Millions of UK homes built before 1919 are haemorrhaging heat through their solid brick and stone walls every single day, adding hundreds of pounds to energy bills year after year. For owners of period properties, this heat loss is especially frustrating because the very design of their homes — built long before modern insulation was even a concept — makes the most obvious solutions complicated, potentially damaging, and sometimes restricted by planning law.
Internal wall insulation for period properties involves fixing insulating boards or natural materials to the inside face of solid brick or stone walls, preserving the exterior appearance while reducing heat loss significantly. In 2026, costs range from approximately £4,000 to £12,000 for a typical semi-detached pre-1919 home, though eligible households may qualify for grants through the Great British Insulation Scheme covering a substantial portion of this cost. The most important consideration is using breathable materials such as wood fibre or mineral wool with lime plaster rather than impermeable foam boards, which can trap moisture and cause serious damp problems in older solid-walled homes. Always commission an independent damp survey before work begins and use a TrustMark-registered installer experienced in traditional building methods.
- Always use a breathable insulation system such as wood fibre or mineral wool with lime plaster in period properties to prevent moisture build-up behind the boards
- Expect to lose between 75mm and 120mm of floor space per external wall treated, so measure rooms carefully before committing to a system
- Get at least 3 quotes from installers registered with the Cavity Insulation Guarantee Agency or TrustMark to ensure quality workmanship and protect your warranty
- Check with your local planning authority before starting if your home is listed or in a conservation area, as permitted development rules may still apply to internal works
- Apply for the Great British Insulation Scheme or ECO4 funding before booking installation, as eligible households can receive grants covering the majority or all of the cost
- Commission a damp survey from an independent surveyor before any insulation work begins, as trapping moisture in solid walls can cause serious structural damage over time
- Budget between £4,000 and £12,000 for a typical semi-detached period property depending on wall area, system chosen, and whether lime plaster finishing is required
- Understanding Internal Wall Insulation in Period Properties
- Why Solid Walls in Period Homes Lose So Much Heat
- The Main Benefits of Internal Wall Insulation for Period Homes
- The Risks and Drawbacks You Must Weigh Up
- Moisture Risk and Breathability Explained for Period Properties
- Best Insulation Materials for Period Properties
- Comparing IWI Materials for Period Homes
- What Internal Wall Insulation Costs in 2026
- Grants and Funding Available for Period Property Insulation
- How to Plan Your IWI Project the Right Way
Internal wall insulation for period properties involves fixing insulating material to the inside face of external solid walls, rather than cladding the outside, allowing the building’s historic character and exterior appearance to remain untouched. It is one of the most effective ways to reduce heat loss in a pre-1919 home, but it carries real risks — particularly around moisture — that must be properly understood before work begins. This article walks through the genuine pros and cons, the best materials to use, realistic costs for 2026, and the funding options available to help make the project more affordable.
Understanding Internal Wall Insulation in Period Properties
Internal wall insulation (IWI) is the practice of adding insulating material to the interior surface of a building’s external walls, creating a thermal barrier from the inside rather than the outside. For period properties, where the outward appearance is often protected or simply cherished, this inside-out approach is frequently the only practical option.
Internal wall insulation is defined here as any system of rigid boards, mineral wool, or natural material fixed or bonded to the internal face of an external wall, usually followed by a new plasterboard or lime plaster finish. The overall wall thickness increases inwards, which means room dimensions shrink slightly — a trade-off that must be factored into planning.
In the UK, a period property generally refers to any home built before 1919. These buildings were typically constructed with solid walls — either brick, stone, or occasionally timber-frame with infill — rather than the cavity walls that became standard from the 1920s onwards. Cavity walls, as the name suggests, have a gap between two layers of masonry, and that gap can be filled with insulating material relatively easily. Solid walls have no such gap. The entire wall is one continuous mass of brick or stone, which conducts heat far more readily than a modern insulated construction.
According to Energy Saving Trust data, an uninsulated solid wall has a U-value of approximately 2.0 to 2.1 W/m²K. A U-value measures how readily heat passes through a building element — the lower the number, the better the insulation. By comparison, an insulated cavity wall achieves a U-value of around 0.3 to 0.5 W/m²K. In practical terms, solid walls allow roughly four to six times as much heat to escape as a well-insulated cavity wall. That difference appears directly on your energy bill every single month.
Period properties also frequently face additional planning constraints. Homes that are Listed Buildings — formally recognised for their historic or architectural significance — require Listed Building Consent for any works that could affect their character, inside or out. Properties in a Conservation Area face additional scrutiny for external changes, though internal works are often less restricted. Always check your property’s status with your local planning authority before commissioning any insulation work.
Practical tip — Before doing anything else, use the Historic England National Heritage List for England (or the equivalent registers for Scotland, Wales, and Northern Ireland) to confirm whether your property is listed, and contact your local authority planning department about Conservation Area status.
Why Solid Walls in Period Homes Lose So Much Heat
Uninsulated solid walls can account for up to 45% of a period home’s total heat loss, making them the single largest source of thermal inefficiency in Victorian and Edwardian properties — far outstripping loft heat loss, draughts, or windows.
Pre-1919 construction was never designed with thermal efficiency in mind. Thick stone or brick walls provided structural solidity, weather resistance, and a certain robustness against the elements, but they were not conceived as insulators. Their builders were working with an entirely different set of priorities: durability, appearance, and the availability of local materials. The coal fires and modest expectations of thermal comfort in that era meant that heat loss through walls was simply accepted as a fact of life.
The physics at work here is straightforward. Brick and stone are dense materials that conduct heat readily. When cold outdoor air chills the outside of a solid wall, that coldness travels inward through the masonry until the internal surface is noticeably cool to the touch — sometimes uncomfortably so in winter. This process, known as thermal conduction, happens continuously whenever there is a temperature difference between inside and outside. In a modern insulated building, a layer of low-conductivity material interrupts this process; in a solid-walled period home, nothing does.
This creates a core tension for period property owners. The thick stone walls, the original lime plasterwork, the decorative cornices, the generous ceiling heights — these are precisely the features that make Victorian and Edwardian homes so desirable. Yet those same features make insulation installation complex, expensive, and, if done incorrectly, potentially damaging to the building’s fabric and long-term health.
guide to solid wall insulation options for UK homes
Practical tip — If you are unsure how much heat your walls are losing, an Energy Performance Certificate (EPC) assessment or a thermal imaging survey carried out by a qualified assessor can give you a clear, visual picture of where the heat is escaping most severely.
The Main Benefits of Internal Wall Insulation for Period Homes
When correctly specified and installed, internal wall insulation offers period property owners meaningful improvements in comfort, running costs, and carbon footprint without altering a single stone of the building’s exterior.
Thermal Comfort Improvement
One of the most immediate benefits homeowners report after installing IWI is a reduction in cold spots and draughts near external walls. In a typical Victorian terrace or Edwardian semi-detached, rooms with uninsulated solid walls can feel chilly even when the heating is running, because the cold wall surface draws warmth away from the room through radiation and convection. IWI eliminates this cold surface effect, making rooms feel warmer at lower thermostat settings — a genuine quality-of-life improvement that goes beyond simple energy saving.
Energy Bill Savings
According to Energy Saving Trust estimates, insulating the solid walls of a semi-detached home could save approximately £390 to £470 per year on energy bills, depending on fuel type, current tariff rates, and the property’s overall efficiency. These figures will vary based on your home’s specific characteristics, heating system, and how the insulation is installed, so treat them as a helpful guide rather than a guarantee. For personalised estimates, the Energy Saving Trust’s online calculator at energysavingtrust.org.uk is worth consulting.
Reduced Carbon Footprint
Lower energy demand means lower carbon emissions, which matters both for individual households working towards net zero commitments and for the UK’s broader climate targets. Improving your home’s Energy Performance Certificate rating through IWI can also increase its market appeal — an EPC rating of C or above is increasingly valued by buyers and mortgage lenders alike.
Preserved Exterior Appearance
Unlike external wall insulation, which wraps the outside of a building in insulating material and render — substantially changing its visual character — IWI leaves the exterior completely untouched. For properties in Conservation Areas, those with original stonework, or simply homeowners who love the look of their Victorian brickwork, this is a decisive advantage. It is also the primary reason IWI is often the only viable option for listed buildings, where external alteration would require consent that may not be granted.
Practical tip — Always get at least three quotes from installers experienced in heritage retrofit, not just standard IWI contractors. The specification matters as much as the price, especially in period properties.
The Risks and Drawbacks You Must Weigh Up
Internal wall insulation is not without significant downsides, and in period properties the consequences of getting it wrong can be severe — including structural damage, persistent damp, and the irreversible loss of historic fabric.
Moisture and Interstitial Condensation
This is the most serious risk associated with IWI in period properties, and it deserves careful attention. Interstitial condensation occurs when warm, moist air from inside the home migrates into the wall structure and meets a cold surface, where it condenses into liquid water. In a modern building with carefully designed vapour control layers, this risk is managed through precise detailing. In a period property with vapour-impermeable insulation boards added to breathable lime walls, the consequences can be damaging: trapped moisture promotes timber rot, mould growth, and in severe cases, structural deterioration of the masonry itself.
Loss of Floor Area
IWI adds material to the inside of external walls, typically reducing room dimensions by 75mm to 125mm per treated wall. In a large Victorian reception room this may be barely noticeable, but in a smaller bedroom or a narrow hallway it can feel meaningful. In some cases, the reduced floor area may also affect the property’s value or its compliance with permitted development rules for future extensions.
Disruption to Period Features
Cornices, dado rails, picture rails, architraves, and original skirting boards all sit at the junction between wall and floor or ceiling. IWI requires these to be removed and reinstated — and in many cases, original plasterwork cornices simply cannot be replicated to the same standard. Once original lime plasterwork is removed, it is gone. This is not a reversible process, and for lovers of period interiors it represents a genuine, lasting loss.
Thermal Bridging at Joist Ends
Timber floor joists in pre-1919 homes are commonly built into the external walls — their ends are literally embedded in the masonry. When IWI is installed without accounting for this, the joist ends sit in a cold zone behind the insulation, which can lead to condensation, rot, and structural failure over time. Historic England has highlighted this issue repeatedly in its guidance on traditional building retrofit, and it requires careful detailing to address — typically involving isolating the joist ends with breathable insulation packing.
how to deal with damp in Victorian and Edwardian homes
Practical tip — Ask any prospective installer specifically how they will handle joist ends and thermal bridges. If they cannot give you a clear, detailed answer, treat that as a warning sign.
Moisture Risk and Breathability Explained for Period Properties
Understanding how pre-1919 buildings manage moisture is essential before specifying any insulation — and it is an area where many standard insulation contractors lack the specialist knowledge required for period properties.
Pre-1919 buildings were constructed using breathable or hygroscopic materials — primarily lime mortar, lime plaster, and porous masonry. These materials can absorb moisture when humidity is high and release it again when conditions dry out, allowing the wall to manage moisture passively without accumulation. This is sometimes described as the wall “breathing,” though the more precise term is vapour diffusion — water vapour moves through the material in response to humidity gradients rather than being blocked at any single point.
Modern vapour-impermeable insulation boards — particularly polyisocyanurate (PIR) and polystyrene — work well in modern buildings specifically designed around them, but they fundamentally disrupt the moisture behaviour of a traditional solid wall. By blocking vapour diffusion at the internal surface, they force moisture to accumulate within the wall rather than allowing it to migrate and dissipate. Over time, this can saturate lime mortar, soften stonework, and rot embedded timbers.
The recommended alternative for period properties is vapour-permeable, hygroscopic insulation — materials that continue to allow some degree of moisture movement through the wall assembly. Woodfibre boards, hemp-lime, and natural cork are the most commonly specified options in heritage retrofit contexts, and all three are endorsed in guidance from organisations including the Sustainable Traditional Buildings Alliance (STBA) and Historic England.
Before any IWI work begins on a period property, a hygrothermal assessment — sometimes called a moisture risk assessment — is strongly recommended. This is a technical analysis of how the proposed insulation system will affect the moisture behaviour of the wall over a full seasonal cycle. Without it, you are specifying insulation largely blind to the risks. This assessment should be carried out by a specialist with experience in traditional building construction, not a standard energy assessor.
breathable insulation materials for traditional buildings
Practical tip — Look for contractors registered with the STBA or who hold relevant heritage retrofit qualifications. TrustMark registration is a minimum baseline; heritage expertise goes further still.
Best Insulation Materials for Period Properties
Choosing the right insulation material is arguably the most important decision in an IWI project for a period home — and it is emphatically not a decision to make on cost alone.
Woodfibre Insulation Boards
Woodfibre boards are widely considered the gold standard for internal wall insulation in period properties by heritage building specialists. They are vapour-permeable, hygroscopic, compatible with lime-based plaster finishes, and available in thicknesses from 60mm to 120mm. Their thermal performance is good, if not quite as high per millimetre as synthetic alternatives, but their compatibility with traditional wall construction makes them the default recommendation in many heritage retrofit projects.
Hemp-Lime
Hemp-lime (sometimes called hempcrete) is a natural composite of hemp shiv — the woody core of the hemp plant — mixed with a lime binder. It is breathable, has excellent moisture-buffering properties, and is highly compatible with existing lime construction. It requires specialist installation and tends to be applied in thicker sections (100mm to 200mm), which means it sacrifices more floor area than board-based alternatives. It is, however, a genuinely sympathetic material for period buildings.
Natural Cork
Cork is a renewable, breathable, and sustainable material that performs well as insulation in heritage retrofit contexts. It is available as rigid boards or as spray-applied cork, the latter being useful for irregular surfaces such as rubble stone walls. Its thermal performance is broadly comparable to woodfibre, and it is increasingly specified by heritage-conscious retrofit specialists.
PIR and Phenolic Foam Boards
PIR (polyisocyanurate) and phenolic foam boards offer the highest thermal performance per millimetre of any common insulation type — useful where space loss must be minimised. However, they are vapour-impermeable and are generally unsuitable for period properties without extremely careful detailing and a thorough hygrothermal assessment. Their use should be limited to specific situations where dryness can be assured and where a qualified specialist has confirmed their suitability.
Mineral Wool with a Vapour Control Layer
Mineral wool is commonly used in standard IWI systems, often fitted within a studwork frame with a vapour control layer (VCL) on the warm side. It offers partial vapour permeability and reasonable thermal performance, but the VCL disrupts the breathable nature of a traditional wall. It is a medium-suitability option and should only be used in period properties following professional assessment.
Comparing IWI Materials for Period Homes
The table below summarises the key characteristics of the most commonly considered insulation materials for period property internal wall insulation, to help you have more informed conversations with contractors and assessors.
| Material | Typical Thickness (mm) | Lambda Value (W/mK) | Vapour Permeable | Heritage Suitability | Approximate Material Cost per m² (2026) |
|---|---|---|---|---|---|
| Woodfibre board | 60–120 | 0.038–0.042 | Yes | High | £40–£75 |
| Hemp-lime | 100–200 | 0.060–0.080 | Yes | High | £60–£100 |
| Natural cork | 40–100 | 0.040–0.045 | Yes | High | £35–£65 |
| PIR foam board | 25–75 | 0.022–0.028 | No | Low to Medium | £20–£45 |
| Mineral wool with VCL | 75–100 | 0.032–0.040 | Partial | Medium | £25–£55 |
These figures represent material costs only. Installation labour, preparation, decoration, and reinstatement of period features add substantially to the overall project cost. Always verify material prices with current supplier quotes, as these fluctuate with market conditions.
Practical tip — The lambda value (thermal conductivity) tells you how well a material insulates per unit of thickness — the lower the number, the better. However, heritage suitability and vapour permeability should carry at least as much weight as thermal performance when specifying for a period property.
What Internal Wall Insulation Costs in 2026
Internal wall insulation for period properties sits at the higher end of the home improvement cost scale, particularly when heritage-appropriate materials and specialist contractors are used — but the long-term energy savings and comfort benefits can justify the investment when the project is well-specified.
For a whole-house IWI installation in a solid-walled semi-detached period home, expect to pay in the region of £8,000 to £15,000 for the full treatment. Larger properties — a three-storey Victorian townhouse, for example — could exceed £20,000. These figures are based on Energy Saving Trust guidance and typical quotes from Ofgem-registered installers in 2026, and they will vary based on property size, material choice, and the complexity of the building’s layout and features.
Some homeowners choose a room-by-room approach, tackling one space at a time to spread the cost. A single room can cost between £1,500 and £4,000 depending on size and material. This is understandable from a budgeting perspective, but it carries an important caveat — treating only part of an external wall can create a sharp thermal boundary between insulated and uninsulated sections, which increases the risk of condensation at the junction. If you do take a phased approach, ensure your installer designs the system with future phases in mind.
Using heritage-appropriate, vapour-permeable materials and engaging specialist heritage retrofit contractors typically adds 20% to 40% to the base cost compared to a standard IWI installation. This premium reflects the additional expertise, the higher material costs, and the more careful detailing required. It is money well spent, given the alternative risks.
Finally, budget separately for reinstatement of period features. Reinstating cornices, skirting boards, architraves, and original decorative plasterwork to a period-appropriate standard requires skilled craftspeople and appropriate materials. Depending on the scope of work and the quality required, reinstatement costs can add a further £1,000 to £5,000 or more to the overall project budget.
| Scope of Work | Approximate Cost Range (2026) | Key Variables |
|---|---|---|
| Whole-house IWI, standard materials | £8,000–£12,000 | Property size, wall area, access |
| Whole-house IWI, heritage specification | £11,000–£15,000+ | Material choice, contractor specialism |
| Single room IWI | £1,500–£4,000 | Room size, material, detailing |
| Period feature reinstatement | £1,000–£5,000+ | Extent of original features, craftsperson rates |
| Hygrothermal assessment | £300–£800 | Property size, complexity |
Practical tip — Always get at least three detailed, written quotes. Ask each contractor to specify exactly which material they are proposing, what thickness, how joist ends and thermal bridges will be addressed, and what their approach to period feature reinstatement will be.
Grants and Funding Available for Period Property Insulation
Funding support for solid wall insulation in period properties exists in 2026, though the picture is more complicated than for cavity wall or loft insulation — and heritage properties face additional eligibility constraints in some schemes.
The Great British Insulation Scheme
The Great British Insulation Scheme (GBIS), administered by Ofgem, provides funding for insulation measures in homes with an EPC rating of D or below. Solid wall insulation — both internal and external — is an eligible measure under GBIS. Eligibility is assessed on a combination of energy efficiency rating and household income or council tax band, with better-off households in lower-rated homes potentially still qualifying through the general group. Period properties frequently have EPC ratings of D or below due to their solid walls, which means many will qualify in principle. Contact your energy supplier or an Ofgem-registered installer to assess your eligibility.
ECO4
The Energy Company Obligation (ECO4) scheme requires large energy suppliers to fund insulation and heating improvements in lower-income and fuel-poor households. Solid wall insulation is a fully eligible measure. ECO4 targets households on qualifying benefits or with low incomes, and the funding can cover a substantial proportion — sometimes all — of the installation cost. A TrustMark-registered and MCS-eligible contractor can assess your eligibility and help you apply through your energy supplier. Note that heritage-appropriate materials may sometimes require additional negotiation within the scheme’s cost frameworks.
Local Authority Grants and Flex Funds
Many local authorities administer their own energy efficiency grant programmes or have access to the ECO4 Flex mechanism, which allows them to refer additional households — beyond those on standard qualifying benefits — for ECO4 funding. Some councils also have specific budgets for heritage retrofit support, particularly in areas with significant concentrations of pre-1919 housing stock. It is always worth contacting your local authority’s energy team directly to ask what is available in your area.
Historic England and Heritage Funding
For listed buildings, Historic England and its equivalents — Historic Environment Scotland, Cadw in Wales, and the Historic Environment Division in Northern Ireland — occasionally provide grant funding for works that improve the energy efficiency of historic buildings in a heritage-sensitive manner. These grants are competitive and not universally available, but they are worth investigating for listed properties. Historic England also publishes freely available technical guidance on insulating traditional buildings, which is an invaluable resource in its own right.
Mortgages and Finance
Green mortgages and retrofit finance products are increasingly available from UK lenders, allowing homeowners to borrow specifically for energy improvement works at preferential rates. Some lenders offer additional borrowing on existing mortgages for retrofit projects, and the interest rates on these products have become more competitive as the sector has grown. Speak to a whole-of-market mortgage broker about the options relevant to your property and financial situation.
ECO4 eligibility explained for UK homeowners
Great British Insulation Scheme how to apply
Always use TrustMark-registered contractors for funded insulation work. TrustMark is the government-endorsed quality scheme for retrofit and home improvement, and it is a requirement for most publicly funded insulation programmes. Verify any contractor’s registration at trustmark.org.uk before signing anything.
Practical tip — Before assuming you do not qualify for any grant funding, speak to an Ofgem-registered installer or your local authority’s energy team. Eligibility rules are more nuanced than many homeowners realise, and a quick phone call could reveal support you did not know existed.
How to Plan Your IWI Project the Right Way
Getting internal wall insulation right in a period property requires more upfront planning than almost any other home improvement project. The sequence in which you carry out assessments, appoint contractors, and specify materials matters enormously.
- Confirm your property’s planning status. Check whether your home is listed or within a Conservation Area before doing anything else. Contact your local planning authority for guidance on what consents, if any, you will need for internal works.
- Commission a hygrothermal assessment. Appoint a specialist — ideally one with STBA membership or recognised heritage retrofit qualifications — to analyse how your proposed insulation system will interact with your wall’s moisture behaviour. This assessment should inform all subsequent decisions.
- Specify the right material. Based on the hygrothermal assessment, agree on a vapour-permeable material appropriate to your wall construction. Do not let cost alone drive this decision.
- Address joist ends and thermal bridges. Ensure your specification explicitly covers how embedded timber joist ends and other thermal bridges will be treated. This should be written into the contractor’s scope of works.
- Plan for period feature reinstatement. Decide in advance which features you want to retain and how they will be reinstated. Commission a joiner and plasterer experienced in period work before demolition begins.
- Obtain at least three detailed quotes. Compare not just price but specification — material type, thickness, detailing approach, and finish. The cheapest quote may be so because it skips the details that matter most.
- Verify contractor credentials. Ensure your chosen contractor is TrustMark-registered. For any funded work, confirm they are registered with the appropriate scheme. Check their registration at trustmark.org.uk.
- Monitor after installation. In the first winter after installation, check for signs of damp or condensation, particularly near joist ends and in corners. Early identification of any moisture issues allows them to be addressed before serious damage occurs.
Internal wall insulation in a period property is not a project to rush, and it is not one where cutting corners saves money in the long run. Done well, with the right materials, the right contractors, and proper respect for the building’s historic fabric, it can genuinely transform a cold, expensive-to-heat Victorian or Edwardian home into a far more comfortable, efficient place to live — without sacrificing any of the character that made you fall in love with it in the first place.
how to find a heritage retrofit contractor in the UK
Practical tip — The Sustainable Traditional Buildings Alliance (stba.org.uk) and Historic England (historicengland.org.uk) both publish free technical guidance on insulating traditional buildings. Reading these before meeting contractors will help you ask the right questions and spot any gaps in proposed specifications.
Frequently Asked Questions
how much does internal wall insulation cost for a period property in the UK?
Internal wall insulation for a typical pre-1919 semi-detached home in the UK costs between £4,000 and £12,000 in 2026, depending on wall area, insulation system, and finish. Rigid phenolic board systems sit at the lower end around £50 to £70 per square metre installed, while natural wood fibre or cork systems with lime plaster finishing can reach £100 to £130 per square metre. Detached period properties with larger wall areas can exceed £15,000 for a full treatment.
will internal wall insulation damage a period property?
Internal wall insulation can cause serious damp and structural problems in period properties if the wrong materials or vapour barriers are used, because solid brick and stone walls need to breathe and release moisture. Using breathable materials such as wood fibre boards, hemp batts, or mineral wool with a lime plaster finish significantly reduces this risk. A pre-installation damp survey and appointment of a specialist experienced in traditional buildings is strongly recommended to avoid long-term damage.
do I need planning permission for internal wall insulation on a listed building?
Listed Building Consent is required for internal wall insulation on any listed property in England, Scotland, and Wales, as the works alter the character of a protected structure even though they are internal. Failure to obtain consent is a criminal offence and can result in enforcement notices requiring the removal of all installed materials. Contact your local planning authority or Historic England for guidance before commissioning any work on a Grade I, Grade II*, or Grade II listed home.
what grants are available for internal wall insulation in period homes in 2026?
The Great British Insulation Scheme offers funding of up to £15,000 for solid wall insulation including internal systems for eligible households, with eligibility based on EPC rating and household income thresholds. ECO4, administered through energy suppliers, can cover the full cost for households receiving qualifying benefits such as Universal Credit or Pension Credit. The Boiler Upgrade Scheme does not cover insulation, but some local councils offer additional top-up grants through the Warm Homes Local Grant programme launched in 2026.
how much room will I lose with internal wall insulation in a period property?
A standard internal wall insulation system with rigid board and plasterboard finish typically reduces the internal floor area of each treated room by between 75mm and 120mm per external wall. For a 3.5 metre wide Victorian bedroom with two external walls, this could mean losing up to 240mm of width, reducing usable floor area by roughly 0.8 square metres. Slimmer aerogel-based systems can reduce this loss to as little as 40mm per wall but cost considerably more, typically £120 to £180 per square metre installed.
