Fine Homebuilding Attic Ventilation

In an attic the primary driving force is the buoyancy of warm air rising in the vault of the roof.

Fine homebuilding attic ventilation.

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. 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. It s one of the more confusing aspects of home building and. If you ve got a roof over your latest building project chances are you ve also given some thought to roof venting.

Intake vents located at the lowest part of the roof under the eaves allow cool. 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. 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 code requires that there be a minimum of 3 sq. 15 articles and videos from the fhb archive that will take you through every step of the roof venting process. Of attic space equally divided between eave and ridge vents.

Of ventilation area 1 sq. Ft of ventilation area at the ridge and the remainder at the soffits. Of vents for each 300 sq. Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents.

In mixed climates ventilation serves either role depending on the season. For every 300 sq. The baffles will create vent spaces and prevent windwash energy robbing convective short circuiting air moving through the insulation 1 1 4 in. This way it s not as big a deal if the ceiling leaks air or if the ducts are leaky and uninsulated.

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. Roofs need a driving force to move air in and out and intake and exhaust vent openings large enough to facilitate this movement. Of attic floor area with between 40 1 2 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.

Vent the roof deck.