Approximately half of all New Zealand houses have no wall insulation*. This results in space heating energy being wasted, makes these houses difficult to heat to healthy and comfortable temperatures and contributes to mould-problems with associated health impacts on occupants.

In houses that have ceiling and under-floor insulation and draught-proofing retrofitted already (for example through the government-funded Warm Up New Zealand: Heat Smart programme) insulating external walls typically reduces heat loss by approximately 40%. This makes wall insulation the most effective next step in upgrading the thermal efficiency of such houses.

Current practice for retrofitting wall insulation requires removing the wall lining or cladding and is usually only done when major renovation work is undertaken. However, even when the opportunity arises to open wall cavities, retrofitting wall insulation is not always straightforward.

Getting a building consent and managing risks associated with the walls’ weathertightness and the safety of electrical wiring are just some of the issues to be considered when retrofitting wall insulation.

Guide for Retrofitting Wall Insulation

To help with this, the Energy Efficiency and Conservation Authority (EECA) and the Ministry of Business, Innovation and Employment (MBIE) have jointly produced a Guide for Retrofitting Wall Insulation. This guide provides best practice guidelines for retrofitting the most common types of wall insulation (blanket, segment, rigid and semi-rigid sheet) into framed external walls of existing houses.

The guide covers the following aspects:

• Choosing a wall insulation product;
• Obtaining a building consent;
• Necessary inspections before wall insulation installation can start; and
• Detailed guidelines for fitting insulation from the inside or outside, in walls with different cladding types, and with or without existing wall underlay.

Installer training

The Insulation Association of New Zealand Inc. (IAoNZ), with support from EECA, has developed a training programme for insulation installers based on this guide. The first wall insulation training course was held in Christchurch in February 2013, further training courses will be offered depending on demand. If you are interested in this training, or want to see the list of trained installers, visit the IAoNZ website.

EQC Christchurch repairs to accommodate insulation

Today, 4 March 2013, the Earthquake Commission (EQC) announced that their customers will be given the opportunity to install insulation where wall cavities and otherwise inaccessible roof and underfloor areas are exposed as part of earthquake repair work. EECA contributed technical advice to help support EQC’s move.

EQC requires that insulation installation during EQC repairs is done by trained installers and refers homeowners to installers who have received the above-mentioned IAoNZ wall insulation training. For more information refer to EQC’s media release.

Insulating existing walls – key differences to new construction

Installing wall insulation in existing walls can present some unique challenges which are not found when insulating new walls. This starts with managing health and safety risks from potential contamination like toxic moulds or unsafe old electrical wiring.

Weathertightness

Thoroughly assessing the walls’ weathertightness and selecting an insulation material and installation method which will not cause moisture problems in the future is absolutely crucial. Many of the houses built without wall insulation (generally before 1978) have cladding systems which are not as weathertight as today’s claddings. Houses built before 1964 often do not have a wall underlay; for masonry veneer walls wall underlay was not commonly installed until 1977.

Older weatherboard walls rely on air movement through the cladding to dry out small amounts of moisture entering the wall cavity in wet weather. Inappropriately retrofitted wall insulation can substantially reduce the drying rate and at the same time form a bridge which allows moisture on the inside of the cladding to penetrate further into the wall cavity.

Masonry veneer claddings rely on a vented cavity behind the veneer to dry out moisture penetrating the cladding. If this cavity is filled with insulation moisture is likely to accumulate in the wall cavity, causing rot, mould growth and structural damage.

For walls without wall underlay the Guide for Retrofitting Wall Insulation requires that only semi-rigid or rigid insulation products be used; installed with a 20mm minimum gap to the external cladding.  The gap is to ensure that the drainage path on the back of the cladding is maintained and that insulation does not allow moisture to bridge across. For walls with direct fixed claddings (e.g. direct fixed weatherboards) this means that the insulation product must be thinner than the wall framing, e.g. the insulation cannot be thicker than 70mm where the wall framing is 90mm thick.

In walls with a drained or veneer cavity, insulation must not protrude beyond the outside of the wall framing into the drained/veneer cavity.

Note that whilst Standard NZS 4246: 2006 (incorporating Amendment No. 1) Energy efficiency – Installing insulation in residential buildings specifies that pieces of wall underlay be installed from the inside before retrofitting insulation to walls without existing wall underlay, this practice was not included in the Guide for Retrofitting Wall Insulation. This is due to the risk of water being guided onto dwangs and the bottom plate by the wall underlay pieces.  Based on the (currently, very limited) research knowledge on wall insulation retrofit practices, maintaining a gap between the insulation and the cladding is considered a safer practice by EECA and MBIE.

Electrical safety

An electrical safety check is another essential part of the installation process regardless of the method for retrofitting wall insulation. The electrical wiring in older houses may have deteriorated over time and be unsafe now. If the wiring is not adequately rated to be surrounded by insulation it could overheat as the insulation makes it harder for the wiring to dissipate heat. Re-wiring or installation of mini circuit breakers may be required in some cases.

Conclusions

Retrofitting wall insulation can offer significant comfort, health and energy benefits to occupants and is an important step in upgrading our older housing stock. The Guide for Retrofitting Wall Insulation published by EECA and MBIE provides guidance to installers to ensure the risks associated with retrofitting wall insulation in older houses can be adequately managed. The associated IAoNZ training on wall insulation installation offers installers the opportunity to upskill and retrofit with confidence and enables homeowners to identify qualified insulation installers. Both the guide and the IAoNZ training also underpin EQC’s offer to accommodate insulation retrofits during earthquake repairs.

Christian Hoerning, Senior Technical Advisor Buildings, Energy Efficiency and Conservation Authority (EECA)

* BRANZ report E466, “Insulation in existing houses”, July 2007