How to Overcome the Challenges of Skillion Roof Installations While  Remaining Energy-Efficient

Energy efficiency is critical for new buildings as the New Zealand construction industry continues to take steps to deliver more environmentally friendly, energy-efficient builds. Under the revised H1 code, changes have been made to the roof insulation requirements for housing and small buildings under 300m² to meet the updated standard. Across all climate zones, building insulation must now meet R6.6 construction values. However, this can be a challenge for skillion roof installations depending on calculation methods and the rafter depth.

Guy Manthel, Technical Product and Compliance Manager, Knauf Insulation, said, “There are three primary methods that can be used to properly insulate skillion roofs: the schedule method, modelling method, and calculation method. The schedule method specifies minimum R-values for building envelope components depending on construction type and climate zone. Comparatively, the calculation method calculates heat loss to identify R-value requirements while comparing results with reference buildings. The more flexible modelling method lets installers demonstrate H1 compliance by comparing proposed energy use against reference buildings.”

Achieving the R6.6 construction value in a skillion roof can be a challenge due to the cavity depth provided by the rafters, and where thermal performance can be significantly affected by thermal bridging. For example, due to its construction, a skillion roof would require a 290mm rafter to accommodate an R7.4 insulation product and achieve compliance with the minimum R6.6 construction value within the existing rafter depth. The R6.6 construction value can also be achieved with a 240mm rafter and the addition of a 45mm R1.3 additional internal insulation layer, The additional layer has a positive impact through an additional thermal contribution and a reduction in thermal bridging.

Meanwhile, modelling and calculation methods let lower roofing thermal values be offset by higher wall and underfloor values.
New skillion roof insulation products maximise the thermal contribution in the given rafter depth. For example, an R7.4 product that’s suitable for a 290mm rafter achieves thermal values above R6.6 requirements, making it suitable for the schedule method and use in modelling and calculation methods.

Guy Manthel said, “Regardless of the compliance method, installers must consider key elements including roof ventilation, and the required separation between the membrane and insulation.”

To help overcome the challenges of insulating skillion roofs, Knauf Insulation has developed a range of H1-compliant skillion roof products which are designed to maximise the thermal contribution in the given rafter depth, helping the New Zealand construction industry achieve compliance with ease.

Earthwool glasswool insulation: Ceiling Batts

Knauf Insulation

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The Earthwool® glasswool insulation: ceiling batt range includes a selection of R-values to provide builders, designers, installers the opportunity to choose the best thermal performance for their project.

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Pre-Consumer Recycled Content

Earthwool® glasswool insulation has been appraised by BRANZ as a thermal insulation material for framed or part-framed walls, ceilings and roofs of domestic and commercial buildings
The insulation is pre-cut to suit a wide range of thermal insulation requirements and framing set-outs.
Comes in a range of R-values — see Product Data Sheet

AS/NZS 4859.1: 2018 Materials used in the Thermal Insulation of Buildings.

In the opinion of BRANZ, Earthwool® glasswool Insulation if designed, used, installed and maintained in accordance with the statements and conditions of this Appraisal, will meet or contribute to meeting the following provisions of the NZBC:

Clause B2 DURABILITY: Performance B2.3.1 (a) not less than 50 years and B2.3.1 (b) 15 years
Earthwool glasswool insulation will meet these requirements. See Paragraph 8.1
Clause E3 INTERNAL MOISTURE: Performance E3.3.1
Earthwool glasswool insulation will contribute to meeting this requirement. See Paragraphs 13.1 and 13.2
Clause F2 HAZARDOUS BUILDING MATERIALS: Performance F2.3.1
Earthwool glasswool insulation meets this requirement and will not present a health hazard to people
Clause H1 ENERGY EFFICIENCY: Performance H1.3.1 (a) and H1.3.2
Earthwool glasswool insulation will contribute to meeting this requirement. See Paragraphs 14.1 and 14.2

See BRANZ Appraisal 648 for full information.

BRANZ Appraised

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Earthwool glasswool insulation: Wall Batts

Knauf Insulation

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The Earthwool® glasswool insulation: wall batt range includes a selection of R-values and densities to provide builders, designers, installers the opportunity to choose the best thermal and acoustic performance for their project.

Declare LBC Red List Free

Green Tag Certified

Pre-Consumer Recycled Content

Earthwool® glasswool insulation has been appraised by BRANZ as a thermal insulation material for framed or part-framed walls, ceilings and roofs of domestic and commercial buildings
The insulation is pre-cut to suit a wide range of thermal insulation requirements and framing set-outs
Comes in a range of R-values — see Product Data Sheet

AS/NZS 4859.1: 2018 Materials used in the Thermal Insulation of Buildings

Clause B2 DURABILITY: Performance B2.3.1 (a) not less than 50 years and B2.3.1 (b) 15 years
Earthwool glasswool insulation will meet these requirements. See Paragraph 8.1
Clause E3 INTERNAL MOISTURE: Performance E3.3.1
Earthwool glasswool insulation will contribute to meeting this requirement. See Paragraphs 13.1 and 13.2
Clause F2 HAZARDOUS BUILDING MATERIALS: Performance F2.3.1
Earthwool glasswool insulation meets this requirement and will not present a health hazard to people
Clause H1 ENERGY EFFICIENCY: Performance H1.3.1 (a) and H1.3.2
Earthwool glasswool insulation will contribute to meeting this requirement. See Paragraphs 14.1 and 14.2

See BRANZ Appraisal 648 for full information.

BRANZ Appraised

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ecoinsulation Thermal and Acoustic Wall Insulation

Knauf Insulation

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ecoinsulation Thermal and Acoustic Wall insulation with DriTherm technology is made using a silicone treatment that is added to the glasswool during manufacture to upgrade the moisture resistance of the insulation, and provide guaranteed water resistance for 50 years.

Green Tag Certified

Pre-Consumer Recycled Content

ecoinsulation glasswool has been appraised by BRANZ as a thermal insulation material for framed or part-framed walls of domestic and commercial buildings.
The insulation is pre-cut to suit a wide range of thermal insulation requirements and framing set-outs
Comes in a range of R-Values — see Product Schedule

AS/NZS 4859.1 Materials used in the Thermal Insulation of Buildings

In the opinion of BRANZ, ecoinsulation glasswool if designed, used, installed and maintained in accordance with the statements and conditions of this Appraisal, will meet or contribute to
meeting the following provisions of the NZBC:

Clause B2 DURABILITY: Performance B2.3.1(a) not less than 50 years, and B2.3.2. ecoinsulation glasswool insulation products will meet these requirements.
Clause C3 PROTECTION FROM FIRE: Performance C3.7(a). ecoinsulation glasswool insulation products are not combustible building materials and will contribute to meeting this requirement
Clause E3 INTERNAL MOISTURE: Performance E3.3.1. ecoinsulation glasswool insulation products will contribute to meeting this requirement
Clause F2 HAZARDOUS BUILDING MATERIALS: Performance F2.3.1. ecoinsulation glasswool insulation products do not present a health hazard to people
Clause H1 ENERGY EFFICIENCY: Performance H1.3.1(a) and H1.3.2E. ecoinsulation glasswool insulation products will contribute to meeting these requirements

See BRANZ Appraisal 1049 for full information.

BRANZ Appraised

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ecoinsulation Thermal Ceiling Insulation

Knauf Insulation

View Product

ecoinsulation Thermal Ceiling insulation with DriTherm technology is made using a silicone treatment that is added to the during manufacture to upgrade the moisture resistance of the glasswool insulation, and provide guaranteed water resistance for 50 years.

Green Tag Certified

Pre-Consumer Recycled Content

ecoinsulation glasswool has been appraised by BRANZ as a thermal insulation material for framed or part-framed ceilings and roofs of domestic and commercial buildings
The insulation is pre-cut to suit a wide range of thermal insulation requirements and framing set-outs
Comes in a range of R-Values — see Product Schedule

AS/NZS 4859.1 Materials used in the Thermal Insulation of Buildings

Clause B2 DURABILITY: Performance B2.3.1(a) not less than 50 years, and B2.3.2. ecoinsulation glasswool insulation products will meet these requirements.
Clause C3 PROTECTION FROM FIRE: Performance C3.7(a). ecoinsulation glasswool insulation products are not combustible building materials and will contribute to meeting this requirement
Clause E3 INTERNAL MOISTURE: Performance E3.3.1. ecoinsulation glasswool insulation products will contribute to meeting this requirement
Clause F2 HAZARDOUS BUILDING MATERIALS: Performance F2.3.1. ecoinsulation glasswool insulation products do not present a health hazard to people
Clause H1 ENERGY EFFICIENCY: Performance H1.3.1(a) and H1.3.2E. ecoinsulation glasswool insulation products will contribute to meeting these requirements

See BRANZ Appraisal 1049 for full information.

BRANZ Appraised

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