TOP 10 Blunders that rot your house, waste your money, and make you sick.


ONE
VAPOR BARRIERS ON BASEMENT INSULATION WILL ROT YOUR WALLS
We anticipate a house’s walls to get wet during construction, either from the weather or from the materials (that’s why joint compound is called mud). But they also can get wet once the house is finished and occupied. Wet walls have to dry. There are two types of wall that can get wet: regular walls over the ground and basement walls under the ground. In addition, there are two sides to a wall: an indoor and an outdoor it’s smart to design walls to dry to both sides, but drying to at least one side is a pretty significant objective. A vapor barrier on the inside of a wall means that the wall can dry only to the outside. This is OK for ordinary walls in cold climates (like Canada, where there are only two seasons: last winter and this winter), but it’s not OK for underground room walls, not in any climate. Basement walls can’t dry into the ground because—you guessed it—the ground is wet. Because basement walls can dry only to the in-side, covering the inside of a finished basement wall with a sheet of plastic is a bad idea. Wet basement walls wrapped in plastic can’t dry. We must build walls so that they can dry during wet seasons. By using extruded polystyrene foam for insulation, you can eliminate the inside condensing surface and prevent water intrusion from the outside.


TWO
VENTED CRAWLSPACES ARE MOIST ENOUGH TO GROW MUSHROOMS
Many years ago, we didn’t insulate crawlspace floors, and we didn’t air-condition houses. Crawlspaces were warmed by the houses themselves. Now that we protect and insulate floors, crawlspaces are within a degree or two of ground temperature. During nearly all of the summer, this temperature is below the dew point of the outside air, even up north. Airing and ventilating a crawlspace allows moist outside air to condense on cool crawlspace surfaces. As a result, the ventilation air is wetting the crawlspace rather than drying it. It’s like opening a basement window in June: The walls sweat.And wet walls turn into moldy walls quickly. The whole point of airing a crawlspace is to remove humidity. If we could import hot, dry air from Tucson to vent moist crawlspaces in Tupelo, venting crawlspaces would be a great idea. But for Tupelo air to vent Tupelo crawlspaces, the air needs to be dry enough to pick up moisture, and it needs heat to evaporate the moisture. This isn’t going to happen, and here’s why: Tupelo air isn’t hot and dry. Neither is Toledo air, Tallahassee air, nor Toronto air. A crawlspace is just a mini-basement and should be treated as such. It’s like a basement for a hobbit. You should condition the air in your mini-basement. Make it part of the house because, regardless of what you may think, it already is. Heat it in the winter and cool it in the summer with a supply duct or grille. Don’t insulate the floor; insulate the outer limits and install a continuous ground cover to keep out humidity.
THREE
DUCTS AND AIR HANDLERS IN ATTICS WASTE MONEY AND SUCK IN BAD STUFF





Why put the heating and cooling system outside the space that it needs to heat and cool? We insulate walls to R-19 and ceilings to R-50, yet we slip an R-4 sleeve over ducts and call it good. Where were the adults when this choice was made? What’s more, ducts leak. Let me rephrase that. Ducts leak a lot—about 15%. It’s like installing a large exhaust fan in the attic to suck conditioned air out of the house and pull unconditioned air in through the cracks. If radon were a valuable commodity, we could mine it this way. And think about winter. Heating bills go through the roof, and escaping air heats the top story, melting snow and forming ice dams. Goodbye, heated air; hello, water damage. You can’t make ducts and air handlers tight enough so that they won’t leak (don’t even think about duct tape). The least you can do is put them in a conditioned zone such as the basement or a conditioned crawlspace, or you can move the attic insulation up to the roof.


FOUR
USING JOISTS OR STUDS FOR DUCTWORK ROTS FRAMING
A panned stud or joist cavity is an air return that uses framing members,sheet metal, and drywall as ductwork (photo above). Why is this bad? Because the air is pulled through a leaky framing cavity instead of a duct, contaminants come along with it. The result is that air will be sucked from any leak available to equalize the pressure (drawing below). In a humid climate, the house will suck wet air into the wall cavities. If the house has a vapor barrier inside the face of the drywall, the water will stay inside the wall (air will make it through the cracks). Wall cavities are a bad place to store water. If the stud-bay or joist-bay return is in the garage, pollutants such as carbon monoxide or vapors from gasoline or solvents can be sucked into theliving space. If the air return is in a furnace room, combustion gases can besucked out of the flue (backdrafting). Here’s the test: Turn on the HVAC unit and spend a romantic candlelit evening with your significant other. Burn those cloying perfumed candles; the fine soot particles in the candles act wonderfully as tracers for airflow. Next day, look for stains on the carpet at the baseboards near a studcavityair return. Air is being sucked into the wall under the baseboard, filtered by the carpet, and marked by the soot. If we did plumbing this way, we’d flush our toilets into the floor framing.




FIVE
WINDOWS AND DOORS WITHOUT PAN FLASHING CREATE A WATER-INJECTION SYSTEM
There are only two kinds of windows in the world: windows that leak now andwindows that will leak later. The only things that leak more than windows aredoors. And the more expensive the door, the more it leaks—especially bigFrench doors with sidelites. And sliding doors. I know, I know, I can hear thesalesman already: “My windows don’t leak. They were tested at the factory.”Right, they didn’t leak at the factory. But they will leak after they’re in a house.
If not today, then tomorrow.Windows are like people; their characteristics change as they age. As windows and people get old, they leak. I don’t leak now, but I will someday. Windows and doors need a dependable backup system: a gutter. These gutters are known as pan flashing, that thing with a back dam, end dams, and a slope toward the outside. They’re simple to install; many come in two pieces that slide together (Jamsill; 800-526-7455). Just don’t put a hole in it because a dab of silicone won’t seal the hole. Silicone is like people: When it gets old …








SIX
DON’T LET BRICK WICK WATER INTO WALLS
I hate brick. No, I don’t—I love brick. I hate bricklayers. No, I hate lazy bricklayers who don’t ventilate cavities and clean up mortar droppings. Let me rephrase that. The old way of installing brick worked. There was a 1-in. cavity behind the brick with air inlets at the bottom, outlets at the top, and a clear pathway connecting the two. Why is this important? Because brick essentially is a dense sponge. When it rains, brick gets wet.Now, let’s pause for a minute to review the second law of thermodynamics:Water moves from hot to cold and from wet to dry. OK, back to the brick. What happens when brick is rained on? Brick gets wet, and we know that water moves from wet to dry (inward toward the dry part of the brick). Now what happens when the sun comes out? Yup, water moves from hot to cool (inward toward the cool part of the brick). If the cavity behind the brick is vented properly, the ventilation air intercepts the flow of moisture and carries it out the top of the wall. No problem. If the cavity is vented improperly, however, water vapor is driven inward, toward the cool, dry house, and through the vapor-permeable exterior housewrap and plywood sheathing; it then condenses on the interior plastic vapor barrier. Here, the water sits and waits for mold to drink it. If the vaporbarrier is leaky or if there isn’t one, the mold eats the drywall instead. If you’re going to install brick, make sure there’s a clear cavity vented at the top and bottom. If you can’t use brick responsibly, don’t use brick.

SEVEN
STUCCO NEEDS TO DRAIN
Stucco is a simple product. A few thin coats of reinforced mud provide a strong, goodlooking protective layer for a house. The entire key to successful stucco is drainage:There must be a drainage space between the stucco and the tar paper that the stucco isinstalled over. This used to be easy because in the old days, tar paper was more robust than it is now: It weighed more, was thicker, and had higher rag and cellulose content. The first coat of stucco would swell the tar paper. After the stucco and tar paper dried, the tarpaper shrunk back and debonded from the back of the stucco. The resulting wrinklesformed a drainage space. Today’s tar papers and housewraps don’t debond because theydon’t swell enough. Because they don’t debond, they don’t drain, and worse, theylose their water repellency over time. To apply stucco successfully with contemporarytar paper, use two layers of tar paper. The first will act as a bond break, and the secondwill act as a drainage plane between the two layers.

EIGHT
WITHOUT THE RIGHT PATHWAY, CONDITIONED AIR GOES TO ALL THE WRONG PLACES
Let’s see. We duct conditioned air (supply air) to a bedroom on the second floor and place the returnair grille in some other room on the first floor. So how does air get back to the return when the bedroom door is closed? It’s sucked under the door. According to my calculations, for this to occur efficiently, the gap at the bottom of the door should be roughly 1 ft. to prevent pressurization of the bedroom. Why is pressurization bad? Because uncontrolled air changes are bad. If your bedroom is pressurized, conditioned (paid-for) air is being pushed through the walls and ceiling. If the pressurized air is moist, water is being pushed into the walls. Remember, wall cavities are a dumb place to store water.Because a knee-high gap at the bottom of the door is unlikely to sell houses, we (repeat after me) ignore the problem. Air rushes under the door, is filtered by the carpet, and creates racing stripes at every door opening. Again, those romantically sooty candles enhance this effect. The retrofit solution at my house was throughwall vents.




NINE
AERODYNAMICALLY COUPLED GAS APPLIANCES CAN’T EXPEL ALL TOXIC GASES
More than 10,000 people visit emergency rooms each year with carbon-monoxide poisoning, and more than 500 people die from it annually. A little more than half of these cases are the result of automobile-exhaust inhalation; the rest are caused by consumer products. About 100 people die yearly because of malfunctioning gas furnaces and water heaters. We’ve come a long way since the caveman days, but when it comes to managing combustion by-products, we haven’t advanced much. Back then, we’d put a hole in our cave, light a fire, and hope the smoke would leave. We’ve advanced from a hole in the cave to aerodynamically coupled gas appliances. We’ve put a pipe over the fire and stuck the pipe through a hole in the ceiling to vent smoke.
In typical gas water heaters, the chimney isn’t connected to the top of the water heater;there’s a gap. Building scientists call this gap a bad idea. Everyone else calls it a draft hood.Except in Germany, where things always are ordered and precise, combustion by-products don’t follow arrows past the draft hood, especially if your house, range hood, or clothes dryer sucks(see No. 4). If your house sucks, the result is called backdrafting, sucking toxic gases into your breathing air. Installing appliances this way is crazy. You should use only sealed combustionwater heaters and furnaces, which are vented directly to the outside. And by the way, they should have a dedicated supply of combustion air piped directly to the flame (drawing above right), also with no holes in the pipe.



TEN-The most dangerous thing to do to your house
UNVENTED GAS SPACE HEATERS AND FIREPLACESPRODUCE COMBUSTION EXHAUST THAT DOESN’T BELONG INSIDE
You’d never run your car in an enclosed space, would you? So why would you run a gas heater or fireplace in one? I’m not talking about portable space heaters, which everybody knows are dangerous in enclosed areas; I’m talking about actually installing an unvented gas heater or fireplace permanently. Sure, they’reinexpensive, but the potential price tag is very high. At Building Science Corporation, we call this the Kevorkian option. Let me explain: There’s really no such thing as an unvented gas space heateror fireplace. The combustion by-products, quite simply, are vented into the room, then into your lungs and shuttled to your brain. This is bad.
When installed, maintained, and operated according to the fine print on their warning labels, gas space heaters and fireplaces have a pretty good safety record। But the potential for mistakes is too great.A window should be open when these heaters or fireplaces are on, but if it’s cold out, many people won’t open a window. Unvented gas heaters and fireplaces can’t be the primary heat source, but if their thermostat is set at the wrong level, they become the primary heat source. What’s more, the room size necessary for a 30,000-Btu unit is unfathomably large. Why in the world would you want to increase your risk ofcarbon-monoxide poisoning? Let’s revisit my cave analogy: We’ve got a fire in the cave and a hole in the ceiling for ventilation. Using an unvented gas appliance is like plugging the hole in the ceiling. By this time, we should have figured out that it makes sense to locate the fire outside the cave. One more thing: Unvented gas space heaters and fireplaces are illegal in five states. Sealed-combustion appliances, good. Unvented combustion appliances, bad. Period.

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