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Musings of an Energy Nerd

On Shutters and Water Management

How to tell good shutters from bad shutters — and what you can learn from water stains on siding

This luxury duplex is overloaded with bump-outs. Each bump-out presents a water-management challenge and exacts an energy-performance penalty.
Image Credit: Martin Holladay

I recently walked through a neighborhood in a Massachusetts town on the South Shore. As you might expect, the homes facing the ocean tended to be more luxurious, while the homes a few blocks in from the beach tended to be more humble.

It’s fun to look at houses from the sidewalk (or, in this case, the beach). During my stroll, I ruminated on house design and construction quality. In this blog, I’ll focus on two themes: the first concerns shutters, and the second concerns flashing and water-management details.

What are shutters?

Shutters serve many purposes. During a storm, they can protect window glass from wind-driven projectiles. When the homeowners are away, they can provide security against burglars. In crime-ridden neighborhoods, they can allow residents to sleep with an open window that admits fresh air while still excluding intruders. On a hot afternoon, they can exclude sunlight while still allowing a breeze to enter the house. In Alaska, they exclude bears.

Traditional shutters are usually made from wood. They can include louvers that permit ventilation, or they can be solid. In most cases, the width of a shutter is equal to half the width of the window it protects. Shutters hinge outward, and are usually secured in the open position by simple hardware so that they don’t flap in the wind.

Sadly, shutters have fallen on hard times in the U.S. In many cases, builders no longer include any hinges, turning the shutters into useless decorations. The shutters are simply screwed to the wall and can’t even be closed. Here’s what I don’t understand: if the purpose of the shutters is decoration, why can’t the builder get the proportions right? Why are decorative shutters almost always too narrow — less than 50% of the window width?

If the designer gets the proportions wrong, the shutters fail to fulfill their decorative purpose. The observer looks at the shutters and thinks, “Hmm — when those shutters are closed, they won’t even meet in the middle. Something is seriously wrong here.” A jarring element doesn’t decorate the house; it disturbs the viewer.

Here is a typical example of decorative shutters that scream, “Someone specified the wrong size shutters!”

Will you look at that! Functional shutters!

Since decorative shutters are now ubiquitous, you can imagine my delight when during my walk I discovered a house with functional shutters. How refreshing! These dogs can hunt!

Too many bump-outs

A little further down the beach I came across the huge luxury duplex shown in the photo at the top of this page. The house is less than ten years old. Since it faces the Atlantic Ocean, this building needs to have topnotch water-management details if it is to have any chance of being durable. So how did the designers and builders do?

I’d have to say that the jury is still out. But there are a few warning signs that there may be trouble ahead.

First of all, the designer of this building succumbed to a classic designer’s temptation: gussying up a perfectly good building by affixing a hodgepodge of bump-outs, balconies, and towers. Each of these bump-outs is an energy-performance liability as well as a water-management liability. Each transition from one plane to another introduces a seam where water can penetrate, and each transition requires the builder to think about where the water wants to go, and what type of flashing is needed to kick the water away from the walls.

Siding stains are clues to flashing performance

Because the building is a duplex, it’s possible to compare the condition of an area of siding on the left unit of the building with the condition of the corresponding area of the building’s right unit. For example, let’s look at the condition of the siding under towers’ south windows.

Hmm — stains on the right, but not on the left. What’s going on here?

I’ll admit that I’m not sure. But the photo reveals an important truth: very small differences in flashing and trim width can make an important difference in flashing and trim performance. I had no opportunity to inspect the window trim up close, but I do know a bit about detailing window trim. Because of capillarity, water can travel sideways, curling under horizontal trim. To interrupt this troublesome phenomenon, the builder needs to provide a hidden kerf to interrupt the water’s travel; such kerfs are common on the underside of window sills. If you forget the kerf, water can dribble down your siding (or even enter your wall cavity).

If you don’t want to trust a kerf, put some metal flashing at the seam of dissimilar materials — for example, where trim meets siding. But be sure that the flashing extends beyond the siding, and be sure that the flashing includes a drip leg. If you forget these details, or make an important component 1/8 inch too short, you’ll get water dribbling down your wall.

It looks like the builder did a good job on the left tower, but did something wrong on the right tower. Whatever the error, it was serious enough to show up as stained siding.

The two sides don’t match

In the two photos below, you’ll see that the flashing details under the right balcony are better than the flashing details under the left balcony. Again, the detail that caused the premature staining may be extremely subtle; the defective component may be piece of flashing that lacks a drip leg or is just a bit too narrow.

Flaring out the wall

In the next photo, you’ll see another designer’s conceit: the wall was flared under one of the windows to provide a little excitement to the wall. What’s wrong with that?

Well, once you flare out a wall, it’s no longer a wall; it’s a roof. If you use cedar shingles for siding, as this house does, perhaps there’s nothing wrong with converting parts of your wall into a roof. After all, cedar shingles can be used for roofing.

The main drawback of this designer’s conceit, ironically, is aesthetic: the flared wall gets much more exposure to the weather, so it turns gray very quickly. The eye is drawn to the stained siding — oops, I mean roofing — and the stains look like defects.

Notice also that the horizontal orange trim under the flared section of wall lacks any metal flashing to kick the water away from the wall. As a result, the water curls under the horizontal trim (through capillarity) and stains the siding below.

Last week’s blog: “Just Two Minisplits Heat the Whole House.”

Click here to follow Martin Holladay on Twitter.


  1. Lucas Durand - 7A | | #1

    Fun read.
    Thanks Martin.

    Hmm — stains on the right, but not on the left. What's going on here?

    I wonder...
    Did you happen to notice if there was staining on the other side of the left tower (on the side facing the right tower)?

  2. User avater GBA Editor
    Martin Holladay | | #2

    Response to Lucas Durand
    To the best of my recollection, there were no noticeable stains on the other side (the north). The reason may, of course, have to do with the locally prevailing winds -- or the flashing details.

  3. Kevin Karlberg | | #3

    Well, here goes
    While on vacation with my family on the cape, I took a moment to read the latest blogs. Imagine my surprise when I saw a photo of the very first residence I ever built. I am primarily a commercial developer, but when the boss asks you to build him a house….So I sighed and thought, “Oh no, what did Martin say about this?” and read on.
    It was actually while building this house that I joined this website so I could learn more. So I knew I had to respond to the article so that I, and perhaps others, can learn. Plus it seemed wrong to come here to ask questions and not give back when the very rare opportunity arises.
    First I will give some specs on the building. It is set on helical piers with breakaway panels on the lower level, has structural steel framing with wood stud infill, 6-8 inches of open-cell SPF, Zip System sheathing, and Jeld-Wen hurricane-rated windows and doors.
    I will also give some background in defense of the architect. The towers were incorporated to allow the owners to have a view of both Boston and the sunset from their home, while staying within the restrictions of the zoning by-laws. The many steel balconies and cat-walks were to pay homage to the owners’ occupation, which is a steel erection. The design also keeps the expansive decks shaded throughout most of the day, while offering privacy from the neighbors when on the deck. Though large, the home is smaller than the previous structure, and an effort was made to increase the view and light that came through for the neighbors. It is also a summer residence with very limited winter use. Thus the owners were not primarily interested in energy efficiency (I am just the messenger) and had other items they devoted their budget to. Finally, the owners love their home and are very happy with the design.
    Martin timed his visit perfectly, as the house started being re-painted last week. Actually, depending on when he visited he may have seen the house before being repainted, but after being power washed. This may be semantics, but when talking to the painter I said the shingles were worn, versus being stained. I am not sure if that makes a difference. Martin could not see it from the beach, but there is some staining/mildew on the siding near the deck, where there is another smaller flare out. The shingles (Cabot Cavalry) were mostly factory dipped, except for some of the arches and upper levels which were locally dipped due to the architect rejecting the arches a few times and a six week lead time from the factory for more shingles.
    To answer Lucas, the shingles were faded on the inside of both of the towers, but not on the outsides. This was strange to me as the sides not shown in photo take the greatest brunt of the winter storms. I had thought it was due in some way to the cat-walk, but after seeing the photos I am not too sure. I must now consider that it could be errors in the detailing as well. I wish this article could have come out before the repainting, so I could investigate better.
    I know I am not really adding too much here, but I am not too sure what else to add. I will answer any other questions I can. Of course, Martin, if you ever plan to be back in the area I would happily ask the owners if you could take a closer look; then after that we can relax on the deck. I will bring the beer.

  4. User avater GBA Editor
    Martin Holladay | | #4

    Response to Kevin Karlberg
    Thanks so much for your informative comments and your kind invitation to share a beer on the deck of the house in the photos.

    When I began reading your comments, I experienced an emotion similar to yours. You thought, “Oh no, what did Martin say about this?” I thought, "Oh no -- I bet my drive-by conclusions were glib and misguided!"

    Anyway, thanks for sharing the builder's perspective. And I hope we get a chance to have a beer and look closely at the flashing together -- maybe next summer.

  5. Kristen Simmons | | #5

    the darn screens get in the way
    Thanks for the very timely post. I'm considering operable shutters to provide shading for a Passive House retrofit. Louvered shutters plus inward opening casements will allow air to come in but not light. Great! But wait, the darn insect screens get in the way of actually operating the shutters as needed on a daily basis for sun control. I'm back to looking at overhangs, awnings, and exterior solar screening unless someone has a good suggestion.

  6. User avater GBA Editor
    Martin Holladay | | #6

    Response to Kristen Simmons
    Casement screens are on the interior -- they are easy to temporarily remove and replace.

  7. John Chrestman | | #7

    Kristen, Australia & New Zealand have a solution
    First I am a home owner and not a builder, but I am always impressed by quality craftsmanship. In both countries they use a lot of high quality steel widows. I have never seen that quality of window here in the states. Most tend to be stacked awning windows, hinged at the top and pushed out from the bottom, so it presents the issue about screening that you mentioned. Their solution is a screen with a rigid yet flexible magnetic strip about a centimeter wide forming the edging of the screen around the entire perimeter. You just slap it in place over the window frame outside the movable window and handle/locking mechanism. When you want to open the window just grab a corner of the screen and pull back till you can reach the handle, open the widow and just drop the screen. It slaps right back in place because of its rigidity and the fact that most of the screen is still adhered to the steel frame around the window. Just do the same to close the window. By the way I found most glass steel sliding-doors to also be very heavy and of high quality.

    Maybe I have gone too far off topic, but I fell in love with the awning windows and sliding glass doors, and what a beautiful, effective and simple screen idea for Steel windows.

    I suppose you could router out a wooden window and put in some small steel strips and create the same effect. As to the availability of such screens here, I don't know. I expect someone on these blogs would know. Just some rambling by a non-builder.


  8. User avater GBA Editor
    Martin Holladay | | #8

    Response to John Chrestman
    If you have steel windows, the screens you describe sound like a good solution.

    Unfortunately, steel windows are a thermal disaster. Window manufacturers know that if they want decent performance specs, they need to build window frames out of pultruded fiberglass, vinyl, or wood.

  9. Brian Wright | | #9

    Exterior Shutters
    I own a company that sells exterior shutters. I find that customers are increasingly concerned about proper size than in the past. We do attempt to educate the consumer and assist in training about proportion. Even though all shutters can be made functional, only about 25% are actually installed with movable hardware. I think about shutters every day, and notice every house and building with shutters that are too small for the opening. Thanks for your article.

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