Most elevations show cladding as a clean outer skin. In a wet, windy climate, that skin will get soaked, and some water will get past it. The real design question is what happens next.
A short research digest from 1963 answered that question better than many modern details do. Architects who need a facade built as drawn often bring in an envelope specialist, and Pine & Harbor takes on that role for design teams north of Boston and into Maine. In that climate, the gap behind the cladding often decides whether a facade ages well or fails early.
What Did a 1963 Digest Get Right About Rain?
In April 1963, G. K. Garden of Canada’s National Research Council published Canadian Building Digest 40. Its subject was rain penetration and how to control it. Its starting point was blunt.
Rain gets in when three things meet: water on the wall, openings for it to pass, and forces to move it inward. Remove any one of the three and leakage stops. Garden then argued that two of the three are hard to remove for long.
A designer cannot keep a wall from getting wet. Wide overhangs help on low buildings, but they rarely protect tall walls in high winds. Openings are just as stubborn. Sealant joints age, and building movement keeps flexing them, so a perfect seal rarely lasts. That leaves the forces, and this is where design has the most control.
Which Forces Push Water Through a Wall?
The digest names four forces. Each one calls for a different response at the facade:
- Kinetic energy. Wind drives raindrops through larger openings. Baffles, battens and interlocking joints block that direct path.
- Capillary suction. Very fine pores, under about 0.01 millimeter, hold water so tightly they seldom cause leaks. Wider cracks and unbonded joints are the real risk.
- Gravity. Water runs down and inward through any sloping passage. An air space behind the wet face stops that flow.
- Air pressure difference. Wind pressure can pull water through an opening. When heavy water covers a wall, openings up to 3/8 inch can be bridged and forced through by small pressure differences.
The first three respond to good geometry. The fourth is the one that defeats sealed facades. It is also the one the rainscreen principle was built to handle.
How Does Pressure Equalization Change the Design?
Garden’s answer was an air chamber behind the outer layer, vented to the outside. If the air pressure in the chamber always matches the pressure on the face, nothing pushes water inward. The outer layer becomes what he called an “open rain screen.”
That idea moves the critical line of the wall. The air barrier must sit inward of the cavity, where it stays dry and resists the wind load. The cladding no longer has to be watertight. It only has to shed most water and shield the cavity.
For designers, that is freeing. The digest notes that joint movement and small flaws become less critical. Sealants last longer because the screen shades them from the sun. The cladding is also relieved of much of the normal wind load, which the wall behind it must carry instead. Open joints, as seen in many timber facade projects, can be a deliberate part of the look.
Where Should the Cavity Be Closed Off?
Wind pressure is not even across a building. The digest notes that pressures range from positive on the face to suctions several times greater. They change fastest near the ends of walls, and air then flows through an open cavity and can carry water with it.
The fix is to divide the cavity into compartments. Garden offered spacing as a suggestion, absent better data:
| Location on the Wall | Suggested Cavity Closure |
| Building corners | Always closed, so air cannot wrap the corner |
| 20-foot perimeter zone | Closures at no more than 4-foot centers |
| Central portion of the wall | Closures at 10- to 20-foot centers |
These figures are over six decades old, and manufacturers now publish their own installation details. The logic still holds, though. Corners and edges need the most attention, and that belongs on the drawings.
What Does This Mean for Cladding In New England?
Energy rules now shape the wall behind the screen too, part of a wider turn toward building science as design. The US Department of Energy lists New Hampshire’s residential energy code as the 2018 IECC. It took effect on January 1, 2023, with mandatory statewide enforcement. Commercial buildings follow the 2018 IECC and ASHRAE 90.1-2016, with state amendments.
As walls get thicker, the cavity, the trim and the window returns all need deliberate design. Pine & Harbor says it holds several manufacturer credentials that bear on this work:
- James Hardie: ranked among the top 1% of James Hardie installers in New Hampshire
- LP SmartSide: certified installer of engineered wood siding
- CertainTeed: SidingMaster Pro and ShingleMaster Premier contractor
Its co-founder Craig Cohen brings more than 25 years of hands-on experience on complex projects.
Design Checks Before the Elevations Are Final
A few questions are worth settling before a facade goes out to bid:
- Where does the air barrier sit, and does it stay dry behind the cavity?
- How is the cavity vented to the outside air?
- Where do compartment closures fall, especially at corners and edges?
- How do flashings lead water out at the base and above openings?
- How do windows seal back to the air barrier rather than the cladding?
Drawing the Screen and the Wall Separately
Garden’s digest leaves designers with one clear habit. Draw the screen and the wall as two separate layers with separate jobs. The screen shapes the look and takes the weather. The wall behind it holds the air and the insulation. When both are drawn with care, the facade can be as expressive as the design calls for.
Frequently Asked Questions
What Is the Rainscreen Principle?
It is a way of controlling rain by placing a vented air space behind the cladding. Pressure in that space matches the outside air, so wind cannot push water inward. The wall behind stays dry even when the outer layer gets wet.
Where Does the Air Barrier Go In a Rainscreen Wall?
It sits inward of the vented air space, behind the cladding. There it stays dry and resists the wind load on the building. Minor air leakage through a dry air barrier will not bring rain with it.
Do Open Joints Let Rain Into the Building?
Some rain passes the outer layer by design. The cavity, flashings and a dry air barrier keep it from reaching the interior. Joint layout still matters, especially near corners.
Why Do Corners Need Extra Attention In a Rainscreen?
Wind suction is strongest near the edges of a building. Air can rush around a corner through an open cavity and carry water with it. Closing the cavity at corners prevents that.
