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Gable End Vent

Solving a new gable end vent puzzle…without a ladder

Sometimes it’s the little jobs that allow us to flex our ingenuity muscle more than the big jobs.

(Click on any image to enlarge)

We were just finishing up a bit of messy work on some foundation waterproofing for a client when they mentioned that they were also getting some leaks into the gable end of their attic. I looked up at the 35-foot-tall brick gable-end wall and could barely see the ratty wooden vent from below, but it seemed like the likely culprit.

While we were eager for some cleaner work, I knew repairing this puppy from the outside would be no picnic. So I said, “Let’s take a look in the attic and see what we can do.”

From inside the attic it was easy to see that the brick and block of the gable end were run up around the form of a combination circular/orthogonal vent. This was typical new construction. Installing retrofit pieces would pose a geometric puzzle. The simplest solution to this puzzle would involve cellular PVC, Festool dominoes, Kreg pocket screws, and (best of all) no ladders.

Here’s how we went about it.

Studying the old unit for replication and improvements

The original unit (see photo, right) practically crumbled out of its existing masonry opening. Demo from the inside was a piece of cake, and we brought the unit back to the shop. I measured the outside diameter at exactly 28 in.

This turns out to be a fairly stock unit, and is still widely available, but it’s built mostly from finger-jointed sugar pine. I wanted our new vent to last much longer than the original, yet I felt obligated to match all outside and visible profiles exactly—after all, this was an historic district.

The one small concession I made to changing the outside look of the original vent was adding one extra louver, which helped prevent windblown storm rain from bouncing inside the attic. No one from the neighborhood could possibly pick up this ‘before and after’ change; they’d have to have one heck of a visual memory!

New materials and tools allow better ingenuity

The solution I came up with in order to improve the durability of the new vent, and work a finished installation from the inside, consisted primarily of four key design aspects:

  1. Building two frames on the inside of the radius work, whereas the original only had one. This would allow for a secondary louvered rectangular assembly to nest inside a primary rectangular frame. Since the primary frame could be locked together securely to the exterior brick mold with a few stainless steel pocket screws from the inside, this solved the geometric puzzle of fitting two different shapes into two different existing masonry openings. A secondary panel was the only way to avoid the problem of fitting louvers into the primary frame on-site. This would have been more troublesome than in a shop, and probably would have involved touch-up paint and caulk from the outside on a 40-ft. ladder.
  1. Improving drainage to secondary louvered frame panel by fitting flashing ‘blocks’ or ‘diverters’ between the lower half of the vent slats, which allows rain to drain quickly toward the exterior. The need to install flashing blocks was another reason I didn’t want to fit louvers in the primary frame on-site.
  1. Constructing everything from cellular PVC, due to its workability and weather-resistant  characteristics. Also, the quick set times of PVC glue allowed us to speed up the process of millwork, and gave us very strong and reliable bonds in our laminations and joints.
  1. Installing a replaceable screen to the primary frame, thereby allowing the secondary frame to be captured and ‘float’ within its nesting place without mechanical fasteners or glue. Having southern exposure, I felt the more massive secondary PVC louvered frame of this vent could potentially expand and contract much differently from the primary frame. I didn’t want it transferring stress to the primary radius work and/or stress the caulk seals. I felt a snug secondary frame fit and an overlapping screen lock were the best choice for this situation.

Getting to work in the shop; radius and primary frame work

A screw is nothing more than a helical clamp. These “mini clamps” allowed us to work from the top side, without having to get under the board with bar clamps.

We started by working off of a scrap of 3/4-in. AC plywood. This provided a good sacrificial base upon which we could fasten multiple layers of PVC flat stock, all with mitered corners. The plywood base was large enough to accommodate the complete width of the finished radius profile.

The brick mold thickness was built up from laminations of 1/2-in.-thick stock on top of 3/4-in.-thick stock with off-set joints. We used regular PVC glue to laminate the layers and Festool dominoes to reinforce the joints. Layers were clamped tightly together using screws that were placed outside the profile and into the sacrificial base (see photo, right).

We placed dominoes in areas that would be buried in the finished brick mold profile, which meant they would not be exposed or ‘revealed’ during the milling phase.

Finally, we padded up our center trammel point with plywood scraps to be flush with the top layer, and worked our router from outside in, and top down.

The sacrificial base allowed us to rout the profile all the way through without cutting into our workbench. There was a 3/4-in. brick mold backer that was routed separately, glued (with PVC glue), and clamped to the brick mold profile, to give full profile to the inside radius. It was roughed-out from an octagonal glue-up (again with dominoes at joints).

Since this backer had to fit and register inside the back of the louvered outer frame, it was not the full outside radius. This was one of the trickier parts to make and attach. Again, to avoid on-site fitting, I used the old vent as a pattern, because we knew that fit!

Here is the brick mold glue-up prior to routing and surfacing. The routing process was all done with the center trammel point. We had four main cutting planes to achieve, and they were easily worked out in multiple passes with two different profile bits.
The final 3/4-in. backer molding is cut to the inside radius size. Here the brick mold is just laying on top. I glued on the backer after cutting it to size. The outside radius was just trimmed with a flush bearing bit wherever it projected beyond the brick mold. The backer did not need to be a perfect edge along the outside of the brick mold since it had to be trimmed to rectangular frame-size later. In fact, you can see a section missing near my thumb.  

Secondary louvered frame

While I worked radius profiles, my helper milled the PVC stock to size, and assembled the secondary louvered frame. All frame and louver components were glued with PVC glue and/or pocket screwed with stainless steel pocket screws. There were no components that would prematurely rust or rot.

Since the inside louver shape is bigger than the circular brick mold, rain water can get behind the perimeter edge at the lower half of louver. In fact, frequent water penetration on the old unit led to its failure. To improve the design, I glued filler blocks between the fins just on the outside edge of radius (and out of view). This serves to divert water down to next lower fin.

I shaved down the excess filler easily with my FEIN multi-master, and sanded it smooth. All water now drains by gravity down to the bottom of the circular trim and vacates at the exterior brick face of the building’s envelope.

Had this new louvered piece been made from wood, I would not have been so confident installing wood ‘deflection’ blocks in this manner, due to the effects of wood fiber expansion and contraction, resulting in stress across the glue joint. However, only having to overcome limited thermal expansion and contraction stress across the glue joint, I felt PVC was a good choice for a detail like this.

You will later see the ‘notch’ in the exterior brick molding that serves as the final evacuation point for any accumulating moisture on the bottom of the brick molding.

Finishing up in the shop

In the photo to the right, you can see all three components of the louvered vent, as a bird would see it from the outside. Note the ‘diverter’ blocks on the vent panel (in back) and drain notches on the bottom of the primary circular brick mold unit. More on the drain notches below.

We painted the finished components (only exterior exposed surfaces) in the shop with three coats of quality exterior latex acrylic paint (Sherwin Williams “Duration”) using High Volume/Low Pressure (HVLP) spray equipment. Spraying is faster, and gives a very even coat; particularly on material like PVC, which doesn’t soak up a paint film like wood, and can often show brush marks.

Some may note that milled PVC is a rougher surface when you expose interior ‘grain’ through the milling process. For this project, where the finished piece is thirty-five feet in the air, we felt nobody would notice; plus, we felt the roughness allowed a better mechanical bond for the paint. If we wanted a smoother finish (say, for a more visible condition) we would have used a couple coats of primer and sanded between coats (in order to fill low spots of pours), and then sprayed the finish coats.

Installing On-site

Since we previously pulled the old unit into the shop to use as a reference model, we only had to remove a temporary plywood panel from the rough opening before installing our new, three-stage unit.

The nesting detail is what made this whole thing workable from inside the attic. The inside frame was pocket-screwed with eight stainless steel screws to the outside circular brick mold. I used a close pair of stainless steel pocket screws (rather than a single at each location) to provide another level of security and insurance, preventing the radius work from ever wanting to jump out of the hole and leave home. Because of the different geometry within the planes of exposed brick and rough block, these screws lock the whole assembly in the hole mechanically and geometrically.

The outside radius was fully caulked and sealed to the brick with matching exterior grade caulk. This may look like I climbed a ladder and took this shot, but I was not that brave. This was about 35 feet off the ground, and since I designed this thing to be installed without taking that risk, I merely stuck my camera outside and shot back towards the work.

In the image to the left, you can clearly see the drain notches on the molding I talked about earlier. The notches allow any accumulating water on the bottom apex of the brick mold to easily drain to the outside. Even though PVC won’t rot, I like this detail—a little extra insurance on the longevity of the unit.
Next, I installed the secondary louvered frame, which fits perfectly inside the primary frame, and is screwed to the exterior circular brick mold.
Next, I just tapped the secondary frame home—no screws necessary. Additionally, the unit can expand and contract separately from the outer frame and the attached brick mold, with a fiberglass mesh screen keeping it secured from ever drifting inward toward the attic. It can’t go anywhere.  
Here is detail of the fiberglass screen fit to the inside of the vent to keep the insects out of the attic. Saw kerfs (dadoes) were made around the inside edge of the primary frame (simple table saw cut during the shop phase). These kerfs accepted rubber screen retaining beads, so that the screen could be easily replaced should it get clogged up with airborne dust and pollen over time.

Below, you can see the freshly re-mortared primary frame within the rough block opening. There is no way rain water can get inside this well-detailed vent. I also suspect that it will remain this way for a very, very long time.

I can tell you that the clients were very pleased with us fixing this annoying leak in their attic with a quality solution. And we were pleased to safely walk away from this job without ever having to scale our 40-ft. ladder.

• • •


I began my building career apprenticing for a master carpenter at age 14. This was after school hours, remodeling homes in historic Clifton, Va. I can still remember my first project—a lattice surround for an air conditioning condenser. Not the most glamorous project; but a nice start. I think my mentor, Louis McFatridge, thought it was a good (and safe) idea to test me on something outside, and seemingly inconsequential. However, since the condenser was on the home’s approach (thus the lattice), I knew all guests would see it. So I took the opportunity (and my mentor’s best chisels) and set out to make it the best lattice surround I could fabricate with my limited skills and knowledge. It was not a masterpiece, but it must’ve turned out pretty darn well because I stayed on with him during the next four summers, up until college. Even during college I got on with any framing or trim crew I could find that would hire me, during holiday breaks and summer recesses. As a designer, this early, and regular, hands-on experience proved invaluable.

I love the design-and-build process, and never consider anything completely perfect. It can always be better. In fact, I earned my bachelors of Architecture degree at Virginia Tech specifically to become a better builder. I started my own design/build company, Vice Versa Builders, in 1993. We specialize in residential remodeling.

I have been truly blessed to be able to do what I love, and love what I do. For me, architecture is problem-solving, with an artistic mindset. Masterpieces are achieved through classical and romantic building elements, living (and aging) in harmony. I always try to keep in mind the advice I give my clients: “Every good solution is preceded by a well defined problem.” Since remodeling problems are usually unique, my goal is to learn, define, and study the specific problems. Then I look to frame the building solution within a harmonic construct that strives for architectural perfection. After 30 years, I’ve been at it quite a while now, and I’m still looking to achieve my architectural masterpiece in every project I take on.


13 Responses to “Gable End Vent”

  1. Dezri Dean

    I hope not to offend! What do you mean by “historic”???
    If it were historic the time frame seems a little short!
    Historic to me is 100 to 200 years old, and I have never seen any historic builder worth his salt to build a “Bald” gable like this.

    • Sonny Wiehe

      As I say in the article, the home is in an historic district (Old town Alex. est. 1695 and declared a National Historic Landmark in 1966). I never claimed the home was historic. It may or not be, but I am not in a position to make that assertion. From what the current owner has told me, this town home is part of a mating pair that was torn down and rebuilt in the 60’s. I speculate that this pair of 60’s era town homes were required to meet stringent criteria for exterior architectural detail in this district when they were “rebuilt” in that era. That doesn’t mean to say that qualifies them as “historic” either. I do mention the vent replaced is still widely available today. I would not be able to make this claim about a vent built or installed 2-300 years ago. That should be one big clue that I not working in the mode of an “historical builder”. In any case, my point was to replace exactly what was there in look and fit so as not to redefine the architectural intention and function of the vent.

  2. Al

    Time is not of essence for a house or building to be considered “historic.”

    his·tor·ic (h-stôrk, -str-)
    1. Having importance in or influence on history.
    2. Historical.
    Historic refers to what is important in history: the historic first voyage to the moon. It is also used of what is famous or interesting because of its association with persons or events in history: a historic house.

  3. Jeff

    I don’t think that “historic” is the focus of this article,or at least that is not what my thoughts were centered on. Nice design on the replacement and well executed, however my question is since this took quite a few man hours to produce, were you able to make money on this project. I know sometimes I do work that helps my reputation more than my bank account.

    • Sonny Wiehe

      Thanks for your kind thoughts. I thought this question may come up. I think the same thing on many other custom projects I see detailed in this magazine and others. You are correct; it was not an inexpensive project to execute. Not many folks are willing to spend a fair chunk of change on something they can’t see and enjoy on a daily basis. However, the old vent was leaking into attic and into their guest bedroom ceiling. This was impetus enough to pay someone like me to fix the problem in a long term manner…and for me to make money doing it. Don’t you like when that happens?…cause it ain’t often enough.

  4. Jon Patterson

    Jeff, thanks for keeping us on target.

    Sonny, very nice article and workmanship. I have no doubt that you saved the customer thousands in repair costs and by using PVC it will protect the house for years to come.

    How long do you estimate the paint will last on the exposed trim?
    What are the exhaust ducts in the way of the vent? Can they be redirected? Is that an electric fan attached to a 2x in the middle of the vent?

    • Sonny Wiehe

      That is a great question. I have used cellular PVC extensively for exterior trim (in both raw and painted conditions) for about 10 years now. I prefer not to paint PVC if the color scheme permits, but the projects that I have painted (and revisited lately) seem to holding up exceptionally well– and don’t require repainting. However, we all know that no paint film lasts forever and I suspect 10-12 years would be the point where repainting might be warranted for a fresh look. When that time comes the nested nature of this vent will be a huge plus. The screen bead could be pulled, the secondary frame pulled, and it could all be easily repainted from the attic. Again, no need to drag out the 40′ ladder!
      The existing exhaust vents are bath fans. I re-installed them just as they were. I suppose they could (and probably should be by code) be brought through the masonry wall and terminated with a wall cap, or roof plane with a roof boot. But that was not within my scope of work. However, I didn’t see them as obstructing the function of the vent very much at all and there was no evidence of moisture or mold issue from this configuration. If dryer vents were involved it would probably be a different story.
      The electric fan looking object is actually an alarm horn.

  5. Gary B


    Great looking work and a very interesting/informative piece to read. I am wondering what type of domino’s you are using. Sipo? Or a custom milled PVC domino?

    Again, great job and great article, thanks.

    • Sonny Wiehe

      Thanks Gary!
      Another good question. Yes. I used the Sipo. Festool says they are designed for exterior applications. They probably won’t last as long as the PVC, but theoretically they’re encased by PVC and are not subject to direct exposure. This, coupled with the fact that the joint strength has redundancy with the glue led me to feel good about using them and not going to the extra trouble of milling my own PVC stock for this loose tenon application.

      Incidentally though, I have used large sheets of 1/2″ PVC on other custom exterior projects that are joined with a continuous tongue and groove slip joint. I do mill my spline stock (1/8″ x 3/4″) from PVC for this application because the joint is not glued and becomes exposed during cool weather cycles.

  6. Bob Fankhauser

    Clearly NOT “historical,” in that PVC only became available a few years ago. BUT I’m pretty sure that the skilled, dedicated carpenters of yesteryear would have gladly embraced PVC where appropriate, especially when confronted with today’s less-than-ideal wood.. As an example, the Inuit happily traded their harpoons and paddles for rifles and outboards and were renowned and respected for their ability to keep them in good working order.

  7. Nate

    Can I vent my bathroom exhaust fan to the gable vent? Or do I have to cut into the roof


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