Installation Instructions
Installation guide for the Active Weep Vent, with spacing based on NHBC guidance, plus fitting notes for the Active Trickle Vent.
Installation Overview
Spacing
Not sure which weep vent to use? See our weep vents compared guide.
- • DPC level: one vent every 900mm (Approved Document C, para 5.5(c))
- • Above openings: a maximum of 450mm apart, with at least two per opening (NHBC guidance)
- • Optional higher row: about 2.1m up, also at 900mm centres. We're testing this layout now, so this guidance may change.
Want the total for your building? The weep vent calculator applies these spacing rules to your walls and openings and shows where each vent goes.
Installation Types
- • New Build: Place in the perp joints during bricklaying
- • Retrofit: Replace existing weep vents or chase out new perp joints
Step-by-Step Installation Guide
New Build Construction
Step 1: Planning Vent Positions
Mark out vent positions:
- One vent every 900mm along the DPC (Approved Document C, para 5.5(c))
- Over openings (lintels and cavity trays): a maximum of 450mm apart, with at least two per opening (NHBC guidance)
- Ensure vents align with cavity space
Step 2: Installation During Bricklaying
Simply place Active Vent in the perp joints during bricklaying:
- Position vent flush with external wall face
- Ensure full contact with cavity
- Bed in mortar as normal
- Check vent is level and secure
Step 3: Optional Higher Row
You can add a second, higher row of vents:
- Fit it at about 2.1m, also at 900mm centres (roughly one vent per 2m² of wall)
- Low vents help clear the moisture that sits low; high vents help clear the humidity that lingers higher up
- We're testing this layout now, so this guidance may change.
Retrofit Installation
Required Tools
- Plugging chisel or mortar chaser
- Lump hammer
- 8mm diameter x 100mm (min) mortar rake
- Safety equipment (goggles, dust mask, gloves)
- Spirit level
Step 1: Preparation
Identify existing weep vents or mark new positions:
- Locate existing weep vents or perpend joints
- Mark positions following building regulations
- Check for cables or pipes before cutting
- Ensure safe access to work area
Step 2: Chasing Out and Cleaning
Carefully create or clean openings (the Weep Vent is 10 × 65 × 100mm, so no drilling is needed):
- Chase or chisel out the perpend joint
- Use mortar rake to clean debris from opening
- Ensure opening reaches cavity (minimum 100mm deep)
- Take care not to damage DPC, cavity trays, or lintels
- Clear all dust and debris from opening
Step 3: Vent Installation
Insert and secure Active Vent:
- Push vent fully into cleaned opening
- Ensure vent sits flush with wall surface
- Check vent is level using spirit level
- Apply small amount of sealant if needed for secure fit
Important Safety Considerations
- Always wear appropriate safety equipment
- Check for electrical cables and water pipes before cutting or drilling
- Take extreme care not to damage DPC or cavity trays
- Work from stable platform when installing at height
- Consider professional installation for complex retrofits
Active Trickle Vent
- Drill a 16mm hole through the window frame
- Fit one section from outside and one from inside, then click them together
- We recommend at least two per window
Advanced Installation Techniques
Optional Two-Row Layout
A layout we are currently testing:
Installation Pattern:
- 1. Install vents at DPC level at 900mm centres (Approved Document C)
- 2. Add a second, higher row at about 2.1m, also at 900mm centres
- 3. That works out at roughly one vent per 2m² of wall
- 4. We're testing this layout now, so this guidance may change.
Targeting Problem Areas
Additional vents for specific moisture issues:
High-Risk Areas:
- • North-facing walls (reduced drying)
- • Near bathrooms/kitchens
- • Areas with visible damp issues
- • Corners and cold bridges
Installation Tools & Accessories
Essential Tools
- • Plugging chisel or mortar chaser
- • 8mm x 100mm mortar rake
- • 16mm drill bit (Trickle Vent only)
- • Spirit level
Safety Equipment
- • Safety goggles
- • Dust mask
- • Work gloves
- • Ear protection
Accessories
- • Sealant (if needed)
- • Measuring tape
- • Chalk line for marking
- • Vacuum for cleanup
Fitting kits coming soon
Shop Active Weep Vents →
Further reading
- Series guide Getting the Most from Active Vent
A practical hub for choosing, installing, inspecting and maintaining Active Vent, including how the removable, inspectable insert lets you keep a cavity clear over the long term.
- Technical Guides Understanding Modern Ventilation Requirements
Why airtight modern homes need better moisture control than ever, what good cavity wall ventilation looks like, and how to avoid trapping damp in your walls.
- Awaab's Law Awaab's Law and Private Landlords: Renters' Rights Act
Awaab's Law does not yet apply to private landlords in England. What the Renters' Rights Act 2025 provides, what is undecided and duties that apply now.
Useful pages
- Active Weep Vent →
The wind-powered weep vent with a removable insert you can inspect and keep clear.
- Active Trickle Vent →
A wind-powered trickle vent for window frames. No fan, wiring or running costs.
- Weep vent calculator →
How many weep vents your home needs, using Approved Document C and NHBC spacing, and what they cost.
- For developers and builders →
Specifying an inspectable, wind-powered cavity vent on new-build projects.
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