The Next Generation of Roofing Membranes Has Arrived

Roofshield - Air & Vapour Permeable Breather Membrane

Roofshield is a unique, three – layer, nonwoven, spunbonded, polypropylene breather membrane with a patented melt – blown core. It is intended for use as a pitched roof underlay (breathable roofing felt) and is fixed beneath tiles and slates.

Roofshield provides a secondary barrier to the ingress of rain, wind and snow. It has a low vapour resistance and is air – permeable; additionally, it eliminates the incidence of interstitial condensation in pitched roofs.

The product provides the most cost – effective solution to controlling interstitial condensation in a pitched roof.

  • Water & UV Resistant
  • Eliminates low & high level ventilation
  • Low Vapour Resistance
  • No vapour control layer required
  • Air Permeable
  • Supplied in 1m x 50m and 1.5m x 50m rolls
  • Hydrophobically treated
  • IAB and BBA Certified
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Condensation In The Roofspace

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This presentation discusses the requirements for breather membranes, air barriers and vapour control layers, looks at the principals of condensation, the effects of condensation, issues of detailing cold pitched roofs i.e. insulation, ventilation and underlay. It also looks at condensation controlling measures and solutions.

Topics covered in this CPD:

  • What is condensation?
  • Pitched roof design considerations
  • BS5250 and BS5534
  • Ventilated and non-ventilated pitched roof constructions
  • Vapour permeable underlay certification
  • Types of vapour permeable membranes and their properties

While the technical and practical benefits of the Roofshield membrane are clear, at first glance the perceived higher cost compared to conventional felt and vents may appear to limit it’’’s suitability to projects where specific non-standard project requirements must be met.

Considered more closely however, the various omissions and specification changes that can be made mean that this gap, based purely on material costs, narrows significantly.

This closer gap in material cost serves to emphasise the potential savings that can then be realised in terms of simplified design and installation, and reduced likelihood of condensation related problems and customer related call backs.

To illustrate this, this document breaks down material costings across twelve typical 2-5 bedroom houses, of a size and general layout typical of national and regional housebuilders in the UK.

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Why Roofshield

As Building Regulations demand ever higher thermal efficiency in both the commercial and domestic sectors, today’s building envelopes are becoming increasingly airtight. While this is undoubtedly beneficial for building energy performance, it also makes careful consideration and management of moisture more critical than ever

Since their introduction in the late 1980s, “breather membranes” have become an important part of the construction industry landscape, however the term itself is widely misunderstood. “Breather membrane” relates to membranes used in timber frame walls, with a vapour resistance of 0.6MNs/g or less, while for those membranes used on roofs, the term “vapour permeable underlay” is more appropriate, these membranes must have a vapour resistance of 0.25MNs/g or lower. It can be argued that higher performance, air permeable membranes such as Roofshield, are “breathable” in the truest sense.

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All activities within a building, from initial construction and wet trades, to cooking and washing, generate substantial amounts of water vapour, which must be managed successfully to ensure the longevity of the building fabric and a healthy indoor environment. The vapour permeable structure used in these membranes allow this to be achieved without compromising temporary weather protection during construction, or requiring complex and expensive passive or active ventilation systems and accessories.

While such systems may once have seemed somewhat alien to the industry, non-ventilated roof constructions, with their speed, efficiency and lower cost are fast becoming the norm. The once radical building physics behind them now well understood and widely accepted across all sectors of the industry.

Roofshield is a vapour- and air-permeable underlay (VPU) for pitched roof applications. First launched in 1996, and with an unchanged specification since, it’s unique blend of physical properties has allowed it to consistently outperform not only competing vapour permeable underlays, but also traditionally ventilated roofs

While the majority of VPUs in use today utilise an airtight VP film layer to achieve their performance, Roofshield’s patented SMS (Spunbond Meltblown Spunbond) structure allows high levels of airflow in addition to the transport of moisture vapour, making the formation of condensation virtually impossible. It was this outstanding air-permeability powered performance in BRE trials that led to the granting of one of the first BBA certificates for non-vented cold roofs in 1999, and which today allows the NHBC to accept its use without high level vents, a position further reinforced by NFRC Technical Bulletin 6 in 2012. Independent studies of the effect of air permeability have confirmed that lofts using Roofshield have a more consistent air flow through the roof than those found in traditionally ventilated lofts, according to BS5250, so whatever side of the vents/no vents debate you sit on, Roofshield has it covered.

Developed and manufactured in Scotland, Roofshield has been widely used in some of the harshest climates on earth, from northern Canada to the Antarctic, and it’s superb resistance to wind loadings allow it to be used without restrictions on batten spacing in any UK exposure conditions, giving specifiers the flexibility to choose whatever configuration of outer roofcovering meets their requirements. Its heavyweight 185gsm three-layer structure is also fully hydrophobic, giving a Class W1 rating under the latest EN13859-1 specifications, and at Euroclass D offers the highest available fire rating in its class.

Over the last 20 years, we have undertaken projects from domestic housing to the refurbishment of historic castles. The performance and design flexibility of Roofshield provides a winning combination time and again. It has become recognised as one of the most dependable solutions for specifiers and contractors available globally

Key Features

Vapour Permeable

Roofshield has a vapour resistance of 0.065 MNs/g and an Sd-value of 0.013m, making Roofshield one of the highest-performing vapour-permeable membranes on the market.

Fully BBA Certified

Roofshield is fully certified for use in non-ventilated warm or cold roof applications, and has been since 1996. In 1999, Roofshield became the first membrane certified for use in cold non-vented roofs. While the construction industry has changed considerably over the last 20 years, Roofshield offers the same benefits as it always has.

Fully Air Permeable

Air permeable membranes allow air movement through the roof, as well as allowing moisture to escape by diffusion. This means that condensation is far less likely to form on the membrane itself, and also allows the membrane to deal with much higher moisture levels within the building, for example during the drying out period.

NHBC Acceptance

With a certified air permeability of 34.4m3 /m2 h.50Pa, Roofshield does not require additional high level ventilation when used on NHBC-approved projects. It also allows the same specification to be used across all your projects, regardless of the regulatory regime applied.

More Uniform Airflow than Vents

The air permeability of Roofshield means a non-ventilated roof fitted with Roofshield allows a more consistent air flow through the roof than a roof ventilated as per BS5250, without expensive and time consuming ventilation hardware fitted to the roof.

No VCL Required

Roofshield is the only vapour-permeable underlay available which the BBA puts enough trust in to explicitly state in their certificate that a vapour control layer is not required for non-ventilated cold pitched roof constructions.

Highly Water Resistant

Roofshield is rated W1 under EN13859-1, and can support a water column of over a metre without leakage. The membrane can be left exposed to provide temporary weather protection to the building envelope for up to 3 months.

BS5534 Compliance

Based on fully independent 3rd party testing, Roofshield can continue to be used across the UK (see table below). This, in addition to no requirement for high level ventilation or the use of a vapour control layer, ensures Roofshield remains the simplest and most cost effective method of achieving regulation compliance.

Typical Roof Constructions

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Wind Uplift Resistance

Batten Gauge Declared Wind Uplift Resistance Pa(N/m2 Accessories Zone Suitability
1252 NONE 1 – 3
≤345mm 2192 ≥11mm* counter batten 1 – 5
2615 Wraptite Tape 1 – 5
≤250mm 2574 NONE 1 – 5
Softwood sarking with slates** 2974 n/a 1 – 5

*Alternatively, a 38mm tile batten can be used instead of a 25mm tile batten which would alleviate the need for an 11mm counter batten.

***The slates were set with a headlap of 54mm; which is the minimum allowed in BS5534. The nail diameter of 2.65mm is also the minimum allowed in BS5534. This roof configuration as tested therefore represents the weakest (with respect to wind uplift) configuration allowed in BS5534 for these slates.

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Warm & Cold Roof

Non-ventilated Warm Roof Construction

A “warm roof” is a roof construction where the insulation layer is placed either over, or between the rafters, and follows the pitch of the roof from eaves to ridge. This configuration keeps the roof structure within the heated envelope of the building, and allows spaces within the roof to be used as habitable spaces, or easily converted at a later date. Warm roofs are typically insulated using rigid boards, and the underlay may be installed either fully supported, or draped, depending on the location of the insulation. Full details of warm roof design and site practice are given in BBA certificate No.96/3220.

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Non-ventilated Cold Roof Construction

A “warm roof” is a roof construction where the insulation layer is placed either over, or between the rafters, and follows the pitch of the roof from eaves to ridge. This configuration keeps the roof structure within the heated envelope of the building, and allows spaces within the roof to be used as habitable spaces, or easily converted at a later date. Warm roofs are typically insulated using rigid boards, and the underlay may be installed either fully supported, or draped, depending on the location of the insulation. Full details of warm roof design and site practice are given in BBA certificate No.In a cold pitched roof construction, the insulation is placed horizontally at ceiling level, running from eaves to eaves, leaving the loft and roof structure above the heated envelope of the building. Traditionally, this cold loft space would require ventilation, but this can be impractical for some roof configurations, and avoiding such ventilation has long been desirable.

Long term studies carried out by the BRE between 1997 and 2006 concluded that the moisture content found in non-ventilated Roofshield roofs were comparable with the moisture content found in a conventionally ventilated roof space, and following this research Roofshield has been certified for this use since 1999. The relevant BBA certificate for cold pitched roof and room-in-roof constructions is 99/3648.96/3220.

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Building Regulations & NHBC

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Condensation control is covered by Approved Document C in England & Wales, Section 3 in Scotland, and Technical Booklet C in Northern Ireland. All of these documents refer to BS5250: “Code Of Practice for Control Of Condensation in Buildings” for detailed guidance on how best to mitigate condensation risk in roof and wall constructions.

BS5250 defines two types of underlay membrane – high resistance type HR membranes (which includes traditional impermeable roofing felts and modern plastic equivalents) – and low resistance type LR membranes (vapour permeable underlays), and gives examples of appropriate ventilation strategies for each. BS5250 does not however deal directly with non-ventilated roof constructions, but does allow for their use, provided the proposed solution is covered by 3rd party certification.

Roofshield is covered by BBA certificates for both warm (no.96/3220) and cold (no.99/3648) pitched roof constructions. Roofs constructed in accordance with the certificates’ conditions will therefore comply with the requirements of BS5250 and hence the building regulations.

NHBC technical requirements

The NHBC operates its own parallel technical standards which differ from national Building Regulations. Although reference is still made to the BS5250 Code of Practice, Standard 7.2 Clause S11 has, since 2011, required high level ventilation equivalent to 5mm/m to be used with type LR underlays regardless of any recommendations given in 3rd party certification. Although not explicitly stated in the technical standards, an exception to this requirement is made where the underlay specified has third party certification of both vapour and air permeability. Having this certification, Roofshield is therefore exempt from this requirement, and can be specified as outlined in the BBA certification, without high or low level roof ventilation. As a result of this, some national housebuilders specify Roofshield on all their developments.

Released by the National Federation of Roofing Contractors in 2012, Technical Bulletin 6 outlines best practice for roof system installers. TB6 aligns itself with the NHBC technical standards by recommending high level ventilation where airtight type LR underlays are used. As with the NHBC standard however, it is recognised that this provision is unnecessary where the underlay is both vapour and air permeable, therefore Roofshield is once again exempt from this recommendation.


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