When looking at the gable end wall of a
building the two verges that meet at the ridge are described the
opposite way around. The one on the right is a left-hand verge and the
one on the left is a right-hand verge. This is due to roof slopes being
described whilst looking at the roof slope, not the gable end.
Verge tiles should overhang the building fabric by between 38 and
50mm. Less than 38mm and watermarks will show down the face of the wall.
Greater than 50mm and end tiles in each row will become unstable due to
the overhang and buffeting on the underside and the suction on the upper
side as wind blows over it.
To support the bedding mortar a 150mm wide fibre cement, or slate,
undercloak needs to lap under the end of the tile batten by no more than
50mm, leaving the outer 50-75mm for mortar and a 25-50mm gap between the
end of the batten and the mortar. The end of the tile batten should not
come into contact with the mortar as moisture from the mortar will wick
into the timber, causing it to swell. This will cause the mortar to
crack at the batten position, and eventually the timber batten will rot.
Plain tile undercloaks should not be used with interlocking tiles with a
gauge greater than 265mm due to the need to lap the undercloak under the
ends of the tile battens. Also, below 30° rafter pitch, as the camber
of the tile can encourage water draining over the verge to run back to
the wall face, rather than dripping clear of the wall.
Underlay at the verge should finish under the undercloak, never
above it, and never come into contact with the bedding mortar. By
putting the underlay under the undercloak, any water on the undercloak
will drain onto (not under) the underlay.
With the end of the tile batten located approximately 100mm from the
verge edge, it is just possible to hang a half tile for a flat
interlocking slate on the end of the batten. British Standard 5534, Code
of practice for slating and tiling: Design: 1997 states that all
perimeter tiles must be mechanically fixed. The correct choice of a nail
or a clip will depend upon the calculation for the individual roof at
that location. Whilst the calculation may say that the verge tiles only
need to be nailed, it is not safe to nail the half tile to the batten,
as in most cases the nail will either miss the end of the batten or
penetrate the batten close enough to the end to cause it to slit, giving
no grip to the nail. It is for this reason that all interlocking tiles