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The importance of Heat Air Moisture Management in DfMA

In this article Adam Taylor, Business Development Manager – Building Envelope of the A. Proctor Group outlines the need for designers and manufacturers to understand and embrace a best practice approach to heat, air, moisture management in DfMA.

As the construction industry seeks to address the challenges which relate to the UK’s housing shortage and deliver more energy-efficient buildings across the residential and commercial sectors, it is clear that Design for Manufacture and Assembly (DfMA) will form an essential part of the delivery process.

The application of DfMA is ideally suited towards offsite modular construction, with its focus on ease and efficiency of both manufacture and assembly. The benefits of fast-track offsite manufacture for assembly onsite can lead to higher outputs, whilst significantly reducing the project programme time, with less material waste and costs, and fewer delays in relation to snagging and re-working on site.

The A. Proctor Group Ltd as a leading manufacturer of vapour permeable membranes and vapour control layers provides essential best practice advice to designers and manufacturers of offsite modular buildings based upon the proven model of Heat Air Moisture Management (HAMM).

The importance of Heat Air Moisture Management (HAMM) to DfMA

Based upon over 50 years of providing solutions and products for the construction sector we understand that a totally holistic approach is required to DfMA building design. In doing so, the points below consider six core aspects in the process:

  • Building
  • Weather
  • Occupants
  • Heat
  • Air
  • Moisture

For any building to be an energy efficient, healthy, moisture free building envelope there is a clear need to manage the balance of Heat, Air and Moisture movement throughout the process of the building’s life cycle from design, construction, completion and use.

Understanding the importance of these key elements upon the building envelope is crucial to the successful construction and operation of a building. Architects, designers, and off-site construction manufacturers must seek to understand the science behind our buildings, managing the external and internal forces, which impact on the quality of the completed building, its performance in use, as well as the health of its occupants and the wider environment.

Airtightness and modular building design

There is absolutely no question that an integral part of modern building design is influenced by energy efficiency. In the EU it is estimated that buildings account for approximately 40% of energy consumption and are responsible for some 36% of CO2 emissions. Closer to home, around 45% of UK CO2 emissions come from the built environment, (27% from domestic dwellings and 18% from non-domestic).

As thermal insulation requirements have increased over the last few years, the proportion of energy lost through air leakage has become more evident. The ever-increasing thermal insulation required will, however, be rendered largely ineffective unless the airtightness of the structure itself is addressed. Air leakage greatly reduces the effect of thermal insulation; therefore if energy efficiency is to be improved within buildings, this is the most critical area to focus on.

In addition to improved insulation, energy efficient heating systems will also be ineffective if warm air can escape the building and cold air can seep in. This is reflected in the fact that total space heating costs in an airtight construction may be considerably less than in a leaky one.

Air leakage through cracks, gaps, holes and improperly sealed elements such as doors and windows can cause a significant reduction in the performance of even thermally insulated envelopes.

Effective airtightness design

The two main ways to achieve airtightness in the building envelope are internally or externally, or in other terms, “inside of the services zone’ or ‘outside of the services zone’.

Traditional use of internal air barriers can be more complex and costly to install, due to the need to accommodate building services such as electrical, lighting, heating and drainage systems. An internal air barrier is only as good as it’s installation. If all the service penetrations are not adequately sealed, performance will be compromised.

For many years, external air barriers have been commonly specified in North American building design and construction. By moving the air barrier to the external side of the structural frame, external air barrier systems such as Wraptite® from A. Proctor Group allow for an almost penetration-free airtight layer, which can be installed faster and more robustly. This offers an effective but simple system comprising a self-adhesive vapour permeable air barrier membrane, plus vapour permeable sealing tape, Wraptite Corners and Wraptite Liquid Flashing, and provides effective secondary weather protection while preventing trapped moisture and air leakage. Far simpler than internal options an external air barrier system like Wraptite will maintain the envelope’s integrity, with less building services and structural penetrations to be sealed, and less room for error.

Fixing Options for Air & Vapour Control

The traditional forms of VCLs and airtightness membranes will often require mechanical fixing. In the case of timber structures using steel staples, and on concrete using a separate double-sided adhesive tape. The self-adhered nature of Wraptite allows for a simple and fast installation process, minimising the use of additional sealants and tapes, and requiring no specialist contractors to achieve a robust result. This one-step solution provides both a damage resistant air barrier layer and effective secondary weather protection in one installation process, allowing a wind and watertight envelope to be achieved more quickly than using traditional methods.

TopHat incorporates Wraptite into the design

One of the UK’s leading modular housing manufacturers TopHat has successfully incorporated Wraptite into the design of its high-quality timber-framed homes.  Wraptite is a patented external air barrier membrane system, which offers manufacturers and designers of modular and off-site buildings the ability to reliably and comfortably exceed current airtightness requirements. Wraptite is the only self-adhering vapour permeable air barrier certified by the BBA and combines the important properties of vapour permeability and airtightness in one self-adhering membrane.

The A. Proctor Group provides a range of high-performance membranes to address the requirements of heat, air, moisture management within the building element, and provides comprehensive guidance using modelling & analysis tools to ensure compliance and guide designers and manufacturers on best practice related to DfMA.

For more information please visit www.proctorgroup.com

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A guide to high-performance membranes for modular construction

The benefits of modular construction have been widely discussed with advocates including the government now recognising its potential to address the UK’s challenges in terms of both housing capacity and skills shortages. However, the growth and benefits of modular off-site construction are equally at home in student housing and commercial developments such as hotels and high-rise buildings.

The opportunities and benefits delivered by modular construction projects may range from significant reductions in programme length, waste and cost, whilst another major factor is the ability to achieve higher levels of quality control in the process.

From design through to construction and completion what is absolutely essential is that the selection of materials and products used within off-site projects is not compromised, ensuring performance is assured during the build process and throughout the lifetime of the building.

Helping to achieve this are some of the most technically advanced construction membranes available. The A. Proctor Group Ltd has been developing vapour permeable membranes and vapour control layers for over 25 years, and provides an extensive range of superior high-performance products suitable for modular and off-site construction.

The move to tighten building regulations

With the increased spotlight and focus on building regulations and the suitability of materials specified for use within external cladding, the correct selection and application of materials are at their most critical.

Following the Independent Review of Building Regulations and Fire Safety and subsequent Interim Report by Dame Judith Hackitt, the Government has introduced an amendment to the Approved Document B: Fire safety, which has a significant impact on the design and construction of buildings above 18 metres. Published in November 2018, the new regulations came into force on 21 December 2018. Guidance on how external walls can meet the Building Regulations requirement for resisting fire spread is set out in Approved Document B.

Changes to materials and workmanship

Regulation 7 of the Building Regulations relates to materials and workmanship and reads as follows:

7. (1) Building work shall be carried out-
(a) with adequate and proper materials which-
(i) are appropriate for the circumstances in which they are used,
(ii) are adequately mixed or prepared, and
(iii) are applied, used or fixed so as adequately to perform the functions for which they are
designed; and
(b) in a workmanlike manner.
(2) Subject to paragraph (3), building work shall be carried out so that materials which become part of an external wall, or specified attachment, of a relevant building, are of European Classification A2-s1, d0 or Class A1, classified in accordance with BS EN 13501-1:2007+A1:2009 entitled “Fire classification of construction products and building elements. Classification using test data from reaction to fire tests” (ISBN 978 0 580 59861 6) published by the British Standards Institution on 30th March 2007 and amended in November 2009.

Changes on the use of membranes within external wall construction

It is important to note that with specific reference to membranes the Regulation provides a critical exemption and further clarification is found within Regulation 7, as stated below:

12.14 Particular attention is drawn to the following points.

a. Membranes used as part of the external wall construction should achieve a minimum classification of European Class B-s3, d0.

In summary, the amendment stipulates significant changes to which membranes can now be used and limits these to a rating of Class B,s3,d0.

It is crucial that all those involved in the construction of highrise modular construction fully understand the implications of this amendment in the wider context of building safety and protection. Critically designers should note that some European membrane products whilst quoting A2 ratings do not breathe sufficiently to comply with BS5250, meaning the use of these membranes in the UK climate could make the building unhealthy and result in a much greater risk of condensation issues and mould growth.

The complexity of manufacturing a non-combustible membrane which is still breathable to BS5250 standard is extremely difficult to achieve. In selecting a membrane it is important that performance is not compromised and that compliance meets the requirements of both Approved Document B: Fire Safety and BS5250 the Code of Practice for Condensation Control.

High-performance membranes – air tightness:

Wraptite

An example of a high-performance membrane in practice is the Wraptite air barrier system. Wraptite offers a safer and simplified membrane system, conforms with the required Class B rating, and it provides a fully self-adhered vapour permeable air barrier certified by the BBA and combines the important properties of vapour permeability and airtightness in one self-adhering membrane. The membrane bonds back to the substrate, ensuring a simplified design to airtightness and simple installation method.

System benefits

• Complies with use on buildings of high rise and over 18m under Part B amendments made in November 2018, Membranes need to be Class B,s3,d0 or better, with Wraptite classified as Class B,s1,d0 when used over a Class A1 or A2 substrate.
• Included within BS8414 testing with cladding manufacturers.
• EPDM not needed to the frame of the building as the self-adhesive membrane continues across the whole envelope of the building against the sheathing board and the frame of the building.
• Less EPDM around window details due to the membrane lapping into the building at junctions.
• Corner detailing for opening and movement joint interfaces are easily treated.
• Improved airtightness and may negate the use of a VCL totally from the design internally, meaning easier a quicker install of dry lining package.
• Hygrothermal Modelling will identify whether the construction requires a VCL or not. In some instances, the use of this self-adhesive without a VCL may be the most efficient option.
• Improving airtightness may allow you to change thickness or type of insulation used when modelled through SAP or SBEM.
• No need to tape sheathing boards as the membrane is positioned across the whole board.
• By using this membrane on the external may show improvement on making the building watertight, allowing the cladding package to come off the critical path and internal works to start earlier, and also internal works may not be installing a VCL so the site program is potentially quicker.

High-performance membranes – fire protection: Fireshield

The culmination of years of research into membranes has led to the development of a vapour permeable membrane with a fireproof surface, which has a unique intumescent composition that actively reacts to prevent fire taking hold and that also significantly reduces the formation of droplets and smoke.

Crucially the new membrane fully complies with BS5250, BS4016 and NHBC requirements for vapour permeable walling underlays. Having succeeded in overcoming the complexity of creating a non-combustible, yet vapour permeable membrane, Fireshield has also been able to meet long term 5000hr UV ageing. This allows the membrane to be used in open jointed rainscreen and cladding applications.

The installation procedure is the same as for standard breather membranes, with the membrane fixed to the substrate using mechanical fixings. Applications include both commercial and residential buildings including apartments and student accommodation, as well as Rainscreen cladding and applications over 18m high.

System benefits

• Fireproof surface – unique intumescent composition actively reacts to prevent fire taking hold
• Vapour permeable walling underlay for use either directly onto sheathing or insulation
• Class B, s1-d0 but performs differently to other similar class products
• Complies with BS5250, BS4016 & NHBC requirements for vapour permeable walling underlays
• Ideal for use in rainscreen/façade construction
• Suitable for applications over 18m high
• Long term UV exposure suitable for open joint facades
• Airtight

Spacetherm A2

Spacetherm A2 is a flexible, high-performance, silica aerogel-based insulation material of limited combustibility suitable for use in exterior and interior applications. Supplied in a variety of finishes, the substantial layers of Spacetherm A2 meet the requirements for A2 classification (insulation, MgO and plasterboard).

The product optimises both the thermal performance and fire properties of façade systems, enhancing the thermal performance of the ventilated façade and addressing thermal bridging in the façade. It is also useful in minimising thermal bridges around windows in areas such as window reveals.

With a thermal conductivity of 0.019 W/mK, Spacetherm A2’s performance credentials qualify it as one of the best Class A2 insulations materials available worldwide. Engineered for space-critical applications, the product offers low thermal conductivity, superior compression strength, plus breathability allied to hydrophobic characteristics.

System benefits

• Class leading fire performance from an Aerogel insulation
• Superior thermal performance
• Limited combustibility
• Water vapour diffusion open
• Permeable
• Flexible
• Thinnest Aerogel insulation available

For more information please visit www.proctorgroup.com.

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Managing heat, air and moisture movement in modular buildings

For modular buildings to be energy efficient, healthy, and moisture free what is required is a holistic approach to a total system which manages the balance of Heat, Air, Moisture Movement (HAMM), considering an integrated approach to airtightness, insulation and condensation control.

Buildings with very low rates of air leakage require correspondingly higher levels of ventilation as part of a balanced, design approach. It’s important to bear in mind that ventilation is controllable, and therefore can be accounted for within the overall design, whereas uncontrolled air leakage is not.

The incorrect specification or installation of effective thermal barriers will lead to unmanaged heat loss, impacting directly on the energy efficiency of the building and its systems.

Airtightness and vapour permeability

Air movement is important in the building envelope both infiltration and escape. We need to control interior conditioned air (whether heated or cooled) escaping and exterior air infiltrating that puts more pressure on heating or cooling mechanisms internally. Airtight membranes are key in this area whether vapour and air open/closed or variable.

Moisture vapour will pass through the various layers of any construction by both convection and diffusion. The objective is to ensure, by design, that the moisture vapour can disperse to the outside atmosphere without being cooled to below dewpoint temperature, thus eliminating condensation and associated problems such as mould growth.

To avoid the occurrence of excess condensation, which can result in mould growth and damage to the building fabric, designers should assess the amount of water vapour likely to be generated within the building and determine the resultant increase in internal vapour pressure above that of external air. They should then consider the physical properties of the construction separating inside from outside.

Why airtightness is crucial to modular building design

There is absolutely no question that an integral part of modern building design is influenced by energy efficiency. In the EU it is estimated that buildings account for approximately 40% of energy consumption and are responsible for some 36% of CO2 emissions. Closer to home, around 45% of UK CO2 emissions come from the built environment, (27% from domestic dwellings and 18% from non-domestic).

Airtightness improves energy efficiency

As thermal insulation requirements have increased over the last few years, the proportion of energy lost through air leakage has become more evident. The ever-increasing thermal insulation required will, however, be rendered largely ineffective unless the airtightness of the structure itself is addressed. Air leakage greatly reduces the effect of thermal insulation; therefore if energy efficiency is to be improved within buildings, this is the most critical area to focus on.

In addition to improved insulation, energy efficient heating systems will also be ineffective if warm air can escape the building and cold air can seep in. This is reflected in the fact that total space heating costs in an airtight construction may be considerably less than in a leaky one.

Air leakage through cracks, gaps, holes and improperly sealed elements such as doors and windows can cause a significant reduction in the performance of even thermally insulated envelopes. Architects are increasingly turning to air barrier membranes as an essential part of the design process in achieving the most effective means of controlling and reducing air leaks.

In terms of the energy efficiency of a building, uncontrolled air flow will almost certainly have a major impact. Initial heat load calculations for heating and cooling equipment will usually make an allowance for a level of natural infiltration or uncontrolled air flow. The higher the infiltration rate, the lower the energy efficiency of the building. Efficiency levels can be affected by both natural and mechanical air movements. The forces of wind and stack effects will lead to a level of air infiltration and subsequent efficiency loss. Sealing the shell of the building and any un-designed holes can reduce the impact of wind and stack effects and improve the overall energy efficiency.

Airtightness protects building fabric and reduces maintenance costs

Unmanaged or uncontrolled air flow will act as a carrier for moist air, drawing it from outside in, or pulling it from inside out, into walls, ceilings, and roofs. The impact of uncontrolled moist air movement can have a long-term detrimental effect on the durability and life of the building. This, in turn, can lead to:

  • Decay of organic materials such as timber frames
  • Saturation of insulating materials, thus reducing their insulative effect (further increasing heat loss)
  • Corrosion of metal components
  • Frost damage where moisture has accumulated on the cold side of the insulation

The design of an effective airtight system will reduce the risk of uncontrolled moisture movement, and the potential for damage caused by condensation within the building fabric.

Effective airtightness design

The two main ways to achieve airtightness in the building envelope are internally or externally, or in other terms, ‘inside of the services zone’ or ‘outside of the services zone’.

Traditional use of internal air barriers can be more complex and costly to install, due to the need to accommodate building services such as electrical, lighting, heating and drainage systems. An internal air barrier is only as good as its installation. If all the service penetrations are not adequately sealed, performance will be compromised.

For many years, external air barriers have been commonly specified in North American building design and construction. By moving the air barrier to the external side of the structural frame, external air barrier systems such as Wraptite from A. Proctor Group allow for an almost penetration-free airtight layer, which can be installed faster and more robustly. This offers an effective but simple system comprising a self-adhesive vapour permeable air barrier membrane, plus vapour permeable sealing tape, Wraptite Corners and Wraptite Liquid Flashing, and provides effective secondary weather protection while preventing trapped moisture and air leakage. Far simpler than internal options an external air barrier system like Wraptite will maintain the envelope’s integrity, with less building services and structural penetrations to be sealed, and less room for error.

Incorporating Wraptite in the design makes sense

Wraptite is a patented external air barrier membrane system, which offers manufacturers and designers of modular and off-site buildings the ability to reliably and comfortably exceed current airtightness requirements. Wraptite is the only self-adhering vapour permeable air barrier certified by the BBA and combines the important properties of vapour permeability and airtightness in one self-adhering membrane. This approach saves on both the labour and material costs associated with achieving the demands of energy efficiency in buildings.

  • Complies with use on buildings of high rise and over 18m under Part B amendments made in November 2018, Membranes need to be Class B,s3,d0 or better, with Wraptite at Class B,s1,d0*
  • Included within BS8414 testing with cladding manufacturers
  • EPDM not needed to the frame of the building as Wraptite is self-adhesive and continues across the whole envelope of the building against the sheathing board and the frame of the building
  • Less EPDM around window details due to Wraptite lapping into the building at junctions
  • Corner detailing for opening and movement joint interfaces are easily treated
  • Improved airtightness and may negate the use of a VCL totally from the design internally, meaning easier a quicker install of dry lining package
  • Hydro-Thermal Modelling (WUFI) showing the difference of not using a VCL within some constructions benefits the building further
  • Improving airtightness may allow you to change thickness or type of insulation used when modelled through SAP or SBEM
  • No need to tape sheathing boards as Wraptite is positioned across the whole board
  • Testing has seen results as low as 0.5 m3/(h.m2) @ 50PA carried out at Windtech on a window façade panel
  • By using Wraptite on the external, this may show you an improvement on making the building watertight, allowing your cladding package to come off the critical path and internal works to start earlier, and also internal works may not be installing a VCL so the site program is potentially quicker

High-performance off-site solutions

The A. Proctor Group Ltd has been providing solutions and products to the construction industry for over 50 years. The company has been developing vapour permeable membranes and vapour control layers for over 25 years, and provides an extensive range of superior high-performance products suitable for modular and off-site construction.

Dedicated in its approach to helping you to achieve best practice, effective and reliable solutions to meet your modular building requirements in line with building regulations and energy efficiency, the A. Proctor Group team of highly experienced industry professionals and technical advisors is on at hand to guide you and support you from design throughout the construction process.

The A. Proctor Group range of products include unique off-site solutions for the following sectors:

  • Private and social/affordable housing
  • Purpose built student accommodation
  • Self-build projects
  • Hotels
  • Education buildings
  • Healthcare including hospitals, health centres and healthcare facilities

*tested over 12mm calcium silicate board / fibre cement board as per BS EN 13238:2010. All tests carried out to EN 13859-2 standard.

IMAGE courtesy of Kingspan TEK

For more information please visit www.proctorgroup.com.
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