Façade Design Engineering to maximise value and minimise risks

MULTIDISCIPLINARY ENGINEERING CONSULTANTS

A building’s façade sets its style, form and brand, but as well as achieving the architect’s vision, the façade engineer’s design must consider many other factors including buildability, maintenance, life-cycle, sustainability and safety.

A Façade Engineer is truly multidisciplinary and must have knowledge of architecture, material science, physics and structural engineering. As contemporary building envelope design evolves and building standards change, the façade design engineer is further challenged to ensure form and performance are achieved.

Achieving and maintaining the visionThe design of the façade will dictate what construction methodologies are chosen which in turn will effect the maintenance and life of the building envelope. This is particularly relevant in the retail and hospitality sectors which rely upon the façade to convey a brand message to consumers and also a platform to advertise, whether it’s with dynamic LED lighting or video walls. Costs can soon escalate if the design hasn’t initially been carefully considered. The implication of the design on maintenance and life cycle needs to be understood, planned and realised to continue to convey the right message.

Environmental considerations also inform design and construction as the impact on façade can be considerable. Sustainable features can include anything from solar shading devices to enhanced specification of glazing to improve customer comfort whilst potentially reducing running costs, achieving government carbon emission targets and future proofing construction based on BREEAM standards.

Future proofingSince 1994, new and refurbished buildings are required to have a maintenance manual in accordance with The Construction, Design and Management (CDM) Regulations 1994 which are aimed at: ‘improving the overall management and co-ordination of health, safety and welfare throughout all the stages of a construction’.

With advancements in façade design and systems there is now more than ever a need to ‘future proof’ the condition of our buildings where key considerations in the maintenance and life cycle include:

• Selection of materials for aesthetic, performance and maintenance • Selection of building envelope construction techniques and understanding the

impact on service life and maintenance • Specification of glazing and solar control to promote occupant comfort and service

life/maintenance • Specification of cladding wall build-up that considers thermal performance and

the risk of condensation and corrosion which impact maintenance and service life • Access plan requirements for façade maintenance

Facade dirt build up

Shrinkage of gaskets

Interstitial condensation in double glazed units

Façade maintenance for new build and existing builds each have their own risks to consider and appropriate regulations with which to conform. The main difference is that for refurbishment of existing buildings, it is important to first undertake a thorough façade condition survey. An understanding of the existing condition of the façade impacts on the proposed design/selection of materials. Monitoring workmanship during construction and the early implementation of a maintenance regime will result in addressing risks promptly as part of a planned process that allows costs to be controlled.

Combustibility risksIt is worth considering here as a separate issue the assessment of combustibility risks associated with cladding. Whilst in the UK we are used to appropriate regulations being applied to the manufacture of products to ensure they are fit for purpose, it has recently been demonstrated tragically that this cannot be assumed to be true.

Fire risk mitigation is obviously something that is already included in Government Regulations as part of Approved Document B. The weaknesses however, other than the specification of accredited cladding and components that make up the build-up of the system, is ensuring that guidance is adopted early on in the process and followed through during construction. This is particularly relevant for D&B contracts where tender designs may be changed, with approved regulators/inspectors signing off installation. The risks can also be mitigated by surveying/monitoring the workmanship of cladding installation.

In relation to combustibility risks of cladding systems on all existing buildings, we advise that credible guidance is sought in review of relevant documentation and drawings by a qualified consultant or fire engineer to establish potential risks and a plan for mitigating.

The review of drawings and documentation should be based upon BRE guidance recommendations which, on writing, have been updated following a number of fire tests carried out by the BRE to a range of cladding system material build ups. Early tests have demonstrated that cladding systems built up with a polyethylene core aluminium composite material (ACM) in combination with PIR insulation, as used in the Grenfell Tower refurbishment, fails based the requirements of BS 8414. The results published also confirm that the use of a fire retardant core ACM with PIR insulation also fails tests; these results have a direct impact on product manufacturers of cladding products that claim suitability of fire retardant ACM cores. This is based on an a perceived understanding of claimed testing that approves the product to perform based on a National Fire class rating of Class 0 which according to Approved Document B is acceptable in terms of surface spread of fire. The BRE test results have however unfortunately shown the opposite and therefore building envelopes employing what was believed to be an acceptable system combination are now unacceptable above 18m.

Loose curtain wall components

Nickel Sulfide inclusions

Thermal stress fracture

The combustibility risk of a cladding system goes beyond surface spread of fire to the cladding itself, and should consider the complete build up, including insulation, fire cavity barriers and fire stops which are all subject to appropriate design and installation guidance. As noted in Approved Document B “The external envelope of a building should not provide a medium for fire spread if it is likely to be a risk to health or safety. The use of combustible materials in the cladding system and extensive cavities may present such a risk in tall buildings.” Each building cladding system needs to be reviewed and considered based on its specific design feature and requirement and as now proven by the recent BRE tests; the combination of materials used.

The BRE have provided guidance in mitigating risks where combustible cladding (which has not met the requirements set out in regulations) on existing builds is inspected and reinstated safely without exposing further risks. Although results from the fire tests by the BRE are beginning to shed light on the performance of systems, the Grenfell incident is still a complex one. Further investigation is required into all the facets that led to the decision to approve cladding refurbishment on Grenfell Tower and a number of other high rises throughout the country. Further review of the current Building Regulation Approved Document B is also being undertaken to identify a more robust route to classifying acceptable cladding materials for high rise buildings. Due to misinterpretation of acceptable fire classification of cladding above 18m it is of paramount importance that revisions to Regulations clearly identify and account for both fire performance and safety.

Common façade defectsThe common problems/defects to facades due to insufficient design, workmanship or degradation can include:

• Glazed curtain walls and window systems – defective gaskets and sealants including splits, openings and shrinkage resulting in air and water infiltration. Latent defects in curtain walls can also include corrosion of fixings due to insufficient isolation and formation of interstitial moisture. Understanding the specification of glass (including solar control) and the required quality assurance testing (heat soaking for heat strengthened glass) is critical to performance and life cycle.

• Stone and pre cast concrete – defective joints and the evaluation of the integrity of anchor systems is integral to maintenance and life cycle.

• Cladding panel systems – defective seals, insufficient specification of fire rated insulation, insufficient build up to allow appropriate ventilation and moisture control, aluminium panel finishes (anodised or PPC effecting life span and maintenance) and corrosion due to insufficient isolation of brackets.

Maintenance planning is keyMaintenance planning considers the life cycle of various materials and façade systems allowing for the selection of appropriate maintenance and repairing strategies. Ongoing inspection is key to addressing defects and maintaining a façade whilst preserving the integrity and safety of the premises; a well-planned preventative maintenance schedule will identify risk and associated costs which contribute to extending the lifespan of the building envelope as a whole. The maintenance of the façade directly impacts the owner, tenant or occupier depending on the type of lease and therefore an understanding is an important aspect in addressing insurance requirements.

Clarkebond are experts in façade design and investigation across many sectors including commercial, retail and hospitality. We have advised developers, contractors, asset managers and insurers during the construction and post construction remediation of façade defects and the implementation of preventative maintenance schedules.

For further information on our façade design services and how we can help you diagnose defects and provide advice on strategic remedial maintenance measures please contact Bill Keane, billkeane@clarkebond.com or Omar Al-Omar, OmarAl-Omar@clarkebond.com who heads up the façade engineering division.

The Cocoa House129 Cumberland RoadBristolBS1 6UY

tel: +44 (0)117 929 2244

GF Suite Bickleigh House Park Five Buisness CentreExeter EX2 7HU

tel: +44 (0)1392 369098

Unit 17.1 The Leathermarket 11-13 Weston StreetLondon SE1 3ER

tel: +44(0)20 7939 0959

www.clarkebond.com

MULTIDISCIPLINARY ENGINEERING CONSULTANTS