My neighborhood listserv is ablaze with people asking for help with repairs due to water damage. The recent rains are a good reminder that Austin gets an average 32.5" of rain every year, which is to say that our buildings are pretty susceptible to rainwater damage. It's common sense, yet, everyday I see houses built using risky construction details and building designs that ignore this significant element of our weather. How you deal with bulk water* at the roof, walls, and foundation (near grade) is very important to the durability of a building. If you are in the process of building your house, pay close attention to the weak spots identified below.
Water Intrusion at roof:
Most people recognize that roof and grade are obvious areas of weakness, when it comes to water intrusion. You've probably lived in a house that has had a leaky roof, most likely leaking around the chimney during a storm. Even if it's not literally dripping water from the ceiling, but just a wet patch or a watercolor stain, you've got a problem on your hands.
Water Intrusion at or below grade:
Perhaps, you live in a house that got flooded in the recent torrential rains. Yes, that was a lot of rain. But, if storm water accumulates outside your house in a downpour and gets precariously close to coming inside, then you may very well have a drainage problem on your lot, or your floor/ slab is not high enough. I've lived in that house and it's not fun.
How about the crawl space under your house that is a pond in a rain event. What about your damp musty basement?
Just think of all the people who walk out in the rain with a small umbrella and rain boots to protect them from getting wet. They've covered their bases - doesn't matter that their leggings are getting sprayed a little. Now imagine that you're wearing an expensive suit or a special outfit to dinner. Or you're going to be out in the pouring rain for a long time. You'd make sure you wear a trench coat and use the biggest umbrella you've got, wouldn't you?
The one good thing about the drought that prevailed over central texas for over 3 years was that our buildings didn't age as much. Because unlike human skin, which ages faster in the absence of moisture, building skins age faster in the presence of moisture. So if you are wondering why your house that was built in 2012 looked great for 3 years and now it looks like @*&#, then you've probably got unprotected walls that are aging from getting wet.
Water intrusion at walls:
The most commonly used exterior building materials such as stucco, brick, and stone do not repel water, but instead they absorb and hold water like sponges. That's why you see growth of mildew, algae, lichen, moss, fungus, etc on masonry walls that are exposed to rain. Not only is this a high-maintenance situation from an aesthetic standpoint, it's recipe for water damage to the innards of the wall.
Notice in both examples, that the part of the stone veneer that has water damage is at the base - the part most unprotected by an overhang. The umbrella isn't big enough. The taller the wall, the bigger the umbrella has to be. Also notice that these walls are more exposed because of their slope/ angle i.e. they are not vertical.
A good power-washing will take care of the mildew and unsightly discoloration on the stone. But if there is any wood framing behind that stone, it needs a good weather barrier and flashing at the base to protect from rot. You need a good trench coat.
In the pictures below, it's very clear what areas of the wall get the most water - it's where the water runoff from the roof hits the wall. Gutters that direct the water away from the wall are highly recommended. Also, the larger the roof area, the more the runoff - so size the gutters to handle the amount of water.
Water intrusion at openings:
The condition is worse when there is an opening in the wall, such as at a window or a door. The picture below shows a very common condition - where roof runoff hits the corner of a window. How long until there is water damage behind that path of water? Even if the window flashing is done well, this is condition that tests the limits of the materials and installation. It's risky.
There is no single solution, but mainly to acknowledge that rainfall is part of our climate and design for it. Include redundancies. Design a large roof overhang, avoid flat roofs, install correctly sized gutters, avoid large expanses of walls and unprotected windows, a good weather barrier installed shingle style, coupled with through-wall flashing and flexible flashing membranes around openings. If you can afford to, cover the wall with a material that sheds water - materials like metals or other large panel products.
*Bulk water - water damage vs. moisture damage
Most of the water damage and moisture damage in buildings occurs from 'bulk water intrusion', the main source for which is rainwater. Other sources being plumbing failures.
'Bulk water' implies large amounts of water, whereas 'moisture' implies trace amounts of water.
When left alone, both can cause significant damage in wood frame buildings. It's the rate of damage that varies. Depending on where the intrusion occurs and how much water enters, it may manifest immediately as a leak (as in dripping water) or wetness, OR it may take years to manifest. Typically, the longer it takes to manifest, the worse the damage. As we all know, we take immediate action when there are extreme conditions such as a leak, whereas a stain on the ceiling takes less priority in our busy lives.
No matter how well built your house is, you need a maintenance plan to keep things from getting out of hand. Question is, would you rather have a low maintenance house or a high maintenance house?