Tempo:
distributed with at least 25 per cent of the vent area located at the bottom of the space and at least 25 per cent at the top.
insulation is installed on top of the roof sheathing (and below the roof covering), the space above the ceiling is not ventilated.
If batt insulation is placed between the roof-ceiling joists in a low-slope roof, a ventilated space of at least 63 mm (21⁄2 in.) must be provided between the top of the insulation and the underside of the roof sheathing. This can be achieved by placing 38 × 64 mm (2 × 3 in. nominal) cross-purlins over the top of, and at right angles to, the roof-ceiling joists. The cross-purlins may be shimmed to provide the required roof slope (see Figure 25 on p. 57). If rigid
Vents must not allow the entry of rain, snow or insects. If a vent is a potential source of moisture entry, a baffle is required to reduce air flow. Corrosion-resistant metal or plastic materials should be used for vents and to screen ventilator openings. Except for very small attic spaces, attics require an access hatch. The area of the hatch must be at least 0.32 m2 (3.4 sq. ft.) with no dimension less than 500 mm (20 in.).
93 High-level roof ventilation Ridge vent
Gable vent
wind flow
airflow
airflow
insulation is installed on top of the roof sheathing (and below the roof covering), the space above the ceiling is not ventilated.
If batt insulation is placed between the roof-ceiling joists in a low-slope roof, a ventilated space of at least 63 mm (21⁄2 in.) must be provided between the top of the insulation and the underside of the roof sheathing. This can be achieved by placing 38 × 64 mm (2 × 3 in. nominal) cross-purlins over the top of, and at right angles to, the roof-ceiling joists. The cross-purlins may be shimmed to provide the required roof slope (see Figure 25 on p. 57). If rigid
Vents must not allow the entry of rain, snow or insects. If a vent is a potential source of moisture entry, a baffle is required to reduce air flow. Corrosion-resistant metal or plastic materials should be used for vents and to screen ventilator openings. Except for very small attic spaces, attics require an access hatch. The area of the hatch must be at least 0.32 m2 (3.4 sq. ft.) with no dimension less than 500 mm (20 in.).
93 High-level roof ventilation Ridge vent
Gable vent
wind flow
airflow
airflow
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