When synthetic is the answer: a new era of roofing underlays

When synthetic is the answer: a new era of roofing underlays

While single-use plastic is out of favour, plastic has distinct benefits when it comes to durability as a building product.

Words by ArchiPro Editorial Team

The roofing industry is always evolving but a significant change has occurred of late that has seen the industry moving towards a product that offers much more than the traditional alternative.

Black paper, the industry’s name for bitumen paper-based underlay, is still a heavily favoured underlay in the residential building sector, however, its limitations have become increasingly clear as technology evolves, Thermakraft’s William Lin says.

“In New Zealand, the Building Code requires that all roofs incorporate either a synthetic or a bitumen, black paper underlay. Black paper underlay has been around for about half a century and traditionally has been the most-used roofing underlay in the residential building market in New Zealand. However, the industry is quickly realising the benefits of synthetic underlays and the market has changed.”

While synthetic underlays are not new, a New Zealand-made product launched in early 2020 has surpassed what was previously possible in terms of durability, longevity and performance in the synthetic market.

Covertek 401 was developed to offer increased performance in a multitude of ways, William says.

Covertek 401 synthetic roofing underlay.
Covertek 401 synthetic roofing underlay.

What are the benefits of synthetic roofing underlays?

“Covertek 401 represents the latest development in the roofing industry. What tended to happen with black paper underlays is that they became brittle over a long period of time. 

“That’s where synthetic underlays outperform this traditional product and the latest iteration means even higher performance specifications than previously available,” William says. 

What is synthetic roofing underlay made with?

Covertek 401 consists of a microporous water-resistant film sandwiched between two layers of shrink-resistant spun-bonded polyolefin. Suitable for use over timber or steel framing and underneath tile or steel roofs, Covertek 401 is much stronger than earlier synthetic roof underlays and is self supported, William explains.

“This is an important characteristic as in the instance that water does reach an underlay, if that underlay is not able to retain its shape in the way Covertek 401 does, water can pond to dangerous levels in areas of the underlay that have sagged. This scenario is not a factor when using 401, as it is designed to ensure water drains to guttering without ponding.”

Its inherent strength also means it is very unlikely to rip or tear, even when being installed in high-wind zones or in extreme weather such as rain or snow. “We’ve also changed the colour from white to light grey, which allows for a safer and easier install as glare is dramatically reduced.”

Covertek 401 is produced in New Zealand under the ISO9001 quality management system standard, and is BRANZ appraised and available throughout New Zealand. It is sold with a 15-year warranty.

Find out more about the latest in synthetic roof underlays for residential construction.

Thermakraft Limited

A recognised leader in the industry, Thermakraft is the sole New Zealand manufacturer of synthetic wall and roofing underlays which have been designed and developed...

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When synthetic is the answer: a new era of roofing underlays
When synthetic is the answer: a new era of roofing underlays

When synthetic is the answer: a new era of roofing underlays

While single-use plastic is out of favour, plastic has distinct benefits when it comes to durability as a building product.

Words by ArchiPro Editorial Team

The roofing industry is always evolving but a significant change has occurred of late that has seen the industry moving towards a product that offers much more than the traditional alternative.

Black paper, the industry’s name for bitumen paper-based underlay, is still a heavily favoured underlay in the residential building sector, however, its limitations have become increasingly clear as technology evolves, Thermakraft’s William Lin says.

“In New Zealand, the Building Code requires that all roofs incorporate either a synthetic or a bitumen, black paper underlay. Black paper underlay has been around for about half a century and traditionally has been the most-used roofing underlay in the residential building market in New Zealand. However, the industry is quickly realising the benefits of synthetic underlays and the market has changed.”

While synthetic underlays are not new, a New Zealand-made product launched in early 2020 has surpassed what was previously possible in terms of durability, longevity and performance in the synthetic market.

Covertek 401 was developed to offer increased performance in a multitude of ways, William says.

Covertek 401 synthetic roofing underlay.
Covertek 401 synthetic roofing underlay.

What are the benefits of synthetic roofing underlays?

“Covertek 401 represents the latest development in the roofing industry. What tended to happen with black paper underlays is that they became brittle over a long period of time. 

“That’s where synthetic underlays outperform this traditional product and the latest iteration means even higher performance specifications than previously available,” William says. 

What is synthetic roofing underlay made with?

Covertek 401 consists of a microporous water-resistant film sandwiched between two layers of shrink-resistant spun-bonded polyolefin. Suitable for use over timber or steel framing and underneath tile or steel roofs, Covertek 401 is much stronger than earlier synthetic roof underlays and is self supported, William explains.

“This is an important characteristic as in the instance that water does reach an underlay, if that underlay is not able to retain its shape in the way Covertek 401 does, water can pond to dangerous levels in areas of the underlay that have sagged. This scenario is not a factor when using 401, as it is designed to ensure water drains to guttering without ponding.”

Its inherent strength also means it is very unlikely to rip or tear, even when being installed in high-wind zones or in extreme weather such as rain or snow. “We’ve also changed the colour from white to light grey, which allows for a safer and easier install as glare is dramatically reduced.”

Covertek 401 is produced in New Zealand under the ISO9001 quality management system standard, and is BRANZ appraised and available throughout New Zealand. It is sold with a 15-year warranty.

Find out more about the latest in synthetic roof underlays for residential construction.

Thermakraft Limited

A recognised leader in the industry, Thermakraft is the sole New Zealand manufacturer of synthetic wall and roofing underlays which have been designed and developed...

Recommended reading
Done tagging
Full screen
When synthetic is the answer: a new era of roofing underlays

When synthetic is the answer: a new era of roofing underlays

While single-use plastic is out of favour, plastic has distinct benefits when it comes to durability as a building product.

Words by ArchiPro Editorial Team

The roofing industry is always evolving but a significant change has occurred of late that has seen the industry moving towards a product that offers much more than the traditional alternative.

Black paper, the industry’s name for bitumen paper-based underlay, is still a heavily favoured underlay in the residential building sector, however, its limitations have become increasingly clear as technology evolves, Thermakraft’s William Lin says.

“In New Zealand, the Building Code requires that all roofs incorporate either a synthetic or a bitumen, black paper underlay. Black paper underlay has been around for about half a century and traditionally has been the most-used roofing underlay in the residential building market in New Zealand. However, the industry is quickly realising the benefits of synthetic underlays and the market has changed.”

While synthetic underlays are not new, a New Zealand-made product launched in early 2020 has surpassed what was previously possible in terms of durability, longevity and performance in the synthetic market.

Covertek 401 was developed to offer increased performance in a multitude of ways, William says.

Covertek 401 synthetic roofing underlay.
Covertek 401 synthetic roofing underlay.

What are the benefits of synthetic roofing underlays?

“Covertek 401 represents the latest development in the roofing industry. What tended to happen with black paper underlays is that they became brittle over a long period of time. 

“That’s where synthetic underlays outperform this traditional product and the latest iteration means even higher performance specifications than previously available,” William says. 

What is synthetic roofing underlay made with?

Covertek 401 consists of a microporous water-resistant film sandwiched between two layers of shrink-resistant spun-bonded polyolefin. Suitable for use over timber or steel framing and underneath tile or steel roofs, Covertek 401 is much stronger than earlier synthetic roof underlays and is self supported, William explains.

“This is an important characteristic as in the instance that water does reach an underlay, if that underlay is not able to retain its shape in the way Covertek 401 does, water can pond to dangerous levels in areas of the underlay that have sagged. This scenario is not a factor when using 401, as it is designed to ensure water drains to guttering without ponding.”

Its inherent strength also means it is very unlikely to rip or tear, even when being installed in high-wind zones or in extreme weather such as rain or snow. “We’ve also changed the colour from white to light grey, which allows for a safer and easier install as glare is dramatically reduced.”

Covertek 401 is produced in New Zealand under the ISO9001 quality management system standard, and is BRANZ appraised and available throughout New Zealand. It is sold with a 15-year warranty.

Find out more about the latest in synthetic roof underlays for residential construction.

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