There are different types of roof ventilation to choose between and it is their location on the roof that sometimes decides what type is best used. When it comes to attic vents and fans, you normally locate them in the highest corner of a gable, on the roof place or ridge or alternatively, underneath the eaves or soffit. In this article I will tell you a bit more about gable ventilators, ridge ventilators, roof plane turbines and fans and last but not least – the soffit ventilators.
Gable ventilators are made of galvanised metal and are triangular in shape. They can be purchased at either a home improvement centre or at a sheet metal shop. Gable ventilators should be installed at the top of the gable and their purpose is to eliminate any heat that collects up by the house ridge.
Everyone knows that heat rises and it is therefore not a surprise to learn that the hottest air collects at the highest point of the house – the ridge of the roof. Therefore, this is the most efficient location to place a vent. Ridge vent systems basically consist of long and inverted metal trough which allows air to leave the house easily and without taking in any rain. Remember to install ridge vents before you lay any roofing materials. I have mentioned this before but if you are doing any major work to your roof, try to deal with other roof related jobs at the same time. This could be work to with the gutters, chimneys, skylights and so on.
Roof Plane Turbines and Fans
The turbine vent is a clever invention. Once placed on the roof it acts in two different ways depending on weather. In calm weather they act as a free ventilation space whilst they generate an air flow when it is windy. When it is hot outside, you can avoid the need to use air conditioners by placing powered attic exhaust fans over ceiling vents. They work by increasing the natural air convection. If you are looking to purchase a normal exhaust fan, take into account its noise level and air flow. The airflow is calculated in cubic feet per minute or CFM for short. Noise levels on the other hand are measured in ‘sones’ where the lower the number, the quieter the fan is.
These ventilators are rectangular in shape and placed, as the name advises, at the soffit or by the eaves of the roof. They provide an in-flow of cooled air whilst warm air convection draws the air upwards and through the gable and/or ridge ventilators. Another great thing with soffit ventilators is that they will assist in drying out the roof decks if they have leaked – especially by the eaves.
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.
When it comes to waterproofing the roof, the chimney is generally the most difficult part to deal with. It has to be made waterproof and kept waterproof. This is trickier than it sounds and this is mostly down to the weight of a chimney. Because of this, a masonry chimney will not only settle but also move independently of the property. With the joints between the chimney and the roof broken, water can easily get in and wreak havoc. Due to this, it is often the norm to install two layers of flashing; a base layer underneath and a cap or counter layer on top. Different roofing materials will decide what type of flashing you use. For an asphalt roof, use either roll roofing for chimney flashing or galvanised metal. For a wood or tile roof, use metal. You can use lead for a tile roof if you so prefer and this is a great choice as it quite easily moulds to the shape of the tiles.
You do not have to make your own chimney flashing unless you want to as there are several ready-made options available. Most of these are made of metal and can be bought from roofing supply companies or even from sheet metal shops. The latter one should also be able to fabricate chimney flashings to whatever your specifications are.
If you are using metal chimney flashing, you can choose to install cap flashing over it. Cap flashing is also known as counter flashing to some. The cap flashing is often made of durable metal sheets such as copper and is to be installed in the mortar and bent down over the four chimney flashing cut-outs (one for each side of the chimney). Simply chisel the mortar by a horizontal joint to a depth of about 1 ½ inches, above the flashings. I would use instant mortar for cap flashing and this can be bought from most hardware stores and home improvement stores. Mix the mortar with a little bit of water, making sure to keep the paste thick and well mixed. Wet the area you chiselled and use a trowel to get the mortar into the chiselled area, before pushing the cap flashing into the mortar. Keep it in place for a few minutes until the mortar hardens. I would always wait a day before bending the flashing into place, just to make sure the mortar have set properly.
Flashing and Re-Roofing
If you are roofing over either asphalt or wood shingles, it is important to leave all of the old shingles in place if possible. It is the same thing with chimney flashings. If the existing chimney flashings are in good condition, then you can leave these in place as well. If they look in bad shape, you are better off making new ones and a good tip is to use the existing flashings as patterns for the new ones.
ABC Guttering Specialists blog is finally here and I have to tell you, I could not be more excited. I’ve had thirty years experience not just with gutter repair and installation but all kinds of home improvement and DIY. Although this blog will primarily focused on everything to do with gutters, there will be many articles and posts on other DIY subjects too. Here at ABC we try not to limit ourselves, as we feel we have a lot to offer our readers. Well, that’s enough from me, if you want to contact me directly you so via the contact page. Thanks for stopping by.