Proper installation is the foundation of every high-performance aluminum casement window. Even the best-engineered system will underperform if fitted incorrectly — leading to air leaks, water intrusion, operational issues, and shortened service life. As a leading casement window manufacturer, ALPES has guided hundreds of installation teams worldwide. This guide walks you through every step of installing an ALPES aluminum casement window correctly, from pre-site preparation to final inspection.
Before any physical work begins, thorough planning prevents costly rework. Aluminum casement window installation differs from sliding or fixed windows in several ways — the sash hinges outward on one side, requiring precise plumb alignment of the jamb for smooth operation and even seal compression.
First, confirm that the delivered window matches the order — check the model number (e.g., C120, C113, or C116 from ALPES), dimensions, handing (left or right swing), and glass specification. Measure the rough opening in three places horizontally (top, middle, bottom) and three places vertically (left, center, right). The rough opening should be approximately 10–15mm wider and 10–15mm taller than the window unit to allow for shimming and leveling.
Pro Tip: Industry experience shows that the vast majority of installation problems trace back to measurement errors. Always measure twice and confirm the opening is square by checking diagonal measurements — they should match within 3mm.
Having the right tools on hand keeps the installation flowing smoothly. Essential items include:
For replacement installations, carefully remove the old window by cutting through sealant and fasteners. Clean the opening thoroughly — remove debris, old caulk, and protruding nails or screws. Inspect the rough opening framing for rot, structural damage, or out-of-square conditions and repair as needed before proceeding.
Apply a sill pan or flashing tape to the bottom of the rough opening, extending the tape up the jambs by at least 150mm. This creates a waterproof drainage plane that directs any water that penetrates the joint back to the exterior.
With at least two people (depending on window size), carefully lift the ALPES aluminum casement window unit and set it into the prepared rough opening. Center it horizontally and position it so that it is plumb in the opening. For outward-opening casement windows like the ALPES C120, C113, and C116 series, ensure the exterior flange or nailing fin sits flush against the exterior wall surface.
This is the most critical step for casement windows. Place shims at the bottom corners and at intermediate points along the sill to support the window's weight. Use a spirit level on the head jamb and side jambs to verify the frame is perfectly level and plumb. Check the diagonals for square.
For custom casement window installations, pay special attention to the hinge-side jamb — it must be perfectly plumb for the sash to swing freely and seal evenly along its entire perimeter. Misalignment here leads to binding, uneven weatherstripping compression, and hardware stress.
Once the frame is perfectly plumb, level, and square, fasten it to the rough opening. Fastener type and spacing depend on the wall construction:
Always fasten through shim points to prevent frame distortion. As you drive each fastener, periodically recheck plumb, level, and square — the act of fastening can shift the frame. Do not over-tighten fasteners, as this can bow the aluminum profile.
After securing the frame, fill the gap between the window frame and the rough opening with low-expansion insulating foam or mineral wool insulation. For foam application, use a low-pressure polyurethane foam specifically formulated for windows and doors — high-expansion foams can bow the frame. Apply foam in layers and trim excess once cured.
Apply exterior flashing tape over the nailing fin or flange, starting from the bottom sill, then the sides (overlapping the sill flashing), and finally the head (overlapping the side flashing). This shingle-style approach ensures water flows down and out, not inward.
Apply a continuous bead of exterior-grade silicone or polyurethane sealant along the perimeter joint between the window frame and the wall cladding. Tool the bead to ensure a smooth, watertight seal. On the interior side, use a paintable acrylic latex caulk for a clean finish.
If the sash was removed for transport or installation ease, carefully re-hang it on the hinges. For ALPES casement windows equipped with premium hardware from ROTO, Winkhaus, or CMECH, use the adjustment screws on the hinges and locking points to fine-tune the sash position:
A thorough final check ensures the window will perform as designed:
ALPES offers three main aluminum casement window series, each with specific installation considerations:
With a 119mm frame width and 1.8–2.0mm 6060-T66 profile, the C120 is a heavy-duty casement system featuring a nail-free rolled press mesh structure. Installation requires ensuring the integrated mesh frame aligns flush with the sash. The ROTO transmission box and anti-pry lock points need careful calibration during the hardware adjustment step. Thermal K-value reaches 1.6, making proper insulation of the installation gap critical to overall performance.
The C113 features a 113mm frame with full glue-injection corner process for a monolithic structure. The triple sealing defense system (wind, rain, noise, temperature) relies on precise frame alignment — the glass centerline, thermal break strip, and equal-pressure sealing strip must all align on the same axis. CMECH hardware (30,000-cycle tested) comes pre-installed but should be verified and adjusted on site.
The C116 stands out with its 28mm slim frame and 22mm slim medium mullion, maximizing the field of vision. Its 34mm–44mm multi-chamber insulation strips deliver a K-value of 1.7. During installation, take care with the oblique press line design — the flush alignment between the glass sash and mesh screen is a key aesthetic feature. German Wehag hardware upgrades are available, and 304 stainless steel high-load hinges come standard.
A jamb that is not perfectly plumb causes the sash to swing unevenly, stressing hinges and creating gaps in the weather seal. Always use a long spirit level (1200mm+) and verify plumb at multiple points before fastening.
Aluminum profiles, while strong, can be bowed by over-tightened screws. This distorts the frame and prevents the sash from sealing properly. Tighten until snug — not to full torque — and recheck frame geometry after each fastener.
Sealant, foam, or debris blocking the weep holes at the bottom of the frame traps water inside the profile, leading to corrosion and water damage. Always clear drainage holes as the final step and verify they are unobstructed.
Shims placed only at corners or at the wrong points can cause the frame to rack or twist. Place shims at all fastening points and at intermediate supports, ensuring even weight distribution. Remove any shims that extend beyond the frame — they can create thermal bridges and moisture paths.
A well-installed ALPES aluminum casement window will provide decades of service with minimal maintenance. To keep it performing at its best:
Installing an aluminum casement window is a precise process that rewards attention to detail. From accurate measurements and proper shimming to careful hardware adjustment and thorough sealing, every step contributes to the window's long-term performance, energy efficiency, and durability.
ALPES aluminum casement windows are engineered to exacting standards with 6060-T66 profiles, PA66GF25 thermal breaks, and premium German hardware. When installed correctly following these guidelines, they deliver exceptional thermal performance (K-values as low as 1.3 on the AW90 series), robust security, and a service life of 30+ years. For project-specific installation guidance or to discuss your aluminum casement window requirements, contact the ALPES technical support team directly.
