Eco-friendly timber barn formula for viability

Building a composting barn has cut one Canterbury dairy farm’s environmental footprint by nearly half while protecting cows and pastures alike on land with imperfect drainage.

Owner Brent Thomas calls it a formula for viability as milk payouts climb, while general manager Matt Iremonger sees it as a practical fix for tough land.

Willesden Farms in Banks Peninsula’s Kaituna Valley is a 300 ha conversion, milking 700 cows this season.

Before the barn, wet winters turned paddocks into mud traps, with cows slipping and pastures taking a beating.

Now, cows are under cover during both rain and hot spells, keeping pastures safe from damage during the wet, and cows shaded from heat stress.

Matt Iremonger didn’t rush into this. He researched composting barns across New Zealand, Australia, and the United States, visiting sites in Waikato, Taranaki, Southland, the West Coast, and Canterbury.

“We looked at how these systems were able to augment our pastoral system,” he says.

The goal was to squeeze more value from wet winter land without ditching pasture, and supplier Numat Agri was chosen for the project.

The barn serves two purposes: wintering 550–650 non-milking cows in June and July, and sheltering up to 800 during bad weather.

“It’s designed for the full eight hundred during adverse weather at any time of the year,” Iremonger notes.

That covers spring rains, autumn mud, and summer heat for shade.

Thirty-one metres wide by 185 metres long, the barn has 3500 cubic metres of woodchip bedding, with 740 metres of feedface.

The frame uses NuSpan laminated timber — essentially glulam — sourced from sustainable NZ plantations.

This eco-friendly alternative to steel-framed barns is up to 20 per cent more cost-effective than traditional builds. It also handles moisture in effluent-heavy settings without corroding.

“We were really attracted to it because it was cost efficient, and highly durable,” Iremonger says.

Plus it delivers a warmer, softer space that fits the farm’s vibe.

Built for 50+ years, the barn is a long-term play.

“We’ve modelled it as a 50-year piece of infrastructure but there’s no reason that it wouldn’t last significantly longer,” he says.

Return on investment lands in five years, with profits rolling in after from higher productivity and lower costs generating savings on off-farm wintering — no more trucking cows off-site.

In severe weather, both cows and staff are more comfortable, and less stressed.

The barn cuts methane and nitrate outputs, key culprits in dairy emissions.

By keeping cows indoors during wet spells, nitrogen leaching drops from 15–20 kg per ha annually to near zero, per industry benchmarks.

Monitoring during consenting shows net gains, putting Willesden ahead of the curve.

Opportunities abound for growth.

High milk prices fuel conversions, with Canterbury seeing consents surge fourfold since last year.

Exports to markets like China drive demand, while NZ’s low-cost production edge keeps farms competitive globally.

Milk output is set to rise, with herd numbers increasing through reduced culling and new setups.

The upsides pull farmers in.

Dairy offers higher returns than dryland grazing on similar land, with asset values climbing in areas like Southland.

Numat Agri says tech like composting barns tips the balance: they cut nitrate leaching by up to 50 per cent, slash methane via better feed efficiency, and enhance sustainability for long-term business resilience.

Willesden’s case fits the pattern.

On Banks Peninsula’s wet slopes, the conversion swaps cropping for year-round grass, avoiding exposed soil and boosting fertility.

The barn’s 46 per cent footprint cut — via captured effluent and indoor shelter — mirrors sector-wide moves to meet 2030 emissions targets without slashing output.

Matt Iremonger’s research echoes broader farmer caution: conversions work when paired with systems that protect assets long-term, turning compliance pressures into straightforward advantages.