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Membrane Choice PITCHED ROOF MEMBRANES: CONTRACTOR CONSIDERATIONS The experts at A Proctor Group outline some of the key considerations when choosing pitched roof membranes. Choosing the right roofing membrane depends on the roof you are covering. Finding a membrane that is best suited to your project can be a straight-forward process after answering a few basic questions: Pitched vs. flat roofs While the shape of the roof should make this point obvious, it’s important to emphasise that flat and pitched roof membranes are not interchangeable. Pitched roof membranes differ from those used on flat roofs in many ways including their material properties, the type of protection they provide, and the roof functions they are designed to support. While this article will cover considerations for pitched roof membranes only, a good starting point is to make sure you’re shopping in the right aisle to begin with. HR vs. LR membranes BS 5534 broadly divides pitched roof membranes into two categories: Type HR (high water vapour resistance) and Type LR (low water vapour resistance) which are also often air permeable. The Standard describes exact values of air and vapour permeability that HR and LR membranes must conform with in order to be classified as such. The primary function of both HR and LR membranes is to be water resistant. This property enables the membrane to protect vulnerable materials beneath it such as the insulation and roofing timbers, and helps prevent water ingress into the roof space for the lifetime of the building. Selecting a membrane with the correct level of water resistance is especially important over the period of time when the primary roof covering has not yet been installed (i.e. tiles, slates). The main difference between HR and LR membranes is in the role they play in preventing condensation in the roof space. LR membranes are sometimes called “breathable” because they allow air and water vapour to pass through them easily, thereby preventing moisture building up and condensation from forming. Conversely, HR membranes are called “non-breathable” because they block air and moisture movement. Roofs that use Type HR membranes will require additional measures to allow moisture to escape from the roof space. Vents or no vents? Water vapour is continuously formed in all buildings by inhabitants and everyday processes, and must be ventilated outside. Water vapour that is allowed to accumulate in building spaces risks cooling and condensing into liquid water. The resulting dampness can cause problems like mold and mildew growth and even structural damage over time. HR membranes by definition do not allow water vapour to pass through them so, if they are used on a pitched roof, additional roof &/or soffit vents must be installed to provide ventilating capacity and avoid condensation problems. Any vents that penetrate through the roof / roofing membrane must be sealed carefully to prevent potential water leakage. Adequate gaps in the membrane along roof ridges and appropriate tile batten gaps must also be observed, all adding extra time and extra costs to a project. On the other hand, LR membranes prevent condensation by allowing moisture to move easily through them and not accumulate in roof spaces. Roofshield: the complete solution BBA certified: For both cold- and warm-pitched roofs. Water resistant: With the highest rating for water resistance (W1), Roofshield can be left exposed to provide effective temporary weather protection on roofs for up to 3 months. Vapour permeable: Roofshield is one of the highestperforming vapour permeable membranes on the market (vapour resistance = 0.065 MNs/g, Sd = 0.013m). Air permeable: By being fully air permeable and providing a more uniform level of ventilation than conventional vents, high-level ventilation is not required on NHBCapproved projects. Suitable for wind zones 1-5: Third-party testing confirms that Roofshield is suitable to be installed on projects across the UK in every wind zone. LR membranes that are also air permeable can save on material costs by making additional roof and soffit ventilation unnecessary. This means installing the membrane will be faster and simpler with less elaborate detailing, plus the integrity of the roof will be better preserved by not having vents creating points of weakness through the fabric. Using the right LR membrane could even take away the need for an internal VCL, further simplifying the job on the inside as well as the outside. Wind uplift zones Contractors should understand the effect that geography can have on a roofing membrane specification. The UK is divided into five wind zones, where Zones 1-3 cover most of England and Wales, whilst 3-5 covers Scotland and the outlying islands. All roofing membranes have a “wind-uplift” classification which determines which wind zone they are suitable for. It is important to look for this rating as not all pitched roof membranes can be used in all wind zones. Contact A. Proctor Group 01250 872 261 www.proctorgroup.com @proctorgroup 34 TC OCTOBER <strong>2019</strong>
Focus... on results When you need a reliable solution, you need a team behind you with experience, dedication and quality unrivalled in the delivery of industry leading products. At SR Timber we FOCUS on: n Product quality and distribution n Sustainability, Certification and British Standards n Continued investment and ranges With decades of experience, our team is more passionate than ever, offering you expertise, independent advice, experience and industry support. TEL: 01623 446 800 sales@sr-timber.co.uk www.sr-timber.co.uk
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Page 3 and 4: I V Editor’s Comment MATT DOWNS E
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October 2019

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