Walls

Walls can be insulated in different locations depending on their construction.

Cavity Wall Insulation (CWI)

Wales is largely in areas of Wind Driven Rain Index 3 and 4. See below:

For areas in exposure zone 4 retrofitted Cavity Wall Insulation is not recommended full stop. For exposure area 3 it can be installed but only if it is done so carefully. Many of the properties that had been insulated using  Cavity Wall Insulation  are now having the insulation removed due to damp problems. Instead it is better to insulate your walls either internally (Internal Wall Iinsulation) or externally (External Wall Insulation). These are risk filled measures and so need to be specified and detailed professionally.

Building regulations were upgraded in 1976 to start to impose minimum insulation levels in domestic homes, so from about this date, walls started to incorporate Cavity Wall Insulation. If your house was built before 1976 it is unlikely to have had insulation built in at the time of construction. Many houses have since then had insulation added retrospectively. This is a relatively easy job to do. (building standards have been revised many times since to gradually increase the requirement for energy efficiency). Installers should drill holes and inspect the cavity in every elevation with a borescope to check that the cavity is suitable for filling as there are some occasions when it is not sensible (e.g. if the cavity has too much mortar filling it).

If installation is agreed, then the installer will drill holes in the mortar joints every 2m over the wall area and inject insulation into the cavity. Often ‘sensitive’ areas – over lintels, around pipework, along wall plates (top of the wall) – are not insulated and this can lead to cold spots. Because of this, Cavity Wall Insulation is not very reliable and can cause unforeseen consequences.

It is also important to check that your cavity wall ties are in good condition. With scaffolding up to do the Cavity Wall Insulation it is advisable to replace wall ties at the same time if required.

Solid Wall Insulation (SWI)

Solid walls are very common in Wales. Victorian, Edwardian and early cavity properties (up to WW2) should all be treated as solid walls. They are generally either stone (random rubble with render, dress stone, coursed stone) or brick structures, although there are some timber frame with wattle and daub infill panels in mid Wales.

These walls are ‘breathable’ and so completely different from post-war and modern buildings as they have the property of allowing moisture to pass through their structures. This is a really important feature of these buildings and needs to be considered when choosing insulation materials. Guidance is available at the Welsh Government website, and at the Sustainable Traditional Buidings Alliance website.

External wall insulation (EWI)

External wall insulation can be applied to both modern and traditional buildings (Solid Wall Insulation) however the choice of materials is vital. Do not use modern nonbreathable materials on traditional buildings unless you have consulted with an expert in retrofit (search for a Retrofit Co-ordinator on https://trustmark.org.uk ). External Wall Insulation for modern houses is less risky but it still requires expert advice to get it right.

External Wall Insulation has the advantages of:

• Can be applied with minimal disruption to the household and its occupants
• No internal access is required
• Does not reduce the floor area (living space) of the property
• Improves weatherproofing and sound resistance
• Will make the building more airtight, reducing heat loss (Need to ensure the building has sufficient natural and mechanical ventilation)
• Reduces the risk of condensation
• Potentially improves the appearance of the property – potentially increasing the property’s value

Disadvantages:

• Potentially detrimental to the appearance of the property.
• Probably not possible in conservation areas / areas of outstanding natural beauty etc.
• May require additional works to roof (or other elements) to facilitate correct installation

Risk areas:

• Thermal bridges around doors and windows, bay windows, party walls
• Incorrect materials specified

For more information see: https://www.gov.wales/sites/default/files/publications/2019-04/external-wall-insulation-project-guide.pdf

Internal Wall Insulation

Like External Wall Insulation, Internal Wall Insulation can be applied to both modern and traditional buildings (Solid Wall Insulation) however the choice of materials is vital. Do not use modern nonbreathable materials on traditional buildings unless you have consulted with an expert in retrofit (search for a Retrofit Co-ordinator on https://trustmark.org.uk ). Internal Wall Insulation for modern houses is less risky but it still requires expert advice to get it right.

Internal Wall Insulation has the advantages of:

• Is generally cheaper to install than external wall insulation.

Disadvantages:

• Will reduce the floor area of any rooms in which it is applied.
• Can be disruptive as works are internal.
• Requires skirting boards, door frames, radiators and external fittings to be removed and reattached.
• Might require movement of electrical circuitry.
• Can make it hard to fix items to inside walls without puncturing the membrane – although special fixings are available.
• Makes external finishes more prone to frost damage / weathering.

Risk areas:

• Intermediate floor voids, reveals, headers and sills around doors and windows need to be insulated to stop damaging cold spots.
• Fixtures like stairs may have to be temporarily removed if on external wall.
• Needs any problems with cracking, penetrating or rising damp or poor mortar joints to be fixed first.
• Should not insulate one side of a pair of semidetached houses.
• Incorrect materials specified.

For more information see: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1019707/iwi-guidance.pdf