Page 60 - The Building Conservation Directory 2013

6 0 t h e b u i l d i n g c o n s e r vat i o n d i r e c t o r y 2 0 1 3 T w e n t i e t h a N N i v e r s a r y e d i t i o n
2
Building Contractorsaesthetically and architecturally elegant
and either neat or invisible: there is no
justifiable reason why modern repairs
should not add character and appeal
in the same way as the historic ones
• Documentation – record the fabric
before intervention and document
the intervention itself so that future
conservation work is well informed.
In choosing the right approach and repair
mechanism you must take all the evidence into
account, including the type of failure that has
been observed and, by deduction, the reason for
it. Things to look for might include the source
of extra loading, or the reason why a beam end
is getting wet. So, for example, you might look
at a cracked upper floor beam in a barn where
the crack at the end of the beam is in an area
of severe insect attack. In this case you would
need to consider the presence of moisture in
absolutely essential to choose the right
specialist, that is: one who is well-versed in
devising sympathetic solutions with minimal
intervention, and who is used to working with
historic construction methods and materials.
However, it has to be said that if you have
the right contractor doing the work, this
also helps greatly. A specialist conservation
contractor who is familiar with executing such
repairs can work most effectively with the
engineer and may well be able to give guidance
on what options are achievable.
The wrong team will invariably result in
a clumsy and/or expensive solution or the
excessive loss of historic fabric.
Like for like repairs
Sometimes the simplest repair is a
straightforward replacement of the
whole timber, like for like: for example a
completely rotten lintel or exposed verge
rafter. At times, replacement provides
the opportunity to fit a stronger or more
substantial piece of timber or to slightly
adjust the design to prevent future failure.
However, as a matter of principle it is
important to try to retain as much historic
fabric as possible, so the best solution
is usually to repair rather than replace
components. A common technique is to
scarf-in a new piece of timber to the old, like
for like. The new section can be connected by
a lightning bolt joint (pegged or bolted) or,
if in compression, a V-shaped splice. Scarfed
joints are particularly useful in cases where
one section of the timber has rotted out, such
as the foot of a post or jamb, or the ends of a
rafter, truss or beam which have been affected
by damp. They provide a nice neat repair, in
keeping with the character of the original, but
require a reasonably high level of carpentry
skill if they are to be done well.
Reinforcement options and
supplementary structures
It’s often possible and preferable to leave
historic timber in place and either take or help
take the strain with an alternative structural
member. For example, the spreading of a roof
truss may be restrained by adding a second
collar, or a rafter may be doubled up with a
new timber either close by or attached to the
original. In some cases the right roof repair
solution is a new framework built around
or over the old. This is sound conservation
practice because it saves the original fabric
and is generally reversible, although it can look
a little clumsy if it is on show.
Where beams or joists are not deep
enough for their loading, the result is excessive
bending, bouncing floors, and possibly even
cracks. One option is to increase the effective
depth by fixing additional timber to the top of
the component to increase its stiffness. If the
depth of a beam only needs to be increased
marginally, one very neat solution is to firmly
attach the floorboard material to the top of
the beam. However, fixing the rest of the
floorboards around it can be a head-scratcher.
When the ends of beams or joists are
decayed, or in cases where either the beam
or its support has moved, leaving too little
These jetty beams had decayed, as had the timber screen wall which they originally rested on. They were renewed and
suspended instead from a steel channel hidden in the floor void above. The hanging bolts are finished with square steel plates
rebated on the underside.
A crude means of strengthening the junction between truss and beam: obviously not a repair that should be on show
the wall in which the timber is embedded,
and whether there is a leak in the roof, an
overflowing gutter or some other source. You
will also need to consider whether the upper
floor is being asked to take particularly high
or increased loads. Perhaps a huge amount of
hay or straw is sometimes stored in the barn,
or maybe there is a repair post mounted onto
the beam which is transferring additional load,
perhaps following a change in the roof covering
and the subsequent deflection of the roof.
Another factor for consideration is the
impact of any particular repair. If the timber
were removed, how much damage or loss of
fabric would occur around it?
Often these observations, decisions and
design solutions are the realm of specific
professional consultants, such as structural
engineers or building surveyors. Obviously
when dealing with historic fabric, it becomes