Who do you call, for through-roof ventilation exhaust ducting?

Who do you call, for through-roof ventilation exhaust ducting ?

The Google AI Overview answer is:

For through-roof ventilation exhaust ducting, you should call a licensed roofing contractor. They have the expertise and experience to properly install ventilation systems on your roof, including assessing your needs, choosing the right type of vent, and ensuring it's installed correctly to prevent leaks.

If that were true, roofers would be constantly willing to work in attics to create the majority of that ducting and the installation of the fan appliances served.

Consider my need of a kitchen exhaust fan in the major remodel of the kitchen of the home I own.

I chose a Panasonic in-line fan, pivoting from flooring over thorough R49 insulation with only a small-bend 6" warm air elbow to complete the path through-roof. Here I drilled a pilot hole through-roof at the center of a tracing of the placed elbow. Duct completion is in several traverses between roof an attic, enabled by a strong attic ladder.

Cut through shingles with a wood block propelling sharp deck screws, preserving a hole saw. Drill through wood with a hole saw. Pry shingles and pull nails as needed. Collect wood debris in the attic upon a sheet.

12/5/2018

Here is the fan ready-to-use.

My vast attic flooring is useful. It adds to insulation value and serves as the top element of extremely strong box beams of the 12" thickness floor.

The insulation is protected forever.

I had to anticipate all of this in placing the register and duct from the kitchen ceiling over the electric (not gas!) stove.

At much of a four-foot periphery the insulation is protected just by being off-path. See top-layer R30 Rockwool insulation except R30 fiberglass at the extreme periphery, accommodating plywood attic ventilation inlet baffles.

9/27/2018

See the kitchen fan register in-line with an operable window, over the kitchen stove. Upon a steamy or stinky cooking adventure, lift the window a bit or a lot, and turn on the fan. The view is from the archway entering the kitchen from the living room. the fan switch is the right-most of a 4-gang switch group at your left hand. The lighting constellation chosen here is Passing Through,  4-Way switched at each of the three entries.

In this, my now-modern and clever 1955 home, I could not imagine calling a Licensed Roofer, for greater competence at the through-roof ducting of the kitchen fan. Roofers by my experience see an attic as merely a trash heap. They will not go there. Roofers will benefit in a new regime where other Trades, or a general contractor, will just stay out of their way. And, that is what I have practiced here.

This illustrates a customer installation of kitchen exhaust ducting similar to my own. 

As a inventive Weatherization Contractor and General Contractor, I almost always confront really-awful ducting of bath and kitchen exhaust fans surely not the work of roofers. I am not taught to call a roofer, but to do what I can, myself. With bath fan ducts, the best and awful practice of weatherization contractors is to just plug the plastic or flexible-aluminum found duct, to a 4" take-off stabbed into a plate that covers a found roof high vent. I know better.

Here is a photo album of my jobs employing penetration adapters, in chronological order, showing evolution of methods.

Search  Label: Roof Penetration Adapter, at this blog, and find posts including these:

Roof Caps For Bath and Kitchen Exhaust Ducts (January 15, 2017)

Note then this post describing the shingle-over of my roof in Spring 2023, being the roofer confronting this roof cap. I could venture into the attic, but there is no need:

 Roof Penetration Adapters and a Composition Shingle Overlay  (April 3, 2024)

Turn out four gasketed deck screws to reveal the roof closure with a 6" penetration adapter and its' transferred flapper, riveted to the adapter rim.

With little nibbling of new shingles, the rain barrier  hinges down, perfectly aligned with and coupled to the duct and fan below.

There was the same accurate simplicity at three 4" plastic Air Vent caps without stems.

Learn an important lesson. Lay down all covering shingle rows before screwing down the roof cap. The shingles will be more-strongly retained including fullest engagement of tar strips. Let the cap not be tucked under shingles anywhere if that is how it works out. Remember, the cap is only a rain cover.

What, really, is needed in a roof cap?

code requirements for ducting a bath fan through a roof

Google AI Overview: 

when ducting a bathroom fan through a roof, the primary requirement is to exhaust the air directly outdoors, not into the attic or any other interior space, meaning the duct must be routed to the exterior of the building and terminate on the roof, with the fan capacity (being met).

There is reference to International Residential Code (IRC) Chapter 15, Exhaust Systems.

code requirements for ducting a kitchen fan through a roof

Google AI Overview:

According to most building codes, when ducting a kitchen fan through a roof, the exhaust duct must terminate at least 12 inches above the roof surface, with some regions requiring even greater heights to prevent snow buildup, and the ductwork should be positioned at least 18 inches away from the roof surface where it attaches to the fan; the fan discharge itself should be at least 40 inches away from the roof surface.

This is surprising in the matter of elevation at discharge!   And, never met in my discoveries. Who offers such a discharge path above the roof? It seems to be concern about flame in a grease fire, or discharge burial under snow.

I find nothing offered, in this Google search: image: 12" tall kitchen exhaust roof cap

Smarter now, I could replace the squat Famco cap with this: 

Goose Neck Exhaust Roof Vent – Painted Famco, $99.95. 

The lesser flow resistance makes sense. Nibble out the stem and flapper, or convince Famco to offer separate cap without stem, and flappered penetration adapter.

Want the elevated discharge for a bath fan too, to tolerate snow.

Let even a not-ducted attic ventilation high vent be only a rain cover. Where placement is set with a penetration adapter, avoid misalignment of the sheathing cut and the cap.

Now move on to report an incident that inspires this post:

Violence against bath fan ducts in my row home residence, July 17, 2024!

In this job photo album, I share the awful and typical conditions of fans and ducting that I found and fixed in a now-pretty and useful attic.

On July 17, 2024, the two bath fan roof caps were ripped off, leaving broken ducts to dump moist air into the attic, blackening the roof sheathing.

We were not consulted We were not informed.

New steel caps with manually-crimped stems were left to again defy roofers, at the next roofing replacement, if we were smart enough to reattach the ducts..

10/30/2024

The steel ducts with new elbows are again screwed and taped to roof cap sterms.

See that this space directly off the wonderful attic ladder is the convenient repository of long ducts and other sheet metal I keep in reserve for my unique A-rated business of Attic Access.

With this post and that album, please understand that a roofing company is not the superior owner of well-performing bath fan ducts, entitled to demolish them for no apparent reason and without notice. The roofing company of this incident is the same as that which installed a penetration adapter under my instruction in 2016.

 3/13/2016

This intermittent leak with a wind-driven siphon, in my home, was repaired in November 2011, by an understanding and highly reputable roofer under my instruction. The repair was properly requested through my HOA management, employing their established contractor.

 1/10/2025 Follow-Up

The cure I organized was in placing an 8" spun-aluminum penetration adapter another layer down under shingles, which would permit lowering the cap for better alignment with the sheathing cut, and placement of "shingle bridges" as needed.

The repair worked although the roofer made no attempt to better center the cap and penetration adapter upon the roof cut.

These were the plans

Despite this cooperative experience, I could not interest tthe roofing company to employ penetration adapters as a beta user for the convincing of a roof cap manufacturer. The roofing company did not appreciate the great need of adapters for ducted vents, where roofers could remain agnostic of attic work.