Concept render
New Zealand builders of granny flats, homes and commercial buildings
Built better.Priced fairly.
Designed with you, made in the factory, built on your site. One team, from drawings to keys.
Based in Auckland
Frames by a chartered engineer
Construction price fixed at signing
We kept seeing the same problems in New Zealand homes.
Cold rooms, damp walls, builds that drag on, prices that move after signing. So we went looking for a way of building that answers those problems directly, and found it in steel frames and factory-made panels.
Why we startedSix ways to build with us.
From drawings to keys.
You pay in three stages: on signing, when the structure leaves the factory, and on completion.
Concept render
01 / 04
Design
We design the building with you.
02 / 04
Factory
Frame and panels are made to the approved design, cut to size and numbered.
03 / 04
Your site
One team assembles it, from drawings to keys.
04 / 04
Keys
We hand over the keys to your finished building.
How we build, explained plainly.
How the system worksInsulation with nothing in the way.
BRANZ, New Zealand’s building research body, measured 47 new homes and found that, on average, more than a third of the outside wall area was timber framing, not insulation. Our wall panels have no studs inside them.
Source: BRANZ ER53Nothing in the walls to rot.
Rot, borer and mould live on timber. Our walls have none: a steel frame, steel on both faces, and a core that barely takes up water.
Engineered for your site.
Most houses follow a standard timber rulebook. Ours doesn’t, so each one is engineered. A chartered professional engineer designs the frame for your site’s wind and earthquake zone.
The construction price is fixed when you sign.
Fixed for a level site. Foundation work beyond that, site works, council fees and any changes you ask for are quoted separately.
Building in New Zealand shouldn’t feel like a gamble.
We live in Auckland too. We know the cold mornings, the mould behind the wardrobe, and the quote that grew after you signed. So we started Castro James Group to do it differently: nothing in the walls to rot, one team from drawings to keys, and a construction price fixed at signing for a level site.
About us.webp)
Reference project
A hospitality module for the Formula 1 United States Grand Prix at Circuit of the Americas, Austin, Texas. Built by our partner’s team in Mexico on this system in three months.
See the projectWhat we found when we checked the research.
All articles
Why New Zealand houses are cold
BRANZ measured 47 new homes. More than a third of the outside wall area was timber framing.
Why New Zealand homes get damp and mouldy
One in five New Zealanders said their home was damp in the 2023 Census.
Granny flat rules in New Zealand, 2026
The national conditions, in plain English, with the official sources.
