Rainwater Mitigation

Water going where it’s not supposed to is one of the leading causes of damage to a home, and oftentimes, one of the most preventable problems.  Though some of those problems can obviously be caused by plumbing issues or a high water table, today we’re going to focus on understanding rainwater from the moment it hits your roof, until it’s safely on it’s way away from the foundation of your home.  How much water are we talking about?  A 1500 square foot house has to deal with 935 gallons of water per inch of rainfall.  Even if that inch accumulates over the course of a week, that’s still a lot of water.  How does your house deal with it?

Your Roof

When most people think of their roof, they’re only considering the part they can see, the shingles, metal, or whatever covering material is used over the underlying structure.  That’s also the first surface rain encounters as it interacts with your home.  Common, easily corrected issues usually center around missing or damaged covering material,  improper flashing around protrusions such as chimneys, plumbing stacks, or attic ventilation, or light vegetation growth.  If you know or suspect these issues might apply to your home, dealing with them early can prevent more major issues down the line.

Problems can also exist in how the valleys of a roof were covered, deteriorating support underneath the covering material (which can be caused by excessive moisture in the attic or mechanical damage from trees and high winds, among other things), or improper maintenance.  For the record, pressure washing asphalt shingle roofs isn’t recommended.  There are products on the market that, when applied regularly and properly, can help minimize the growth of moss which not only obstructs and slows water being shed from your roof, but grows under your roof’s covering material, causing separation and permitting further water intrusion.

Your Gutters

Attached to the fascia on the horizontal edges of your roof are your gutters, which provide a channel for water being shed from your roof to be carried away.  Too often, roofs are installed without proper flashing or a drip edge between the edge of the shingles and the gutter, which can allow water to penetrate behind the gutter, into the soffit, and lead to rotten wood.  Maintaining clean gutters ensures that water has an unobstructed path to the downspouts, assuming the gutters themselves are properly sloped.  Noticing water seeping behind the gutter isn’t always that easy to do in the rain, but if you notice the tell-tale trail on the ground directly beneath your gutters, a problem exists somewhere – either water is dripping off the roof and not making its way into the gutter, or the gutter is backed up and overflowing, or the gutter has holes; something.

Granted, some areas of the country (and even some areas here in the Pacific Northwest) don’t install gutters because the weight of snow and ice tears them off every winter.  But if you’re not in one of those areas (if you’re unsure, just take a walk through your neighborhood and note how many of your neighbors have gutters – that’ll give you a good idea if you don’t already know) then simple maintenance like cleaning your gutters will help them do their job and give you an opportunity to visually check them for other problems.

Your Downspouts

Assuming you’re not using rain barrels or cisterns to capture and store rainwater, downspouts and their associated extensions are going to be providing a controlled decent from upper roof and gutter sections into lower ones (hopefully in a manner that doesn’t damage the covering material of the lower section) or down to the ground and away from the structure.  If the junction between the gutter and the downspout has failed, then all of the rainwater that would normally be handled by that hardware is now focused on a few square inches of your roof, or deposited within a foot or so of your home’s foundation which will lead to erosion and a path for water to get into your crawlspace, or soften the soil underneath your slab or foundation wall.

Flexible extensions at ground level are better than nothing, but will simply collect water if not installed properly – at least until it overflows or the plastic fails and begins leaking all that water right back to your foundation wall.  Going back to our 1500 sqft home, let’s assume this house has 4 downspouts, one on each corner of a rectangular footprint, that each have to deal with 25% of the rain that runs off the roof.  This means each downspout and downspout extension has to channel 233.75 gallons of water per inch of rainfall – or 1,940lbs of water.  Still think a piece of brick pushing water 12 inches away is sufficient?  Granted, depending on your yard’s slope and how quickly that inch accumulates, those downspout splash blocks may suit you just fine.  I know it means a few minutes of being cold and wet, but I hope you’ll at least go watch what happens at your downspouts during heavy or even moderate rainfall.  If water isn’t being taken at least 2-3 feet away from your foundation (or worse, is being directed towards your foundation), the time to correct the issue is now – not at the end of the rainy season next spring.

Your Yard

Even if your roof is perfect, your gutters are brand new, and your downspouts and extensions correctly funnel water away from your foundation, if your house sits in a bowl, earth has to be moved to correctly drain your property.  It’s easy when the slope is obvious, but very gradual slopes can be hard to see with the naked eye.  The slope away from your house should measure an inch per foot for six feet, or six inches of drop in the ten feet surrounding the structure.  Water is looking for the easiest path to get to the lowest point, and swales, small ditches, storm drains, or french drains are often employed to direct water where we want it to go.  Put on an old pair of shoes the next time you get some appreciable rainfall and walk around your home and watch what the water is doing.  I look for signs of problems on every inspection, but the only way to know what water is actually doing on and around your home is to observe it, which can’t be done on a bright, sunny day.  Remember, excess water can come from your neighbor’s yard, too.

Once you’ve identified the problem areas, your contractor or landscaper should be able to help you implement solutions if you need a hand.


Sometimes, no matter what you do, a high water table will lead to water seeping up from the earth into your crawlspace.  The vapor barrier on the floor of your crawlspace should already be in place, properly installed, and checked regularly for problems caused by animals, or simply being dislodged by breezes or water intrusion into the space.  Sump pumps can be installed in the lowest point of your crawlspace and connected to your home’s drainage to pump out excess water.  These systems typically employ some kind of float or other method of turning the system on when the water rises past a certain point, and like any other mechanical system, should be properly maintained and checked regularly.  Replacing a broken pump is always easier and safer if your crawlspace isn’t already flooded.


No matter what the source, water is not your home’s friend.  We’ve gotten pretty good at preparing sites beforehand, utilizing better building practices and materials, and dealing with issues before they become problems.  However, entropy is always in play, and I encourage you to be proactive in looking for problems in and around your home.  What was installed perfectly 5 years ago will still age and fail in time.  Soil settles, erosion takes place, and a new problem can present itself that was not present the year before.  As you look over your home’s components and systems, be safe and err on the side of caution.

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