{"id":4898,"date":"2026-09-27T09:18:47","date_gmt":"2026-09-27T09:18:47","guid":{"rendered":"https:\/\/mywarmhome.co.uk\/stage\/?page_id=4898"},"modified":"2026-10-01T20:20:36","modified_gmt":"2026-10-01T20:20:36","slug":"internal-wall-insulation-2","status":"publish","type":"page","link":"https:\/\/mywarmhome.co.uk\/stage\/internal-wall-insulation-2\/","title":{"rendered":"Internal Wall Insulation"},"content":{"rendered":"\n
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INSULATION \/ MY WARM HOME<\/p>\n\n\n\n

Internal wall insulation.<\/h1>\n\n\n\n

Improve comfort from the inside \u2014 with moisture, junctions and living space considered from the start.<\/p>\n<\/div>\n<\/div><\/div>\n\n\n\n

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01<\/p>\n\n\n\n

Understand<\/h3>\n\n\n\n

How IWI improves comfort and changes wall behaviour.<\/p>\n<\/div>\n\n\n\n

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02<\/p>\n\n\n\n

Detail<\/h3>\n\n\n\n

Moisture, airtightness and thermal bridges.<\/p>\n<\/div>\n\n\n\n

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03<\/p>\n\n\n\n

Materials<\/h3>\n\n\n\n

Compare systems before choosing a product.<\/p>\n<\/div>\n\n\n\n

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04<\/p>\n\n\n\n

Check<\/h3>\n\n\n\n

Assessment, installation, ventilation and safety.<\/p>\n<\/div>\n<\/div>\n<\/div>\n\n\n\n

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THE SHORT VERSION<\/p>\n\n\n\n

IWI is a complete wall system \u2014 not just insulated plasterboard.<\/h2>\n<\/div>\n\n\n\n
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Internal wall insulation (IWI) adds a thermal layer to the room side of an external wall. It can help reduce heat loss and improve comfort where insulating the outside is not practical.<\/p>\n\n\n\n

Unlike EWI, the original masonry or other wall structure can become colder after internal insulation is installed. Moisture management, the wall\u2019s ability to dry and details at edges and penetrations therefore need deliberate design.<\/p>\n\n\n\n

An IWI scheme also affects the inside of the room: radiators, sockets, skirting, reveals, coving, joinery and floor area may all change. The full scope of reinstatement should be agreed before work begins.<\/p>\n\n\n\n

Read the official retrofit IWI best-practice guide \u2192<\/a><\/p>\n<\/div>\n<\/div>\n<\/div>\n\n\n\n

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01 \/ UNDERSTAND THE SYSTEM<\/p>\n\n\n\n

Four principles behind a good internal insulation design.<\/h2>\n\n\n\n

IWI can be suitable for solid-wall homes and other constructions following assessment. No single board, adhesive or vapour-control approach suits every wall.<\/p>\n\n\n\n

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01<\/p>\n\n\n\n

Insulate the room side<\/h3>\n\n\n\n

Improve the thermal resistance of the existing external wall and raise the temperature of the new inner surface.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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02<\/p>\n\n\n\n

Assess moisture first<\/h3>\n\n\n\n

Investigate external water ingress, existing damp, exposure and whether the original wall can dry safely after insulation.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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03<\/p>\n\n\n\n

Detail every junction<\/h3>\n\n\n\n

Reveals, intermediate floors, ceiling edges, skirting zones and internal-wall junctions need a continuous strategy.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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04<\/p>\n\n\n\n

Plan the whole room<\/h3>\n\n\n\n

Consider heating, services, room dimensions, ventilation, occupant disruption and reinstatement before selecting materials.<\/p>\n<\/div>\n<\/div>\n<\/div>\n\n\n\n

A thicker board is not automatically a safer or more appropriate result. Thermal benefit must be balanced against building-fabric and moisture performance.<\/p>\n<\/div>\n\n\n\n

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BEFORE WORK STARTS<\/p>\n\n\n\n

Health and safety comes first.<\/h2>\n<\/div>\n\n\n\n
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The work takes place inside occupied rooms. Plan access, isolation of services, dust control, safe removal of fittings and reinstatement before the installers arrive.<\/p>\n\n\n\n

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Existing services<\/h3>\n\n\n\n

Electrical cables, sockets, radiator pipework, heating equipment and concealed services should be surveyed and made safe before strip-out.<\/p>\n<\/div>\n\n\n\n

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Hazardous materials<\/h3>\n\n\n\n

Older coatings, boards, ducts or other components may contain asbestos or other hazardous substances. Do not disturb suspect materials without competent assessment.<\/p>\n<\/div>\n\n\n\n

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Fire and structure<\/h3>\n\n\n\n

Retain the necessary fire protection, compartmentation and safe detailing of wall and floor junctions. Do not cut or alter structural timbers or supports without appropriate advice.<\/p>\n<\/div>\n\n\n\n

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Flues and ventilation<\/h3>\n\n\n\n

Combustion air, chimney breasts, flues and existing ventilation must not be obstructed or compromised by the work.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n\n\n\n

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02 \/ MOISTURE MATTERS<\/p>\n\n\n\n

The original wall becomes colder behind the insulation.<\/h2>\n<\/div>\n\n\n\n
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Heat flow from the room into the original wall reduces once IWI is installed. That is the point of insulation but the colder wall may dry differently and can be more vulnerable to moisture accumulation if the proposed system is unsuitable.<\/p>\n\n\n\n

Start with the outside of the wall<\/strong><\/h3>\n\n\n\n

Repair defective gutters, pointing, render, flashings and other sources of water ingress. Examine rain exposure and allow existing moisture problems to be understood and addressed before covering the internal surface.<\/p>\n\n\n\n

Assess vapour and liquid moisture<\/strong><\/h3>\n\n\n\n

Some designs use a specified air and vapour control layer, others use carefully matched vapour-permeable and capillary active materials. Neither approach is universally suitable. Follow the designed system and consider hygrothermal assessment where appropriate.<\/p>\n\n\n\n

Stop warm air bypassing the insulation<\/strong><\/h3>\n\n\n\n

Gaps behind boards, poorly sealed perimeters and unsealed service penetrations can carry warm, moist indoor air to cold surfaces. Airtight detailing is essential, whatever system is selected.<\/p>\n\n\n\n

Do not confuse two forms of condensation<\/strong><\/h3>\n\n\n\n

Surface condensation appears on an exposed cold surface. Interstitial condensation forms within a wall build-up or at a concealed interface. A newly warm room-side surface does not prove that the hidden assembly is moisture-safe.<\/p>\n<\/div>\n<\/div>\n<\/div>\n\n\n\n

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02 \/ THERMAL BRIDGING<\/p>\n\n\n\n

The weak points are usually around the edges.<\/h2>\n\n\n\n

IWI is interrupted by floors, ceilings, partitions and openings. The junction designs should show where the insulation and airtightness layers go including details that are not visible once the room is redecorated.<\/p>\n\n\n\n

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01<\/p>\n\n\n\n

Window and door reveals<\/h3>\n\n\n\n

Use an appropriate thin or specialist insulating return and deal with frames, sills, condensation risk and opening clearances.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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02<\/p>\n\n\n\n

Intermediate floors and joists<\/h3>\n\n\n\n

Joist ends and the wall\/floor junction need special moisture and thermal-bridge assessment; avoid trapping vulnerable timber in a colder, wetter zone.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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03<\/p>\n\n\n\n

Internal-wall junctions<\/h3>\n\n\n\n

A return of insulation on adjoining surfaces may be required to mitigate cold strips; detail the transition and its moisture behaviour.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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04<\/p>\n\n\n\n

Ceilings and ground floors<\/h3>\n\n\n\n

Plan how wall insulation meets loft, floor and perimeter insulation without leaving a cold edge or an unsealed air path.<\/p>\n<\/div>\n<\/div>\n<\/div>\n\n\n\n

Do not simply push insulation behind a socket, skirting or floorboard and assume continuity.<\/strong> The specification must explain how each junction is completed.<\/p>\n<\/div>\n\n\n\n

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THE IMPORTANT DIFFERENCE<\/p>\n\n\n\n

Airtight does not always mean vapour-tight.<\/h2>\n<\/div>\n\n\n\n
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Moisture safety is a property of the complete wall assembly and the external exposure, not a marketing claim made for one insulation product.<\/p>\n\n\n\n

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Air leakage<\/h3>\n\n\n\n

Warm, moisture laden air can travel quickly through cracks and gaps. A continuous airtight layer limits that unwanted movement.<\/p>\n<\/div>\n\n\n\n

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Vapour diffusion<\/h3>\n\n\n\n

Water vapour can also move through materials. Whether a vapour-control layer is appropriate depends on the wall and the complete system.<\/p>\n<\/div>\n\n\n\n

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Liquid moisture<\/h3>\n\n\n\n

Rain and other water ingress need independent consideration. A vapour-open system cannot compensate for an unrepaired leak.<\/p>\n<\/div>\n\n\n\n

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Drying potential<\/h3>\n\n\n\n

Traditional solid walls may need materials and finishes that maintain suitable pathways for moisture transport and drying.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n\n\n\n

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VENTILATION AND HEATING<\/p>\n\n\n\n

Do not improve the wall and forget the air.<\/h2>\n<\/div>\n\n\n\n
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Insulation work can reduce uncontrolled leakage and change room temperatures. Before and after IWI, the ventilation strategy should be checked against the property, occupancy and moisture sources.<\/p>\n\n\n\n

Background and transfer air<\/strong><\/h3>\n\n\n\n

Check designed background ventilators and internal transfer routes where required. Do not cover or seal working air inlets with the new lining.<\/p>\n\n\n\n

Extract ventilation<\/strong><\/h3>\n\n\n\n

Confirm appropriate extract provision and performance in kitchens, bathrooms, WCs and utility rooms. Check the complete house strategy, not only the room receiving IWI.<\/p>\n\n\n\n

Heating and controls<\/strong><\/h3>\n\n\n\n

Radiators may need temporary removal, brackets and pipework extended, and room controls revisited. Heat-loss calculations can help establish the post-retrofit heating requirement.<\/p>\n\n\n\n

Explore the MyWarmHome ventilation guide \u2192<\/a><\/p>\n<\/div>\n<\/div>\n<\/div>\n\n\n\n

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03 \/ CONSTRUCTION METHODS<\/p>\n\n\n\n

Common ways to install internal wall insulation.<\/h2>\n\n\n\n

Construction methods must be selected against wall condition, moisture performance, fire requirements, available room space, fittings and the intended finish.<\/p>\n\n\n\n

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01<\/p>\n\n\n\n

Direct-bonded board system<\/h3>\n\n\n\n

Boards fixed to a suitably prepared wall using a manufacturer-approved method. Prevent unwanted air paths behind the insulation.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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02<\/p>\n\n\n\n

Framed lining system<\/h3>\n\n\n\n

A timber or metal frame carries the insulation and finish. The design must address thermal bridging through framing and service penetrations.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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03<\/p>\n\n\n\n

Capillary-active bonded system<\/h3>\n\n\n\n

Selected vapour-permeable materials and compatible adhesives\/plasters may help manage moisture in suitable wall constructions.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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04<\/p>\n\n\n\n

Insulating plaster<\/h3>\n\n\n\n

A specialist lime or other formulated insulating plaster can follow irregular surfaces and may suit selected traditional interiors.<\/p>\n<\/div>\n<\/div>\n<\/div>\n\n\n\n

Adhesives, mechanical fixings, preparation, boards, air\/vapour control, joint tapes, plaster and finishes are not interchangeable across unrelated systems.<\/p>\n<\/div>\n\n\n\n

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03 \/ MATERIAL OPTIONS<\/p>\n\n\n\n

Which internal insulation material?<\/h2>\n\n\n\n

Compare the complete specified system \u2014 insulation alone does not tell you enough about hygrothermal suitability, fire protection, thickness or installation detail.<\/p>\n\n\n\n

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01<\/p>\n\n\n\n

Mineral wool<\/h3>\n\n\n\n

Fibrous insulation used in appropriately designed framed systems. Insulation continuity, frame thermal bridges and air\/vapour-control detailing need attention.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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02<\/p>\n\n\n\n

PIR and phenolic boards<\/h3>\n\n\n\n

High thermal resistance at relatively modest thickness. Assess the full lining system, vapour strategy, fire protection and existing wall compatibility.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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03<\/p>\n\n\n\n

Wood fibre<\/h3>\n\n\n\n

A vapour-permeable option for some older or traditional walls when adhesives, plasters, rain exposure and moisture design are compatible.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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04<\/p>\n\n\n\n

Calcium silicate \/ mineral foam<\/h3>\n\n\n\n

Mineral, often capillary-active options used in selected moisture-conscious systems. Manufacturer-compatible preparation and finishes are essential.<\/p>\n<\/div>\n<\/div>\n<\/div>\n\n\n\n

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05<\/p>\n\n\n\n

Aerogel-based products<\/h3>\n\n\n\n

Specialist high-performance materials can help at reveals or other locations with little available depth; check tested build-up and cost.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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06<\/p>\n\n\n\n

Cork and other natural fibres<\/h3>\n\n\n\n

Can form part of vapour-permeable assemblies in suitable buildings. Confirm product properties, moisture exposure, fire and complete-system suitability.<\/p>\n<\/div>\n<\/div>\n\n\n\n

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07<\/p>\n\n\n\n

Insulating lime plaster<\/h3>\n\n\n\n

A possible alternative where wall irregularity, internal features or heritage constraints make conventional boards difficult; thermal performance is design-specific.<\/p>\n<\/div>\n<\/div>\n<\/div>\n\n\n\n

A vapour-permeable board is not, on its own, proof that an IWI installation is safe.<\/strong> Installation detail, external exposure and moisture assessment still govern the design.<\/p>\n<\/div>\n\n\n\n

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CHOOSE THE SYSTEM<\/p>\n\n\n\n

Select for the building, not just the U-value.<\/h2>\n<\/div>\n\n\n\n
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The objective is comfort and lower heat loss without harming the original fabric or creating a concealed moisture defect.<\/p>\n\n\n\n

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Existing wall and weather<\/h3>\n\n\n\n

Solid brick, stone, cavity and non-standard structures have different moisture behaviour. Consider orientation, wind-driven rain and maintenance history.<\/p>\n<\/div>\n\n\n\n

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Available depth<\/h3>\n\n\n\n

Allow for loss of floor area, window reveals, door clearances, kitchen units, fitted furniture and access routes.<\/p>\n<\/div>\n\n\n\n

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Fire and acoustic needs<\/h3>\n\n\n\n

Assess the entire lining build-up, fixings, protection and compartmentation where relevant.<\/p>\n<\/div>\n\n\n\n

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Thermal and moisture modelling<\/h3>\n\n\n\n

Specify a justified target and evaluate thermal bridges and the wall assembly. More insulation is not always the same as less risk.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n\n\n\n

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WHAT CHANGES IN THE ROOM?<\/p>\n\n\n\n

Agree reinstatement before anyone removes the skirting.<\/h2>\n<\/div>\n\n\n\n
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Unlike EWI, internal insulation normally involves disruption to lived-in rooms. The project quotation should clearly cover removal, protection, alterations, repositioning and the final finish.<\/p>\n\n\n\n

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