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Roofshield

 

 

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
  • Low Vapour Resistance
  • Air Permeable
  • LABC & LABSS Certified
  • Covered by SIG One Warranty
  • Hydrophobically treated
  • Eliminates low & high level ventilation
  • No vapour control layer required
  • Supplied in 1m x 50m and 1.5m x 50m rolls

Roofshield's air permeability provides superior performance.




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We use Roofshield as our default membrane for use on all of our quotes confident in the knowledge that no matter which build up is specified it will perform to meet all necessary requirements. Craig Hopkinson. MIoR - Senior Estimator, Elliotts
We have used Roofshield now for some 20 years, recommending it for major housebuilders such as Bellway Homes and have never received one complaint regarding condensation. Keith Soulsby, Wensley Roofing Limited
Roofshield provides a cost effective solution, allowing our clients to provide more new roof coverings for the same budget. Roofshield is an exceptional product we recommend to all clients . G Hirons - Commercial Manager, O'brien Roofing & Leadwork


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.

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 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.

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.

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 four months.

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

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.

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 nonventilated cold pitched roof constructions.

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

Cold Roof Slate Sarking Detail

  • 1 - Slate
  • 2 - Roofshield
  • 3 - Timber sarking / board
  • 4 - Rafter

Cold Roof Tile Detail

  • 1 - Tile
  • 2 - Batten
  • 3 - Roofshield (draped)
  • 4 - Rafter

Metal Roof Profile Detail

  • 1 - Metal Cladding
  • 2 - Ventilation Air Space
  • 3 - Roofshield
  • 4 - Insulation
  • 5 - Vapour Control Layer
  • 6 - Metal Lining

Warm Roof Slate Sarking Detail

  • 1 - Slate
  • 2 - Roofshield
  • 3 - Timber sarking / board
  • 4 - Insulation
  • 5 - Rafter

Warm Roof Tile Alternate Detail

  • 1 - Tile
  • 2 - Batten
  • 3 - Roofshield (draped)
  • 4 - Insulation
  • 5 - Rafter

Warm Roof Tile Detail

  • 1 - Tile
  • 2 - Batten
  • 3 - Counter Batten
  • 4 - Roofshield
  • 5 - Insulation
  • 6 - Rafter

Warm Roof Tile with OSB Alternate Detail

  • 1 - Tile
  • 2 - Batten
  • 3 - Roofshield (draped)
  • 4 - Insulation
  • 5 - Rafter

Warm Roof Tile with OSB Detail

  • 1 - Tile
  • 2 - Batten
  • 3 - Counter batten
  • 4 - Roofshield
  • 5 - OSB
  • 6 - Insulation
  • 7 - Rafter

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.

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.

Non-ventilated Cold Roof Construction

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.

Building Regulations & NHBC

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.

Roofshield Details

Duopitch Ridge Detail

Monopitch Ridge Detail

Eaves Detail

Verge Abutment Detail

Valley Detail

Pipe Detail

FAQs

How “Breathable” is Roofshield?

While “Breathability” is a commonly used term, it is more technically accurate to refer to a material’s “vapour permeability”. As Roofshield is air permeable as well as vapour permeable, it can certainly be argued that it does breathe, as it allows air movement, but this does not hold true for all “breathable” materials. In terms of vapour permeability, Roofshield, with a vapour resistance of 0.065MNs/g (Sd-value 0.013m) is one of the most vapour permeable membranes on the market, as well as benefitting from the additional advantage of air permeability.

What difference does air permeability make?

Roofshield, in addition to having the lowest vapour resistance available, is also air permeable. Industry research concluded that air permeability, combined with very low vapour resistance, inhibits the formation of condensation in a pitched roof to the point where it’s virtually impossible for condensation to occur under normal conditions.

Studies conducted by the BRE and Glasgow Caledonian University have concluded that not only does an air permeable roofing underlay outperform conventional airtight underlays, but also provides a higher air change rate (50-60ACH vs 10-12ACH) than a roof ventilated according to the recommendations in BS5250.

Does Roofshield suffer from “tenting”?

As anyone who’s slept in a cheap tent can tell you, some vapour permeable fabrics can lose their water resistance if anything happens to touch the underside. Developed in Scotland, where the use of underlays fully supported on timber sarking board is standard practice, ensuring Roofshield does not suffer from this effect was always an important consideration for the A. Proctor Group. In fact while the first generation of VPUs suffered from this problem, most modern roof underlays are unaffected by this phenomenon.

So vents aren’t required?

Over the course of its more than 20-year lifespan, Roofshield has undergone extensive testing to prove that ventilation is not required to the underside of the underlay in both warm and cold roof applications, and is BBA certified to that effect. Roof features successfully assessed include duo-pitched, mono-pitched, hipped, mansard, gable-end, valleys, room in the roof, dormers and timber sarking. In more complex roof configurations, the use of Roofshield will provide a far more robust solution than a complex layout of ventilation openings.

The sole remaining situation where ventilation below the underlay is required is in a cold roof with Plywood or OSB sarking. If in doubt, our team of technical experts can assist specifiers in achieving the most appropriate solution for their specific project.

How about high level vents?

Although non-ventilated roofs have been specified successfully for many years, recently BS5250, the NHBC technical standards and NFRC Technical Bulletin 6 have recommended that ridge only ventilation equivalent to 5mm per metre is used when vapour permeable underlays are specified. In both cases, the exception to this is where the underlay specified is both vapour AND air permeable. As Roofshield meets this requirement, this additional high level ventilation is not required when using Roofshield.

Does Roofshield “chatter” in the wind?

Wind blowing up into the eaves of a roof can cause a ‘chatter’ type noise with some types of underlay. Roofshield is silent in such situations. As Roofshield does not suffer from this problem, the membrane does not have to be pulled taut and does not have any special fixing instructions compared to that of some underlays. Counterbattens can be provided to increase the air movement when used with close-fitting slates or tiles, or to provide drainage below the tile battens when used fully supported, but otherwise Roofshield may simply be draped between the rafters as normal

Can I use Roofshield with timber treatments?

All three layers of the Roofshield underlay have additives to increase the water hold out of the membrane. Timber treatments containing fungicides, insecticides and wood preservatives are extensively used in the building trade to protect rafters, sarking boards and tile battens. As such, a number of tests have been carried out to see if these timber treatments will affect the water hold out properties of Roofshield.

Four timber treatments were investigated - two water based micro-emulsions, a solvent-based treatment, and a CCA. Treatments were applied to the fabric and allowed to dry, then the water resistance of the material was tested. The water resistance of the Roofshield was not affected by these timber treatments.

What is the “drying out period”?

This is the period immediately after the building is completed, during which there are significantly higher amounts of moisture within the building. These include moisture in damp timber, from wet trades (concrete, plaster etc) and moisture that may have found its way in, prior to the building shell being wind and watertight. Although this moisture will eventually dry out, condensation is more likely to occur as it does so. This will usually be most apparent in the first winter when the building is heated. Roofshield roofs are far less prone to this effect.

Is Roofshield expensive?

In terms of the cost per roll, Roofshield is more expensive than a traditional non-breathable felt, however if we consider the costs associated with ventilation hardware then using Roofshield will save you money. Independent assessments carried out by Hardies Property and Construction Consultants of installed costs have shown that Roofshield can offer savings of between 4% and 6% when compared with either impermeable felt and full ventilation, or a lower specification VPU with high level ventilation only

What about severe weather conditions?

Although Roofshield is highly water resistant, the BBA, in its Site Practice Bulletin Number 2, states: “An underlay is not a total waterproof barrier and if used as a temporary waterproof covering, some rain penetration may occur. In certain conditions, particularly if there is persistent heavy rainfall combined with subsequent severe freeze/thaw conditions, an underlay should not be exposed for more than a few days.” If such conditions are expected, the temporary use of a tarpaulin covering is recommended.

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