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Ask A. Proctor BREATHER MEMBRANES & ROOFING UNDERLAYS: WHAT’S THE DIFFERENCE? The team A. Proctor Group explain all... Many people use these terms interchangeably. BS 5250:2021, Management of moisture in buildings – Code of Practice, defines a breather or vapour permeable membrane as one with a vapour resistance lower than Sd 0.12m (0.6MNS/g). These are generally considered walling membranes. Underlays are then split into two main categories, High Resistance, or HR underlays and Low Resistance, or LR underlays. HR underlays are equivalents to the traditional 1F felts and will require full ventilation below them. LR Underlays must have a vapour resistance below Sd 0.05m (0.25MNS/g). There are other key performance criteria that are required, i.e. water resistance. Walling underlays require a minimum Water Hold Out Classification of W2, whereas roof underlays are required to be W1 which is more onerous to achieve. A further distinction is the air permeability or airtightness of the underlay, both have benefits depending on the design. What are the benefits of air permeability in a roof? Air permeable low resistance (APLR) underlays allow air to circulate through the layers of the membrane, in combination with having low vapour resistance. Airtight underlays, the most common type in the UK, allow vapour to disperse via diffusion through the layers, having been made with a microporous film layer in the middle of the underlay. Air permeable underlays allow vapour dispersal by two mechanisms, diffusion, as well as in the air passing through the underlay. This is down to the unique meltblown core. Images: Proctor Air Valley detail (above), eaves detail (left). Assessments carried out by BRE and Glasgow Caledonian University have shown that air movement through the underlay increases the vapour removal from the roof and can be similar to that achieved by both eaves and ridge ventilation. The ability to remove ventilation from the roof can be a huge benefit with the increased need for insulation, and the difficulty in maintaining ventilation pathways, stopping cold bridging, as well as making complex and historic roofs easier to detail and more aesthetically pleasing. “Underlays are NOT designed to be primary weatherproofing layers – they should not be relied on as a temporary protection during adverse weather” If you are building a project that is NHBC registered, the use of an air permeable underlay can also mitigate the requirement for high level ventilation in cold roof constructions – this ventilation is required where an airtight underlay is used. Proctor Air falls into the category of APLR and therefore can be used without vents. For project specific advice our Technical Team are on hand to review your designs. How does Proctor Air perform in extremes of weather? Developing Proctor Air allowed us to look at what the membrane needed to do, which therefore meant we could enhance attributes that are important for the UK climate, i.e. wind, rain and UV exposure. Underlays are NOT designed to be primary weatherproofing layers, and as per BS 5534:2014, Code of practice for slating and tiling, they should not be relied on as a temporary protection during adverse weather, such as storms and freeze/thaw cycles. In these conditions, especially re-roofs, the use of a protection layer, i.e. tarpaulin, should be considered. UV exposure guidance relates to the effects of sunlight on the membrane and does not mean that the membrane will remain water resistant for this length of time. Proctor Air contains hydrophobic additives in all three layers to help improve water resistance. Wind uplift resistance is also excellent with Proctor Air. At 345mm batten centres it can be used in Zones 1-4 in the UK and with centres at 250mm, or laps sealed with Wraptite Tape, it can be used in Zones 1-5. Does Proctor Air have a warranty? Yes, it does. We are delighted to be able to offer a 15-year warranty on Proctor Air. Details of this can be found in our literature and installation guide. Contact A. Proctor Group A.Proctor Group Ltd. proctorgroup.com 20 TC FEBRUARY <strong>2024</strong>
ONDULINE® BATTEN CLOAKING PIECE ISOLINE® LOW LINE Bituminous corrugated underlay sheet, made from 50% recycled fibres. Robust with guaranteed waterproofing for 30-years. ONDULINE® EAVES VENTILATOR STRIP ONDUTISS® AIR Highly vapour permeable, breathable membrane with superior tensile strength and durability. ONDULINE® EAVES TRAY ISOLINE® LOW LINE Complete sub-roof system for low pitch roofs A unique under roof waterproofing system that can be used on a roof pitch as low as 10° for all roof tiles. The ISOLINE® sub-roof acts as the primary waterproofing, making roof tiles a secondary line of defence. Protection like no other! onduline.co.uk 0207 727 0533 enquiries@onduline.net
Page 1 and 2: FEBRUARY 2024 The Air To The Throne
Page 3 and 4: Editor’s Intro MATT DOWNS EDITORI
Page 5 and 6: REGULARS 16 NFRC ROOFING TALK What
Page 7 and 8: WestWood Liquid Technologies Limite
Page 9 and 10: Meet 25 YEARS WE’VE GOT YOU COVER
Page 11 and 12: NORTHWEST ALUMINIUM REBRANDS & STRE
Page 13 and 14: LEARN MORE You may just see a roof.
Page 15 and 16: Safety on site SIMPLE TIPS FOR WORK
Page 18 and 19: Skills & Development BUILDING NEW H
Page 22 and 23: Ventilation IN-ROOF SOLAR ROOFING:
Page 24 and 25: Advertorial DON & LOW INVESTIGATES
Page 26 and 27: While it is good to have a choice o
Page 28 and 29: Project Focus BESPOKE SYSTEM FROM K
Page 30 and 31: Roofing Updates SOUND AND DRAINAGE
Page 32: Project Focus TOP MARKS We take a c
Page 35 and 36: WRAPTITE FITS FOR ISLE OF MAN SEA F
Page 37 and 38: (including airtightness). With more
Page 40 and 41: Inverted Flat Roofs WATERPROOFING A
Page 42: Updates For further info on all the
Page 45 and 46: mitigating one of the most signific
Page 48 and 49: Updates For further info on all the
Page 50: Updates For further info on all the

February 2024

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