For the sixth entry in our Marley series, Kevin Taylor, Marley’s Technical and Training Manager, with over 40 years’ experience in the roofing industry, shares his knowledge and expertise to provide practical advice for professional roofing contractors, this month, focusing on the eaves.
Checking the fascia board height
Kevin said: ‘Many people may be surprised to learn that, to comply with BS5534 (Slating and tiling for pitched roofs and vertical cladding – Code of Practice) that all roof slates and tiles at the eaves should be supported in substantially the same plane as the main roof.
‘This means setting the fascia board to the correct height so the tiles neither noticeably drop nor kick up. Tiles and slates which are not sufficiently supported can drop with the result being an unsightly gap below the second course of tiles. This gap, if large enough, can also be vulnerable to driving rain ingress if not addressed before the tiles are laid.
‘If the fascia board is set too high, the bottom row of tiles will kick up and there is a risk that they could be sitting below their recommended pitch. Too much kick at the eaves can also cause flat spots or even negative fall on the underlay/support trays which could lead to ponding and eventually water ingress, this is especially a problem where the roof pitch is equal to, or close to, the minimum pitch of the roof tile.
‘There are three factors involved in setting the correct upstand of a fascia board – the type of roof tile or slate, whether to include additional over-fascia vents, and finally the roof pitch. Marley provides tables on the minimum fascia board heights, both with and without over-fascia ventilation strips. It is best to follow such guidance before the fascia board is fixed as lowering or raising the fascia board can be very disruptive and time consuming later, especially if the guttering has also been fixed.
Checking on site
‘It is always best to perform a simple check on site using two short pieces of batten and a couple of roof tiles before work commences. The first batten should be fixed to allow the tail of the tile to finish 50mm over the fascia board on the rake to provide effective drainage into the gutter (although this can be extended for larger gutters or gutters which are off set from the fascia board). The second batten should be fixed at the maximum batten gauge for the roof tile. The two tiles can now be laid loosely to check whether the tiles noticeably drop down or kick up.
‘If the tiles drop down, then the fascia board will need to be raised, or a timber batten of suitable thickness fixed to the top edge, to make up for the shortfall. This should be installed before any of the roofing materials and before any setting out of the battens is carried out.
‘If the tiles kick up, then two checks need to be made. Lay the support tray loosely (or 5U felt or other UV stable carrier) at the eaves and check there is still sufficient fall to guide any rainwater into the gutters. Using a pitch finder, check the laying angle of the first roof tile, if it is more than 5 degrees below the minimum recommended roof pitch (known as the laying angle of the tile), then the fascia board may need to be lowered or cut down.
‘For most common roof pitches, I find that upstands totalling between 35mm and 50mm work for most interlocking tiles depending on their thickness, and around 55-65mm for plain tiles. For slates, the upstand should be approximately the batten depth + two thicknesses of slate (e.g., 25mm + 2 x 5mm).
Bell-cast or sprocket eaves
‘Traditionally, steep roofs, often with long rafters (such as church roofs, spires, and turrets) were designed with bell-cast or sprocket eaves. This is where additional short sections of rafter are fitted to the eaves at a significantly shallower angle to slow the flow of water down before it hits the gutter. Such details are not suitable for interlocking tiles and should only be used for smaller format materials such as plain tiles and small slates and cedar shingles.’
For advice and further details on Marley’s full roof system visit Roofing Systems | Marley roofing systems.