"Understanding Your Home" by Building Inspector Mark Visser
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Top and lower gable vents

Ventilation for 1 1/2 and 2 1/2 Storey Homes
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1 1/2 and 2 1/2 Storey homes have attic sections behind the knee wall that are in most cases, not properly vented. Each section should have its own ventilation as shown.
Cross ventilation for the top section can be provided by installing gable vents on each end of the house. In this illustration all three attic section run the full length of the house without interruptions.
However, the lower attic is often divided in smaller sections by stairways, bathrooms or dormers. If that is the case, each section can be vented by a roof vent placed approximately 5 ft. or 1 1/2 m. up from the eaves.

The sloped (or rafter) section of the finished room is usually not deep enough to accommodate adequate insulation and 3" or 75 mm air space for ventilation. between the insulation and roof sheathing. Additional ventilation space can be added as shown
in "Insulating Cathedral Ceilings"

For information on insulation requirements for this type of roof construction go to "Insulation for 1 1/2 and 2 1/2 Storey Homes"

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