How membranes can help maximise the potential of offsite manufactured SIP systems

Erect the building envelope for a three-bedroom home, from sole plate to ridge, in a single day. In doing so, demonstrate the products and supply chain – including membrane products – capable of supporting the rapid delivery of quality homes at scale, while reducing health and safety risks on site.

Ultrapanel’s Category 2 MMC SIP system features the vapour permeable Proctorwrap Reflect® membrane in its external wall panels. An innovative new cold roof panel features the air permeable, low resistance underlay (APLR) Proctor Air®.

Factory-fitted membranes allow Ultrapanel’s finished SIP system panels to be delivered straight to site and installed quickly, providing a watertight building envelope in a matter of hours. The rapid installation of the cold roof panel also significantly cuts down time spent working at height compared to traditional construction techniques.

Both products supported Ultrapanel’s goal of producing a system capable of delivering high performance. Using the two membranes, panels can be specified to meet a range of regulations and standards, including the performance levels required to achieve Passivhaus certification, while minimising risks associated with moisture.

Proctor Group worked closely with Ultrapanel Building Technologies to establish appropriate membrane specifications specifically designed to support the offsite manufacture of the panels. For example, Proctor Air was supplied in 3m wide rolls (rather than the standard 1m wide), which was better for the production line and ensured the quality of the panel was maintained once it reached site.

“With a system that is 40% faster and 70% lighter than traditional masonry , we’re aiming to accelerate the rapid delivery of homes, without compromising on compliance or quality – and Proctor Group are a key member of our supply chain.”
Helen Wildin – Head of Sales, Ultrapanel Building Technologies

Prefabrication and panel systems are not new in housebuilding. However, if the benefits of offsite manufacture are to finally be adopted at scale, systems need to show they can deliver their promised speed and quality on a consistent basis.

A crucial starting point for that proof – and for making properties mortgageable – is independent review, which is why Ultrapanel Building Technologies’ SIP system has been assessed under the NHBC Accepts scheme. The review includes the system design and details, and means the NHBC will accept installation on site.

As the NHBC website notes: “With the demands on the industry to increase the volume of new homes’ supply and the simultaneous challenges around materials and skills, we are at a critical stage in the development of modern methods of construction (MMC).”

For MMC solutions that don’t yet have the longevity in the marketplace, one poor installation could open the door to unfavourable comparisons with post-war prefabrication. For that reason, Ultrapanel Building Technologies chose to build a demo house in front of an audience of guests, assessment bodies and supplier partners. The aim was to show that a weather resistant building envelope in a single day is possible.

A successful system review and demonstration depends on selecting appropriate components that support the intended outcomes – including membrane products.

An important aspect of the Ultrapanel SIP system is its flexibility to support a variety of thermal performance targets, from building regulations to voluntary standards like Passivhaus. To help provide that flexibility, Ultrapanel Building Technologies already used Proctorwrap Reflect in their wall panel specifications.

Fixed to the external face of the panel, the vapour permeability of Proctorwrap Reflect allows the passage of moisture vapour and reduces condensation risk. It also has a W2 resistance to water penetration classification, meeting the standard required for external walls and providing secondary weather protection behind the primary covering.

Meanwhile, the low emissivity foil of Proctorwrap Reflect contributes to the overall thermal performance of the wall build-up by changing the way heat transfer takes place across an adjacent air cavity. A higher thermal resistance can be claimed for the air space in U-value calculations, which helps to lower U-values and keep panel thicknesses to a minimum.

This is crucial when seeking to make a SIP system as efficient as possible, in terms of both heat loss and material use/embodied carbon.

Another area of flexibility offered by the Ultrapanel system is the pitched roof. Homes can be built with traditional truss designs, or the manufacturer’s own warm and cold roof options.

The demo house featured a brand-new cold roof panel, which folds out so as to minimise work at height on site. The panel took just 90 minutes to install before it was ready for finishing with the final roof covering.

Proctor Group’s pitched roof underlay, Proctor Air, was fitted as part of the panel’s offsite construction and plays its own part in reducing the amount of work required on the roof.

Thanks to its air permeability, Proctor Air eliminates the need for roof ventilation components to be installed in a roof. Instead, the underlay itself provides a consistent and more uniform flow of air from the cold roof space. Also, it requires no vapour control layer in the ceiling.

In combination with its air permeability, Proctor Air is also one of the highest performing vapour permeable membranes available. With a vapour resistance of 0.075 MNs/g (or Sd of 0.015m), condensation risk in the roof space is reduced.

Getting the most out of offsite construction methods means looking at ways to adapt existing product specifications to help achieve the best possible results.

As standard, Proctor Air is supplied in 1m wide rolls to allow for easier manual handling when installers are on the roof. However, manual handling is much less of an issue in a factory environment, where the production line can handle heavier products. Proctor Group therefore worked to supply Ultrapanel with a bespoke 3m wide roll to suit the width of the cold roof panels.

The advantage of using a wider roll size continued beyond the production process. A single 3m wide sheet of underlay has no laps, compared to three 1m wide sheets. This introduces a slight saving in the amount of material used.

Of even greater value from an offsite perspective, removing laps also removes the potential for wind to get under the membrane during transportation of the completed panels. Should panels arrive on site damaged, it is both costly to the system manufacturer and potentially harmful to the reputation of MMC and offsite construction more generally.

Proctor Group’s Sales Director, John Johnston, attended the demo house construction day and was impressed by what was achieved in just one day.

“At a time when labour costs are so expensive, Ultrapanel’s SIP system will likely be very appealing to housing associations, and social housing providers in particular,” John said. “That could make a real difference to whether the UK can achieve its ambitious housing targets.”

“With a system that is 40% faster and 70% lighter than traditional masonry , we’re aiming to accelerate the rapid delivery of homes, without compromising on compliance or quality,” said Helen Wildin, Head of Sales, Ultrapanel Building Technologies. “Proctor Group are a key member of our supply chain, and we’re very grateful for their support.”

Find out more about Proctor Air: https://proctorgroup.com/products/proctor-air
Find out more about Proctorwrap Reflect: https://proctorgroup.com/products/proctorwrap-reflect