How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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How is water getting into the outside walls of my home?
Wednesday, July 7, 2021
To better understand the ways that water can penetrate an exterior wall of your home, let’s start with the fact that water intrusion is not always liquid. It has three different states according to temperature, each with unique properties. The other two are solid (ice), or gas (water vapor).
Liquid water rolls downhill due to gravity, right? Yes, except where capillary action, the phenomena you see when a sponge sucks up water out of a puddle, comes into play. And, of course, wind-blown water in a storm can be pushed upward six inches or more into any unsealed opening in a home’s exterior, where capillary action sometimes takes it even further.
Then there’s ice. Most materials shrink when frozen, but water expands. And it expands with tremendous force. This is the property that causes burst plumbing pipes during a hard winter freeze.
And finally, there's water vapor. House-wrap material, which is applied over wall sheathing of a house under construction before the siding is applied. It is specifically designed to deal with the perplexing issue of water vapor movement through walls and it’s tendency to condense back to liquid form when it reaches a colder surface. Modern house-wrap allows water vapor to pass through, but not liquid water, because trapped water vapor that condenses inside a wall creates an insidious mess.
Liquid water can enter a wall from the bottom, vertical surface, or top. A concrete foundation sitting in extremely wet ground or a high water table can suck moisture up into the base of a wall by capillary action if not sealed by plastic sheeting barrier below. Openings in the exterior surface of the wall allow driven rain or the spray from a misdirected sprinkler head into the wall. Even a small crack admits some water, a long crack is equivalent to a hole punched in the wall, and cracks typically open further after admitting water for a long period. A roof leak near the edge of the roof, especially under deteriorated flashing at the end of a valley, will drip into the top of the wall corner below.
Humidity in outdoor air wants to migrate to the drier air inside your air-conditioned home in Florida. In physics it’s called seeking equilibrium. If you put any type of impermeable barrier on the inside surface of the wall—such as foil wallpaper—the moist air moving through the wall will condensate into liquid on the back surface, and eventually grow mold.
We don’t deal with water’s solid form much here in Florida, other than uninsulated pipes bursting during a hard winter freeze, or freeze-cracking of some types of bricks if wet. But ice formation is a big problem up north.
What can you do? Keep up with the caulking around windows, doors, faucets, light fixtures and other wall penetrations. Check regularly, and seal any cracks in the wall as they appear. Also, gutters with downspout extensions are great for avoiding rain splash-back onto walls and keeping puddling water away from the base of the house.
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