Why Curb Mount Skylight Installation Is Worth Getting Right

Curb mount skylight installation is one of the most effective ways to bring natural light, better ventilation, and real value into your Atlanta home — but only when it's done correctly.

Here's a quick overview of the core steps:

1. Plan your location — check roof pitch (must be 0°–60°), assess attic for obstructions
2. Prepare the rough opening — remove shingles, cut decking, frame with double headers
3. Build the curb — use pressure-treated lumber, minimum 1½" thick and 3½" high
4. Waterproof the curb — wrap completely with adhesive underlayment
5. Install flashing — choose ECL or ECW kit based on your roofing material and pitch
6. Mount the skylight — center on curb, secure with #8 1¾" stainless steel screws
7. Seal and finish — integrate shingles, apply PVC foam gasket or silicone, inspect for leaks

A curb mount skylight sits roughly 5.5 inches above the roofline — higher than other skylight types. That elevation is what gives it better drainage, stronger condensation protection, and the ability to fit custom sizes.

But that extra height also means more steps, more materials, and more room for costly mistakes.

This guide walks you through every stage of the process — from framing to final seal — so you know exactly what a quality installation looks like.

Understanding Curb Mount vs. Deck Mount Skylights

When you start looking into adding light to your home, you’ll quickly realize there are two main contenders: curb mount and deck mount. While they both serve the same purpose, their construction and installation profiles are quite different.

A curb mount skylight is essentially a glass "cap" that sits on top of a wooden box (the curb) that you or your contractor builds on the roof. This raises the unit about 5.5 inches above the roof surface. In contrast, a deck mount skylight has a built-in wood frame and sits lower, roughly 3.5 inches above the roof.

Why choose the higher profile? The 5.5-inch elevation of a curb mount provides superior protection against the elements. Because it sits higher, water and debris are less likely to pool against the seals. It also offers much more versatility for replacements; if you have an odd-sized opening from an old 1980s skylight, you can simply build a custom curb to fit the existing hole rather than reframing your entire roof.

Feature Curb Mount Skylight Deck Mount Skylight Height Above Roof ~5.5 inches ~3.5 inches Frame Type Requires site-built wooden curb Built-in wooden base Best For Replacements, flat roofs, high humidity New construction, low profile look Condensation Large gaskets; better protection Requires precise drywall channel Custom Sizes Highly customizable Limited to standard sizes

Understanding how these units sit on your home is the first step in mastering What Makes Up Your Roof? A Guide to the Components of a Roof.

Planning and Preparation for curb mount skylight installation

Before you pick up a saw, you need a solid plan. Curb mount skylight installation isn't just about making a hole; it's about structural integrity.

First, check your roof pitch. Most curb mount units are rated for pitches between 0° and 60° (or up to a 21:12 slope). However, if your roof is very flat (below 15° or 3:12 pitch), you need to be aware of potential condensation dripping or glass smudging, which manufacturers often don't cover under warranty.

Next, head into the attic. You’re looking for "deal-breakers" like HVAC ducts, plumbing stacks, or complex electrical wiring that might be in the way. You also need to maintain specific clearances:

• 18 inches from roof valleys or hips.
• 24 inches from the roof ridge.
• 12 inches from any slope changes or wall intersections.

If you aren't sure if your roof can handle the structural change, it's always wise to consult with our Skylight Services team to ensure your rafters aren't compromised.

Essential Tools and Materials for curb mount skylight installation

You can't do a professional job with amateur supplies. For a successful curb mount skylight installation, gather the following:

• Lumber: Use pressure-treated 2x6 or 2x8 boards. Building codes require a minimum thickness of 1½" and a height of at least 3½".
• Adhesive Underlayment: High-quality "ice and water" membrane (like VELUX adhesive underlayment) is non-negotiable for waterproofing the curb.
• Flashing Kit: Choose an ECL kit for thin roofing materials (shingles) on 10°-60° pitches, or an ECW kit for profiled materials (tile/metal) on 14°-60° pitches.
• Fasteners: Use #8 1¾" stainless steel screws. They must penetrate the curb by at least ¾" to provide a secure mount.
• Gaskets: We recommend a one-sided PVC foam gasket for the top of the curb. Unlike silicone, PVC foam doesn't have harmful chemical reactions with some building materials and allows for easier removal if you ever need to perform maintenance.
• Safety Gear: Fall protection harnesses, eye protection, and sturdy ladders are mandatory.

Safety and Building Code Considerations

Safety isn't just a suggestion; it’s a requirement. If you’re working on an older home in the Atlanta area, be mindful of lead paint when cutting through interior ceilings.

From a structural standpoint, never cut a roof truss without consulting a structural engineer. Trusses are engineered units; cutting one can lead to roof failure. If you are cutting traditional rafters, you must install temporary 2x4 braces that span at least two rafters on either side of the opening to support the weight while you work.

In Georgia, permits are often required for structural changes like this. Ensuring your project meets local codes is a key part of any professional Roof Replacement or modification.

Step-by-Step Guide to the Installation Process

Now for the heavy lifting. The goal is to create a seamless transition from your roof deck to the sky.

Framing the Rough Opening and Building the Curb

1. Mark the Spot: Inside the house, find the center of your desired location. Drill a pilot hole through the ceiling and roof.
2. Align with a Plumb Bob: Use a plumb bob or a long level to transfer the corners of your ceiling opening up to the roof rafters. Drive nails through the four corners so you can see them from the outside.
3. Remove Shingles: On the roof, pull back the shingles about 10-12 inches away from your nail marks on the top and sides.
4. Cut the Decking: Set your circular saw to the depth of the roof deck and cut your rough opening.
5. Frame with Headers: You must install "headers"—horizontal pieces of lumber the same size as your rafters—at the top and bottom of the opening. Use double headers (two boards nailed together) if you had to cut a rafter. Use three 16d nails to secure these to the existing framing.
6. Build the Curb: Construct a box using pressure-treated 2x6s. The outside dimensions of this box must match the manufacturer's specifications exactly. Secure the curb to the roof deck using construction adhesive and toe-nailed fasteners every 12 inches.

Waterproofing and Final curb mount skylight installation

Water is the enemy of every roof. To keep it out, you must wrap that new curb like a birthday present.

1. Underlayment Wrapping: Start at the bottom. Apply a 3"x7" piece of adhesive underlayment to the bottom corners. Then, wrap the bottom sill, followed by the sides (overlapping the bottom by at least 6 inches), and finally the top. This "shingle-style" overlap ensures water flows over the joints, not into them.
2. Flashing Integration: Install your flashing kit. If using step flashing, overlap each piece by about 2 inches and ensure it extends 4 inches under the shingles. This directs water away from the curb and down the roof.
3. Mount the Skylight: Place the skylight unit over the curb. Center it carefully. Most modern units (like Kennedy or VELUX) have a pre-applied foam gasket. If yours doesn't, apply your PVC foam tape to the top of the curb now.
4. Secure with Screws: Drive your #8 1¾" stainless steel screws through the skylight frame into the wooden curb. Don't over-tighten, but ensure a snug fit.
5. Final Seal: Replace the shingles around the unit, tucking them under the flashing at the top and over the flashing at the bottom. Use a high-quality sealant to cover any exposed fastener heads.

For more information on how we handle these complex layers, visit our Services page.

Best Practices for Long-Term Performance

A skylight that doesn't leak today might still cause problems tomorrow if you don't account for condensation. Because warm, moist air rises, it often gets trapped in the "light shaft" (the tunnel between your ceiling and the roof).

• Insulate the Shaft: Treat the walls of your light shaft like exterior walls. Wrap them in thick insulation and a vapor barrier to prevent moisture from reaching the cold underside of the roof deck.
• Splayed Shafts: If you want more light, consider a "splayed" shaft. This is where the ceiling opening is larger than the roof opening. It’s harder to frame, but it floods the room with much more natural light.
• Maintenance: Every year, check the seals and clear away any leaves or pine needles that have gathered against the high 5.5-inch curb.
• Warranty: To keep your 20-year seal warranty (common with brands like VELUX) or your 10-year installation warranty, you must follow the manufacturer’s flashing instructions to the letter.

Frequently Asked Questions about Curb Mount Skylights

What is the minimum roof pitch for a curb mount skylight?

While curb mount units can technically be installed on flat roofs (0°), most manufacturers only offer their "No Leak" warranty on pitches of 10° (2:12) or higher. For glass skylights, a 2:12 pitch is generally the absolute minimum to prevent water from pooling on the glass.

Should I use silicone or PVC foam gaskets to seal the curb?

We strongly recommend one-sided PVC foam gaskets. They provide an excellent seal, have a "memory" that helps them retain their shape over years of temperature swings, and won't chemically bond to the skylight, making future repairs much easier. Silicone can be messy and sometimes reacts poorly with the finishes on the skylight frame.

How do I prevent condensation in my skylight shaft?

The key is insulation and ventilation. Ensure the light shaft is fully insulated to the same R-value as your attic floor. In high-moisture rooms like bathrooms or kitchens, choose a vented skylight that can be opened to let steam escape.

Conclusion

Mastering curb mount skylight installation is a journey of precision, from the first attic inspection to the final shingle. While the DIY route is possible for those with advanced framing skills, the risks of roof leaks and structural damage are high.

At Matt’s Exteriors, we bring the expertise of over 12,000 successful projects to every home in Metro Atlanta. As a family-owned company serving communities from Alpharetta to Peachtree City, we pride ourselves on exceptional customer care and workmanship that lasts.

Whether you’re in Marietta, Woodstock, or right here in Atlanta, don’t leave your roof to chance. Contact us for expert curb mount skylight installation today and let us bring the Georgia sunshine into your home the right way.