Sun Tunnels for Philadelphia Row Homes

The Dark Middle of a Philadelphia Row Home

A Philadelphia row home is long, narrow, and attached on both sides. Windows at the front and windows at the back, and between them a stretch of house with no exterior wall at all.

That's where the dark rooms are. The second-floor bathroom with a loud fan and a 60-watt bulb. The hallway you light at noon. The stairwell that's dim on the brightest day of the year. The closet, the middle bedroom, the back half of a kitchen that was extended years ago.

A skylight fixes this — when there's a straight run from roof to ceiling. Often there isn't. Sometimes the room sits under two more floors. Sometimes there's a bathroom above it. Sometimes the ceiling is nine feet below the roof deck with joists, ductwork and a bathroom vent in between.

That's the problem a sun tunnel solves.

How a Sun Tunnel Actually Works

Three parts, and it's worth knowing all three because the middle one is where quality lives.

• On the roof: the collector. A dome or a flat glass unit sits in the roof surface and gathers daylight. It's flashed into the roofing the same way a skylight is — this is a roof penetration and it gets treated like one.
• Through the house: the tube. A reflective tube carries the light down. This is the part that does the work, and the part people don't see.
• In the ceiling: the diffuser. A round trim ring with a diffuser lens, flush with the ceiling. It looks like a recessed light. It spreads the daylight evenly instead of dropping a hard circle on the floor.

There's no glass you look through and no opening to the outside air. What you get is daylight.

Rigid vs. Flexible — and Why We Push Rigid

VELUX makes both. Rigid models have an R in the code (TGR, TMR); flexible ones have an F (TGF, TMF).

Flexible tube is a concertina-like duct that bends around obstacles. It's forgiving on a messy run, and it's what makes an awkward install possible.

Rigid tube is straight, hard-walled, highly reflective sections that you assemble, with elbows where you need to turn.

Rigid wins on the thing you're buying, and here's the honest reason: every bend and every corrugation costs you light. Light bounces down a tube, and each bounce loses some. A ribbed, flexible wall scatters light sideways at every ridge. A smooth rigid wall sends it down. The longer the run, the bigger that gap gets — and a row home run is long.

There's a second reason that isn't about physics. VELUX's 2026 residential catalog (XUS 20183-1025) attaches a 20-year tube warranty to its rigid tube models. It makes no such statement about the flexible ones. When a manufacturer puts twenty years in writing for one version, that tells you something.

We use flexible when the run genuinely demands it. We tell you when we do, and why.

What Size Fits What Room

VELUX builds three diameters, written as 010, 014 and 022 — nominally 10", 14" and 22". The ceiling openings below are the figures VELUX publishes in its 2026 catalog.

The 14" is what goes into most row homes. On a pitched roof, if you're deciding between two sizes, go bigger — the cost difference is small next to the labor, and nobody has ever asked us to make a room darker.

Two cautions. Not every model comes in every size: in VELUX's catalog, only the rigid low-profile TGR comes in all three. The rigid pitched TMR comes in 10" and 14", and the flexible models in 14" (TMF) or 14" and 22" (TGF). And on a flat roof, the two models VELUX rates down to flat — covered in the next section — come in 14" only. On most row homes, that settles the size question for you.

Your Roof Decides More Than Your Ceiling Does

Most Philadelphia row homes have a flat or low-slope roof. That single fact rules some models out and rules others in.

VELUX publishes a working pitch range for each model, and much of the line starts at 14° — roughly 3:12. A flat row-home roof is below that. The models that work on a flat roof are specific:

Standing seam deserves its own note. A metal roof isn't shingles — you can't weave a flashing into courses that don't exist. The curb-mounted approach builds a curb, sets the unit on it, and counterflashes into the seams. It's slower and it costs more. Anyone quoting you the same price on standing seam as on shingle hasn't thought about it.

Framing: Will It Actually Fit?

The usual worry is that a tube has to thread through joists. It generally doesn't. VELUX states that Sun Tunnel skylights “fit between ceiling supports, allowing light to fill the space below uninhibited” — the tube is sized to drop through a joist bay. It's designed around your framing rather than through it.

What we're actually looking for on a site visit:

• A clear bay from roof deck to ceiling. Joists are fine. A bathroom vent, a soil stack, a duct run or an old chimney in the way is the real problem.
• The run length. VELUX sells additional rigid tube sections and elbows, but every elbow costs light. Two turns is a lot. Three and we'll tell you honestly what you're going to get.
• What's above. If there's another floor above the room, a sun tunnel has to pass through it. Sometimes that works inside a closet or a chase. Sometimes it can't be done, and we'll say so.
• Row home party walls. Everything happens inside your own footprint — we don't touch a shared wall. The roof edge on those walls is its own subject: parapet coping on your party walls .

Night Light, Dimmer and Diffusers

VELUX makes accessories that fit inside the rigid tube:

• Solar Night Light — a solar panel on the roof charges a battery during the day and gives off a soft glow at night. VELUX notes it “collects available sunlight, even on cloudy days.” In a windowless bathroom, this is the difference between a daylight fixture and a light fixture.
• Daylight Controller — the dimmer. For a bedroom or a TV room where full midday sun isn't always wanted.
• Electric Light Kit — a wired bulb inside the tube, for a room that needs guaranteed light after dark.
• Diffusers — Frosted is standard. Micro Fresnel, Triple Wave, Brushed Metal, Prismatic and Neutral Light are available.

Decide on the night light or the light kit before installation. Retrofitting means going back into the tube.

What a Sun Tunnel Is Not

The honest part, and the reason we'd rather tell you now than after.

• It is not a view. You will never look up through a sun tunnel and see sky. It's a lit disc in the ceiling. If you want to see weather, you want a skylight.
• It does not ventilate. Nothing opens. A steamy bathroom still needs its exhaust fan — a sun tunnel will not replace it, and won't help with humidity.
• It does not make daylight out of nothing. On a grey February afternoon in Philadelphia it gives you grey February daylight. It tracks the real sky, which is most of the appeal and occasionally a disappointment.
• It's a roof penetration. A hole in your roof, done properly, is fine for decades. Done badly it leaks, exactly like a skylight. The flashing is the whole job.
• Long runs lose light. Physics, not brand. Anyone promising a full 22" of daylight at the bottom of a three-elbow run through two floors is guessing.

Sun Tunnel or Skylight?

If the room is directly under the roof and you want to see the sky, get a skylight — see our skylight article for the types and the flashing that makes them work. If the room is buried in the middle of the house, a sun tunnel is often the only thing that will work at all.

If there's a room in your house you light during the day, it's worth ten minutes to find out whether a sun tunnel can reach it. We'll look at the roof, the ceiling and what's in between, and tell you honestly whether it'll work — including when it won't.

Our owner is VELUX Pro Partner Academy Trained.

ALFE Roofing · PA HIC #PA227632