Responsibilities Under Design and Build Contracts
Who Leads the Design Team?
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.
Responsibility for Leaking Walls
This was brought out recently in a design and build project which leaked. Without determining the causes of the leaks, the general contractor sought to pass the problem to everyone who could have contributed to the leaking fabric and blamed separately: the architect, the bricklaying subcontractor and the curtain walling subcontractor 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 each specialists’ designs with each other.
Without regard to the lack of investigation into, and evidence on, the causes of the leaks, the general contractor withheld money from all whose work might be at fault.
How Does Rain Penetrate 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- 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.
 BS 8104 Code of practice for assessing exposure of walls to wind-driven