search.noResults

search.searching

note.createNoteMessage

search.noResults

search.searching

orderForm.title

orderForm.productCode
orderForm.description
orderForm.quantity
orderForm.itemPrice
orderForm.price
orderForm.totalPrice
orderForm.deliveryDetails.billingAddress
orderForm.deliveryDetails.deliveryAddress
orderForm.noItems
BUILDING FABRIC & EXTERIORS


the roof tiles, then it ceases to perform this primary function, as the wind load taken by the underlay is transferred onto the roof tiles. The tile manufacturers’ fixing specifications do not allow for this additional load and roof tiles can subsequently be blown off the roof during a storm even if they are fixed in accordance with the tile manufacturer’s fixing specification. A related problem concerns the bursting open of unsealed underlay laps when subjected to wind pressure which can also cause the removal of roof tiles. Both the old and new code of practice recommend that a timber batten be installed over the horizontal lap between courses of underlay to prevent the risk of this happening. In practice this can be achieved either by increasing the horizontal lap of the underlay to coincide with an existing tiling batten, or installing an additional batten also known as a “fly” batten over the horizontal lap. Many roofing contractors do not like installing these additional battens as they can cause a trip hazard when working on the roof. The preferred alternative is to increase the underlay lap which has the disadvantage of increasing the amount of underlay required as well as requiring more care during setting out of the roof.


The 2014 version of BS 5534


introduced a new single test that measures the ability of an underlay to resist stretching when exposed to wind pressure. These test results are then used to establish which types of underlay are suitable for the various regions around the UK. Before commissioning or undertaking any work, it would be prudent to ensure


that any preferred underlay has the necessary checks and testing in place to ensure it is fit for use for the project in question. These changes are a significant step forward from what has been the baseline standard for roofing practice in the UK.


Dr Kevin Ley is technical manager at Redland


march/april 2018


www.sbhonline.co.uk


33


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