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FAQs

Existing Homes - Retrofit

Do I need building consent to retrofit insulation?

Generally no consent is required for adding insulation to ceilings or floors in existing homes, but retrofitting insulation into external walls typically requires building consent (unless your council confirms an exemption).

Where should I insulate first in an existing home?

Start with the biggest, easiest wins: ceiling/roof space, then underfloor, then walls (walls are typically the hardest/most invasive). Ceiling and underfloor retrofits are usually the most cost-effective comfort upgrade in older NZ homes.

What R-value should I choose for my retrofit?

Treat minimum R-values as the baseline, not the goal. Aim for the best R-value that fits your home’s constraints (space, access, moisture risk, existing services). Also note: the way insulation is installed (no gaps, no compression, correct support) can matter as much as the label on the bag.  Your recommended IAONZ Installer can provide options that best suit your house and budget.

Can insulation help with damp, mould and condensation?

Insulation forms part of the solution by limiting the energy loss - but only when paired with good moisture management: stop subfloor moisture, improve ventilation where needed, and avoid trapping moisture in the building envelope. Poor drying/ventilation can allow moisture to build up in walls and create conditions for fungal growth.

Should I install an underfloor ground vapour barrier (polythene)?

Often yes for suspended timber floors: it helps reduce moisture vapour rising from the ground into the subfloor space, which supports a drier, healthier home and protects insulation performance. NZ installation guidance is covered in NZS 4246.  IAONZ Installers are trained to install to these requirements.

How do I know the insulation has been installed properly (quality checklist)?

Ask your installer to confirm installation aligns with NZS 4246 guidance and request evidence/photos where access is limited.

Key quality checks include:

  • Correct thickness (not compressed) and full coverage with no gaps

  • Secure fixing/support (especially underfloor)

  • Safe clearances around heat sources and services (e.g., downlights/vents)

  • Dry materials only—replace any damp or degraded insulation
    NZS 4246 is the NZ reference used for bulk insulation installation quality.

What documentation should I ask for (quality assurance)?

For high-quality outcomes, request:

  • Product data sheets (R-values, intended uses, limitations) - Select insulation from supporting IAONZ Manufacturers

  • Installation statement confirming alignment with NZS 4246

  • Evidence the design uses construction R-values suitable for H1 (often via BRANZ guidance/tools)
    This makes it easier to prove compliance and protect performance long-term.

Why should I choose an IAONZ Member instead of “any installer” or the cheapest quote?

Insulation performance is won or lost at installation. IAONZ Members commit to quality-first workmanship, correct material selection for the application, and install practices that protect the insulation’s stated R-value (no gaps, no compression, correct support and detailing).

The outcome is a warmer, drier home - and far lower risk of costly rework.

What proof do I get that the job was done properly?

IAONZ Members can provide clear documentation: the products used, where they were installed, and quality checks (often including photos where access is limited).

They also understand compliance expectations for NZ Building Code H1 (new builds/major renovations) and good-practice installation guidance such as NZS 4246—so you have confidence the work will stand up to scrutiny, resale, and time.