Attics or roofs can be designed and constructed
“Attics or roofs can be designed and constructed to be either vented or unvented in any hygrothermal zone (Moisture/Heat zone). The choice of venting or not venting is a design and construction choice not a requirement determined by the physics or by the building code. The model building codes allow both vented and unvented roof assemblies. The applicable physics impacts the design of attic or roof systems as does the applicable building code but neither limit the choice. ” Joseph Lstiburek *(highlighting is mine) Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 1
So you live where it is Hot and Humid? • WHERE IS THE DEW POINT? (A bit like “Where’s Waldo, ” it can surprise you where it is. ) • Problems with Venting • It “can” work, but you better keep your HVAC equipment and ducts out of the attic. • Hot roof solution • Shorter shingle life? • Use of non-air sealing types of insulation Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 2
Photo Courtesy Gary Smith, Safe. Home Inspections, Mississippi Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 3
Photo Courtesy Gary Smith, Safe. Home Inspections, Mississippi Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 4
Pretty much everything you need to know about attic ventilation can be summed up in two words: Air Sealing! Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 5
If you think additional venting is “the answer, ” you will be wrong, WAY more often than if you assume it is not the answer. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 6
What IS “Air Sealing? ” Air sealing is simply using whatever means is practical to stop or slow the movement of air from one space to another. • Vapor retarder (paints, plastic sheets, some types of insulation) • Caulk • Paints • Spray foam • House wrap • Drywall • Liquid WRB • Sheathing (Plywood/OSB/Foam Board/Etc) • Tape • Weather-stripping • Insulation • Etc Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 7
Would you ever recommend fixing a roof leak by adding ventilation? Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 8
But what about ventilation? Myth #3 EVERYBODY knows inadequate ventilation is the cause of everything! • Cold Climate • Hot Climate • Mixed Climate Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 9
So what about Ice Dams? Or maybe “damns” is more appropriate. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 10
Myth #4: • Everyone knows ice dams can be fixed with more ventilation ** 11
Hey! I have trained him to walk backwards! Air Sealing has to happen first Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 12
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Solid Wood is not sufficient to prevent ice dams Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 14
Picture courtesy of Jim Quarello, JRV Home Inspection Services, Llc. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 15
Picture courtesy of Don Hester, NCW Home Inspections, Llc. Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 16
50/50 or 60/40? Lower Upper 1/150 or 1/300? Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 17
Myth #5: • The more ventilation the better. 18
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What the 2015 IRC says: R 806. 2 Minimum vent area. The minimum net free ventilating area shall be 1/150 of the area of the vented space. Exception: The minimum net free ventilation area shall be 1/300 of the vented space provided one or more of the following conditions are met: Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 20
1. In Climate Zones 6, 7 and 8, a Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling. 2. Not less than 40 percent and not more than 50 percent of the required ventilating area is provided by ventilators located in the upper portion of the attic or rafter space. This presentation is mostly geared toward colder and mixed climates Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 21
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IT IS COMPLICATED! Myths of Attic Ventilation © Charles Buell, Charles Buell Inspections Inc 23
Myth #6: • Attic sheathing temperature, on a sunny day, will be similar to attic air temperature. 24
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