# weathertightness By [dj](https://paragraph.com/@dj-2) · 2023-03-31 --- Wind pressure is a crucial factor in the design of both the building frame and façade. In the UK, the Eurocode 1: part 1-4: General actions - Wind actions (EC1-1-4) standard is used for the design of the building frame, while the British Standard BS EN 12152:2000 is used for the façade design. EC1-1-4 considers the building's location, height, exposure, shape, surrounding buildings, and ground surface roughness. The standard provides a set of wind speeds and pressures that must be used to design the building frame to withstand the wind loads. It also provides different pressure coefficients for different building elements such as walls, roofs and chimneys. The wind pressure is applied in both the transverse and longitudinal direction to ensure that the building can withstand the forces. BS EN 12152:2000 considers the building envelope performance, including air and water infiltration, and structural requirements such as resisting wind load. It provides wind speeds and pressures for the façade design to withstand the wind loads, along with pressure coefficients for different types of glazing and their fixing methods. The crucial difference between wind pressure applied to building frames and façades is the magnitude of pressure used. Wind pressure applied to building frames is usually higher as the structure must be capable of withstanding the full impact of wind, while façades only need to resist wind loads to a certain extent. Wind pressure is applied to the glazing, framing systems, and their connections for curtain walls. The design must guarantee that the glazing won't blow out and that the framing can resist wind forces without twisting or buckling. The design must meet the wind load specifications stated in BS EN 12152:2000, which are lower compared to EC1-1-4. In curtain walls, as there is no airtight layer, net pressure considering both external and internal pressure is used. In the case of rain-screen walls, wind pressure applied to the wall's design must consider the building envelope's performance requirements, including air and water infiltration. The wind pressure is applied to the outer layer of the wall. The design must ensure that the panels can withstand wind force without detaching from the building, meeting the wind load specifications in BS EN 12152:2000, which are lower compared to EC1-1-4. Rain-screen walls are not structural elements and are supported by an airtight backing wall, which uses only external wind coefficients. As a specifier, I am searching for a curtain wall (assuming it’s an aluminium 6063 stick curtain wall with DGU glass), with two variations - one without an opening light and another with an opening light. Assuming the building has a length of 100m, a width of 120m, and six stories, each 3m tall. In both cases, the curtain wall options should meet the CWCT standards and achieve the following performance ratings: • Air permeability A4 (600 Pa) According to CWCT, the air infiltration rate at peak pressure should not exceed 1.5 m3/hm2 and the leakage through opening joints should not exceed 2 m3/hm2. The exfiltration rate at a test pressure of up to 100 Pa should not exceed the specified value of 0.6 m3/hm2. • Water tightness R7 (600 Pa) As per the CWCT criteria, there should be no water leakage onto the internal face of the system during testing, and no standing water in dry locations after testing. Any modifications should be reported. A water flow rate of 2.0 l/min/m2 is allowed for large specimens. For opening lights, water may remain within opening joints but must be reported before testing. • Design wind load (1900 Pa) The CWCT performance criteria include: 1. Visual acceptance: Image distortion is controlled by deflection limits measured between support points, with a limit of 1/175 of the length along the edge for double-glazed framing members, and 3 mm or 1/500 span for vertical deflection under dead or live load and deformation is limited to 1mm or 5% of the measured peak value. 2. Support of infill: Deflection limits depend on the type of infill and the supported edge length. For four-edge support, the limit is 1/175 of the length along the unit edge, or 15 mm. For two-edge support, the limit is 1000/540 of the square of the span between supports where deflection is measured in mm and span in metres, or 20 mm. 3. Check for no failure in the one-off over-stress situation. • Operable ventilation should not be taped; it should be closed. • Opening lights, if included, must be opened and closed 5 times before testing. • A single pulse of 1.5 x design wind load must be applied following preparation pulses, maintained for 15 +/- 5 s, in both directions. • There should be no permanent damage to framing members, panels, or anchors during positive and negative applications of the peak test pressure. Framing members should not buckle, panels, glazing beads, and decorative capping pieces should remain securely held, and gaskets should not be displaced. • For windows, there is also a requirement for 50 cycles of load at half the serviceability wind load. The common information required for both curtain wall and curtain wall with opening light, according to CWCT TN8 (2000), is as follows: • Durability? A certificate or assurance of the durability and quality of products is required to determine the life of the components, which are essential for maintaining weather tightness. For example, if the quality of the seal is poor, it could peel off and result in a breach of weather-tightness. • Repair? The owner of the building should be informed about the type of service and cost involved in case of damage or resealing. Glazing may need to be replaced due to factors such as limited lifespan, damage to edge seals, or poor workmanship during glazing installation. This will provide the owner with a rough estimate for future maintenance and replacement costs. • Design/Installation Process? The installation time, factory vs site fabrication, dimensional tolerances, and compatibility of tolerances at the window-cladding interface should be considered. Factory-based fabrication is preferred for better craftsmanship, while on-site fabrication may lead to poor installation and weather-tightness, potentially causing the system to fail under wind load despite passing lab tests. • Trained Installers? Proper installation is crucial for the system's performance. Certified and trained installers registered with the CWCT should be used to reduce the risk of issues from improper installation, such as improper tightening of fixings or hardware adjustments. Installers should have access to current installation manuals for their system. Poor craftsmanship can lead to poor weather-tightness, for example, poor installation of seals or inadequate wind resistance due to incorrect fixing locations. • Cost? Two separate quotations are required, one for just a curtain wall and another for a curtain wall with an opening light. The quotations should state inclusive and exclusive costs, such as labour, glass, and fixing costs. This will provide a brief idea to the building owner and financial management to determine if the cost is acceptable. • Warranty? A warranty for the system and its components should be provided with conditions to buy insurance if needed. • Condensation risk? State if any spaces have high relative humidity and any exceptional internal or external temperatures. It is important to know the occurrence of condensation as it will result in the formation of moulds in the building which can be hazardous to the occupants and may cause the degradation of materials. • Lab Test? The test results and report should be provided. It will give information on when and how the system failed the respective test and identify specific areas of concern. For example, if water leaked in, the report will indicate where it leaked from. It will also show the ultimate strength of the system. The report is necessary to confirm what has been tested, check for hidden defects, and verify the specimen dimensions. If necessary, the product can be retested with the desired dimensions, for example, if the thickness of the test specimen is 3mm but the contractor provides a test certificate for a 1.5mm profile, the system will underperform when installed. Any modifications made during testing should be recorded and carried out on-site. The test report and certificate should clarify that the test was conducted according to CWCT standards and the test sequence (Standard Sequence A or B), where Sequence B provides better information on the system's performance due to the dynamic water penetration test. • Glazing Seal? The life and type of seal are crucial as it is one of the key components responsible for weather-tightness. It also allows room for movement accommodation. Silicon is more robust and flexible, the outer seal should be the primary barrier to water ingress, while the inner seal provides airtightness and acts as a secondary seal to prevent water ingress, accommodating building movement while preserving weather-tightness. • Corner Sample and Drawings? A sample will give the architect an idea of how well the system will integrate with the building design, while drawings will help the façade engineer understand the system's functioning, advantages, and disadvantages. Drawings will also show the water drainage route and voids, helping to understand pressure equalization. • Design? It's important to know if the transom/corner joint is a straight cut or has an overlapping joint. An overlapping joint provides better system strength and improves weather-tightness. • Kite Marked? Does the system have a kite mark? A kite mark indicates that the system has been tested and passed according to government test criteria. For example, a kite mark will state that the window has been tested according to EN 14351-1. Requirements specific to curtain walls as per CWCT TN8 (2000): • Movement accommodation? The curtain wall system must be able to accommodate building movements within the specified limit and have the necessary provision such as split mullion or edge clearance. The assistance of the structural engineer and the contractor’s data will clarify the system's ability to handle movements and its impact on weather-tightness. • Drainage system? It is important to understand the drainage system for both mullion and transom. Inadequate drainage of water can lead to decreased energy efficiency, draft, condensation, mould growth, corrosion, and compromised weather tightness. Drainage is necessary for safety and durability as per building codes. • Impact test? The curtain wall system must pass the impact test as per EN 14019:2016. The system may face impacts on lower floors due to human interaction, panel lifting, or installation. An impact may cause bending in the frame, creating gaps between the frame and glazing, leading to poor weather tightness. Opening Lights The inclusion of an opening light in a curtain wall can negatively impact the wall's structural stability and increase its cost and complexity due to the requirement of additional frames and hardware. The opening creates a weak point that may not be able to handle loads as well as the rest of the wall, and the additional components necessary for managing the tightness of the opening light and its interface with the curtain wall will affect the overall weather-tightness and wind resistance of the building. According to CWCT TN95,2015, testing of the curtain wall system should at a minimum include the interface detail between the window and the curtain wall. This is a drawback when compared to just curtain walls in terms of weather tightness and wind resistance. Requirements for Opening Lights (CWCT, TN8, 2000): • Hardware? The types of hardware used, such as window handles, hinges, and locks, should be compatible with the frame material, able to support the weight of the window, suitable for the environment, and able to withstand frequent use. Based on the hardware, the locking of the opening can affect the water tightness. For example, the locking mechanism with a tightly locked window provides better weather-tightness. • Style? The type of opening provided by the window can impact its weather tightness. Table 1 provides information on the types that offer better weather tightness. Table 1 (CWCT lectures, 2023) • Interface Design? The design of the interface is critical for weather-tightness. The glazing rebate must provide adequate edge cover to support the glass under wind load according to BS 6262. The window perimeter is typically sealed with a butt sealant joint, and the design of the sealant joint width must take into account the installation, movement capability, and weather-tightness requirements of the sealant, as well as deviations and dimensional changes in the window frame and opening. • Lab Test? The interface should undergo laboratory testing to assess its weather-tightness. BS EN 13049 provides information on the impact test for the window, while BS EN 6375 helps to understand the performance, operation, strength, and test requirements. The opening light should be tested together with the curtain wall and the performance of the water-tightness should be tested at 25% of the design wind load for satisfactory results, provided that the installation is carried out correctly. The information from the tests will help understand the weather-tightness in all conditions of the window. For instance, if the window experiences impact from human interaction, the test will provide data on deflection and indicate whether the weather-tightness is breached or not. Testing on Site Site testing and laboratory testing aim to achieve the same results, but on-site installation may introduce variables that affect the results obtained in the lab. This is often due to workmanship issues, such as incorrect component edge alignment, improper placement of gaskets, and incorrect application of sealants. The manufacturer and installer of a cladding system are responsible for ensuring proper installation to maintain the desired weather-tightness and wind resistance. • Hose Testing: A hose test involves using a compressor to create a strong water jet through a nozzle, aimed perpendicular to the plane of the cladding at a fixed distance of 300mm. This test is defined in Test Methods for Curtain Walling (CWCT, 1996). The hose test can be used on sloped cladding as long as the water jet is directed straight at the joint. However, if the goal is to observe water flow and drainage from cladding or roofing, the spray bar test may be a better option. The standard water pressure used in hose testing is 220kPa ± 20kPa. A flow of 22 ± 2litres/minute is achieved through a standard nozzle with a cone angle of 30 degrees. The nozzle is held 0.3m from the joint and the joint is inspected in 1.5m increments. Testing begins at the lowest joint and moves upward, covering all intersecting vertical joints before moving to the next horizontal joint. If water leakage is detected, all joints are masked with tape and tested one by one by moving the hose back and forth for 5 minutes. Once the source of the leakage is fixed, the area is retested. Each 1.5m test length is completed in 30 seconds, resulting in ten passes during the five-minute test. For opening lights, the water pressure from the nozzle may need to be decreased to 140kPa. If the test is passed, the pressure is increased by 20kPa and retested until the maximum pressure of 220kPa is reached. The distance between nozzle and joint should remain consistent. Spray bar test is a better option for testing this type of joint. Before installing insulation and rainscreen panels, it's appropriate to hose-test the backing wall and its interfaces for rainscreen walls. • Spray bar testing: This method, defined in BS EN 13051, uses a pipe with evenly spaced nozzles that produce a spray of water over the cladding system. Only a single row of nozzles should be used, and water should be allowed to flow down the face of the cladding. This test is ideal for open-jointed systems as it doesn't force water into the joints. Nozzles should be placed no more than 400mm apart and 250mm away from the cladding surface. Water is sprayed at a pressure of 2-3bar, with a flow rate of 5litres/minute/meter length of the spray bar. Spray bar should run for 30 minutes in each test location, and the internal surface should be observed for signs of leakage. • Cabinet testing: Test is based on guidelines in standards like BS 5368: Part 2, which defines parameters such as water flow rate and nozzle position and spacing. Test typically includes a cabinet that can be sealed to the cladding system (one face made up of the cladding), a device for pressurizing or depressurizing the cabinet, and a spray system (spray bar or a grid of nozzles). This test is suitable for doors and windows. Water is sprayed on the external face of the cladding and due to the pressure differences the water leaks where there is an opening. • Smoke testing: Test is used to detect air leaks through openings and curtain walls. Smoke is generated inside the building using a smoke generator or pencil, and a positive pressure environment is created using an HVAC system or external fans. The smoke will flow from positive pressure to negative pressure via gaps and openings. The smoke that escapes the building can be observed from the outside to determine the area of leakage. It's important to notify local emergency services and disable smoke alarms before conducting the test and remove dry lining in the locations being tested to prevent false results. • Thermography: Test uses infrared cameras to detect damp areas or air infiltrations by detecting temperature differences in leak areas. It can be used both internally and externally, and infiltration may be detected behind dry linings. However, test doesn't provide precise values and is limited by • Emissivity of the surface (which may vary from one part of the surface to another); • Distance from the surface to the camera; • Temperature of the air between the camera and the surface; • Relative humidity of the air between the camera and the surface; • Temperature of the environment facing the surface; • Angle at which the surface is being viewed. --- *Originally published on [dj](https://paragraph.com/@dj-2/weathertightness)*