What Is a Rainscreen Behind Siding?
A common misconception about exterior siding is:
“If water gets behind it, something has failed.”
Modern walls are often designed more realistically.
They assume that some moisture may get past the outer cladding.
Then they give that moisture a controlled way to drain.
That is the basic idea behind a:
Rainscreen.
Building Science Corporation describes rainscreen systems as wall assemblies where exterior cladding is separated from the drainage plane so incidental water can drain and, depending on the system, the space can also promote drying.
The Siding Is the First Layer
The exterior cladding’s first job is to shed most rain.
This could include:
- Vinyl
- Fibre cement
- Other siding systems
But cladding is not always intended to be a perfect waterproof barrier.
Building-science research specifically identifies vinyl siding as an example of a drained wall system.
What Happens Behind the Siding?
A properly designed wall may include:
- Exterior siding
- A drainage space
- A water-resistive barrier
- Wall sheathing
- The rest of the wall assembly
If incidental moisture gets behind the siding, gravity helps move it downward toward an appropriate exit.
Why Is the Gap Important?
The space can perform several functions.
It can:
- Allow drainage
- Reduce capillary movement
- Create separation between wet cladding and the wall
- Support drying depending on design
Building-science research has shown that even small continuous drainage spaces can allow water to move downward effectively.
Is Housewrap the Same as a Rainscreen?
No.
They work together but perform different jobs.
Housewrap or WRB
Creates the drainage plane that helps resist water moving farther into the wall.
Rainscreen/drainage space
Provides separation and a path for moisture to move.
This is why siding installation is more than fastening panels to plywood.
Do All Siding Systems Need the Same Gap?
No.
Different cladding systems have different:
- Installation requirements
- Built-in drainage characteristics
- Manufacturer details
For example, some vinyl-siding assemblies inherently provide drainage space because of the profile of the siding itself.
Always follow the selected product’s requirements.
Windows and Doors Are Critical
A drainage system only works if moisture is correctly redirected around:
- Windows
- Doors
- Penetrations
Flashing needs to connect those openings back to the wall’s drainage plane.
Why This Fits Envirotech’s Approach
Envirotech installs siding and customized aluminum exterior work, so the project needs to consider more than the final colour homeowners see.
Great Siding Is Not Only About Keeping Rain Off the Front. It Is About Managing the Water That Gets Behind It Too.
Planning new siding? Envirotech Exteriors can evaluate the wall, flashing, drainage details, trim, and cladding as one exterior system.