Cavity wall bridging ducts are produced in red terracotta and a variety of lengths to suit different wall thicknesses. The standard size of ducts is 200mm; other sizes are available on request.
| Horizontal pattern |
Inclined pattern one course rise (75mm rise) |
Inclined pattern two course rise (150mm rise) |
| List No. 400-402 |
List No. 407-409 |
List No. 403-405 |
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| Type |
List no. |
Size |
Effective length (200mm) |
Horizontal |
400
401
402 |
215 x 65mm
215 x 140mm
215 x 215mm |
100 - 300mm in 25mm progressions |
Inclined one course rise |
407
408
409 |
215 x 65mm
215 x 140mm
215 x 215mm |
150 - 300mm in 25mm progessions |
Inclined two course rise |
403
404
405 |
215 x 65mm
215 x 140mm
215 x 215mm |
150 - 300mm in 25mm progressions |
Typical installations
The use of rectangular hole airbricks and inclined ducts as shown provides maximum ventilation and eliminates rain penetration.
Summary of minimum provision
Ventilation:
- Habitable rooms - background ventilation: 4000mm²
- Kitchens - background ventilation: 4000mm² or one air change per hour by fan
Combustion air
All combustion appliances need air to work efficiently and in many instances it is compulsory to provide permanent open background ventilation. For further information on minimum ventilation requirements please refer to Approved Document ‘J’ 2002.
Extendable cavity wall bridging duct (list no. 420)
The “periscope” type design allows the suspended floor to be at or below surrounding ground level, thereby saving on brickwork in construction, and gives vertical adjustment for 3 to 4 brick courses. The lower end is protected by a 9mm grille. It provides a clear airway which cannot be blocked by mortar and will bridge cavities from 50 to 100mm. The sleeve joint may besealed with tape if necessary.