Telescopic Underfloor Vents Explained: When & Why They Are Used
When external ground level and an underfloor void are at different heights, a direct airbrick opening may not line up with the space that needs ventilation. Telescopic and ducted underfloor vent systems are designed to bridge that level difference while maintaining an airflow path. This guide explains when these components are considered and how they relate to brick ventilation accessories.
Why a Direct Airbrick Is Sometimes Not Enough
A suspended floor void may sit above or below the external airbrick course. Raised paving, deep wall construction or extension details can make a straight-through opening impractical.
What Does a Telescopic Vent Do?
A telescopic vent creates an offset path through the wall so the exterior opening can connect to the underfloor void at a different level. Extensions can alter the effective height to suit the wall detail.
Planning the Air Path
The full route needs to remain open: exterior airbrick, duct or telescopic section, internal outlet and any openings through sleeper walls. A single blocked section reduces the benefit of the system.
Ground and Paving Levels
Keep the external opening clear of finished ground and paving. Landscaping changes made after construction can cover vents, so final levels should be considered in the design.
Free Ventilation Area
As with an airbrick, the system should provide the free area required by the ventilation design. Bends and grilles can affect airflow, so use compatible components and product data.
Extensions Over Existing Vents
When an extension encloses a previously external wall, existing airbricks may no longer discharge to outside. A new ducted route may be needed to carry ventilation through the extension to an external face. This should be designed before floors are completed.
Shop Related Brick Vents
JJ Building Materials stocks airbrick, weep and peep vent accessories. Use compatible products required by the project detail and check availability for any additional ducting components.
FAQs
What is a telescopic air vent?
It is a ducted component that offsets the ventilation path between an external opening and an internal underfloor void.
Do I need one for every airbrick?
No. It is used where the wall and level arrangement requires an offset route.
Can an extension block existing vents?
It can, which is why the ventilation route needs to be redesigned when building over or against existing airbricks.
Does duct length matter?
The complete system should meet the required ventilation performance. Use the specified compatible components.
Can paving cover the external grille?
No. The ventilation opening must remain clear and effective.