When architects no longer coordinate designs and builders no longer accept responsibility for the building, how do you make sure a building is weatherproof?
From the outset of my career as an architect, I found it regarded
as a normal and essential part of the architect’s role to coordinate the design
team and integrate architectural, engineering and specialist designs into a
working whole. More recently, as a
forensic architect, I find troubled projects where the project architect’s role
is diminished, leaving no member of the design team with overall responsibility
to coordinate the team and check the compatibility of each specialists’
contribution to the design. This was
brought out recently in a design and build project which leaks. The general contractor blamed separately: the
architect, the brick laying sub-contractor and the curtain walling
sub-contractor for the failure.
The main contractor entered a contract under which it was
responsible for design, supply and build and then subcontracted all of the
work. When the finished building leaked,
the contractor took the stance that, as it had not in fact designed or built
anything, it must be blameless and fault must lie with its consultants and
subcontractors.
The architect sought to distance himself from the
problem. As is typical under a design
and build contract, the architect was given a limited brief and even more
limited fee. Accordingly the architect
stated; ‘We do not approve drawings, we only provide the design intent and a
visual concept, along with our understanding of how things go together’. Despite
the usual mishmash of project managers, coordinators, etc. no one had been
charged with the task of checking the compatibility of each consultants’ and
specialists’ designs with each other.
Without
establishing the causes of the leaks, the general contractor withheld money
from all whose work might be at fault.
How does rain penetrate a masonry walls?
By their nature, masonry walls are not waterproof. The specification, design, detailing and
construction of walls should be tailored to local weather conditions. The likely severity of rain driving through
masonry can be assessed from the wall spell index[1]
- the more severe the exposure, the
more vital the correct detailing.
Particularly important is the detailing of d.p.c.’s, joints and
junctions.
D.p.c.’s have limited ability to bond to mortar and, especially
if dry bedded, may form continuous capillaries to draw water in. Even without d.p.c.’s, water may enter
through the microscopic labyrinth of voids at mortar to masonry junctions and
through movement cracks. Inappropriate
detailing, such as recessed mortar joints, can further worsen performance.
Even well designed and built masonry walls may leak if
connected to poor roof details.
Parapets, poorly jointed copings and the lack of overhangs, drips and d.p.c.’s
commonly let water into walls but may go unnoticed until emerging it manifests
itself as damage.
Where does the water go?
Once water has entered masonry walls, it may spread unseen
and reappear as leaks, typically at places where the masonry construction is
interrupted, such as: floors, doors, windows, etc.
This is a common problem in cavity walls. Good practice is to design on the basis that
water will penetrate the outer leaf of cavity walls and run down the wall cavities. To prevent damage, weep holes and cavity
trays are customarily installed to drain water harmlessly to the outside.
Careful detailing is required to prevent water damage where
the masonry is interrupted. Water
running through masonry and wall cavities may not be noticed until it flows
onto lintels, window heads, etc. and causes visible damage. This often leads too readily to the
assumption that glazing systems are faulty or incorrectly installed as this is
where the water damage is seen. With good design and supervision, glazing and
masonry can be combined without problems but when it does go wrong, informed
inspection and simple testing can reveal the causes of water damage, allowing
effective repair and the correct apportionment of blame.
Getting it Right
Successful teamwork is engendered by good planning and
management with clearly allocated responsibilities and effective
communication. Empowering skilled
designers and tradesmen to work well as a team requires leadership,
organization, proper funding and timely payments. Designs should be well prepared in advance
and developed in work as required. This
happens when tradesmen and professionals develop mutual respect and have the
resources to work together as and when needed.
Sometimes each trade, specialist, contractor,
etc. is left to decipher what is wanted from the contract documents and what
they find when it’s their turn on site. Cost cutting jeopardizes supervision, inspection
and design leadership. Most have, of
necessity, developed practical ways of handling the problems arising and
produce good work despite the difficulties.
Occasionally the problems can seem intractable. When this happens,
independent experts can help.
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