In This Guide
Skylight Types: Fixed, Vented, and Tubular
Choosing the right skylight type is the first decision in any installation project. Each type serves different purposes and has different installation requirements.
Fixed Skylights
A sealed, non-opening skylight designed solely for natural light. No moving parts means the simplest, most reliable installation with the fewest potential leak points. Fixed skylights are available in the widest range of sizes, including custom dimensions.
Installation: Simplest installation. The unit is set into the roof opening and sealed with flashing. No electrical work needed. Can be installed in virtually any roof location.
Best for: Hallways, stairwells, closets, and cathedral-ceiling rooms where ventilation is provided by other means. Most DMV installations are fixed skylights.
Considerations: No ventilation capability. Cannot be opened for cleaning the exterior glass surface from inside.
Vented (Operable) Skylights
Skylights that open to allow hot air to escape and fresh air to enter. Available in manually operated (pole or crank) and electrically or solar-powered versions. Electric models can connect to rain sensors for automatic closing.
Installation: More complex than fixed -- requires hinge mechanism integration and weathertight seal when closed. Electric models need wiring or solar panel placement. Solar-powered models (like VELUX solar-powered units) require no wiring -- the solar panel charges an internal battery.
Best for: Kitchens and bathrooms where heat and moisture accumulate. Upper-floor rooms where the natural stack effect draws hot air upward. DMV homes benefit significantly in summer when vented skylights exhaust trapped heat.
Considerations: Higher cost than fixed. Moving parts and seals require periodic maintenance. Electric motors have a 15-20 year service life. Rain sensor is strongly recommended for the DMV climate.
Tubular Skylights (Sun Tunnels)
A small dome on the roof connected to a highly reflective tube (typically 10-14 inch diameter) that channels light down to a diffuser lens in the ceiling. The tube can flex to navigate around attic obstructions like ducts, wires, and structural members.
Installation: Fastest installation -- typically 3-5 hours. Small roof penetration (14-inch diameter) minimizes structural impact. No rafter cutting required. The flexible tube routes through the attic space to the ceiling diffuser location, which does not need to be directly below the roof dome.
Best for: Interior bathrooms, hallways, and closets where a traditional skylight cannot reach. Rooms on lower floors with attic space above. Situations where minimal roof modification is desired.
Considerations: Limited light output compared to a full skylight. Cannot see the sky -- only diffused light reaches the room. Not suitable when the primary goal is a view or a design statement.
Curb-Mount vs. Deck-Mount Installation
The mounting method is determined primarily by your roof pitch. Using the wrong mounting type for your roof is a common cause of skylight problems.
| Feature | Curb-Mount | Deck-Mount |
|---|---|---|
| Roof pitch | 0-14 degrees (flat to low slope) | 14-85 degrees (standard to steep) |
| How it mounts | Sits on a raised wooden curb built on the roof | Attaches directly to roof deck (sheathing) |
| Profile | Elevated above roof surface | Low profile, blends with roofline |
| Water management | Curb sheds water away from unit | Integrated flashing channels water |
| Replacement ease | Curb stays; only unit replaced | Full removal and re-flashing needed |
| DMV application | Flat-roof townhouses, commercial | Most DMV residential pitched roofs |
| Standard sizes | Wide range available | Matched to common rafter spacing |
The Installation Process Step by Step
Understanding the installation process helps you prepare your home and evaluate the quality of the work. Here is what a professional skylight installation involves.
Step 1: Site Assessment and Planning
The installer evaluates your roof from both exterior and interior. Key assessments include roof pitch and condition, rafter spacing and structural framing, attic space and obstructions (ducts, wiring, plumbing), ceiling type (cathedral vs. flat with attic), optimal placement for light distribution, and any required structural modifications. For DMV homes, tree canopy assessment is also important -- heavily shaded roofs may not benefit from skylights.
Step 2: Interior Preparation
Furniture and belongings below the work area are protected with drop cloths. If a light shaft is being built, the ceiling opening is marked. Interior work begins only after the roof opening is weather-protected.
Step 3: Roof Opening
From the attic, the opening is located relative to the rafters. If the skylight fits between existing rafters, only the sheathing and roofing material are removed. If rafters must be cut (for wider skylights), headers are installed to transfer the structural load. This is the most critical structural step and may require engineering documentation for the building permit.
Step 4: Framing and Curb (if applicable)
For curb-mount installations, a wooden curb (frame) is built on the roof deck and secured to the structural framing. The curb is wrapped with ice and water shield membrane. For deck-mount installations, the rough opening is prepared and the roof deck around the opening is protected with ice and water shield.
Step 5: Skylight Installation
The skylight unit is set into the opening (deck-mount) or onto the curb (curb-mount). It is shimmed for level and square, then fastened to the framing or curb with manufacturer-specified fasteners. The unit is checked for proper operation (vented models) before proceeding to flashing.
Step 6: Flashing Installation
The manufacturer flashing kit is installed according to the specific instructions for your roofing material (asphalt shingle, standing seam metal, flat membrane, etc.). This is the most critical step for long-term waterproofing. See the Flashing section below for details.
Step 7: Roofing Material Restoration
Shingles or roofing material around the skylight are restored, integrated with the flashing. Sealant is applied at specific points per manufacturer instructions. The roof surface is inspected for any damage from the installation process.
Step 8: Light Shaft Construction (if needed)
If the room has a flat ceiling with attic space above, a light shaft connects the roof-level skylight to the ceiling-level opening. The shaft is framed, insulated, drywalled, and painted. Splayed (angled) shafts distribute light more broadly than straight shafts.
Step 9: Interior Finishing
Interior trim is installed around the skylight or light shaft opening. Drywall is finished, sanded, and painted. The skylight glass is cleaned. For vented models, controls are tested (manual operation, electric motor, rain sensor, remote).
Step 10: Final Inspection
The installation is inspected for proper flashing integration, interior finish quality, operation (vented models), and compliance with the building permit. We walk through the installation with the homeowner and provide maintenance instructions.
Flashing: The Key to Leak Prevention
The flashing system is the weatherproof connection between the skylight and the roof. It is the single most important factor in skylight longevity -- improper flashing is responsible for the vast majority of skylight leaks we repair across the DMV.
Never Accept Field-Fabricated Flashing
Every reputable skylight manufacturer (VELUX, FAKRO, Wasco) produces flashing kits specifically engineered for their skylight models and for specific roofing materials. Always insist on the manufacturer flashing kit -- never accept field-fabricated sheet metal flashing, even from an experienced roofer. Manufacturer flashing kits are designed to channel water through multiple redundant drainage paths. Field-fabricated flashing cannot match this precision. Using non-manufacturer flashing also voids the skylight warranty.
Head Flashing (Top)
Channels water from above the skylight around and away from the frame. Integrates under the shingle course above the skylight. This is the most vulnerable point because all water flowing down the roof toward the skylight hits this flashing first.
Step Flashing (Sides)
L-shaped metal pieces woven into each course of shingles alongside the skylight frame. Each piece overlaps the one below, creating a shingled water barrier that directs water away from the frame at every shingle course.
Apron Flashing (Bottom)
Channels water from the bottom of the skylight frame onto the shingle surface below. Extends under the skylight frame and over the shingles below to ensure water drains completely clear of the installation.
Ice and Water Shield Underlayment
In addition to the metal flashing, a self-adhesive waterproof membrane (ice and water shield) is applied to the roof deck around the skylight opening as a secondary water barrier. This membrane seals around nail penetrations and provides backup protection in case any water gets past the primary flashing. Ice and water shield is required by code in most DMV jurisdictions for skylight installations and is a non-negotiable part of a quality installation.
Energy Performance and Glazing Options
Skylight energy performance is governed by the same metrics as windows -- U-factor and Solar Heat Gain Coefficient (SHGC) -- but skylights receive direct overhead sun exposure, making glazing selection even more critical than for vertical windows.
| Glazing Option | U-Factor | SHGC | DMV Recommendation |
|---|---|---|---|
| Single-pane clear | 1.10+ | 0.80+ | Not recommended -- does not meet code |
| Double-pane Low-E, argon (standard) | 0.29-0.35 | 0.22-0.40 | Good -- standard for most DMV installations |
| Double-pane Low-E, argon (solar control) | 0.29-0.35 | 0.19-0.25 | Excellent for south and west facing |
| Triple-pane Low-E, argon | 0.19-0.25 | 0.18-0.27 | Premium option for maximum efficiency |
| Acrylic dome | 0.90+ | 0.70+ | Not recommended -- yellows in DMV UV exposure |
SHGC by Orientation
For south- and west-facing skylights in the DMV, specify a lower SHGC (0.25 or below) to limit summer heat gain -- this is the primary comfort concern. For north-facing skylights, a higher SHGC (0.35-0.40) allows more passive solar heating in winter with minimal summer overheating risk. East-facing skylights receive morning sun and benefit from moderate SHGC values (0.25-0.35).
ENERGY STAR for DMV (Zone 4)
ENERGY STAR requirements for skylights in Climate Zone 4 (DMV): U-factor of 0.37 or lower and SHGC of 0.30 or lower. Meeting ENERGY STAR criteria qualifies for federal tax credits. Most double-pane Low-E argon-filled skylights from major manufacturers meet or exceed these requirements. We specify ENERGY STAR-compliant skylights on all residential installations.
Light Shafts and Interior Finishing
In homes with a flat ceiling and attic space above, a light shaft connects the roof-level skylight to the ceiling opening. The shape and finish of the light shaft significantly affect how much light reaches the room and how it distributes.
Straight Shaft
The ceiling opening is directly below and the same size as the roof opening. The shaft walls are vertical. This is the simplest and most cost-effective shaft construction. Light output is concentrated in a column directly below the skylight.
Lowest cost. Works well for narrow spaces like hallways where concentrated light is acceptable.
Splayed (Flared) Shaft
The ceiling opening is larger than the roof opening, with angled shaft walls that spread light across a wider area. The angle can be symmetrical or asymmetrical depending on where you want the light to reach. This is the most common approach for living spaces.
Distributes light more evenly. Recommended for kitchens, living rooms, and bathrooms where broad illumination is desired.
Angled Shaft
The ceiling opening is offset from the roof opening, with the shaft angled to redirect light toward a specific area. Used when the optimal roof location for the skylight is not directly above the desired ceiling location.
Solves placement conflicts between optimal roof location and desired ceiling position. More complex construction but enables skylights where straight shafts are not possible.
Light Shaft Insulation
The light shaft passes through unconditioned attic space, so it must be insulated to prevent heat loss in winter and heat gain in summer. The shaft walls should be insulated to the same R-value as the surrounding attic insulation (R-38 to R-49 for DMV climate zone). Vapor barrier on the warm side prevents condensation inside the shaft. Paint the interior shaft walls white or use a light-colored finish to maximize light reflection down to the room.
Permits and Code Requirements in the DMV
Skylight installation involves cutting a new opening in the roof structure, which triggers building permit requirements in virtually every DMV jurisdiction. Here is what to expect.
Building Permit
Required in DC, all Virginia jurisdictions, and all Maryland counties for new skylight installations. The permit application typically requires: a site plan showing the skylight location on the roof, framing details if rafters are cut, product specifications (manufacturer, model, size), and the installer's contractor license. Some jurisdictions accept manufacturer installation guides as the framing detail.
Structural Engineering
If the skylight is wider than the space between two adjacent rafters, one or more rafters must be cut and headers installed to redistribute the structural load. This may require a structural engineer's stamp in some jurisdictions, particularly for wide skylights or homes with engineered roof trusses (which cannot be cut without engineering approval).
Safety Glazing (IRC R308.6)
All overhead glazing -- including skylights -- must be safety glazed. The inner pane (room side) must be laminated glass or have a protective screen below it. This is a universal code requirement across DC, Virginia, and Maryland. All skylights from major manufacturers meet this requirement.
Energy Code (IECC)
New skylights must meet the energy performance requirements for Climate Zone 4A: U-factor of 0.55 or lower and SHGC of 0.40 or lower (IECC 2021). ENERGY STAR skylights exceed these requirements. DC's energy code may be more stringent than the base IECC.
Inspections
Most jurisdictions require two inspections: a framing/rough-in inspection (after the opening is cut and framed but before interior finishing) and a final inspection. Some jurisdictions combine these into a single final inspection. We coordinate inspection scheduling as part of our installation service.
Maintenance and Long-Term Leak Prevention
A properly installed skylight requires minimal maintenance, but regular inspection prevents small issues from becoming expensive problems. Here is the recommended maintenance schedule for DMV homeowners.
Twice per Year (Spring and Fall)
- Clear leaves, pine needles, and debris from around the skylight frame and flashing
- Check that no branches are resting on or near the skylight
- Inspect visible flashing for lifted edges, rust spots, or missing sealant
- Clean exterior glass if safely accessible (or hire a professional)
- Check interior trim for water staining that might indicate a hidden leak
Annually (Before Winter)
- Test vented skylight operation -- open and close completely several times
- Test rain sensor (electric vented models) by simulating moisture
- Inspect weather stripping on vented skylights for compression or deterioration
- Check weep holes (drainage channels) on the frame for blockage
- Inspect interior drywall around the light shaft for any discoloration
Every 5 Years
- Professional inspection of flashing condition and roof integration
- Reapply sealant at flashing joints if showing deterioration
- Inspect insulated glass for seal failure (fogging between panes)
- Check all hardware -- hinges, locks, cranks, motors -- for wear
- Assess surrounding roof condition within 3 feet of the skylight
When to Call a Professional
Contact Expert Glass Repair at (703) 679-7741 if you notice: any water staining on the ceiling or walls near the skylight, condensation between the glass panes (foggy skylight), cracked or chipped glass, difficulty opening or closing a vented skylight, or any visible damage to the flashing or frame. Early intervention prevents small issues from causing extensive water damage.
Frequently Asked Questions
How long does a skylight installation take?
A single skylight installation in a home with accessible attic space and a straightforward roof structure typically takes 1-2 days. Day one involves cutting the roof opening, installing the skylight unit, and completing exterior flashing and waterproofing. Day two covers interior finishing -- building the light shaft (if needed), installing drywall, trim, and paint. Tubular skylights are the fastest, typically completed in 3-5 hours. Complex installations involving structural modifications, long light shafts, or multiple skylights may take 3-5 days.
Do I need a permit to install a skylight in DC, Virginia, or Maryland?
Yes, in most jurisdictions. A skylight installation involves cutting a new roof opening, which is a structural modification requiring a building permit. Fairfax County, Arlington, Montgomery County, Prince George's County, and DC all require permits for skylight installations. The permit process typically involves submitting a plan showing the location, size, and framing details. Some jurisdictions require engineering if rafters are cut. Expert Glass Repair handles permit applications and scheduling of inspections.
Will a skylight make my house too hot in summer?
Not if properly specified. A skylight with Low-E glass and an appropriate Solar Heat Gain Coefficient (SHGC of 0.25 or lower for south- and west-facing installations) limits solar heat gain while admitting visible light. Vented skylights can actually reduce cooling loads by exhausting hot air that accumulates at the ceiling. Interior cellular shades or exterior solar screens provide additional heat control. The key is selecting the right glazing for the skylight orientation -- something we assess during our free on-site consultation.
What is the difference between curb-mount and deck-mount skylights?
Curb-mount skylights sit on a raised wooden frame (curb) built on the roof, elevating the skylight above the roof surface. They are standard for flat and low-slope roofs (0-14 degrees). Deck-mount skylights attach directly to the roof deck with an integrated flashing system and sit lower on the roof. They are standard for standard-pitch residential roofs (14+ degrees). Deck-mount provides a sleeker appearance; curb-mount provides better water shedding on low-slope applications. Your roof pitch determines which type is appropriate.
How do skylights handle rain and snow?
A properly installed skylight with manufacturer flashing handles rain and snow as reliably as any other roof component. The flashing system channels water around the skylight frame and down the roof slope. In winter, the heat escaping through the skylight glass melts snow accumulation (this is actually an advantage -- skylights rarely have ice dam problems when surrounded by snow-covered roof). Vented skylights with rain sensors automatically close when precipitation is detected.
Can I install a skylight if I have a flat roof?
Yes. Flat and low-slope roofs use curb-mount skylights installed on a raised curb that provides positive drainage away from the skylight. The curb height (typically 4-8 inches above the roof surface) prevents standing water from pooling against the frame. Flat-roof skylight installations require special attention to membrane roofing integration and curb flashing. Many commercial buildings and some modern DMV homes have flat roof sections suitable for skylight installation.
What happens if a skylight starts leaking after installation?
Legitimate leaks after a professional installation are rare. If a leak does occur, the most common cause is a flashing issue that becomes apparent during the first heavy rain. A reputable installer will return to diagnose and repair any leak at no charge during the warranty period. Expert Glass Repair provides a comprehensive warranty on all skylight installations covering both materials and labor. If you have a leaking skylight -- whether we installed it or not -- call (703) 679-7741 for a free assessment.
Are there energy tax credits for skylight installation?
Yes. The federal Energy Efficient Home Improvement Credit (25C) covers qualifying ENERGY STAR skylights at up to 30% of the product cost, up to the annual cap for windows and skylights combined. The skylight must meet ENERGY STAR performance criteria for your climate zone (Zone 4A for the DMV). Keep the manufacturer certification statement and purchase receipt for your tax filing. Some utility rebates may also apply -- check with your provider or ask us during your consultation.
Related Guides
By the Expert Glass Repair Team
Skylight specialists serving the DMV since 2004
Expert Glass Repair installs, repairs, and replaces skylights across DC, Northern Virginia, and Maryland. We carry VELUX, FAKRO, and Wasco products and provide manufacturer-backed installations with proper flashing. Fully Insured. Call (703) 679-7741 for a free on-site skylight consultation.
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