Did you know that breathing, cooking, showering and washing all add water into the air? It is believed to add between 5-10 pounds of water into the air in your home – every day! If you are washing and drying your clothes, you can add another 30 pounds of water on top of that. This moisture will condense once it reaches the attic and will cause damage to insulation, sheathing, rafters and if the moisture problem is really severe – it can even damage roofing materials made out of asphalt and wood. It is therefore very important that your house has adequate ventilation. Thanks to modern ventilation products such as attic fans and roof vents, you can allow the house to breathe, ridding the house of unwanted moisture. Good ventilation will also get rid of accumulated heat, fumes, smoke and vapours. If you are looking to improve the ventilation of your house, make sure to implement this when you are preparing the roof deck. Always try to deal with roof related work such as cleaning and repairing gutters when you are already doing work up on the roof.
There are certain factors that decide how much ventilation a house needs. Things like sun, shade and wind direction has to be taken into account and the roof lines themselves can either encourage or interrupt the flow or air. A building inspector or a ventilation contractor can tell you what the ventilation needs of your house are and if need be, what size vents you need and where they are best placed. There are some rough guides about the amount of ventilation needed.
Generally, 1 square foot of a free vent opening should be enough for 150 square feet of an attic floor. A free vent opening is an opening with no wire or grill-work taken into consideration. Remember that any wire or grill-work area will have to be subtracted. If your vent is covered by a wire mesh of 1/8 of an inch to ¼ of an inch, it will have to be about 1 ¼ times larger than a free vent opening. If your vent is covered by either 1/16 of an inch of insect screening or ¼ of an inch of mesh and a louver – make sure that the vent opening is twice as large. When it comes to the attic floor space, you can possibly get away with 1 square foot of free vent opening for about 300 square feet, providing you have vapour barrier installed. The vapour barrier has to be on the ‘room side’ of the insulation. Also, half of the vent space should be close to the gables tops or alternatively, along the ridges. An attic fan is a good idea if the natural venting is not enough to push hot air through the vents.