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Perfectly Pitched ROOF COVERING CHOICE: THE KEY CONSIDERATIONS Following on from his recent series of articles on different roof shapes, John Mercer looks at the considerations when choosing the most appropriate roof covering for roof structures... In my recent series of articles, I have discussed various roof shapes, from the seemingly straightforward gable-to-gable roof, through to more complicated shapes such as hipped and mansard roofs, to curved roofs. Presented with a roof structure, how do we go about deciding on the best and most appropriate roof covering? This decision is of course influenced to a large degree by the surrounding roofscapes and local preferences. But we must also consider the technical aspects of a roof design to determine an appropriate roof product. The most obvious example is curved roofing. It is almost always the case that double lapped plain tiles or slates must be used on a curved roof slope. Although having said that, I have seen fixed gauge traditional clay pantiles used to great effect on a roof with an eyebrow window. Now there’s a challenge for you! Experienced pantilers tend to prefer non-interlocking clay pantiles for use on uneven old roofs, as the lack of interlocks means the tiler, by careful manipulation of the headlap and side lap, can to a degree compensate for variations in the roof. Cost Cost is obviously a big consideration when deciding on a roof covering. Double lapped plain tiles tend to be more expensive than single lapped tiles to purchase and to install. I have come across many examples of proposed curved roofs that have then been constructed as a series of flat, faceted slopes, to enable the use of single lapped tiles. This can be fine, but the necessary junctions – valleys on a concave slope and hips on a convex slope – can introduce a risk of failure, either right from the start, or at a future Left: John Mercer. Above: image shows Condron Double Pantiles. date as materials weather and degrade. Junctions on the concave side, which are really a form of valley, must be designed and constructed to account for the relative shallow angles at which the roof slopes on a faceted roof meet. Rafter length and pitch A roof should be designed with the type of roof covering in mind. Long rafter lengths combined with a low pitch should be avoided wherever possible. Tile manufacturers give maximum recommended rafter lengths for their products, with guidance on increasing the roof pitch for long rafter lengths. When using single lapped tiles, consider the complexity and size of roof features such as dormer windows. Large tiles may look out of place on small roof slopes or very short rafter lengths, therefore it may be worth considering the use of medium format tiles. Roof systems should not discharge water in point loads from a higher roof slope onto lower roof areas, or into a junction such as a side abutment. If practical, break up the roof into smaller sections. For example, allow the upper roof to shed directly into a gutter rather than onto a lower roof. Features such as raking verges can look architecturally interesting, but remember that if the rake is such that water will run off it, then it is really a sloping eaves and will require a gutter system. If the rake is the other way, then it is really a sloping mono-pitch roof, and so needs a top edge weathering system. Detailing junctions With regards to detailing junctions, use the appropriate weathering system for the tile or slate. For example, at side abutments slates and plain tiles require soakers, cover flashings are generally used with single lapped profiled tiles and secret gutters or proprietary soakers with flat single lapped tiles. Underlay considerations Something that is not always understood or sometimes not even totally accepted is that the underlay layer should act as a second line of defence against snow, rain, or dust driven 18 TC DECEMBER <strong>2022</strong>
through the slates or tiles, as well as making the building weathertight before the tiles are installed. Lay the underlay with a drape between rafters and consider the use of nail tape and counterbattens, particularly at low roof pitches. Nail tape seals between the underlay, battens, and counterbattens to prevent water ingress. The counterbattens encourage air flow within the batten cavity and provide a gap for any water to flow under the tile battens. Ensure the underlay is weathertight at junctions such as side abutments, valleys and around roof windows and chimneys, and is properly supported at the eaves, with adequate fall behind the fascia or tilt fillet. If water can pool behind the fascia, it will inevitably leak into the structure. There are different types of permeable underlays, all with their own methods of installation. Some air-permeable underlays can be used without additional ventilation; most vapour permeable underlays require a level of additional ventilation when used in a cold roof structure, i.e., where the “The importance of obtaining a roof tile manufacturer’s written fixing specification cannot be over-emphasised” insulation is laid across a horizontal ceiling – check with the manufacturer. Fixing specifications A final word on fixing; the importance of obtaining a roof tile manufacturer’s written fixing specification cannot be over-emphasised. As well as making sure that the roof is secure and installed in compliance with BS 5534, site supervisors and inspectors may want to see the specification. Obtain the fixing specification before tendering for the work so that the method of installation, such as nailing and clipping, can be factored into the tender price. In summary: • Choose the most appropriate roof covering, with decisions based on locality, compatibility with the roof design and, of course, cost. Ensure the manufacturer’s recommendations can be complied with. • Ensure roof junctions are detailed to suit the roof tile type. Avoid shedding water from one roof slope onto a lower slope in point loads such as from a fall pipe or lower end of a valley. • Install the underlay to make certain it acts as a watertight layer. Follow the underlay manufacturer’s recommendations for installation and condensation control. • Always obtain a written roof tile fixing specification from the tile manufacturer before work commences and, ideally, as a guide to tendering. Contact John Mercer www.johnmercerconsultant.co.uk Johnmercer 3 For further r inform ation or a hire quotation call 01858 412 100 Email: sales@cookerhire.com www.cookerhire.com
Page 1 and 2: DECEMBER 2022 >>> • WINTER WORKIN
Page 3 and 4: Editor’s Comment MATT DOWNS EDITO
Page 5 and 6: REGULARS 12 NFRC ROOFING TALK Ruth
Page 7 and 8: SPEED AND SIMPLICITY, BY DESIGN. In
Page 9 and 10: Handrails:- EasyGuard free-standing
Page 11 and 12: oof lantern 10% NEW TRADE CUSTOMER
Page 14 and 15: Ask the Solicitor SELLING-UP PART 2
Page 16 and 17: Roofing Battens BE ALERT TO COUNTER
Page 20 and 21: Pitched Roofs DRY VERGE SYSTEMS: QU
Page 22 and 23: Pitched Roofs Continued from page 2
Page 24 and 25: Green Roofs: Substrates SUBSTRATE S
Page 26 and 27: i-folding door 15% INTRODUCTORY DIS
Page 28 and 29: Rainwater Systems DEEP GUTTERING: P
Page 30 and 31: Roof Structures A JOINED-UP APPROAC
Page 32 and 33: Total Talk: Rob Ward, RLW Roofing
Page 34 and 35: EPDM Systems WATERPROOFING THAT MOR
Page 36: EPDM Systems Continued from page 34
Page 39 and 40: DATAC CONTRACTORS HAVE THE EDGE Con
Page 41 and 42: Technical support Roofing experts o
Page 44 and 45: Roofing Updates For further info on
Page 46 and 47: Material Choice SYSTEM ARCHITECTURE
Page 48 and 49: ADVERTORIAL: ROCKWOOL UK INSULATION
Page 50: Updates For further info on all the
Page 54 and 55: Knauf Insulation Tech Talk TOP TIPS
Page 56 and 57: Cover Story: ROCKWOOL UK ROOF INSUL
Page 58 and 59: Insulation Updates For further info
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Page 64 and 65: Updates For further info on all the
Page 66 and 67: Updates For further info on all the
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FALL PREVENTION 30 Year Product War
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December 2022

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