Boiler Fault Finder

Notching and Drilling Requirements

Notching and Drilling requirements in joists when 1st fixing When notching or drilling structural timbers, it is crucial that the holes/notches are made in such a way that does not compromise the integrity of the structure. On new build sites and large developments, any installer intending to notch/drill holes in structural timbers must first seek permission from the architect, structural engineer and/or supervising officer for the building. Notches and holes in simply supported floor joists should be cut no deeper than 1/8 of the depth of the joist. They should not be cut closer to the support than 0.07 times the span, nor further away than 0.25 (1/4) of the span. It is essential that structural members are not weakened by indiscriminate notching and boring. In this respect, both the size and positioning must be in accordance with the diagrams shown below. Requirements for notching traditional joists: Notching traditional joists For a traditional joist (150mm deep x 50mm wide and spanning 3000mm): Minimum distance from supporting wall = 3000mm x 0.07 times the span = 210mm Maximum distance from supporting wall = 3000mm x 0.25 times the span = 750mm Maximum depth of notch = 150mm / 8 = 18.75mm Therefore, notching may occur between 210mm and 750mm from the supporting wall, and notches should be no deeper than 18.75mm. Requirements for drilling holes through traditional joists: Drilled holes should be no greater in diameter than ¼ of the depth of the joist. They should be drilled on a neutral axis and should not be less than three diameters apart, measured from centre to centre. Drilled holes should be located in the area between 0.25 and 0.4 times the span of the joist from the support. Drilling holes through traditional joists For a traditional joist (150mm deep x 50mm wide and spanning 3000mm): Minimum distance from supporting wall = 3000mm x 0.25 times the span = 750mm Maximum distance from supporting wall = 3000mm x 0.4 times the span = 1200mm Maximum hole diameter = 150mm / 4 = 37.5mm Therefore, holes can be drilled at the neutral axis between 750mm and 1200mm from the supporting wall. The maximum hole diameter should not exceed 37.5mm and holes should not be located less than three diameters apart (centre to centre), meaning 37.5mm holes should be separated. Engineering joists Buildings that incorporate timber “I” joists (engineering joists) allow for more flexible drilling of holes for pipework. I joists incorporate 38mm knockouts (dependent upon the manufacturer), and also allow for larger holes to be drilled through the joists. The same rule applies when drilling through I joists as for drilling traditional joists where horizontal measurements between holes are concerned. However, as the strength of I joists is in the flange, these joists are not suitable for notching, as notching the flange will damage the structure of the joist, which will have a detrimental effect on its strength. The size and positioning of holes drilled through I joists must be in accordance with the diagram shown below. Example: (Refer to previous diagrams for clarity):…

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