PROVIDING PROTECTION IN CONSTRUCTION

DuPont Tyvek membranes: Pitched roof applicaTMRoofing underlayTyvek Supro and Tyvek Supro Plusare extremely durable flexible sheetmaterials for use as roofing underlaysin pitched roof construction. They canbe incorporated into all tiled or slatedpitched roofs, whether they benew-build or refurbishment projects.As a secondary water shedding layer aTyvek membrane will provide a barrierto minimize the wind load acting onthe slates and tiles and will adequatelyresist wind blown snow and dust fromentering the roof construction. Satisfying the BuildingRegulationsApproved Documents containpractical guidance on how to meetthe requirements of the BuildingRegulations. Part C covers Resistanceto moisture under C2.The requirement is as follows: Tyvek membranes are suitable foruse as roofing underlays as definedin BS5534:2014 and ICP2:2002. C2. The floors, walls and roof of thebuilding shall be designed andconstructed as to prevent the passageof moisture to the inside of the buildingor damage to the fabric of the building.b) precipitation and wind driven spray.Tyvek membranes are also suitablefor use in metal clad industrial roofs.c) interstitial and surface condensation;and,Insulation - Condensationd) spillage of water from or associatedwith sanitary fittings or fixedappliances.Tyvek membranes offer benefitsover traditional impermeable roofingunderlays by minimising the risk ofinterstitial condensation occurringwithin roof constructions:Protection from external moisture andcondensation will ensure the structuralperformance of a roof construction andthermal performance of the insulationwill not be compromised. Over the last 30 years or so, as wehave become more aware of the needto conserve energy, the required levelsof insulation within roofs havebecome greater. This has had theeffect of increasing the likelihood ofcondensation forming on the undersideof the roofing felt. Prior to theintroduction of modern vapourpermeable membranes, the only wayof reducing this risk was to introduceventilation openings in the roof toeffectively “change the air”. In orderto ensure that a sufficient amount ofventilation was provided to preventcondensation, Building Regulationsand Standards were amended.4Resistance to moistureDuPont Tyvek SolutionTM Tyvek is a vapour permeable materialwhich, as a Type LR roofing underlay(BS5250), will offer a low resistanceto the passage of vapour. During thewinter, when a bulding is heated andthe internal vapour pressure is high, aTyvek underlay will, by diffusion,allow water vapour within the roofspace to permeate through to thebatten space. Natural air movementthrough the joints of the roof coveringwill subsequently allow any moistureladen air to escape to atmosphere. The ability of a Tyvek underlay toprovide this function of condensationcontrol eliminates the need to ventilate any roof voids between theunderlay and the insulation.In every case during the design stageit is important to consider the entireroof element, from the interiordry-lining to the outer roof covering,to assess the capacity of the systemto control condensation.This is dependant on a number offactors, but from a fabric point of viewefficient external vapour release andinternal vapour control must beestablished. In accordance withSection 6 of Approved Document C,moisture transfer throughpenetrations and gaps in the internallining should be avoided.This requirement encourages us toaddress the airtightness of the ceilingand it’s ability to reduce convectivevapour and heat transfer. Methods forwhich are described in BS 9250:2007(Code of practice for design of theairtightness of ceilings in pitched roofs).Using a Tyvek underlay in conjunctionwith a suitable air & vapour controllayer (AVCL) will fulfil all therequirements for weather protection,condensation control and convectiveheat loss (airtightness), as well asmeeting the requirement of ApprovedDocument C2. Further information on internal air &vapour control can be found on page 8.Please refer to page 34 for theDuPont AirGuard range of AVCL’s.

tionsBBA ApprovalsIn order to determine the risk ofcondensation in non-ventilatedpitched roof constructions usingTyvek as the roofing underlay, theBritish Board of Agrément (BBA)conducted a long term researchprogramme. The exhaustive researchcovered a wide range of pitchedroofs, typical to the UK, varying inpitch from 12.5 to 70 , in differentlocations throughout the country,using various roof coverings. Thetests were conducted over twowinter periods and data collated andassessed using sophisticatedcomputer modelling. More than 100cases were analysed using readingstaken from sites in Wiltshire andGlasgow, which were selected toreflect the prevailing weatherpatterns in these regions. The results from the research werevery successful, with insignificantamounts of condensation recorded,especially in the sealed roofsystems. The results were furtherverified by additional measured datathat had been gathered from otherprevious site monitoring.Not surprisingly, the BBA grantedapproval in the form of certificate08/4548 for the use of Tyvekmembranes in non - ventilated andsealed cold pitched roofs. Together with the warm roofapprovals granted originally in 1991and most significantly in 1994 and2004, DuPont now have universalapproval for the use of Tyvekmembranes in pitched roofconstructions. Non-ventilated vs ventilatedBBA certificate 08/4548 states thatwith Tyvek , “the risk of condensationis equivalent to, or less than, thatattending current conventionallyventilated cold roof systems.”The certificate also states thatTyvek membranes may be used in“dwellings of any conventional planand of any size.” This documentationis sufficient to satisfy currentlegislative requirements: BuildingRegulations Approved Document C2. The solution of ventilating roofconstructions in order to preventexcessive condensation beneathimpermeable underlays is oftenregarded as “the traditional way”of meeting the regulations. However,traditional methods of constructionand practices are often supercededby more efficient and effectivesolutions. From an energy conservationperspective, introducing cold externalair into roofs can be to the detrimentof the construction by: reducing the effectiveness offibrous insulation. promoting warm air leakage fromthe building into the roof space. Increasing air infiltration into theheated building. Introducing dirt, dust and insectsinto the roof construction. Introducing external moisture ladenair into the construction.A non-ventilated Tyvek system willnot only prevent excessivecondensation, as required, but willalso offer substantial gains in energyefficiency by reducing these factors. 5

Non-ventilated or Sealed roofs?DuPont currently promote two methods of application for Tyvek membranes in pitched roof construction. This reflectsthe in-depth research that DuPont has undertaken to ascertain the most effective ways of not only controlling condensation,but also improving energy efficiency in roof construction. Extensive monitoring of test houses incorporating Tyvekmembranes at the BRE’s test facilities also confirm the benefits of using Tyvek non-ventilated and sealed roof systems. Non-ventilated roofsNon-ventilated systemsRoofs with no provision for airflow beneath the underlay willbe more energy efficient than conventional, ventilated roofs.This is where a Tyvek membrane is laid over the roof,parallel to the eaves, as in traditional practice. A horizontallap of 150mm minimum is maintained between eachconsecutive Tyvek run. No ventilation is incorporatedat eaves or ridge.Sealed roofsRoofs with no airflow beneath the underlay and with all airleakage paths sealed will be more energy-efficient thannon-ventilated roofs and will provide a higher degreeof comfort.Results from tests carried out on the non-ventilatedsystems showed this to be an efficient form ofconstruction. However, further improvements wereindicated in tests carried out on the sealed roofs. Sealed roof systemsA Tyvek membrane is laid over the roof in a taut condition,parallel to the eaves and counter battened. A horizontal lapof 150mm minimum is maintained between eachconsecutive Tyvek run. All membrane laps, junctions, pipepenetrations, rooflights and perimeters are sealed with anappropriate sealing tape. No ventilation is incorporated ateaves or ridge. Fig. 3 - An infrared thermography was carried out on two UK matchedpair houses at BRE Watford to corroborate the test findings.6

Benefits of DuPont Tyvek sealed roof systemTM Tyvek non-ventilated roofs will significantly reduce the likelihood of condensation, have less air leakage and are moreenergy efficient than conventionally ventilated roofs. However, they are still subject to air infiltration at laps, perimetersand penetrations. Air movement through those gaps can result in significant heat losses. Adopting the Tyvek sealed roofsystem will not only reduce the risk of condensation, but will also minimise the heat losses caused by air infiltration. Fig. 4(())Eliminating air movement substantially improves energy efficiencyDuPont Tyvek Sealed Roof System was extensivelyresearched during early studies by the BRE and VTT.Further tests were carried out by the BBA for thepurposes of independent accreditation. The followingresults and conclusions were achieved:TM a signifi cant reduction in air leakageThese test results are indicative of the followingenergy savings: a 3.2kWh saving in energy consumption per day a 700kWh saving in energy consumption over a fullheating season 25% saving in heat lost through the roof whencompared to a typical ventilated system a 135kg reduction in CO2 emissions over a full heatingseason If correct and thorough sealing work is carriedout to the roof construction further improvements in energysavings can be made: an air leakage rate as low as 2ach. 4.2kWh saving in energy consumption per day* a 7.1% reduction in overall energy consumption 927kWh saving in energy consumption over a fullheating season* 179kg reduction in CO2 emissions over a full heating season* Air leakage rate as low as 1.7ach*.* Data obtained from additional tests after extensive sealing work was carried out.Please note: It is of benefi t to recognise the importance of making internal linings convection tight when consideringthe need to reduce uncontrolled air leakage. This is particularly relevant for the purposes of complying with the airpermeability requirements of Approved Document L.The conditions of BBA certificate 08/4548 should be referred to when sealing work is to be carried out.With a lower risk of condensation in comparison with a standard roof using a traditional felt underlay and a ventilated loft space.In addition to this the BBA have concluded: “In conventionally ventilated roof constructions energy loss by ventilationcan account for up to 25% of the total heat lost through the roof. The Tyvek non-ventilated roof system will substantiallyreduce this mechanism of heat loss.” To gain maximum benefit an air & vapour control layer (AVCL) should be installed above the ceiling. DuPont AirGuardControl, Reflective and Smart are available for this purpose.TM 7

Agrément certificate coverageAgrément certificate coverageTMBBA certificate 08/4548 state that Tyvek underlays aresuitable for use in dwellings. Due to the wide range ofconditions that they offer, dwellings are used by the BBAfor the purposes of assessing product performance. Thetest environments include appropriate temperature andhumidity levels which prevail within bathrooms andkitchens. It is generally accepted that the majority ofcommercial and industrial buildings will present saferconditions within which the membrane is to perform. Anoffice for instance will generally have lower temperatureand humidity levels than a domestic dwelling. Tyvekmembranes can therefore be incorporated into domestic,industrial and commercial specifications. Previouscertification was restricted, in that the BBA approved theuse of Tyvek membranes only in roofs of simple planrectangular shapes. Certification now allows for typical roofdetailing such as lean-to roofs, valleys, dormers andScottish boarded roofs. Certificate 08/4548 approves theuse of Tyvek membranes in both warm and cold pitchedroof construction. These are categorised according to thepositioning of the insulation: Cold roofs (Fig. 5)This is where the insulation is installed at joist level with acold loft - space ( attic) between the insulation and roofingunderlay. In the main, quilt insulation is laid between andover ceiling joists.Warm roofs (Fig. 6)This is where the insulation is installed at rafter level usingrigid and/or semi rigid insulation. The insulation wouldideally be positioned in a continuous layer above the raftersso that the roof structure is situated in a “warm”environment. However, certain roof specifications canresult in the insulation being installed over rafters, betweenrafters or under rafters. With increasing thermalrequirements it is quite common for a combination of theseoptions to be employed.Room in the roof applications (Fig. 7)The BBA have assessed room in the roof applicationsas included in Agrément certificate 08/4548. Tyvekmembranes may therefore be installed into this formof construction without ventilation at eaves or ridge. Roomin the roof constructions very often incorporatea combination of both warm and cold roof constructions,employing varying types of insulation. Cold roof areasusually include “vapour open” fibrous insulation suchas mineral wool quilt, whereas the sloping ceiling areasinclude closed cell or foil backed rigid board insulants,of which the majority are highly vapour resistant.This variation in vapour resistance can result in animbalance in vapour drive. To equalise the internal vapour 8resistances throughout the construction it is recommendedthat a AVCL such as DuPont AirGuard Control, Smart orDuPont AirGuard Reflective be installed beneath the“vapour open” quilt insulation.TM Air & Vapour Control Layers (AVCL’s).As the requirements of Approved Document L tighten andfabric thermal performance levels increase, heattransmission into a cold roof space by conduction will bereduced. In a cold pitched roof this will result in a loweroperating temperature within the loft space, which couldpotentially increase the probability of interstitialcondensation occurring. However, in a normal domesticenvironment of 20 C at 60% RH the expected quantity ofvapour should egress the building safely and efficiently viatrickle vents and other internal ventilation measures. TheTyvek underlay can be relied upon to diffuse any normallevels of vapour that migrates into the roof construction tooutside atmosphere. There may however be circumstances where the internalair will contain a higher level of moisture than the systemcan efficiently manage. Excessive humidity levels can begenerated by swimming pools for example or when a newbuilding is undergoing a period of drying-out during a winterseason. As heat will displace air in an upwards trend, themajority of vapour will migrate into the roof void. Coldvapour resistant surfaces such as structural steelwork andvapour impermeable (Type HR) underlays are at great riskfrom a build-up of condensate even when properlyventilated. Similarly, vapour can also potentially condenseon vapour permeable (Type LR) underlays (such as TyvekSupro) if moisture in the air is excessive. This is most likelyto happen whilst the building is drying out. Once the moisture levels within the building havedecreased, so too will the risk of conden

Tyvek Metallised Tape Single-sided reflective tape for sealing laps in Tyvek Reflex and DuPontTM AirGuard Reflective. Ideal for making good around penetrations, pipework, windows and doors. Made of metallised Tyvek and acrylic adhesive. Provides durable and long-lasting bond once cured. Roll siz