The 1986 edition of IS 11818 outlines a laboratory procedure for evaluating the air permeability of fixed, non-opening joints in external building walls. It assesses air leakage under controlled pressure differences, including after simulated ageing, providing critical data for engineers and researchers ensuring building envelope airtightness and energy conservation.
Overview
The 1986 edition of IS 11818 outlines a laboratory procedure for evaluating the air permeability of fixed, non-opening joints in external building walls. It assesses air leakage under controlled pressure differences, including after simulated ageing, providing critical data for engineers and researchers ensuring building envelope airtightness and energy conservation.
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Contents
Structure
IS 11818 defines the laboratory protocols for testing the air permeability of joints installed between building components, addressing the effects of dimensional tolerance variations. Clause 8.1 specifies testing joints under four scenarios: nominal width with correct alignment, minimum width aligned, maximum width aligned, and variable width with perpendicular misalignment within limits. This ensures the joints' functional performance under practical installation deviations, verifying durability and sealing effectiveness. Typical parameter ranges include nominal joint widths as per design, minimum widths approximately 75% of nominal, maximum widths about 125% nominal, and misalignment tolerances of a few millimeters.
This standard is primarily intended for assessing air permeability of joints in windows and door assemblies. It incorporates references to related International Standards (ISO 6613 and ISO 6589) detailing test methodologies. The scope includes testing air leakage at joint intersections under controlled differential pressures, using devices capable of rapid pressure variation. The air permeability is calculated as the volumetric flow rate divided by specimen area, guiding the procedure rather than prescribing design criteria.
IS 11818 adopts terminology consistent with ISO 6589, defining key terms such as air permeability—the volumetric airflow through a unit area under a specified pressure difference—and differential pressure devices that enable controlled, rapid pressure changes. It clarifies the concept of joint intersections critical for leakage assessment and refers to ISO 6613 for comprehensive definitions and test methods.
The testing setup requires apparatus capable of generating and controlling rapid differential pressure changes up to typically 600 Pa or higher (Clauses 5.3 and 5.4). Airflow measurement devices must accurately quantify air volume entering or leaving the test chamber. Tests involve applying positive and negative pressures by reversing joint orientation, recording airflow to the nearest 0.1 cubic meter per hour, and reporting the higher values measured during increasing and decreasing pressure phases. Results are expressed per meter of joint length, per junction, or per unit surface area where applicable, alongside detailed reporting of apparatus, installation, ambient conditions, extraneous leakage, and ageing cycles.
Joints must be installed between authentic components designed to withstand test pressures without performance degradation, with adjacent surfaces mimicking realistic conditions including irregularities. For positive differential pressure tests, the joint's external surface forms part of the test chamber’s internal face; this orientation is reversed for negative pressure tests. Extraneous leakage not related to the joint is measured by sealing the joint and quantifying leakage at test pressures, using appropriate air metering equipment, with lab and chamber air temperatures recorded. Tests cover nominal, minimum, maximum joint widths, and misaligned conditions, with results corrected for extraneous leakage and plotted against differential pressure.
The standard mandates installing the joint between actual components to resist imposed pressures without harmful deformation, simulating real surface irregularities. Measurement and elimination of extraneous air leakage are required, with sealing of the joint during leakage measurement. Temperature monitoring of laboratory and chamber air is essential. Tests are conducted across various dimensional deviations and misalignments, ensuring replicable and reliable air permeability data.
The test involves mounting the joint specimen to resist deformation, applying differential pressures in controlled increments up to and beyond 600 Pa as needed, with rapid pressure transitions per Clause 5.3. Both positive and negative pressure tests are conducted by reversing joint orientation. Airflow is measured precisely, with corrections for extraneous leakage. Results are recorded to the nearest 0.1 cubic meter per hour, expressed per meter length or junction, and graphically plotted against pressure.
Differential pressure (94P) is defined as the difference between external and internal absolute pressures, positive when external exceeds internal. The procedure initiates with three positive pressure pulses increasing from zero to 110% of maximum test pressure (not less than 500 Pa), each maintained for at least three seconds. Subsequently, pressures increase stepwise (typically 50 to 600 Pa with increments), then decrease in reverse order. The equipment must enable rapid and precise pressure control, simulating realistic wind loads at the joint location.
Air permeability readings are recorded at each differential pressure to the nearest 0.1 m93/h, reporting the higher value from increasing and decreasing pressure cycles. Results are expressed by joint length, junction location, or unit surface area when known, with plots of permeability versus pressure included. Extraneous leakage corrections are applied. The test report must comprehensively document apparatus details, joint installation, ambient conditions, leakage measurement methods and values, sectional joint descriptions, test data, ageing cycles if any, testing organization and date, and include a validity statement restricting results to test conditions.
Reporting requires detailed documentation of air permeability at each differential pressure, expressing results per meter length or junction, with optional area-based values. Graphical representation of results against pressure is mandatory. The report must incorporate apparatus schematics, installation specifics, ambient and chamber temperatures, extraneous leakage methodologies and data, joint construction details with sections, test outcomes, test organization identification, dates, and descriptions of simulated ageing if performed. Explicit declarations on the conditions limiting result applicability are essential.
Frequently Asked
IS 11818 (1986) focuses exclusively on laboratory testing procedures for assessing the air permeability of joints in buildings and does not categorize or list specific joint types. The standard aligns with ISO 6589-1983 and emphasizes testing airtightness performance rather than joint classification. While general joint types in building envelopes include expansion, control, construction, movement, and sealant joints, IS 11818 is solely concerned with their air leakage testing methodology.
The standard defines differential pressure (94P) as the external absolute pressure minus the internal absolute pressure, positive when external pressure exceeds internal. Testing begins with three positive pressure pulses rising from zero to 110% of the maximum test pressure (not less than 500 Pa), each held for at least three seconds. Then, the pressure is incrementally increased in steps (e.g., 50 to 600 Pa) with durations of at least 10 seconds per step, followed by a reverse decrement sequence. Equipment must provide precise, rapid control of these pressures to simulate realistic conditions.
The testing requires a differential pressure measurement device such as manometers or pressure transducers to determine pressure differences across the joint surfaces. Air flow metering instruments, including flow hoods or calibrated sensors, measure volumetric air flow through the joint. A sealed test chamber replicates actual component installation and allows positive and negative pressure application. Sealing materials prevent extraneous leakage, and temperature sensors record ambient and chamber air temperatures to ensure test condition accuracy.
Test results are recorded at each differential pressure with precision to 0.1 m93/h, reporting the higher flow measurement from increasing and decreasing pressure cycles. Results are conveyed per meter length of joint, per junction location, or on a per unit surface area basis when joint distribution is known. Air permeability is graphed against differential pressure in the test report, which also includes detailed descriptions of the apparatus, joint installation, ambient conditions, leakage measurements, sectional joint diagrams, testing organization details, and ageing cycle information. A clear statement limits results’ validity to test conditions.
Yes, IS 11818 mandates the inclusion of simulated ageing of joints prior to air permeability testing to evaluate the effects of material degradation on airtightness. The standard requires testing joints after such ageing processes to reflect realistic service life conditions. Airflow is measured under differential pressure before and after ageing to assess durability and performance changes, ensuring the joint’s long-term effectiveness in maintaining airtightness.
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