| SLATE ROOFING
A slate roof should last 80 years; failure
is usually caused by corrosion of the nails rather than of the slate
itself. Thus, reroofing in recycled slates is a good option; cheaper
than new slates and giving a far more attractive result than modern
concrete tiles. However, slate can delaminate, becoming absorbent.
Slates like this must be replaced.
When restoring a slate roof the options
are:
new Welsh
slates
These are very expensive, but the best option. They can last for
more than 100 years. They come in a range of grey colours, and with
plum and blue tints.
recycled Welsh slates
These tiles are a good compromise between cost and longevity
Other slates
A good alternative to Welsh slate is Canadian slate.
Spanish slate is too soft and has an unpredictable
grain.
Chinese slate does not have a British Standard
kitemark. Furthermore it sometimes goes rusty due to iron oxide,
and is brittle and therefore hard to fit without cracking.
new Spanish slates
These give an authentic look but because of irregular grain, they
can split early in their life. They are likely to last 40 or 50
years, being softer than Welsh slate. They are blue/black in colour.
composite
This is a modern material; a cheap solution but it does not weather,
is very smooth, and does not have a long life. It looks very shabby
in 10 years.
concrete tiles
Although they are available in grey, they are not authentic-looking,
and because they are heavier than slates, the roof timbers typically
need to be strengthened. When in an interlocking design, they look
very different from other slates and tiles.
If you are having a new roof, insist on
Tyvek underlay as this does not require unsightly plastic vents
on roof.
In rare cases, a roof may have Westmoreland
green slates. These are irregular in size and usually laid in diminishing
courses with the smallest at the ridge and the largest at the eaves.
Slates may be nailed at the top or, more
usually, in the centre.
When repairing an old slate roof, ensure
that you match the size, texture, colour and detailing of the existing
roof.
When seeking a roofing contractor, get references
and visit their previous work. Slate should be sorted into three
grades of thickness, with the thickest laid at bottom of the slope,
the thinnest at the top. Battens need to be set out horizontally
and vertically with stringline before slating. Copper nails should
be used for fixing. Check the lines of slates: good slating when
viewed from the ground should have straight, perpendicular courses
from the base to the top. There should be no 'kickers', tiles which
are lifted up to leave a gap underneath. There should be no thick
slates laid in amongst thin slates.
There are several elements of a slate roof:
Eaves
There should be a double course of
slates at the eaves using a short under-eaves slate, supported by
a tiling fillet (or fascia board), above which is laid the first
full course of slates. The overhang should be approximately 50mm
to ensure that water discharges into the centre of the gutter.
Verge
The verge (the edge of a roof at a gable end), should normally comprise
an undercloak course of slate, which is bedded on mortar and nailed
if possible. The upper slate should be well bedded in mortar and
finished flush with the undercloak slate course. It is good practice
to carry the battens over the edge of the undercloak slate to give
additional support. The unsupported overhang of a verge should not
normally be less than 40mm and not more than 50mm.
Ridges
and Hips
Ridges and hips may be protected with a half or third round terracotta
or clay ridge tiles or with dark grey/black angle tiles or, as is
usual on lower pitched roofs, a lead roll ridge or hip. Hips may
also be formed from mitred slates, interleaved with lead soakers.
In exposed situations, the mitred hip slates can be fixed with brass
screws and washers.
Valleys
Valleys may be formed by a lead gutter lining – gutter width
minimum 100mm; by mitred valley slates interleaved with lead soakers
fixed by nailing to battens at the top edge. More rarely there may
also be swept valleys or laced valleys using specially sized and
cut slates.
Other Details
Sloping edge abutments and junctions or roofs with parapets or chimney
stacks or changes in roof pitch (as for example in mansard or gambrel
roofs) should always be detailed with lead flashings and not cement
fillets.
|
about
quality
