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It is nice to see some well constructed and detailed brickwork
that shows off the skill of the bricklayer. Often this extends to the
finishing of the brickwork at the eaves and the verge. But unlike the
verge where the bricklayer knows that he must finish flush with the top
surface of the end rafter, at the eaves there is a range of options that
will affect the tiling on the roof, and which can go wrong. So what can
the roofer do to overcome the construction that has been dictated by the
architect, and constructed by the brick layer?
We need to understand the thinking behind the brick
corbelled eaves detail. Firstly the architect will be trying to finish
the building using as much brickwork as possible, in a decorative way,
and to reduce or eliminate completely the use of painted timber or
plastic fascia and barge boards, to create a maintenance free external
envelope. In itself this aspiration is a good idea. But to achieve this
it takes co-ordination between the trades, as the bricklayer will lay
bricks in courses 75mm high, meaning that the exact height of the
leading edge of the brick work for the tiles or slates, is likely to
finish at the wrong level.
But what is the right level? When the tiles or
slates are laid on battens the first three courses should all lay in the
same plane. The practice of sprocketing the eaves tiles or slates is
common but presents further technical difficulties, and so should be
avoided at all cost. The excuse used by some architects and roofers that
the sprocket is there to slow the water down as it runs off the roof is
bunkum. If anything, during severe storms, a pronounced sprocket can act
like a ski jump and encourage the rain to jump over the guttering. It is
better that the brickwork is left low allowing the roofer to pack up the
top surface with a suitable sized piece of timber. It is easier to build
up the wall than to cut down the brickwork.
The other option would be to counter batten the
complete roof to bring the top surface of the rafters up, but this will
probably affect the brickwork on the verge and the flashing around any
chimneys, or at side abutments.
Secondly the architect will be trying to copy or
match a look from an older generation of buildings, where the
construction will be different. By this I mean the walls may be solid,
not cavity brickwork, or the roof structure not trussed rafters. Unless
the total building construction is the same the relationship of
components will be different, so a full understanding of the old and new
construction is needed. Often the trussed rafters will finish on the
wall plate on the inner wall skin, and the distance across the cavity
and out to the face of the outer skin of brickwork, which has been
corbelled forward by between 10mm and 50mm, could be in excess of 250mm.
This means that installing plain tiles or most double lap slates will be
almost impossible as there will be nothing to fix the first batten to.
Therefore interlocking tiles should be the preferred option, which may
not fit in with the architect’s desired look.
Thirdly the architect will be trying to show his
artistic flair, by showing indented toothing or creasing tile fans, or
something that is normally only seen on older buildings. This can result
in the top course of bricks being less secure than the brickwork below.
This will make it difficult to plug and screw a timber batten into the
top surface to pack up the eaves course of tiles, or for the guttering
to be fixed to. In windy locations and on steep pitch roofs interlocking
tiles will need to be clipped along the eaves course and so there needs
to be a semi structural timber batten that the eaves clips can be nailed
to and transfer the wind uplift loads into the wall structure.
If the interlocking tiles are profiled,
reform eaves filler units, or an eaves comb, will be needed to keep
birds and small rodents out of the batten cavity, and they need to be
nailed to something, which is not easy directly into brickwork. Then
there is the presence of an over fascia ventilation system. In many
instances VP underlay is specified to eliminate the need for eaves
ventilation, but there are instances where eaves ventilation is needed
and the over fascia grills need to be fixed to something. There are vent
units that are compatible with brickwork having tabs that fit into
regular brick joints, but these are the exception rather than the norm.
Quite often at the junction of the verge and the eaves
a projecting quoin is constructed that finishes 50mm forward of the
brick corbelled eaves, which makes a nice corner feature but causes the
corner eaves/verge tile to kick up, unless the top surface of the
brickwork is cut at the rake of the roof. Also it stops the guttering
from extending to the verge edge resulting in the water running off the
verge tiles missing the guttering.
Another problem can be the bottom of an inclined gutter
that needs to discharge through the brickwork and into the gutter
without kicking up the tiles on either side. If there is an eaves batten
fixed to the top of the brickwork, this can be cut down to accommodate
the valley construction, especially with GRP valley troughs.
Brick corbelled eaves when installed correctly can be very effective and
good looking, but can be difficult to get right. The relationship of the
tiles specified, the rafter pitch, the brick coursing, the amount of
step forward and the corner detail can all have an effect on the
finished article. The tiles should not be sprocketed, and there should
be some form of timber onto which an eaves comb, eaves clips and perhaps
an over fascia ventilation system can be installed, easily and safely;
plugging and screwing into brickwork close to the edge is not
recommended. Finally the underlay needs to be fully supported between
the rafter and the wall face with an underlay support tray or timber
tilt fillet, and the underlay must not drape into the gutter.
- Large format interlocking tiles
rather than plain tiles or small format slates should be used with
brick corbelled eaves
- The detail of the eaves should be
drawn at 1:1 at all junctions such as the verge, valley, hip and
general to ensure that the carpenter, bricklayer, plumber and roof
tiler all agree and can comply with the detail, before work
commences, and that any amendments are made and agreed if it is
found not to work.
- All plug and screw fixings
into the top course of bricks should be made into the centre line of
the brickwork at approx 450mm centres.
by Chris Thomas, The Tiled Roofing Consultancy, 2 Ridlands Grove,
Limpsfield Chart, Oxted, Surrey, RH8 0ST, tel 01883 724774