Roofing
a view that a consensus was desirable on whether it was necessary to ventilate buildings using vapour permeable membranes. It had the result of “dispelling a lot of theories around ventilation” says Iain Fairnington.
In fact the study contained the crucial finding that when a roof was unventilated, and used in air and vapour permeable underlay, such as Roofshield, this would further reduce and inhibit the formation of condensation on the underlay. This contributed to the NHBC making a statement in their Technical Extra bulletin Issue 6 that independently certified air and vapour permeable underlays, such as Roofshield, could be used without additional ridge ventilation in cold roofs. This has seen a groundswell of interest in the product recently, aided by its hydrophobic and UV resistant qualities. Another key benefit for installers is that the product is manufactured in lightweight 1m wide rolls, the same size as traditional IF felt underlay, and can therefore be fixed and laid on open rafters in the same way, reducing health and safety risks of overreaching with wider membranes on open rafters.
MEETING THE NEW CODE OF PRACTICE ON WIND UPLIFT
While there has been widespread acceptance of the abilities of air permeable membranes to offer a range of benefits for contractors and developers, the 2014 revision of BS 5534 Slating and tiling for pitched roofs and vertical cladding - Code of Practice caused a stir in the world of roof construction and again put the spotlight on their differences. This was particularly with regard to the technical specification of underlays, in particular lightweight membranes, and how they behave under wind.
The revision of the standard includes a number of recommendations which affect the way all slated and tiled roofs will be constructed in future. Advice contained in Annex A has been introduced to avoid incorrect specification which has been perceived, in extreme cases, to potentially lead to underlays being lifted by wind, ballooning and dislodging slates or tiles. The annex includes a new wind uplift resistance test and classification system for underlays in relation to the batten gauge being used and the location of the particular project. It requires manufacturers to provide a Zonal Classification label to enable specifiers to easily identify a suitable underlay.
The change has led to some membranes manufacturers introducing tapes, or integral adhesive strips, which will enable them to be used, sealed at the overlaps. However as Iain Fairnington, who sat on the standards committee, explains, this was not a requirement for Roofshield being a heavier membrane, a factor which has been welcomed by installers: “I was told by the roofing industry that they do not want tapes, they may work well in a lab, but out on site, the situation with wind, dirt and dust does not lend itself to tapes.”
The A Proctor Group has undertaken independent, third party testing, in accordance with Annex A, to establish that Roofshield is fully compliant and are providing specifications to interested parties on that basis. This enables Roofshield to be used in three of the five specified zones with no additional requirements such as time-intensive taping, and in all zones if an 11mm counter batten or 38mm tiling batten is used.
The new requirement for compliance with wind uplift issues brings the conclusions of the Partners in Innovation research back into the foreground again, as the findings were based on roofs with open overlaps (ie. not taped). In that study, even in the case of air tight membranes there was a degree of vapour escape. Now however, if laps must be taped, that mechanism for escape has gone. Iain concludes: “While there does not seem to be much appetite to confront this issue, there is a very real risk that we will see moisture occurring again in such specifications.”
The recent Code of Practice revision, plus the previous statements from the NHBC and the Pil Research, adds up to a compelling case for air and vapour permeable membranes as a robust and installer-friendly solution for healthier buildings. In the case of Roofshield the manufacturer is able to make a credible case that the product will comply with all standards and avoid the need for additional measures such as ventilation and tapes. Before the Pil study and research into implications of omitting ventilation, there had been a lot of resistance to change in the industry; however specifiers now have more and more reasons to believe that Roofshield offers the simple answers.
A PROCTOR GROUP LTD
TEL: 01250 872261 47
WWW.PROCTORGROUP.COM
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64