Eco Refurb Scotland

Our guidance vs conventional guidance

• The installation of cavity fill insulation is represented by the National Insulation Association (www.nia-uk.org), which also supports external and internal solid wall insulation works. They host the Cavity Insulation Guarantee Agency (CIGA), which guarantees works undertaken. Guidance to best practice is given along with guidance on handling complaints and broader guidance on how companies should operate.

• Our first recommendation is that owners ensure that all guidance is strictly followed, and to support this, we further recommend that an independent specialist undertake the suitability review and a thorough check afterwards.

Insulation Materials

Mineral Wool

+ Cheap -

- Most commonly associated with failure and we believe should be avoided mainly due to its capacity to ‘hold onto’ moisture, should any get into the cavity.

Foam

+ Relatively cheap and efficient.

- We would counsel against foams because, being impervious to moisture, they more fundamentally alter the nature of the wall, making it more difficult for moisture to escape.

Expanded Polystyrene

+ Robust and more liable to hold their shape.

+ Less liable to ‘slump’ than mineral wool

+ Don’t ‘hold onto’ moisture in comparison with mineral wool.

+ Vapour permeable

+ Potential for both moisture and air movement.

- Polystyrene is a chronic environmental polluter.

Preparation

• Before starting, it is essential to assess the property against a range of criteria that inform suitability for installation.

• Exposure to wind-driven rain - BRE has produced a map of the UK, which indicates four zones of exposure. The higher the exposure, the higher the risk of water being forced across the cavity under wind pressure. However, local geography and features will have an effect, and some judgment is required in interpretation. The risks increase at greater heights from the ground, so installations over 12m from the ground are subject to different guidance.

• Building characteristics – a number of individual features of a building might offer clues as to suitability. Existing signs of dampness and works to rectify dampness might indicate a higher-than-normal risk, and structural problems like leaning, bulging, or cracking might indicate issues that could exacerbate or be exacerbated by insulation installation. Buildings should be checked externally and internally, noting where changes might have been made (e.g. old openings, now blocked up). External walls where the mortar beds are recessed create a greater risk of rainwater sitting and being blown in.

• In all cases, cavities should be checked carefully. A borescope survey should be undertaken in several places in addition to extensive external and internal visual surveys. Cavities less than 50mm wide are at greater risk of water penetration across, and there may be areas of the cavity that make installation difficult or impossible for one reason or another. Wall ties should be checked for adequacy and ensure they are not running downwards towards the inner leaf (which could lead to water running across). Sometimes, cavities are filled with lumps of mortar from untidy workmanship, which can block the cavity and help move moisture from one side to the other. Cavities are not always closed off, for example, in an attic or where services have penetrated them, so an important part of any survey is to ensure that they are closed off before insulation is pumped in. Check that weep holes at the base are sufficient to drain any water in the cavity safely.

• The most critical aspect of the preparation is establishing whether the external wall is adequate to keep water out of the cavity. Any weaknesses in this wall may previously have been managed by

The ability of water to run out within the cavity and exit through weep holes at the base. This ability will be compromised when insulation is installed, so the first line of defence becomes more important. Any required maintenance or improvement works will need to be included.

• Complications occur where a cavity extends beyond the property's boundary, where it is part of a terrace or block of flats, for example. Cavity barriers should be installed unless the whole block is to be insulated, but this increases costs, of course. Where cavities extend below ground level, insulation should not be installed unless it is clear how water will escape to avoid problems with temporary flooding.

• Complications can also arise when the main external wall to be insulated is covered by a subsequent extension such as a conservatory. Bespoke arrangements must then be agreed upon and documented regarding that area.

• It is important to check any services which run through (or sometimes within) the cavity. Any cables with PVC sheathing (most) could be affected by polystyrene beads and should be moved, replaced with non-pvc alternatives or placed within a conduit. At every penetration, there is a risk of the insulation emerging from the cavity under pressure, so all penetrations must be carefully sealed.

• Some wall vents are formed by a continuous casing that extends through the cavity, but some vents (for example, to solums beneath the ground floor) are formed by an air brick in each masonry leaf. Cavity insulation would block the air path between them, so these will need to be made good such that the flow of air remains unimpeded.

• The location of chimneys is important where they exist (often blocked over, so it is difficult to know) to ensure that insulation is not inadvertently pumped into the chimney.

• It is important that any defects in the building as pre-existing are carefully documented before any work takes place. This protects both parties: installers are protected from spurious claims, while the most likely way that a guarantee won’t be honoured is the argument that the defect existed before the works took place. We suggest that this process is carried out by an independent specialist either instead of or in addition to the documentation provided by the installer.

• Once insulated, some homeowners find that draughts which emanate from the cavity will be reduced. This is essentially a good thing, adding an airtightness benefit to the installation and raising the risks associated with lack of ventilation. For this reason, we suggest that all cavity-fill installations are accompanied by a review of, and where necessary, an upgrading of the ventilation arrangements in the property. For more information on this, refer to the section on ventilation.

• Before undertaking the work, the installer should agree on several items with the occupant, such as schedule, access for vehicles, method of making good holes, any unusual areas or internal access required, the extent of installation (some areas may not be accessible) and when the guarantee will be received.

• In Scotland, a building warrant application is not required for cavity-fill insulation, although the work should comply with the regulations.

• Grants may be available for the installation depending on the area, property type or occupants, so it is worth contacting The National Insulation Association (NIA), The Cavity Insulation Guarantee Agency (CIGA) or The Energy Saving Trust (EST), all of whom will be able to advise.

Injecting the Cavity

• Usually, the insulation is injected from outside using the mortar beds between brick or stonework and at about 1.2m centres. The holes are then filled up afterwards using a matching material. In some cases, more holes will be required around obstacles like windows, and where access isn’t possible from outside, by agreement, it might be necessary to inject some insulation from inside.

• A complication that is not easy to solve is thermal bridging, usually at openings in older buildings. Around doors and windows in older cavity walls, the inner masonry leaf ‘returns’ to form a solid wall around the opening for robustness. Structurally, this makes sense, but in terms of insulation, it creates a problem because heat is more readily transferred. When the cavity fill is installed, this area will become colder than the warmer areas around and may increase the risk of condensation and mould formation. It may be advisable to provide additional insulation on the inside to avoid this. The diagram alongside shows such an arrangement. However, doing this around every window and door considerably increases costs, not just for the work itself but for the redecoration of all rooms.

• Once the installation has been checked, and holes made good, that should be it. All combustion appliances are checked to ensure they have been unaffected. Associated works recommended, such as ventilation, should also be considered. Still, we also recommend undertaking a thermographic survey to see, as far as possible, if the works have been completed fully. It is only fair to let the installer know that you intend to carry this out. Since thermography works best when there is a significant temperature difference between inside and outside, it can sometimes only be done in the colder months. Several long-term problems can be traced back to inadequate installation. For those committed to doing this as well as possible to avoid longer-term costs, such an additional survey and discussion with the installer is probably worth it.

Alternatives

Where the property is found to be unsuitable for cavity fill due to the likelihood of water penetration from outside, one possibility is to install the insulation as planned but also to install some form of additional weatherproofing to the outside of the building. This could be in the form of rain-screen cladding (for example, timber cladding, large format boarding, or even matching render over a mesh substrate) or external wall insulation. This is far less cost-effective initially, but the proposal has some logic.

Some cavity wall housing cannot be made sufficiently weatherproof due to location or exposure. Internal insulation may not be feasible for various reasons, and if cavity fill isn’t safe, the only option is external insulation. However, installing this external layer makes little energy efficiency sense outside the ventilated cavity. Carrying out both means the building can be effectively insulated and robustly protected long-term.

Cavity wall insulation

Important to know