Velux Roof Window Dimensions: A Comprehensive Guide to Sizes
Velux roof windows, also known as skylights, come in a range of dimensions designed to fit different roof pitches, installation depths, and interior spaces. Understanding the relationship between exterior size, frame size, and rough opening helps homeowners choose the right skylight for light, ventilation, and energy efficiency. This guide explains the essential terminology, how to measure accurately, and common size ranges you’ll encounter when shopping for Velux roof windows in the United States.
Understanding Velux Dimension Terminology
When evaluating Velux skylights, several terms determine how a window will fit and perform. Exterior size refers to the outermost dimensions of the skylight assembly. Frame size is the size of the visible frame around the sash inside the room. The Rough Opening (RO) is the measured cut-out in the roof that a skylight must fit into, and it often differs from both exterior and frame sizes. Clear opening is the actual size of the glass that allows light to pass through when the window is open. Understanding these terms helps ensure proper fit and installation with flashing kits and insulation accessories.
How To Measure For A Velux Skylight
Begin with a checklist to ensure accuracy and a successful fit. Use a steel tape measure, a ladder or harness as needed, and a helper for safe handling.
- Measure the RO width. In the attic or attic hatch area, measure the width of the existing rough opening from inside framing to inside framing. Take multiple measurements at top, middle, and bottom to account for irregularities.
- Measure the RO height. Measure from the bottom of the rough opening to the top, again at multiple points to detect any slack or bowing in the framing.
- Record interior frame dimensions. Note the dimensions of the current interior frame or drywall opening to guide the selection of frame size and trim options.
- Check roof pitch and install depth. The roof angle affects the required installation depth and flashing kit selection, so include pitch (in degrees or rise over run) in your notes.
- Consider interior space and headroom. Decide how much glass area you want and whether you prefer a venting sash or a fixed skylight for ceiling clearance.
Velux product literature provides precise exterior, frame, and RO measurements for each model. Always compare your measured RO to the official dimension charts to ensure a proper fit and warranty compliance.
Common Velux Window Size Categories
Velux skylights are commonly grouped by approximate RO and frame dimensions rather than a single universal sizing scheme. In the United States, you’ll encounter several widely used size families that correspond to typical roof openings. The following categories offer a practical sense of scale while encouraging verification with manufacturer specifications.
- Small skylights often fit compact roof spaces and are ideal for closets, halls, or bathrooms with limited headroom. RO widths typically range from roughly 14″ to 22″ and RO heights from 28″ to 40″.
- Medium skylights balance daylight with reasonable installation complexity, suitable for living rooms or kitchens with moderate roof space. RO widths commonly span 22″ to 34″ and RO heights around 34″ to 46″.
- Large skylights maximize natural light for spacious areas or open floor plans. RO widths frequently run 34″ to 46″ or larger, with RO heights in the mid-40s to mid-60s inches, dependent on roof configuration.
Note that interior frame sizes and exterior dimensions may differ by model, so always cross-check the exact numbers from Velux product sheets for each specific skylight.
Choosing The Right Velux Size For Your Space
Selecting the appropriate skylight size involves balancing light, ventilation, energy efficiency, and structural considerations. The following factors influence size decisions:
- Room function and orientation The purpose of the room, its ceiling height, and the direction it faces affect how much light and air you want. East-facing windows catch morning light, while west-facing ones provide afternoon sun.
- Roof pitch and daylight penetration Steeper roof pitches can accommodate larger skylights while maintaining proportional light distribution. Flatter roofs may require smaller or multiple units to avoid glare.
- Thermal performance Larger skylights can affect heat gain and loss. Look for double- or triple-glazed units with inert gas fills and low-emissivity coatings to optimize energy efficiency.
- Ventilation needs If ventilation is a priority, consider a venting model with a suitable sash height to allow airflow without compromising headroom.
- Structural considerations Ensure the roof framing can support the skylight’s weight and that roof flashings, insulation, and weather sealing are compatible with the chosen size.
The Relationship Between Exterior, Frame, And Rough Opening
The exterior skylight size, frame size, and rough opening are interdependent. An exterior size may dictate the roof penetration and flashing kit required. The frame size determines how much of the interior wall space will be visible around the skylight and how trim will look. The RO must be slightly larger than the exterior size to accommodate flashing and weather sealing. When replacing an old skylight, ensure the RO can accommodate the new exterior dimensions or be prepared to adjust the opening.
Practical Tips For Retailers And Homeowners
To simplify selection and installation, keep these tips in mind. Always consult Velux official dimensions for the exact model you plan to install, as sizes vary by product line (for example, GGL and GGU families). When in doubt, order a sample or use Velux’s skylight size calculator if available. For renovations, consider multiple skylights to achieve even light distribution rather than one oversized unit. Finally, hire a qualified installer familiar with Velux flashing systems to ensure proper weather sealing and warranty compliance.
Sample Comparison: How Two Popular Velux Models Differ In Size
The following is an illustrative comparison to show how two commonly referenced Velux models can differ in size without implying exact factory specs. Always verify current specifications from Velux directly.
| Model Family | Exterior Size (approx.) | Frame Size (approx.) | Rough Opening (approx.) | Notes |
|---|---|---|---|---|
| GGL | Varies by series | Similar range to exterior | Designed to fit specific RO | Common for living spaces; good ventilation |
| GGU | Varies by series | Similar range to exterior | RO compatibility varies | Skylight with integrated vent options |
Because Velux offers multiple series with different framing and installation kits, exact measurements must be taken from model-specific literature prior to purchase and installation.
Final Steps Before Purchase
Before finalizing a Velux skylight order, confirm the following. 1) precise rough opening measurements in inches, 2) exterior dimensions of the skylight unit, 3) frame dimensions and trim needs, and 4) compatibility of flashing and insulation components for the roof pitch and region. Additionally, verify lead times for custom configurations if your RO deviates from standard sizes. By aligning RO, exterior, and frame measurements with Velux specifications, homeowners can achieve a seamless installation, optimal daylight, and reliable performance for years to come.