Spec Finish

Technical www.thefis.org 11 The issue of weathertightness of buildings has been discussed throughout all the years I have been involved with the drylining industry, and the destructive effects that the UK climate can have on drylining is often underestimated. Common-sense would indicate that installing materials such as plasterboard (drylining) into a building that is not weathertight is counterproductive, leading to a poor quality finish. The system’s performance will be compromised; not to mention the additional costs and time needed for putting right and replacing materials (even if covered by insurance). We review designs and monitor the installation of the drylining works for our clients and ensure they are compliant. If the building is not suitably weathertight all the hard work will be undermined when the drylining systems suffer damage. I have lost count of how many times I have been asked to survey water damaged drylining and report back to clients that the drylining systems need to be removed and replaced The following is stated in BS 8212: 1995 Code of practice for drylining and partitioning using gypsum plasterboard ‘ It is essential that the areas to be drylined or partitioned are watertight, weatherproof and dry. This is of particular importance as drylining materials are vulnerable to wet or high humidity conditions’ . ‘Weathertight’ (weatherproof) means the building should be sealed so that elements such as rain and wind are not able to penetrate into the interior. There are five major issues that should be considered, when the weathertightness of a building is not complete: • performance; • aesthetics; • programme delays; • cost; and • material waste. The expectation on subcontractors is for them to provide high quality, compliant work. However, if the right site conditions are not provided, this becomes more challenging. At the end of the project when there may be disputes over quality of the workmanship, the site conditions are often quickly forgotten. Consult the manufacturer The result of tighter programming periods inevitably leads to drylining being installed well before the external envelope is complete or the building is made weathertight. Therefore, water damage of performance systems, which often tend to be around riser locations or façade locations is commonplace. If it is not possible to provide a fully weathertight building, the designers should consider alternative systems that may be capable of providing better weather resistance during construction, or review the programme and sequence of works. Standard plasterboard systems using gypsum-based boards are not designed to provide water resistance, however, it is possible to specify certain board types which may have better moisture resistance during the construction phase. It is good practice if the manufacturer of the drylined systems is consulted regarding the use of materials if the weather conditions expected during the construction phase are likely to be inclement. The impact on drywall systems in buildings that are not weathertight may not just be aesthetic, but often more serious where the fire performance of the systems could be compromised. It needs to be remembered that the drylining systems are not fire tested when they are water damaged, and therefore the fire test evidence will not be available for these damaged systems. On average, around 40% of the interfaces within a drylining package are not included within the system manufacturer’s standard details. On projects with emphasis on bespoke internal layout arrangements, this proportion can be as high as 85%. Even interfaces provided as standard details by the drylining system manufacturer often encounter complications when applied to the individual requirements of a construction site. These complications can include coordination with structure or services, which can result in additional installation requirements. This has the potential to make Alex Double , Managing Director of A D Design Consultants , felt that weathertightness should be a major consideration, because if it isn’t, water damaged drylining will eventually need to be removed and replaced. Matt Taylor , Director at Taylor Design Consultancy , notes that the most frequent source of design-related installation defects within the drylining package sits within system interface construction. WEATHERTIGHTNESS CORRECT INTERFACE CONSTRUCTION Alex Double, A D Design Consultants Limited Matt Taylor, Taylor Design Consultancy If it is not possible to provide a fully weathertight building, the designers should consider alternative systems that may be capable of providing better weather resistance during construction, or review the programme and sequence of works.