Wednesday, December 11, 2013

Roof Ventilation - Tips for successfully ventilating you new roof

How To Successfully Ventilate Your New Roof

Hi I’m Brendan Foster from Louisville Roofing Contractors. These Videos focus on how to buy a new roof for your home. Folks asked me why I am producing these Videos and really the answer is very simple, over the years I’ve gained from my involvement in the roofing industry, I’ve gained a great deal of insider knowledge that is provided me with helpful ideas to present to home owners to allow them to make sure that when they make decisions to re-roof their home, they make sure that they're making the right decision by using the right product, they’re using the right details and they’re using the right contractor. 

In this series of Videos, I’m trying to provide you with insider information if you will to help you make a sound decision for the roof of your home and a decision that is right for you as well. This again is the 4th of our series; this particular segment is going to focus on ventilation. Ventilation is one of my favourite topics and is a very important thing to think about when you're re-roofing your home. Let’s start, first question is, why do we need ventilation in our attics? Most homes do need ventilation in their attics, the reason is really very simple and in fact with building technology, the need for ventilation has increased rather than decline over the years. 

Basically you've got a space in your attic that catches things, it catches heat from the sun, and it also catches moisture that is generated inside of your home that migrates up and ends up in the attic. When you have this combination of warm, moist air in your attic, you’ve got really risk there. First of all, the warmth during the summer is making it harder to cool your home. If your attic is very hot and we've all experienced that, where we go up in our attics in the summer and we find that it is very warm up there, you know that that's making your air conditioner run longer and as a result increasing your electricity cost. 

Second of all, if this warm moist air ends up in your attic, what happens is there is a very high chance of it condensing. If it condenses in the bottom side of your roof deck when your roof deck maybe gets cool at night as the temperature goes down, then you got condensation in your attic. Condensation of course if a very dangerous thing because it can eventually lead to mildew, mold, rot, and all kind of nasty stuff that you really don’t want it going on. One of the questions is, why it even gotten more critical this question of ventilation over the years, well that again is fairly simple, what happened is over the years we've made our homes tighter.  

We’ve installed windows that are tighter, we put house wraps, we put other sorts of siding materials on the outside of our homes, we have doors that are tighter, all kinds of things that our homes don’t simply breathe the way they used to be. the moisture that you would generate inside your home, and we generate a lot of moisture inside our houses, whether its from cooking, taking showers, whether its from house plants or ventless gas stoves, these all things all generate a lot of moisture.  

What used to be that moisture would migrate outward just through the breathability of your home that would go out from those leaky windows or through leaky doors, or through the walls of your house. But today since we've made all these things tighter in a good attempt to be energy efficient, that moisture stays inside of our homes and what happens, and it ends up in the attic. One thing I want to point out to is you know you do have the responsibility to make sure that you minimize the amount of moisture inside your home. Make sure that things like bathroom vents, your clothes dryer vents, the exhaust vent of your fan or the hood over your range, make sure that all those things are vented out. Sometimes I’ve seen even roofing contactors try to cut those things off and just vent them into the attic, "well, we'll just direct it over here towards your sofa vent and it will find its way out. I’ve seen people tried to vent those things just under their cross bases, don’t do it. it is very dangerous, that moisture needs to get outside of your home in no way shape or forms it should be kept inside your home. Basically, we have this attic that creates or builds up a great deal of heat and moisture, we've got to get that vented out, so that is the reason why ventilation is important. 

I’m not going to go a whole lot of detail on this, but there is one other option which is basically called a hot roof where new building technology will go in and spray the inside of your attic with a icing foam or a close urethane foam, they'll spray the entire sides of the attic, the sides, the cable ends, the roof, deck, floor, they'll spray all with this foam. Basically they’re creating a high value of insulation that is also air permeable in terms on not letting moisture through it. 

They will create a conditions space in your attic so it’s much like turning your attic into part of your living space if you will. Basically when they do this, through this foam they use, they keep moisture out of your attic, they also keep the warm air out of the attic so you don’t need ventilation if you got this what we call hot roof theory. The reality is though, well hot roofs are great and you can achieve them very well with new construction, they are very difficult to build and achieve what we call a hot roof with an existing home. 

There is so much in that attic and if the home wasn’t built to be hot roof, it’s going to be very difficult to achieve that. So that puts us back in the situation of needing to have ventilation. Basics of ventilation, how do you vent your attic? Well, ventilation takes 2 things, two types of vent, you've got to have intake vents where the air comes in and you got to have exhaust vents for the air that goes out. when we vent an attic, we take advantage of what we call "convective air forces" which is basically the warm air tend to rise so what we'll do is we'll put vents in the over hangs down at the bottom of your roof, well put at on the sofa through the overhangs. Those are intake vents, that where the air will come in. That air then by convective force will travel upward through the attic to vent out at the top. one of the most effective ways to vent out of the top is through a ridge vent. 

There are other types of exhaust fans you can use, I like ridge vents because they tend to be continuous rather than spotty. when you have just say a large turbine vent up on your roof, all the air rushes towards that turbine and sometimes areas of the attic that are not in the pathway of that air movement can end up really with not having very much air exchange going on. So I like ridge vents. It doesn’t mean that they are the end on or beyond or the only way to use and in fact ridge vents have their limitations. 
You don’t want to use them on a really low pitch roof; they are also some roofing materials that are not really conducive to the use of ridge vents. ridge vent is not the end all be all, you can use other types of static vents, you can use all of the ridge vents and use slant vents, back vents, or you can use turbine vents which will move a lot of air but again they kind of create this channel areas of air movement to you your attic that may mean some areas in the attic are not moving the amount of air that they should be. Basics of ventilation, you've got to have intake usually at the bottom of your roof, you've got to have exhaust usually at or some place near the peak or the ridge or the top of the roof. 

Other basics of ventilation, when you vent our attic, you look at the amount of the free air flow. Basically, you're looking at the amount of holes or perforations or vents that are in that area where the air comes in and you want to make sure that you've got a similar amount of free air flow at your ridge vent. Usually at your ridge vent, I’m going to talk in terms of ridge, but then again it could apply to other types of vents as well. Usually your ridge vent is going to be feeding 2 sets of soffits vents, 2 sets of overhang vents on opposing sides of the roof. 

You’ll add up the total amount of your sofa vents, your free air flow, venting products that you buy will tell you what the free air flow is. You want to make sure that the total amount of the soffit vents is very close to being equal to the total amount for free airflow through your ridge vents. You create this situation where air comes in, all the air that comes in can go out at the peak. as far as how much ventilation do you need, general rule of thumb is to look at the square feet of your attic and you look at how many square feet there are on the floor of your attic space. let's say you come up at 3000 square feet on the floor of your attic, then you want to look at how much free airflow do I need for my vents and basically you want 1 square foot of net free air flow, one square foot for every 300 square feet of attic floor space. 

For example, on that 3000 square foot attic, you are going to need 10 square feet of net free air flow allowed through the ventilation of your ridge vent and your soffit vents. That net free airflow number is not the intake of soffits combined, its just one or the other. You want to have that much on whatever is the lower number of your soffits and your ridge vents. Then again, hopefully your soffits and ridge vents numbers are about the same. The 300 square foot of attic floor space applies if you got a vapour barrier behind the ceilings on your home. I am going to explain vapour barriers in a second, but if you do not have a vapour barrier behind the ceiling in your home and that would be particularly a case of an older home perhaps a home prior to about 1970 or 1975. If you do not have a vapour barrier, then you'll need to have one square foot of net free airflow ventilation per just 150 square feet of attic floor space. In my example, that 3000 square feet attic, you would need 20 square feet of net free air flow to serve as that amount of attic space. What is the vapour barrier? 

Well vapour barrier is basically and usually a sheet of polyethylene. A lot of times on home construction, before they put the dry wall up your ceilings, they will put this layer of polyethylene behind the dry wall. They do this on walls also. Basically, the purpose of that polyethylene is that what we call vapour barrier. It means that vapour which would be moisture does not pass through it. If we have this vapour barrier behind your dry wall, they're never going to be a 100%, but they're going to be very helpful in containerizing the moisture inside your home. Basically the theory is, or what we are accomplishing there is, we keep that moisture that is created or generated inside you home. we keep it inside the house, that vapour barrier blocks it and keeps it from getting into the attic. If does get in to the attic, we don’t need to vent it out. 

That is the reason that if you got a vapour barrier, technically, you probably need to less ventilate your attic than if you do not have a vapour barrier. if you do not have a vapour barrier especially again if it is an older home or if quite simply one wasn’t installed, then you're going to need more ventilation in your attic because that moisture from the inside your home to a greater degree is going to end up in the attic and you need it to get it out there so it doesn’t cause problems like condensation, rot, mildew, mold and all that horrible stuff.

Louisville Roofing Contractors

624 E Market St, suite 2, 
Louisville, KY 
502 208 3778

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