Which insulation should you do first?

The essentials

Plan together, carry out in stages if needed

For a poorly insulated attic, attic insulation is usually a sensible first upgrade to investigate. Damp, repairs and existing insulation can change the order.
Plan insulation, unwanted air leaks and ventilation together. Reducing draughts must not remove the fresh air your home or a fuel-burning appliance needs.
A BER assessment and its advisory report help you compare improvements. A One Stop Shop home energy assessment gives a more detailed plan for several upgrades.
If you want a heat pump later, ask for its suitability assessment early. Settle the insulation plan before the installer sizes the heating system.

The Sustainable Energy Authority of Ireland (SEAI) runs home energy grant schemes. Its insulation guidance describes attic insulation as generally the most cost-effective home energy upgrade. That is a starting point for a survey, rather than a rule that every home should buy another layer.

The aim is to reduce heat escaping before choosing a new heating system. This is often called fabric first: the fabric is the roof, walls, floors, windows and doors enclosing the heated rooms. A whole-house plan considers these together, even if you only have the budget for one job now.

Heat leaves through those surfaces and through unwanted air gaps. SEAI’s guide to home energy ratings explains how insulation, windows and air leaks affect a home’s energy performance. A survey of your house sets the priorities. Plan draught reduction alongside ventilation so the home keeps the fresh air it needs.

Start with condition and your plans

Before choosing a product, write down which rooms feel cold, where there are draughts or signs of damp, and what work you already intend to do. Bring photographs, any previous insulation paperwork and your available budget to the survey.

Ask the contractor or retrofit designer to inspect leaks, damp, damaged timbers and the condition of existing insulation before specifying new work. A retrofit designer is a building professional who plans improvements to an existing home. For persistent or unexplained defects, get a building surveyor or other suitable specialist to investigate the cause and specify repairs first. Covering a problem makes it harder to inspect later.

Tell them if you are planning a new roof, windows, kitchen, extension or heating system. Ask what needs designing now so the first job will connect properly to the next. In an older stone or solid-wall house, choose someone experienced in traditional buildings and discuss how moisture passes through the existing materials before choosing wall insulation.

Use an assessment to set the priorities

A Building Energy Rating (BER) rates a home’s calculated energy performance. The accompanying advisory report recommends improvements. It is a useful starting point, but the recommendations still need a house survey and a design before construction. SEAI explains that the report starts the discussion with a retrofit professional; it does not resolve every construction detail.

You can find an existing BER and advisory report using the BER number or your Meter Point Reference Number (MPRN), shown on the electricity bill. If the house has changed since that assessment, tell the assessor what work was done. If you need a new assessment, follow SEAI’s BER assessment steps and assessor search. Ask for the assessment and advice you need before booking, including its fee.

For a coordinated renovation, compare One Stop Shops: SEAI-registered providers that manage whole-home energy upgrades. Their home energy assessment includes a BER, a technical upgrade report, a heat-pump assessment and estimated costs. Ask several providers what their assessment costs and includes. SEAI says you can take the report to another registered provider and are under no obligation to proceed with the upgrades.

Bring one question to either assessment: “Given my budget and the work I plan later, what should I do now, and what must I prepare for?” Ask for the reasons, not just a target BER letter.

Choose the first job from the survey

Use the following as questions to test with the surveyor, rather than a fixed shopping list:

Little or uneven attic insulation: ask whether adding insulation on the attic floor, above the ceilings of the rooms below, suits the way you use the attic. Check the roof condition, airflow and access. Start with our attic guide.
An unfilled cavity wall: ask a registered contractor to inspect the wall’s suitability, exposure to wind-driven rain, damp and any existing fill. A cavity is the gap between the inner and outer layers of a brick or block wall; not every house has one. See the cavity-wall guide.
Walls needing a different approach: compare external wall insulation with internal wall insulation, including moisture assessment, lost room space, reinstatement and how adjoining surfaces will meet.
Floors already being opened: investigate insulation before replacing the finish or fitting units. Ask about changes in height, damp and protection against radon, a radioactive gas from the ground that can enter the home. Ask about testing as well as protection; the EPA’s household guidance explains how to arrange a test. Our floor guide explains the insulation options and ventilation below timber floors.
Draughty or failing windows and doors: ask whether repair and draught sealing are suitable or replacement is needed. If wall insulation is planned, have the window position and the connection to the insulation designed before ordering either.

Ask for the expected benefit, complete installed price and disruption of each suitable option. Compare the price after any confirmed grant, but do not make the largest grant the reason to choose a method. A grant does not establish that the house needs that work.

Plan ventilation alongside insulation

Airtightness means limiting uncontrolled air leaks through gaps. Ventilation is the deliberate supply of fresh air and removal of stale, moist air. Draught sealing and new windows can change the airflow even when the job is sold as an insulation upgrade.

SEAI’s ventilation guidance describes options from designed vents with extract fans to continuous mechanical systems. Ask the designer to specify the system your home will need after the work, who will fit and check it, and how you will use and maintain it. Ask for the ventilation price in the quote now.

Do not block wall or roof vents as a draught fix. Some fuel-burning appliances draw combustion air from the room and need permanent ventilation; have the installer check the appliance’s requirements before changing airflow. Preserve ventilation below a suspended timber floor as well: this is a timber floor supported above an air space, where airflow helps prevent damp and rot. Removing unwanted leaks is different from closing an intentional air supply.

Prepare for a heat pump before replacing the heating

A heat pump takes heat from outside and uses electricity to deliver it indoors. Insulation reduces the heat the system must replace. Ask for a suitability assessment early if a heat pump is part of your plan, so any required insulation can be included in the budget and sequence.

For SEAI’s individual heat-pump grant, a home built before 2007 normally needs an SEAI-registered technical advisor’s assessment before application. Current grant rules allow a self-declaration instead for homes built from 2007 onwards, or a pre-2007 home with a valid BER showing a Heat Loss Indicator of 2.3 W/(K·m²) or less. The Heat Loss Indicator expresses calculated heat loss per square metre of floor area for each degree of temperature difference; lower means less heat loss. Ask the advisor or installer to check which evidence your application needs. An exemption from that assessment does not replace heating-system design.

SEAI’s installation guide explains that the installer calculates each room’s heat demand to size the heat pump and check radiators or underfloor heating. Have them use the agreed insulation and ventilation design, rather than size the system for the old house and hope later work will suit it. Ask which radiators, pipes, controls and hot-water equipment need changing and include them in the quote.

Phase the work without paying twice

Ask for a short written plan with a sequence, an owner for each task and the dependencies between them. A dependency is something that must be settled before another job can go ahead. SEAI’s technical standards cover pre-installation surveys and connections between insulation and windows. Use these practical questions to turn the design into a work sequence:

Repair first: who resolves the damp, leaks or unsafe services, and who checks that the house is ready to cover up?
Draw the connections: who shows how roof, wall, window and floor insulation will meet, including the work left for a later phase? Cold gaps at these connections can allow heat to escape and condensation to form.
Coordinate access: can scaffolding, room clearance or lifting floors serve more than one planned job? Ask what must be completed before plaster, decoration, flooring or fitted furniture is reinstated.
Include ventilation and heating: who fits and checks the air supply, and when will the heating installer confirm the final design?
Record completion: who keeps photographs of concealed insulation, product details, invoices, warranties and test results? Ask what evidence the BER assessor and grant scheme require before the work is hidden.

For example, if the survey finds a poorly insulated attic and suitable unfilled cavity walls, those may be useful early phases while larger floor work waits for renovation. If a new kitchen will soon prevent access to internal wall insulation, investigate that wall before fitting the units. These are planning examples; your survey determines the appropriate work.

Choose the grant route before starting a phase

With individual grants, you manage the work and choose registered contractors. Get quotes, choose your contractor, apply and accept the grant offer before work starts or materials are bought. Read the grant steps and confirm the completion deadline for that offer. Do not assume a later phase can claim support again for the same work.

With a One Stop Shop, the provider manages the application and a qualifying package. The current whole-home rules require a home built and occupied before 2011, a finished BER of B or better, and either a heat pump or a reduction in calculated primary energy use of at least 100 kilowatt-hours per square metre per year. Primary energy includes the energy used to produce and supply what the home consumes. Have the provider calculate the package, check previous support and confirm grant approval before work begins. Do not assume a few separate jobs automatically qualify.

If you own and live in your home and receive a qualifying welfare payment, also check Warmer Homes, SEAI’s fully funded route. Our grant comparison links the official payment list and explains the survey and eligibility conditions. Check that option before committing to privately funded work.

Your next step

Gather the existing BER, previous insulation records and the list of work you want to do. Book the appropriate assessment, ask for a phased written plan and compare itemised quotes for its first job. Use Check grant eligibility for published insulation costs and possible grant routes; it does not survey the house, size heating or approve funding. Our contractor guide helps you turn the plan into comparable quotes.

Common questions

Do I have to insulate everything at once?

No. You can plan the whole house and pay for suitable work in stages. Ask your surveyor to show what can stand alone and what must be designed together, such as ventilation and draught sealing. If using grants, confirm the route and approval for each phase before starting; future support is not guaranteed.

Is attic insulation always first?

No. It is often the first option to investigate when the attic has little or damaged insulation. A leak, damp, unsafe wiring, an already well-insulated attic or floors already open for renovation may change the priority. Have the condition and existing insulation checked before ordering more.

Does a good BER prove my house is ready for a heat pump?

The overall BER letter alone does not settle heat-pump suitability. Your installer needs to assess heat loss and design the heating system. For an individual heat-pump grant, SEAI has separate rules about technical assessment and the evidence that can replace it; the heat-pump section on this page explains them.

Should I change the windows before insulating the walls?

Ask your designer to settle both details before either job starts. New windows and wall insulation need to meet without leaving a cold strip around the opening. The installation order depends on the chosen wall system and window position; ask who will draw and take responsibility for that connection.

Work out your own numbers

Grant total: add up what each SEAI route pays for your upgrades.
Which grant route: five questions to find where to apply first.

Sources and review

Sources were last checked on 30 October 2026. The review checks published guidance; ask a contractor to survey and design the work for your home.