Fine Homebuilding Attic Ventilation

Vent the roof deck.

Fine homebuilding attic ventilation.

In an attic the primary driving force is the buoyancy of warm air rising in the vault of the roof. Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents. For every 300 sq. Attic fans are intended to cool hot attics by drawing in cooler outside air from attic vents soffit and gable and pushing hot air to the outside.

Roofs need a driving force to move air in and out and intake and exhaust vent openings large enough to facilitate this movement. But building scientist joe lstiburek takes issue with that opting instead for more ventilation at the eaves say a 60 40 split with the eaves getting the greater proportion. Of ventilation area 1 sq. Absent that try to provide at least a net free vent area of all ventilation openings of 1 150th of the horizontal area of the attic with reasonable cross flow to eliminate stagnant pockets of air.

Intake vents located at the lowest part of the roof under the eaves allow cool. Of attic space equally divided between eave and ridge vents. In a hot climate the primary purpose of ventilation is to expel solar heated hot air from the attic or roof to reduce the building s cooling load and to relieve the strain on air conditioning systems. In a situation where mechanical systems or ductwork has to be in the attic space or when there are lots of penetrations in the ceiling below the attic it s best to bring the entire attic area inside the thermal envelope.

Of vents for each 300 sq. Ft and 50 1 5 sq. If an attic measures 900 sq. However if your attic has blocked soffit vents and is not well sealed from the rest of the house attic fans will suck cool conditioned air up out of the house and into the attic.

The baffles will create vent spaces and prevent windwash energy robbing convective short circuiting air moving through the insulation 1 1 4 in. Codes require a net free ventilation area nfva of 1 sq. As the warm air escapes through vents high on the roof cooler air enters the lower vents. Ft of ventilation area at the ridge and the remainder at the soffits.

Of attic floor area with between 40 1 2 sq. This way it s not as big a deal if the ceiling leaks air or if the ducts are leaky and uninsulated. If you ve got a roof over your latest building project chances are you ve also given some thought to roof venting. It s one of the more confusing aspects of home building and.

Slots notched in the top of the timberstrand blocks placed between the tji rafters lets air flow into the ventilation channels from the cor a vent s 400 vent strips installed between the soffit boards.