The first of many home inspection tips: Attic, ice dams and mold contamination

Of the hundreds of homes I’m in a year a third have issues with Attic Mold Contamination.  When purchasing a home the most basic part of a Home Inspection should ensure there is no appliance direct venting into the Attic, there is adequate insulation in the Attic and the Attic exhaust/intake venting is correct.

A client several years ago experienced respiratory issues.  They had just purchased the home four years prior.  This home was less than 10 years old.  During my air quality inspection I discovered their bathroom vent and kitchen stink pipe was direct venting into the soffitt area of the attic.  A significant amount of Stachybotrys mold gowth was identified. They had a home inspection when they purchased the home, all the inspector had to do was unscrew four screws and look inside the attic area and would have seen the vent. This cost my client over $15,000 to clean up.

Mold contamination in an attic is caused, the majority of the time, by one or more of the following:
I. Inadequate ventilation
2. Lack of insulation between the attic and rooms below allowing moisture to enter into the attic.
3. Appliances (dryers and bathroom vents) being directly vented into the attic.


TP Environmental does not recommend mixing two types of exhaust vents on the same roof when it’s a common attic because it could result in short-circuiting the attic ventilation system in which one of the two exhaust vents becomes intake resulting in possible weather infiltration and less than optimal attic ventilation for the entire underside of the roof deck.

There are generally four groups of exhaust vents: ridge vents, wind turbines, roof louvers/gable louvers, and power vents. Intake vents would be soffitt vents. Gable vents can act like either exhaust or intake vents depending on the set up.  Each group uses the wind differently. If any of these different groups of exhaust vents are mixed there will potentially be a short-circuiting situation. Short-circuiting the ventilation system will result in areas of the attic being bypassed (skipped). The system will still be venting, but it will not be performing optimally. Furthermore, weather infiltration is a very real possibility.

Increase the ventilation in the attic by balancing intake and exhaust venting. Money will be saved. HVAC machinery will wear less. Your kids asthma might go away because hot humid attics, which are filled with organic material, are breeding grounds for mold. The house will feel more comfortable. The roofer will be delayed because your roof last longer. The home won’t need to be painted as often. Little known is that ventilation was not started in the south for cooling purposes but in the north by paint companies in the 1930’s and 40’s because humid attics were causing paint to peel.

*****See Below for how to Calculate your Attic Ventilation*****

Insulation should prevent the warm air from the rooms below from rising into the Attic and mixing with the cooler air, causing condensation…..and MOLD.

Ice dams are caused by heat loss from inside your house. Heat rises into the attic, warms the attic and the underside of the roof and helps melt snow when the warm sun is shining. To prevent ice dam formation in homes, you need to prevent this heat loss or inadequate insulation.

An ice dam is a ridge of ice that forms along the lower edge of a roof and blocks melting water (snow) from running off the roof. Over time, the dam of ice builds up as more and more water freezes and the runoff water pools behind the dam–eventually working its way under the shingles right into the roof structure–and even down into the house.  Ice dams are caused by heat loss from the house, so in newer construction with good insulation and proper attic ventilation–ice dams aren’t much of a problem. However, in older homes–ice dams remain a constant problem and cause millions of dollars worth of damage in northern climates. Here’s how you can prevent an ice dam on your roof.

Ensure your attic insulation is up to modern standards. Modern building codes require attic insulation to be at least R 38 or even higher. This is approximately 12 inches of fiberglass bat insulation.

Allow cold outside air to flow through your attic. A properly ventilated attic has open soffits (under the eaves) where outside air can come in and upper vents (either individual roof vents or a ridge vent) that allow the cold air to move up underneath the roofline and out the top. This air movement keeps the roof cold and prevents an ice dam from forming.

Install baffles between the roof joists to stop any insulation from migrating over the top of the soffits, blocking the air and preventing proper air movement.

Insulate and seal all openings from the house into the attic. This includes plumbing stacks, heating ducts, attic access hatches (this I find alot as the culprit of mold growth), lights and ceiling fixtures. Any and all of these openings into the attic will allow warm air into the attic raising the temperature to help melt snow on the roof.

Prevent a large buildup of snow on your roof. A roof rake will allow you to pull any snow buildup off of your roof while you stand safely on the ground.

Ensure that the vent hoses from a dryer or bathroom fans do not vent directly into the attic. They should be vented to the outside.


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Step 1

If you need to calculate the attic area yourself you need to sketch a footprint of the foundation and measure each side. Graph paper will make it much easier. Determine how many square feet of foundation you have and you now know how large the floor of your attic is.

Step 2

The square footage needs to be interpreted in square inches as all vents are calculated in square inches. Different roof exhaust and soffit intake vents have different capacities. To make this change multiply the square feet of attic by 144, the number of inches in a square foot. For example, if you have a 3000 sq foot foundation you will multiply 3000 x 144= 432,000 square inches of attic floor.

Step 3

Divide the attic floor area, 432,000, by 300 and you’ll know how much total venting, intake and exhaust, your home needs. 432,000÷300=1440 net free area of venting. Half of that is exhaust and half is intake. You’ll need 770 inches exhaust and 770 inches of intake.

If you have too much exhaust you’ll create a negative pressure in the attic that will try to pull air from wherever it can. Light fixtures, attic access, hot water closets, and anywhere else it can rob air it will.

It can also make the carbon monoxide from your gal flues return down the pipe or cause Radon gas to infiltrate up through the cracks in the foundation or along the sewer vents as they pass through the slab.

Too much of a good thing is still too much, even in attic ventilation

Step 4

Time to go on the roof and in the attic and evaluate your current exhaust. If you have a combination of different types of vents your venting is probably short circuited. Turbines, low profiles, power vents, and gable end and louver vents are not compatible. They will talk to each other and stop the “chimney effect” of air moving from bottom to top. The soffit vents will be left out of the conversation as the heated air will take the path of least resistance.

Air entering a gable end vent will exit the vent ridge just inches away and a lower vent ridge will feed a higher one. All of your vents must be on a plane so as to have equal voices in exhausting air. If one is higher than the others it will have the loudest voice and silence the soffit intake.

Step 5

Besides the holes underneath the existing vents might be too small. That is why the best course usually to start from scratch and close off or fill in all existing vents.

Some vents are more difficult to install. The easiest to install is the low profile vent. The others are more likely to leak or blow off. The wind turbine is the most common and least effective. In fact, it’s name is a oxymoron. Wind inhibits the effectiveness of the vent because the attic will need to build up pressure to bypass the spinning turbine. There is no magic pull from the turbine by virtue of its spinning. The wind is pushing it instead of the escaping hot air. The other type of vents have a downwind vacuum that keeps them working in the wind. This is called the “Bernoulli Effect.” This is the same force that lifts airplanes off the ground. An attic is much less complicated.

Step 6

All vents have a certain amount of NFA that can be determined by the labeling, from the manufacturer, or sometimes even from the name. A RV50A low profile has 50 NFA and a SSB960A has 60. Therefore take the 770 NFA needed for exhaust and divide it by the NFA of the exhaust vent you choose. The result is how many vents you need.

If a 50 NFA vent is needed you’ll need 15.4. That means 16. The 60 NFA vent requires 12.8 or 13 vents. Be sure to install then at equal altitudes or in a row.

Step 7

Now it’s time to figure the intake. Some say that if you had to choose between only exhaust or intake vents, intake is the one to choose. Making sure that there is balance between the exhaust and intake is critical. You may put in extra exhaust vents but you’ll need to increase the intake to keep up with it or the negative pressure monster will come.

Soffit vents can be continuous or individual in different sizes or NFA. Take the size of soffit vent you have and divide its NFA into the 770 and you’ll know what your minimum number soffit vents is. Be sure to not install them over doors or windows, not for the aesthetics, because of the building codes concerning fire.

If fire breaks out the glass of a window and then jumps into the attic rather than burn through the soffit, the fire department has less time to save your property and maybe your children.

Usually the soffit vents that are in place are closed off with paint, dust, or roof debris but also most have holes cut too small by the builder. Everyone is surprised by the hammer hole that the carpenter made for the 16″x8″ soffit vent that was supposed to have 65 NFA but only has 2. The smaller 16″x4″ soffit has 26 NFA. The model attic of 3000 sq ft. needs 770 NFA intake which requires 12 of the 16″x8″ intakes and 30 of the 16″x4″.

Step 8

Hold the vent up to the soffit and pencil the perimeter so you’ll know where to cut. After cutting the whole make sure that the insulation is not obstructing the air passage above the top of the wall and beneath the roof deck. If needed you can install thin foam baffles to keep the critters or repairmen from scooting the insulation back into the cavity.

Step 9

Re-inspect the vents on the roof and soffit to make sure there won’t be roof leaks or animal infestation and while cleaning the attic floor of the debris caused from cutting the holes inspect the various ducts and tubes inside.

A loose water heater flue can cause carbon monoxide poisoning. A bathroom fan or kitchen vent a hood not vented through the roof can destroy the decking with humidity. A loose plenum or porous duct will rob you of your hard earned money, which you’re trying to save by doing all this work

Look at the insulation to see if it is evenly spread and not covering a can or eyeball light. The older lights could cause a fire if covered with insulation. Check the wiring, A/C Creon line, and anything else you might find. If you don’t see daylight coming from the soffit then its probable that air is not moving into the attic from there.

Step 10

Remember to inspect the soffit vents annually for blockage and blow them out with compressed air if necessary. Do not cover the exhaust vents in the winter to save on utilities because it won’t help and might destroy your decking with humidity. Roofing has no “R” value and once the heat is past the insulation it is gone. An attic is not a buffer from cold.