CPD 08 2022: Streamlining Weatherproofing In Modular Construction  

This J&W sponsored CPD explains how modular buildings benefit from a different kind of weatherproofing and how to specify the appropriate materials

Effective waterproofing systems play a vital role in increasing the performance of a building

This CPD sets out a roadmap to a new weatherproofing approach, one designed for modular building and reflecting the materials used to take advantage of the technology’s flexibility, from manufacturing and construction to efficient installation. 

It will look at the importance of modular buildings for a viable route to net zero construction; considerations for weatherproofing of modular buildings and the impact on a modular project; weatherproofing for healthier and more sustainable buildings; and dealing with modular building envelope penetrations. 

Introduction 

Modular construction aims to revolutionise the way we deliver buildings, while providing a route to speed up the construction industry’s drive towards achieving net zero carbon emissions.  

Modular technology can help this by replacing inefficient processes connected with the unpredictability of working on site.  

Moving a large proportion of construction off site and prefabricating parts of buildings in a controlled manufacturing environment can speed up the delivery of better-quality and more energy-efficient buildings and help deliver a significant decrease in embodied and operational carbon of both buildings and the construction industry. 

Weatherproofing for modular construction 

Waterproofing for modular buildings needs to be approached differently

The role of weatherproofing goes beyond the protection of the building envelope. Effective weatherproofing systems play a vital role in increasing the performance and extending the lifecycle of a building. 

However, there is a notable performance gap between traditional weatherproofing methods and modular construction objectives. Traditional weatherproofing methods place a high demand on often costly materials, with excessive wastage. Installation is labour- and time-intensive and offers little in the way of scheduling flexibility. 

Such a disconnect suggests that weatherproofing for modular buildings needs to be approached differently.  

Modular and the road to net zero construction 

Multiple factors account for the recent increase in the specification of both permanent and temporary modular structures. The deepening housing shortage and the urgent need for more schools and hospitals and for improved infrastructure across the UK are putting growing pressure on project delivery times and construction costs.  

In the global effort to combat climate change and address sustainability and environmental protection, carbon emissions are under the spotlight, particularly in the traditional building process, which directly accounts for 10% of UK carbon emissions.  

The government’s commitment to decarbonise the grid by 2050 means society will need to build more energy-efficient buildings, with better-performing building envelopes. Closely connected to building energy efficiency is build quality and the impact of both parameters on the operating and lifecycle costs of buildings.  

While the impending changes to Part L and Part F as part of the Future Homes Standard are focusing on improvements to energy efficiency, new standards target the delivery of healthier structures for the benefit of occupants. 

These standards impact the design of buildings that need to achieve better daylight and fresh air provisions and inevitably lead to an increase in the number of building penetrations that may affect the thermal efficiency of the building envelope. 

The objective of modern modular construction is to achieve all these performance markers through the innovation of materials and methods along with increases in productivity and efficiency. 

Cost savings and faster delivery times 

Prefabricating large proportions of a building, including the MEP elements in a controlled environment, helps eradicate errors and timing issues. The subsequent modular installation phase is also much shorter, faster and more economical. The building envelope can also be improved, and the overall quality of the delivery which makes compliance much easier to achieve and extends the lifecycle of the building. 

Shortening or removing the unpredictable construction phase and replacing it with modularity and a short, intensive installation phase derives multiple benefits. Delivering more buildings on schedule reduces the project costs and produces earlier capital returns.  

According to McKinsey’s Modular Construction: From Projects to Products, modular buildings can be delivered 20% to 50% faster than a building constructed using traditional methods. The financial implications can be approximated to reach similar values, although they are much harder to generalise. 

Sustainability, environmental protection and improved energy efficiency 

The flexibility of a modular building means that a demolition process can be replaced with deconstruction, and the modules can be reused or the building redesigned. Less waste, reduced carbon emissions and a decreased impact on the environment also make modular construction a key component of a future green economy. 

The high level of prefabrication guarantees end-to-end quality. The controlled environment makes it easier to innovate and test materials and techniques and, as a result, the building envelope of a modular build is more thermally efficient and provides a variety of options for the specification of efficient low carbon energy technologies. 

Considerations for weatherproofing modular buildings  

It is important to look at how weatherproofing for modular buildings is different from traditional methods. 

We know that the methodology of modular construction is vastly different from traditional building processes. According to a 2013 report, Off-site Construction: Sustainability Characteristics, published by Building Intellect, “dramatic improvements over conventional techniques are commonly acknowledged, with the time required to construct and commission an offsite building being typically reduced by 60% in cases where large elements can be pre-fabricated”. This leaves a short and intense assembly period and therefore each phase needs careful planning.  

Early consultation with a weatherproofing expert will ensure that the weatherproofing becomes a part of the design process. The result is a system that works in harmony with the building envelope for complete protection. The detailing can be premanufactured and preinstalled where possible, making the overall scheduling work within the modular approach.

Sequencing and scheduling 

The key to success is in planning, and this is especially true in weatherproofing for modular construction. The ability to work within a precise schedule and a high degree of flexibility when the unexpected happens is essential, and not just for on-time delivery. 

Consideration needs to be given to the value of integration of weatherproofing with the building design, and minimising the risk of damage to module joints during on-site traffic. 

Damage to preinstalled elements needs to be avoided, while the integrity of the building envelope similarly needs to be protected. The protection of the envelope and modules during installation is crucial to the delivery of a high-quality, thermally efficient modular building. 

Sustainability and flexibility play a huge role in the rising popularity of modular buildings and the weatherproofing solution must inevitably reflect this. The weatherproof detailing should be removable and reusable where possible. The redundant penetrations must be capped off and weatherproofed to the required U-value to maintain the thermal efficiency of the building envelope. 

Weatherproofing for healthier, more sustainable modular buildings 

The challenges of human-centric design and MEP element installation for modular buildings have a common cause: lack of standardisation. It is this lack of uniformity and predictability that impacts the sequencing of building penetration works, the installation of ancillaries and final weatherproofing. 

Close collaboration with all contractors is required to overcome any timing issues in the supply chain or unexpected changes in product specifics.  

The vast range of fixing methods, the possibility of lead time changes and requirements for specialist installation must be considered to prevent the possibility of water ingress and subsequent damage to the building envelope. 

Installation and weatherproofing of as many elements as possible off site, if logistics allows, is preferred. This should be followed by careful scheduling of works during the intense on-site phase. 

Despite their location being initially out of sight to people on the ground, large amounts of roof penetrations can lead to a busy, unsightly roof that may be unattractive in the urban landscape where buildings are often overlooked by neighbouring structures. The design of weatherproofing systems should therefore aim to create an aesthetically pleasing finish. 

Supporting energy efficiency and sustainability 

The efficiency of modular construction leaves extra room to innovate and deploy new materials and techniques at speed. The introduction of new materials in modular construction and the accuracy of the offsite module assembly have resulted in an improvement to the building thermal efficiency. 

Weatherproofing systems should echo this with a move away from the traditional to new, more thermally efficient materials. In addition, weatherproofing should avoid thermal bridging and match the specified U-value to the overall thermal efficiency of the building. 

A variety of joints and penetrations may require different weatherproofing techniques and some of the works will inevitably have to take place on site. A holistically designed weatherproofing system will aim to achieve maximum performance by becoming an integral part of the building. 

In-situ adjustments reduce the efficiency of delivery and should be minimised by addressing the supply chain variations at the design stage. 

Detailed proposals for the weatherproofing system must be followed by an accurate manufacturing process, and early co-operation between manufacturers and installers can reduce the unpredictability factor that modular construction seeks to remove. 

A variety of joints and penetrations may require different waterproofing techniques and some of the works will inevitably have to take place on site

 

Installation issues 

In some instances, full preinstallation of weatherproofing during the module manufacture phase is not possible or practical. This may be due to height restrictions making complete module transport impossible, or because the lead time for the MEP parts or glazing is delayed or not completely accounted for at the right stages.  

Partial preinstallation, however, may still be advantageous and should be considered.  

Regardless of how well the critical stage is planned, we cannot ignore that unexpected changes are part of on-site construction. Accidents, scheduling clashes, and weather changes can all have impacts on weatherproofing. Late positional changes may also have to be deployed to navigate any unexpected on-site challenges.  

The installation of weatherproofing systems needs to be flexible and the process robust enough to accommodate these unexpected events with minimal or no impact on the overall project timeline and quality of delivery. 

Modular construction materials and methods are evolving at a rapid rate and address a costly side of traditional construction: errors.  

Weatherproofing materials need to keep up with this trend to remain effective. Traditional weatherproofing materials and mechanical fixing methods are increasingly replaced with flexible mouldings, improved adhesives or cold-applied liquids and new application processes.  

Streamlining the on-site installation process 

While this seems an obvious requirement in any industry, process inefficiency is where the largest gap between traditional weatherproofing methods and modular construction lies. Traditional labour-intensive and time-consuming weatherproofing techniques cannot offer the efficiencies and productivity of modern construction methods.  

Although traditional weatherproofing methods can be slightly improved, they cannot support further process improvement that modular construction drives.  

However, there are considerations with modular methods such that the extra footfall on a roof can cause damage to the joints of a modular building. Requirements for additional materials if damage occurs can add unnecessary costs and reduce the modular sustainability credentials. 

Testing of materials and processes 

Testing of materials and processes will vastly increase the integrity of the weatherproof detailing. This is particularly important because the conditions during offsite installation are likely to be materially different from the conditions when the building is assembled.  

Testing should include temperature and humidity changes but also resistance to impact or mechanical damage.  

Conclusion 

Modular methodology is being embraced for all tenures and building types across the sectors.  

Weatherproofing contractors must be prepared to review and innovate materials and processes to align with the modular values that make the prefabrication industry so attractive in the challenging times ahead. 

The need to reflect the aesthetics of the design or speed of delivery should not impact the quality of the weatherproofing. 

Co-operation across industries, alongside modernisation and innovation, should focus on the delivery of sustainable and cost-effective solutions that support healthy and energy-efficient buildings. 

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