Deep Retrofit

What is a “Deep Retrofit” (and how is it different from a standard insulation retrofit)?

A Deep Retrofit is a planned, whole-home upgrade that targets the entire thermal envelope and key comfort systems, so you get a step-change in warmth, dryness and running costs (not just a small improvement from topping up one area).

What typically gets included in a Deep Retrofit package?

Common elements include high-quality insulation upgrades (ceiling, underfloor and - where feasible, walls), draft/air-leakage reduction, improved windows/doors (or targeted upgrades), and a ventilation approach that keeps the home healthy as the envelope improves. The exact mix depends on the home’s construction, moisture risk and renovation scope.

Why do Deep Retrofits talk so much about airtightness and ventilation?

Because once you reduce air leakage and add insulation, you can change how the building keeps dry. Done well, airtightness improves comfort and efficiency - but it must be balanced with appropriate ventilation to control moisture and indoor air quality. (This is one reason “quality of installation” matters as much as product choice.)

When is a Deep Retrofit worth considering instead of piecemeal upgrades?

Deep Retrofit becomes especially relevant when you’re already planning a major renovation, or when a home has persistent comfort/health issues (cold rooms, condensation, dampness) and you want a coordinated solution rather than repeating smaller jobs. NZ research continues to show a large portion of the housing stock still needs meaningful retrofit improvement.

What consents or compliance should I expect for Deep Retrofit work?

Some deep retrofit measures are straightforward, but retrofitting insulation into external walls typically requires building consent (unless your council confirms otherwise). If your project is an alteration/addition, the new work must comply with Building Code, while the rest of the building generally doesn’t have to be upgraded to current H1 unless it’s part of the scope.

How do I stage a Deep Retrofit without creating moisture or condensation problems?

Sequence matters. A practical “do no harm” order is:

1. Fix bulk water first (roof leaks, flashing, cladding defects, plumbing leaks).

2. Reduce ground/subfloor moisture (often with a ground vapour barrier where appropriate) before adding/repairing underfloor insulation.

3. Plan ventilation as you tighten the home—better insulation + less leakage can increase indoor humidity unless ventilation is improved (especially kitchens/bathrooms).

4. Install insulation to a high standard (no gaps, no compression, correct clearances/support) and follow NZ guidance for tricky roof types (e.g., maintaining required clearances to avoid moisture issues).

5. Treat wall insulation as a higher-risk, consented step—it can change drying rates and increase moisture accumulation risk if the wall system isn’t suitable or the method/materials are wrong, so it must be assessed case-by-case.