A drainage gap is the physical air space maintained between exterior cladding and the water-resistive barrier in a rain screen wall system, typically created using furring strips or specialized spacer products, allowing water to drain freely and air to circulate for drying rather than the cladding sitting in direct contact with the barrier beneath.
This intentional physical separation distinguishes a true rain screen assembly from a more basic wall system where cladding is installed directly against the water-resistive barrier without this enhanced drainage and drying capability.
Typical drainage gap dimensions range from a fraction of an inch to about three-quarters of an inch, depending on the specific system and product manufacturer recommendations, with the gap needing to remain clear and unobstructed to function effectively.
What Does a Drainage Gap Involve?
- Furring strips or specialized spacer products
- A consistent air space typically a fraction of an inch to three-quarters of an inch
- Openings at top and bottom for airflow and drainage
- Unobstructed space free from debris or improper fastening
Why Is a Drainage Gap Important?
The physical air space a drainage gap provides gives water an actual pathway to drain freely and allows air circulation for drying, meaningfully improving moisture management compared to a wall assembly without this feature, particularly valuable in climates with significant wind-driven rain exposure. This enhanced performance is the core advantage that distinguishes a true rain screen system from more basic wall construction.
Ensuring the drainage gap remains genuinely open and unobstructed throughout installation, avoiding fastening patterns or debris accumulation that could block airflow, is essential to actually realizing this system’s intended performance benefits rather than simply adding cost without functional improvement.
Drainage Gap vs. Drainage Plane
A drainage gap is a physical air space specifically created in rain screen assemblies. A drainage plane is the surface itself, typically the water-resistive barrier’s face, that directs water downward, a concept applicable even in simpler wall systems without a dedicated air gap.