the property.

Rather than having builders return for a separate retrofit project in a few years, you can coordinate the work under one overall plan.

2. Potentially Save on Construction Costs

Combining an extension with a retrofit doesn’t automatically make every improvement cheaper, but there may be opportunities to reduce duplicated costs.

These can include:

• Scaffolding required for external wall insulation and extension works.

• Plumbing and electrical work carried out as part of the overall renovation.

• Heating system upgrades coordinated across the existing home and new extension.

• Floor insulation installed while existing floors are being replaced.

• Window and door replacements completed alongside other building work.

By planning these improvements together, homeowners may be able to make better use of their renovation budget.

3. Improve Your Home’s BER Rating

A Building Energy Rating (BER) measures the energy performance of a property, with A-rated homes being the most energy efficient and G-rated homes the least.

While a new extension must meet applicable building regulations, the original house may still have poor energy performance.

For example, you could build a highly insulated kitchen extension while the rest of your home still has inadequate attic insulation, older windows and an inefficient heating system.

By upgrading the existing property alongside the extension, you can work towards improving the energy efficiency of the entire home.

Depending on the property and the measures installed, a comprehensive retrofit may help achieve a significantly improved BER rating, potentially reaching an A rating.

4. Create a More Comfortable Home

One of the biggest benefits of combining a retrofit with an extension is the opportunity to improve comfort throughout the property.

A new extension may be warm and well insulated, but if the original house remains cold and draughty, you could notice a significant difference in temperature between the two areas.

Upgrading insulation, windows, airtightness and heating together can help create a more consistent indoor temperature.

This is particularly important for homeowners planning open-plan kitchen, dining and living spaces that connect a new extension with the existing house.

What Energy Upgrades Can You Complete While Building an Extension?

There are several energy efficiency improvements worth considering when extending your property.

Wall Insulation

If your home has poorly insulated external walls, an extension project can provide an opportunity to address this.

Depending on the construction of your property, suitable options may include cavity wall insulation, internal wall insulation or external wall insulation.

External wall insulation can be particularly beneficial for older properties, helping reduce heat loss and improve thermal comfort.

However, the junction between the existing house and the new extension needs careful planning to minimise thermal bridging and maintain effective insulation continuity.

Heat Pump Installation

If you’re considering replacing an older gas or oil heating system, combining a heat pump installation with an extension can be a sensible option.

An air source heat pump provides an energy-efficient alternative to traditional fossil fuel heating systems when properly designed and installed in a suitable property.

Planning the installation alongside an extension allows you to consider:

• Heating requirements across the entire property.

• Underfloor heating in the new extension.

• Radiator upgrades in existing rooms.

• Hot water requirements.

• Suitable locations for the heat pump and associated equipment.

A heat pump should be sized for the heat demand of the completed property, rather than just the original house.

Windows and Doors

Replacing older windows and doors during an extension project can improve insulation, airtightness and comfort.

If your extension includes large glazed doors or windows, it’s important to consider how the glazing performs alongside the rest of the property.

Upgrading existing windows at the same time can help create a more consistent level of energy efficiency throughout the home.

Floor Insulation and Underfloor Heating

If you’re building a new kitchen or living room extension, underfloor heating may be part of your plans.

However, it’s also worth considering the condition of the existing floors.

Where existing floors are being excavated or replaced, there may be an opportunity to install additional insulation and potentially extend underfloor heating into adjoining rooms.

This can be particularly useful when creating a large open-plan space connecting the old and new sections of the property.

Attic and Roof Insulation

While your extension will have its own roof insulation requirements, the existing attic may still be losing significant amounts of heat.

Upgrading attic insulation during the wider renovation can be a relatively straightforward way to improve the energy performance of the original house.

Solar PV Panels

A house extension may also create opportunities to install solar photovoltaic (PV) panels.

Solar PV systems generate electricity from daylight and can help reduce the amount of electricity purchased from the grid.

If you’re changing the roof layout or adding a new roof, it’s worth assessing the available space, orientation and shading before deciding on a solar installation.

Can You Get SEAI Grants When Building an Extension?

Yes, you may still qualify for SEAI home energy upgrade grants while undertaking an extension, provided the relevant works and property meet the scheme’s eligibility requirements.

However, there’s an important distinction between the cost of building an extension and the cost of upgrading your existing home’s energy efficiency.

SEAI grants are designed to support eligible energy efficiency improvements, not to fund the construction of additional living space.

For example, eligible insulation, heating or renewable energy upgrades to the existing dwelling may qualify for financial support, but the construction of a new kitchen extension itself would not generally qualify.

Grant eligibility depends on factors including the property’s age, previous grant history, the measures proposed and the relevant SEAI scheme.

It’s also important to ensure that eligible works are correctly identified and that the grant application and approval requirements are followed before work begins.

House2Home is an SEAI-registered One Stop Shop and can help homeowners understand the grants potentially available for eligible energy upgrades.

Do You Need Planning Permission for an Extension and Retrofit?

Whether you need planning permission depends on the type, size and location of the proposed works.

In Ireland, some house extensions may qualify as exempted development, subject to specific conditions and limitations.

For example, certain rear extensions may be exempt from planning permission where they comply with the relevant requirements, including applicable floor-area and design restrictions.

However, larger extensions, certain alterations to the front of a property and works involving protected structures may require planning permission.

Some retrofit measures, such as external wall insulation or changes to the external appearance of a property, may also have planning implications depending on the circumstances.

Even where planning permission isn’t required, the work must comply with applicable Building Regulations.

For homeowners planning both an extension and an energy retrofit, it’s advisable to establish the planning and regulatory requirements at the earliest stage.

Should You Retrofit Before or After Building an Extension?

In many cases, the best approach is to plan both projects together, even if individual works are completed in stages.

For example, it may make sense to complete structural work on the extension before installing certain insulation systems or carrying out final finishes.

However, decisions about heating systems, insulation, ventilation and airtightness should ideally be made before construction begins.

A coordinated approach can help avoid situations where newly completed work needs to be altered to accommodate energy upgrades.

At House2Home, we recommend assessing the existing property’s energy performance early in the planning process so that suitable improvements can be incorporated into the overall renovation.

How Much Does It Cost to Retrofit a House While Building an Extension?

The overall cost of combining a house extension with an energy retrofit will depend on several factors, including the size and condition of the existing property, the scale of the extension and the energy upgrades required.

A relatively straightforward extension combined with attic insulation and window replacements will have a very different budget from a major renovation involving external wall insulation, a heat pump, new flooring and a complete heating system upgrade.

Some of the main factors affecting costs include:

• Size of the extension: Larger extensions generally require more materials, labour and structural work.

• Existing BER rating: Homes with poor energy performance may require more extensive upgrades.

• Insulation requirements: The type and extent of insulation needed will influence the overall cost.

• Heating system: Installing a heat pump and upgrading radiators or pipework can represent a significant investment.

• Structural alterations: Removing walls, changing layouts and connecting old and new spaces can add complexity.

• Available SEAI grants: Eligible energy upgrades may qualify for financial support, reducing the net cost of the retrofit element.

It’s important to establish a realistic budget for both the extension and the energy efficiency improvements before starting construction.

For an initial indication of potential retrofit costs, homeowners can use our House2Home Online Cost Calculator.

Why a Home Energy Assessment Is an Important First Step

If you’re considering a significant energy retrofit alongside your extension, a Home Energy Assessment (HEA) can help identify the most appropriate improvements for your property.

A Home Energy Assessment examines your home’s existing energy performance and provides recommendations for improving its efficiency.

This can help establish:

• Which insulation measures are most suitable.

• Whether the property is suitable for a heat pump.

• What improvements may be needed to achieve your target BER rating.

• Which energy upgrades could qualify for SEAI grants.

• How the proposed improvements can be incorporated into your renovation plans.

At House2Home, our Home Energy Assessment costs €700, with a €350 SEAI grant available for eligible homeowners, bringing the net cost to €350.

If you decide to proceed with your retrofit through House2Home, we also deduct the €350 customer contribution from your project cost.

The assessment provides a valuable starting point for planning energy upgrades, although extension design, planning and structural requirements will need to be considered separately.

Why Choose House2Home for Your Extension and Retrofit?

At House2Home, we understand that improving your home isn’t just about achieving a better BER rating. It’s about creating a space that works for you and your family.

Whether you’re planning a new kitchen extension, a complete home renovation or a comprehensive energy retrofit, our team can help you explore how these improvements can work together.

Our services include:

• Home extensions and renovations.

• Whole-house energy retrofits.

• Insulation upgrades.

• Heat pump installations.

• Window and door replacements.

• Solar PV installations.

• Home Energy Assessments.

• Assistance with eligible SEAI grants through our One Stop Shop service.

By considering your extension and energy upgrades as part of one overall project, we can help you plan towards a warmer, more comfortable and energy-efficient home.

Frequently Asked Questions

Can I get an SEAI grant for a house extension?

SEAI grants do not generally cover the construction of a house extension itself. However, eligible energy efficiency improvements to the existing home may qualify for grant support, subject to scheme requirements.

Is it cheaper to retrofit a house while extending it?

It can be more cost-effective to coordinate both projects because certain construction activities, such as scaffolding, plumbing and electrical work, may overlap. However, the actual savings depend on the scope of the project.

Can I install a heat pump while building an extension?

Yes. An extension project can be a good opportunity to install a heat pump, particularly if you’re also upgrading insulation and heating throughout the existing property. The system must be appropriately designed for the completed home.

Can I achieve an A-rated BER after extending my house?

Potentially, yes. Achieving an A-rated BER depends on the energy performance of the entire property and the improvements carried out. A Home Energy Assessment can help identify the measures needed to work towards your target rating.

Can House2Home manage both my extension and energy retrofit?

House2Home offers extensions, renovations and energy retrofit services. We can discuss your proposed project and assess how the different elements could be coordinated, subject to the scope and suitability of the works.

Planning a House Extension and Energy Retrofit? Talk to House2Home

If you’re thinking about extending your home, now could be the ideal time to consider improving its energy efficiency too.

Rather than building a modern, energy-efficient extension onto a poorly insulated house, why not explore the opportunity to upgrade the entire property?

At House2Home, we can help you understand your options, explore available SEAI grants and plan a project that combines additional living space with improved comfort and energy performance.

Ready to get started?

Use our Online Retrofit Cost Calculator to receive an indicative estimate for energy upgrades, or book a free telephone consultation with our team to discuss your extension and renovation plans.