Internal Wall Insulation (Solid Masonry)

SYSTEM OVERVIEW – Internal Solid Wall, IWI

Application Type:
Internal insulation to solid masonry walls

System Classification:
Internal Wall Insulation (IWI) – Certified Build-Up

Primary Function:
Thermal insulation + Vapour Control Layer + Radiant Barrier

Installation Orientation:
Horizontal installation across vertical battens

Batten Centres:
Maximum 600 mm

Staple Fixing:
Maximum 300 mm centres

Minimum Overlap:
50 mm (all joints)

Airspace Requirement:
Continuous internal airspace created by counter battens

Vapour Resistance:
1200 MNs/g (acts as VCL when sealed)

Finish:
12.5 mm plasterboard fixed to counter battens

Condensation Control:
System must be designed in accordance with BS 5250 principles
Condensation risk analysis recommended for hybrid constructions

Internal Wall Insulation (IWI) improves the thermal performance of existing solid masonry walls by installing a continuous insulation layer on the internal face of the structure.

This system is typically specified for:

• Solid brick walls
• Blockwork walls
• Retrofit projects
• Buildings where external insulation is not feasible

When correctly designed and installed, the SuperFOIL IWI system provides:

• Continuous thermal barrier
• Integrated Vapour Control Layer (VCL)
• Radiant barrier performance
• Airtight internal envelope

Certified IWI System (KIWA Agrément)

The SuperFOIL IWI system is covered under KIWA Agrément certification when installed in accordance with the approved system specification and installation guidance.

Key technical characteristics:

• Designed in accordance with BS 5250 (Condensation Control)
• Hygrothermal testing to BS EN 15026
• Vapour resistance: 1200 MNs/g
• SuperFOIL performs as a Vapour Control Layer (VCL)

The certified build-up must be installed exactly as specified within the IWI system documentation to maintain compliance and performance.

Pre-Installation Assessment

Before installation begins:

• Inspect masonry walls for dampness, structural damage or signs of condensation
• Confirm pointing, render and external envelope are in good condition
• Check roof, guttering and rainwater goods are functioning correctly
• Ensure windows show no signs of water ingress
• Maintain existing ventilation outlets
• Plan repositioning of sockets, radiators and services where necessary

All electrical and plumbing work must comply with relevant regulations and be carried out by qualified personnel.

Copper pipes must be wrapped in non-metallic insulation before contact with aluminium foil to prevent material reaction.

How the Internal Wall System Works

1 - Initial vertical timber battens fixed to masonry at maximum 600 mm centres
2 - SuperFOIL installed horizontally across battens
3 - Minimum 50 mm overlap between layers
4 - Staples fixed at maximum 300 mm centres
5 - All overlaps fully sealed using SuperFOIL MultiFOIL Tape
6 - Secondary counter battens installed to create required internal airspace
7 - 12.5 mm plasterboard fixed to counter battens

The system forms:

• A continuous internal thermal barrier
• An airtight layer
• An integrated vapour control layer

When finishing at:

• Ceiling
• Floor
• Window openings
• Door openings

Leave a 50 mm overlap to seal beneath perimeter battens.

All service penetrations must be sealed immediately after cutting to maintain airtightness.

Airspace & Batten Logic

Airspaces are fundamental to multifoil insulation performance.

To achieve the designed thermal performance:

• Correct batten depth must be used
• Counter battens must be installed at maximum 600 mm centres
• Continuous internal airspace must be maintained
• The product must not be compressed

Without an airspace:

Radiant heat converts into conductive heat, significantly reducing insulation performance.

Typical batten guidance:

SF19+ → 38 mm battens
SF40 → 50 mm battens
SF60 → 63 mm battens

Final batten depth must match the selected product thickness to prevent compression and maintain reflective performance.

Airspace:

Ceiling Junction Detail

The junction between ceiling and internal wall is a critical thermal bridge location.

Correct installation requires:

• Horizontal sealing batten installed at ceiling plate
• SuperFOIL compressed between battens
• 40–50 mm overlap folded behind and under perimeter batten
• No gaps between battens and ceiling surface

Loft insulation and wall insulation must overlap to create a continuous thermal envelope and eliminate cold bridging.

Floor Junction Detail

The wall-to-floor junction presents a high thermal bridge risk if incorrectly detailed.

For solid floors:

• Install a continuous base batten along the slab surface
• Tape any cut edges before installation
• Seal insulation at floor junction
• Ensure airtight continuity behind skirting level

No gaps should exist between insulation and floor junction.

Window & Door Reveal Detail

Reveal depth must be assessed prior to installation.

Where frame depth is limited:

• Full airspace may not be achievable
• SuperFOIL may compress locally
• Shim battens may be required to allow correct plasterboard fixing

Installation sequence:

• Install batten at reveal edge
• Fold SuperFOIL into reveal
• Fix using appropriate shim
• Seal all cut edges
• Tape reveal perimeter fully

All reveal edges must be sealed to maintain airtightness and thermal continuity.

Service Penetrations

For cables, pipes, sockets and data points:

• Cut minimal opening
• Feed service through
• Fully seal with MultiFOIL Tape
• Avoid unnecessary perforations

Minimising penetrations improves airtightness and reduces condensation risk.

Sealing & Airtightness

Airtightness is essential for system performance.

Ensure:

• All overlaps taped
• All cut edges sealed
• Ceiling, wall and floor junctions sealed
• Service penetrations sealed
• Tape applied with firm pressure

Improper sealing may result in:

• Air leakage
• Reduced thermal efficiency
• Increased condensation risk

Overlapping:

Moisture & Interstitial Condensation

The SuperFOIL IWI system is designed to limit the risk of interstitial condensation when properly designed and installed.

Important considerations:

• All overlaps must be taped
• Ceiling and floor junctions must be sealed
• Service penetrations must be minimised and sealed
• When combined with additional insulation, vapour resistance must be assessed

A professional condensation risk assessment is strongly recommended for hybrid wall constructions.

Ventilation & Existing Building Condition

Before installation:

• Ensure masonry walls are dry and structurally sound
• Check pointing, render, roof and drainage systems
• Maintain existing ventilation outlets
• Consider ventilation requirements when improving wall insulation

In kitchens and bathrooms:

• Use moisture-resistant finishes
• Maintain adequate ventilation
• Ensure compatibility with humid environments

Installation Checklist

Before completion ensure:

• Wall inspected for suitability
• Product cut and trimmed correctly
• Ends sealed before installation
• Staples fixed at maximum 300 mm centres
• All joins and overlaps taped
• Correct counter battens installed
• Counter battens at maximum 600 mm centres
• Plasterboard securely installed
• Installation stages photographed for documentation

Counter battens, Plasterboard fitting: