Traditionally, airtightness happens inside. But applying Passive Purple External to the outer face of your timber frame (on the sheathing board) offers massive advantages:

1. Instant Weather Protection
   Timber hates water. By spraying Passive Purple External early in the build program, you make the frame water-resistant and wind-tight immediately. This protects your valuable timber structure from the elements while internal works begin
2. Zero "Flapping"
   Standard breather membranes are stapled on. In high winds, they flap, tear, and pull away from the fixings.Passive Purple External adheres fully to the OSB or sheathing board. It becomes part of the wall. It cannot flap, it cannot tear, and it effectively resists wind pressure loads.
3. Passivhaus Performance
   Achieving Passivhaus standards requires a continuous seal. External
   application allows you to wrap the entire building envelope without being interrupted by internal floor zones or partition walls.
   
   
   
   

You need your timber frame to "breathe" to prevent rot.

• High Breathability: Passive Purple External is highly vapour open. It allows moisture trapped within the timber structure to escape outwards, keeping your frame dry and healthy.
• Fire Safety (Class B): Unlike standard paper membranes which can be flammable, Passive Purple External offers Class B-s1, d0 fire protection. It upgrades the safety of your facade
  assembly.

Passive Purple External replaces your traditional Tyvek-style sheet.

1. The Board: Ensure your external
   sheathing (OSB, Plywood, or Cement Particle Board) is clean.
2. The Joints: Bridge the panel joints with Passive Purple Brush (or IM Fleece Tape if preferred) to handle movement.
3. The Spray: Spray the liquid membrane over the entire external face.
4. The Result: A seamless, UV-stable,
   purple (or black) skin that acts as your primary weather and airtightness line.

Construction delays happen. Passive Purple External is UV Stable, meaning it can be left exposed to the sun for longer periods than many standard membranes without degrading. Your timber stays protected even if the cladding installation is delayed.