Home & Garden Columns
Disregard any fictitious tales you may have heard about me doing inspections in the buff. Aside from the danger of sunburn, electric shock or harm to the casual observer, it would be unprofessional and I am, if nothing, unflinchingly professional. OK, check your legs for matching length, but I do think I have your attention and it is flashing that I want to talk about (and not the naughty kind).
Flashing is a word that every learned builder and architect knows well, but is one that means little or nothing to the inhabitants of even the leakiest house, though they would certainly benefit from the knowledge.
Flashings are a class of building components that are easy to miss because they are largely hidden. Nonetheless, they play such a vital role that it would not be an exaggeration to say their absence or misapplication in construction is involved in the majority of investigations in which buildings were found to leak.
In short, flashings keep buildings from leaking. You might say, “Well, I thought that roofs did that and siding and trims.” Well, this is true but the reason that those parts don’t leak is because they are flashed (or have inherent elements of flashing built into them).
A flashing is any of a series of shaped components designed to prevent water from entering a building where materials change shape or direction. When a pipe penetrates roof surface, a special flashing (this is a penetrated cone, bonded to a flat sheet that can be laid into the flat arraying of a roofed surface) is installed. Where a roof meets a higher story wall, a roof-to-wall flashing (or set of “leaf” flashings) is used. When a doorway penetrates a wall, a “head” flashing, among others is used.
Flashings address the water that wants to leak through a building surface at the most vulnerable points, those places where water running down a surface encounter a change in direction. It’s not easy to punch a hole in something and keep it from leaking. A flat surface is pretty easy to protect from leakage (though leaks still sometimes happen) through any of a catalogue of layering methods. Shingles have their layers, stucco has its too and wood planking as well. Each has a set of layers that make it “less” vulnerable to leakage if the rules get followed.
The real trouble occurs when we change direction or start punching holes in things. No matter how great the roofing material may be, one improperly installed skylight can easily leak during the first or fourth year. A 40-year roofing warrantee (remember that this only applies to the material and that installation is nearly always at fault) doesn’t help you much if water is leaking around the shingles through a hole or gap somewhere.
Window leaks are usually flashing leaks (though some windows are ready to leak when they leave the factory and I’ve heard estimates of failure as high as 15 percent in recent years).
When water comes running down a wall and hits a trim or opening, some of it has the potential to sneak inside by gravity or through capillary action (which is a process that can actually suck water into your house; so when you say that this leak sucks, you may well be right). Only the very careful assembly of the window, using an array of shaped or flexible materials and membranes can prevent water from finding its way inside.
The exact position of each substrate is critical and windows often leak from a simple mis-folding of a piece of tar-paper or felt. The best installation relies on several layers of protection, often referred to as a “belt and suspenders” approach in which we use felts or house-wrap to direct the water back out of the house, as it tries to sneak inside, and then to add metal or flexible tape flashings on top of these as a second tier protection. It’s not at all unlike the way our bodies repel infection. We start with skin, which is multi-layered itself and then have layers of protection below that, if invaders make it past the gates.
The ancestors of today’s buildings employed many of the same techniques but with a different set of materials. Galvanized metal strips (the most common flashings) may not have been available but a window assembly could still be made of a series of elements that have inclines and that puzzle together in such a way as to force water to go uphill in order to get inside (which can happen but usually doesn’t). If you then add good adhesion or cohesion of materials to this methodology and thick lead-laden paints, you stand a good chance that you’ll keep the water out. As we’ve moved into a fast-paced world of cheapness, we’ve come to rely more and more on technologies such as flashings to keep the water out. That said, I think that well-installed flashings are a huge advance over the old-world methods involved in the assembly of the building envelope. If for no other reason, they allow us to perform tricks that would have been considered nuts in the past, including the installation of skylights in roofs.
If you want to find the flashings on your own house, it can be tricky (since many are either completely or partially hidden) but here’s a short tour. If you can step across the street and your house has a well-pitched roof, you will likely see some conical flashings (as noted above) around the pipes and vents that penetrate the roof. If you have walls that ascent from the roof to enshroud a higher story or dormer, you may be able to see some metal that runs along the corner where the roof meets that wall (the upper edges should be hidden under the bottom of that wall’s siding but are often improperly stuck to the surface and will therefore require periodic application of sealants). The edge of a roof often has a metal trim that prevents water from getting into the structure of the roof or walls below. With all of these, the same principle applies, that being that they must be placed in such a way that water cannot get behind them under reasonable circumstances. Therefore, they will usually be tucked up under the upper material and splay out onto the lower material so as to assure that water cannot get up underneath. This job varies with the landscape and if you take your time to think about it, you can usually see whether they’re doing the right thing. It ain’t rocket science.
Another stop on our tour is the “head” flashing on a door or window. If you think about it, the most vulnerable place on the door or window for water leakage is the top where water splashes against the top trim or the frame of the window itself. If you fold a piece of metal so that the top part fits under the siding above the window and hangs out over the trim at the top of the window, it will then take a very hard stiff wind to push water up to the top. If we do this right, there isn’t a likely wind sufficient to make it leak. We do the same thing on the sides of windows and doors but mostly, we just use the paper and plastic sheeting that we are already laying below the siding and by clever folding and careful use of fasteners (so as to avoid poorly placed puncture points) on these sides and bottoms. A doorway to the outside should be fitted into a shallow pan that allows drainage only to the exterior, although this is a newer practice and one that’s not being eagerly received by many in the construction community. Notwithstanding, many a leak that has plagued lower floors below a second story doorway can be avoided with this clever use of folded metal or cast plastic.
While the full understanding of flashings is certainly part of the master class of building, looking for them during construction and understanding their intelligence or potential efficacy isn’t beyond the ken of the average adolescent.
Here’s your assignment of this week. Stop at the next construction site you see if you can follow the imaginary drips of water down the roof and down the wall, looking for how the paper and metal have been laid as repellants. You might just find that one of those sheets or strips is upside down and waiting with yawning thirst to drink in and rot that wall. Nothing would surprise me less than a discovery such as that by a patient, inquisitive person who doesn’t even own a hammer.