Specifications & Testing Data
| Frame material | Wood-core frame and sash with maintenance-free aluminum exterior cladding (copper cladding optional on FS) |
|---|---|
| U-factor (NFRC) | 0.37 – 0.53 |
| Solar heat gain coefficient (NFRC) | 0.23 – 0.26 |
| Design pressure (DP) rating | FS tested to NAFS (AAMA/WDMA/CSA 101/I.S.2/A440); uplift/downward ratings vary by size and glass — FS with snowload glass tested to 1,180 lbs/ft² downward at M08 |
| AAMA performance class | NFRC-certified as a skylight (rated at 20° slope) — not comparable to window U-factors |
| ENERGY STAR zones | Northern |
| Glass options | Clean, Quiet & Safe laminated Low-E (standard), Impact laminated (06), White laminated diffusing (08), Snowload laminated (10), i89 interior coating upgrade, Triple-pane (FCM special order) |
| Available styles | FS deck-mount fixed (14 standard sizes, 14–85° pitch), FCM curb-mount fixed (0–60° pitch, custom sizes available) |
What the Fixed Skylight Actually Is
A fixed skylight is glass that does not open. That sounds like a downgrade until you have installed a few hundred of them: no hinge, no motor, no rain sensor, and a sash that is sealed to the frame for life. The VELUX fixed line comes in two models that differ only in how they meet the roof.
The FS is the deck-mount version. Its wood-core frame is clad in aluminum, the perimeter carries a factory-applied deck seal, and the unit nails directly to the sheathing. Over it goes an engineered flashing kit — EDL for shingle, shake and slate roofs, EDW for tile — with pleated corners and a roll of adhesive underlayment as a second water barrier. VELUX rates the assembly for 14° to 85° pitches, which covers essentially every pitched roof in the Treasure Valley. Fourteen standard sizes run from a 14½" x 45¾" slot (A06) that drops between 16"-on-center trusses to a 44¼" x 45¾" square (S06); the D26 and D06 sizes are cut for 24"-on-center truss bays.
The FCM is the curb-mount version. It sits on a curb we frame from 2x4 or 2x6 lumber, sealed with a pre-attached gasket and flashed with the ECL (shingle, 10–60°) or ECW (tile, 14–60°) kit. Because the curb does the waterproofing geometry, the FCM works from 0° to 60°, and it comes in more than twenty stock sizes plus custom dimensions in quarter-inch increments. It is the model you want when replacing a 1990s builder skylight whose curb is already there and sound.
Above the fixed units in the VELUX lineup sit the venting Fresh Air models (VS, VSE, VSS and their curb-mount siblings); below them, the Sun Tunnel tubular skylights for spaces too small for a shaft.
The Numbers That Matter
Skylights are certified under NFRC's skylight procedure, tested at a 20° slope facing the sky, and the resulting numbers are not interchangeable with wall-window numbers — a skylight in the 0.40s is doing the same job as a window in the high 0.20s. Compare skylight to skylight.
| Glass option | Code | FS U-factor | FS SHGC | Notes |
|---|---|---|---|---|
| Laminated Low-E (standard) | 04 | 0.43–0.44 | 0.23–0.26 | Tempered outer over laminated inner, argon fill |
| Impact laminated | 06 | 0.41–0.42 | 0.23–0.26 | Thicker 0.090" interlayer; wind-borne debris rated |
| White laminated | 08 | 0.43–0.44 | 0.22–0.25 | Diffused light, VT drops to about 0.40 |
| Snowload laminated | 10 | 0.41–0.42 | 0.23–0.26 | Tempered over laminated tempered |
| Standard + i89 coating | 89/94 | 0.37–0.38 | 0.23–0.25 | Fourth-surface coating; best winter number |
Those figures come from VELUX's published tested-performance sheets; the FCM, which loses a little to its curb geometry, tests about 0.47–0.53 with SHGC 0.23–0.25, and a triple-pane FCM is available by special order. Every unit ships with its NFRC label, and we quote the exact glazing code on your paperwork.
Structurally, the FS is tested to NAFS (AAMA/WDMA/CSA 101/I.S.2/A440). Standard glass in the M08 size rates 105 lbs/ft² uplift and 350 lbs/ft² downward; snowload glass pushes the downward rating to 1,180 lbs/ft². Water resistance is tested to 720 Pa with no leakage across all glass options.
Where It Fits in Idaho — and Where It Doesn't
The best fixed-skylight jobs in the valley share a pattern: a room that faces north or sits under a deep eave, has a ceiling within a few feet of the roof deck, and already breathes. North-facing kitchens in 1980s and 1990s two-stories are the classic case — one M06 over the island changes the room more than a full cabinet refinish would, and the north exposure means the shade rarely needs to come down. Windowless master baths and interior laundry rooms are next.
Snow country changes the spec, not the model. In McCall, Cascade and the Bogus Basin road homes we order snowload glass as a matter of course, keep the pitch steep enough to shed, and run the EDL with ice-and-water shield lapped well past the kit's underlayment. On low-pitch roofs up there, the FCM on a taller curb is the safer geometry.
Where a fixed unit is the wrong buy: a south- or west-facing vaulted room with no cross-ventilation. Daylight is not the problem in that room; heat is, and a fixed skylight adds solar gain without a way to purge it. That house wants a venting VSS with the shade closed on July afternoons, and we will say so at the walkthrough. Likewise, a hallway or closet with a ten-foot attic run is Sun Tunnel territory — a full shaft that deep costs more than the light it delivers.
Warranty and Service, Locally
VELUX backs the FS and FCM with 20 years on the insulating glass seal, 10 years on the product, and 5 years on shades and controls. Installed with the matching VELUX flashing kit, both models also qualify for the 10-year installation warranty — VELUX's no-leak commitment on deck- and curb-mounted skylights, backed by the three-layer deck seal, adhesive underlayment and engineered flashing system. We install the complete kit every time because a skylight without it is a hole in the roof with a better view.
Wood Windows Inc has installed skylights for 46 years with our own employee carpenters out of Garden City — never a subcontracted roofing crew. If anything ever fogs, drips or cracks, the people who cut the hole are the ones who come back.
Want a roof and attic assessment before anyone quotes a size? Request a quote on this page or call (208) 376-2200.
Frequently Asked Questions
What is the difference between the VELUX FS and FCM fixed skylights?
Mounting. The FS nails straight to the roof deck with a pre-attached deck seal and an engineered EDL or EDW flashing kit, giving a low profile and the tightest possible seal; it needs a 14–85° pitch. The FCM sits on a site-built 2x lumber curb that we frame, so it works from dead-flat to 60° and is the natural fit when replacing an old curb-mounted skylight without reframing. On a new cut-in on a pitched shingle roof we almost always spec the FS.
Should I choose a fixed skylight or a Fresh Air venting model?
Fixed if the room already has a way to exhaust heat — an operable window, a range hood, or a ceiling fan running to a return — and the goal is daylight only. Venting if the space is a vaulted great room, second-floor bath, or bonus room where summer heat stacks at the ceiling with nowhere to go. Fixed costs less, has nothing mechanical to service, and in a north-facing kitchen is usually the right call.
Do VELUX fixed skylights meet snow load requirements for mountain homes?
With the snowload glass option (glazing code 10), yes for most applications — that glass is tempered over laminated tempered and tested to markedly higher downward pressure than standard glass. We spec it on any install above the valley floor and on low-pitch roofs where snow sits rather than sheds. The structural engineer or building department sets the required ground snow load; we match glass and size to it.
What does a fixed VELUX skylight cost installed in the Treasure Valley?
Typical installed pricing runs about $1,800–$3,200 for a standard-size FS or FCM including the flashing kit, a framed and drywalled light shaft, and paint-ready finish. The shaft depth and roof type move the number more than the skylight does. Snowload or impact glass and larger sizes add to that; see our skylight cost guide for a full breakdown.
Sources & Testing Data
Last reviewed 2026-09-10 by Wood Windows Inc — (208) 376-2200