Windows, Doors & Exterior Cladding

Windows, doors, and exterior cladding form the visible skin of a house — but they do far more than provide appearance. Together with the water-resistive barrier (WRB), they create the building's weather barrier — the system that keeps rain, wind, and air infiltration out while allowing moisture vapor to escape. Improper installation of any of these components leads to water intrusion, the single most common and costly defect in residential construction.

Window Types by Operation

• Double-hung: Two sashes that slide vertically. The most traditional residential window. Both sashes tilt inward for cleaning.
• Casement: A single sash hinged on the side, swinging outward with a crank handle. Excellent air sealing (the sash presses against the frame when closed).
• Sliding: Sashes slide horizontally. Common for wide openings and patio access.
• Awning: Hinged at the top, swinging outward at the bottom. Can be left open during rain.
• Fixed (picture): Non-operable; used for large viewing areas and is the most energy-efficient (no operable seals to leak).

Performance Ratings (NFRC Label)

All residential windows carry a National Fenestration Rating Council (NFRC) label with standardized performance ratings:

• U-factor: Measures heat transfer through the entire window assembly (glass + frame). Lower is better. Range: 0.20–1.20. Energy Star requires U ≤ 0.30 in northern zones, ≤ 0.40 in southern zones.
• Solar Heat Gain Coefficient (SHGC): The fraction of solar radiation that passes through the window. Range: 0–1. In cooling climates, lower SHGC is better (reduces solar heat gain). In heating climates, higher SHGC on south-facing windows can provide beneficial passive solar heating. Energy Star: SHGC ≤ 0.25 in southern zones, ≤ 0.40 in northern zones.
• Visible Transmittance (VT): The fraction of visible light passing through. Higher VT means more natural daylight.
• Air Leakage (AL): Cubic feet of air per minute per square foot of window area. Lower is better. Maximum 0.30 for Energy Star certification.

Glass Technologies

Modern residential windows use multiple glass technologies to achieve high performance:

• Insulated glass units (IGUs): Two or three panes of glass with sealed air spaces between them. Double-pane is standard; triple-pane is common in cold climates.
• Low-emissivity (Low-E) coating: A microscopically thin metallic coating on the glass that reduces radiant heat transfer. Hard-coat Low-E reflects both heat directions; soft-coat (sputtered) Low-E can be tuned for solar control (reflecting solar heat out) or for passive solar (allowing solar heat in while retaining interior heat).
• Gas fill: Argon or krypton gas between panes (instead of air) reduces convective heat transfer. Argon is standard; krypton is used in thinner triple-pane assemblies.
• Warm-edge spacers: Insulating spacers between glass panes (replacing aluminum) to reduce heat conduction at the glass edge and prevent condensation.

• Exterior entry doors: Solid wood, fiberglass (most common — durable, insulating, and can mimic wood grain), or steel (most economical, highest security, but prone to dent and limited insulation). All exterior doors require a threshold and weatherstripping.
• Sliding patio doors: Large glass panels; one fixed, one slides. Economical and space-efficient but historically less air-tight than hinged doors.
• French doors: Paired hinged doors with glass panels. Attractive but require careful weatherstripping and threshold details.
• Garage doors: Insulated or uninsulated steel or aluminum. Wind-rated doors are required in hurricane zones. Garage doors with windows have lower impact resistance.

The water-resistive barrier (commonly called house wrap) is a critical layer in the wall assembly. It is installed over the wall sheathing and behind the exterior cladding (siding). The WRB must:

• Resist liquid water from reaching the sheathing and framing
• Allow water vapor to pass through (breathable) so that any moisture in the wall cavity can dry to the exterior
• Serve as an air barrier (when seams are properly taped)

Common WRB types:

• Plastic housewrap: Tyvek (DuPont), Typar (Fiberweb), or similar spun-bonded polyolefin sheets. Lightweight, durable, and highly permeable to vapor. The most common WRB in residential construction.
• Asphalt-saturated felt (#15 felt): The traditional WRB. Less expensive than housewrap but heavier, more difficult to install, and less vapor-permeable. Still code-compliant and widely used.
• Fluid-applied WRB: Liquid coatings sprayed or rolled onto the sheathing, creating a seamless WRB. Increasingly used in high-performance and commercial-residential construction.

Installation principles:

• Install from bottom to top, with upper layers overlapping lower layers (shingle-lap principle — water running down the wall flows over each lap, not behind it)
• All seams taped with manufacturer-approved tape
• Integrate with window and door flashing (see below)
• Maintain a minimum 2-inch overlap at horizontal seams and 6-inch overlap at vertical seams

Proper integration of windows and doors with the WRB is the most important waterproofing detail in the wall. The flashing sequence follows the shingle-lap principle:

Window flashing sequence (flanged window):

1. Sill flashing first: Apply a strip of self-adhesive flashing tape (or peel-and-stick membrane) across the rough opening sill, extending 6 inches up each side (jamb). The sill tape runs under the WRB below the window.
2. Install the window: Set the window in the rough opening on a bead of sealant. The window's nailing flange (integral flange) laps over the WRB at the sides and bottom.
3. Jamb flashing: Apply flashing tape over the nailing flange at each jamb, bridging from the window to the WRB.
4. Head flashing: Apply flashing tape across the top of the window, overlapping the jamb tapes. The head tape goes under the WRB above the window.
5. Seal the WRB above: The WRB above the window laps over the head flashing tape.

The result: any water that penetrates the cladding encounters the WRB and is directed downward. If water reaches the window, it flows over the head flashing, down the jamb flashing, and out over the sill flashing — never entering the wall cavity.

Common flashing errors (leading to water damage):

• Reverse lapping (upper layer tucked behind lower layer — directs water into the wall)
• Missing sill flashing (water pools on the rough sill and enters the wall)
• Gaps in the flashing tape (untaped corners create water entry points)
• Relying solely on caulk (caulk fails within 5–10 years; flashing lasts the life of the building)

The exterior cladding is the outermost layer of the wall. It provides the building's appearance and serves as the primary weather barrier — the first defense against rain and wind. However, all cladding systems eventually leak to some degree, which is why the WRB behind the cladding is essential.

Common residential cladding types:

• Vinyl siding: The most common residential cladding in the U.S. Economical, low maintenance, and available in many colors and profiles. Installed with nails in slotted holes (allowing thermal expansion — nails should not be driven tight). Not structural; relies entirely on the WRB for water management.
• Fiber cement siding (e.g., Hardie Board): Cement, cellulose fiber, and sand formed into planks, panels, or shingles. Extremely durable, fire-resistant, termite-proof, and dimensionally stable. Can be painted. Heavier and more expensive than vinyl.
• Wood siding: Traditional clapboard, board-and-batten, or shingle siding. Beautiful and classic but requires regular maintenance (painting or staining every 5–10 years). Susceptible to rot if not properly maintained and flashed.
• Brick veneer: A single wythe (layer) of brick attached to the wood frame through metal ties screwed to the studs. The brick is not structural — it hangs on the frame. A 1-inch air space (drainage cavity) between the brick and the WRB is essential for drainage and drying. Weep holes (openings in the mortar at the base of the brick) allow water to drain from the cavity. Missing weep holes and filled drainage cavities are common installation errors that cause water damage.
• Stucco (traditional or EIFS): Traditional stucco is a Portland cement plaster applied over metal lath. EIFS (Exterior Insulation and Finish System) is synthetic stucco over rigid foam insulation. Both require careful flashing details. EIFS gained a poor reputation in the 1990s due to water intrusion failures from missing flashing and drainage — modern drainable EIFS with a drainage plane behind the foam has largely resolved these issues.
• Stone veneer: Natural thin stone or manufactured stone adhered to the wall with mortar over metal lath and a WRB. Requires a drainage plane behind the mortar.