For every 300 sq.
Fine homebuilding attic ventilation.
Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents.
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.
Ft code requires that there be a minimum of 3 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.
Of ventilation area 1 sq.
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 attic space equally divided between eave and ridge vents.
It s one of the more confusing aspects of home building and.
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.
Of vents for each 300 sq.
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.
Ft and 50 1 5 sq.
Ft of ventilation area at the ridge and the remainder at the soffits.
15 articles and videos from the fhb archive that will take you through every step of the roof venting process.
This way it s not as big a deal if the ceiling leaks air or if the ducts are leaky and uninsulated.
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.
Vent the roof deck.
In an attic the primary driving force is the buoyancy of warm air rising in the vault of the roof.
The baffles will create vent spaces and prevent windwash energy robbing convective short circuiting air moving through the insulation 1 1 4 in.
If you ve got a roof over your latest building project chances are you ve also given some thought to roof venting.
If an attic measures 900 sq.
Codes require a net free ventilation area nfva of 1 sq.
In mixed climates ventilation serves either role depending on the season.
Intake vents located at the lowest part of the roof under the eaves allow cool.
