In the 1950's and 60's heating was very cheap, so builders and home owners didn't care much about insulating too much, but as heating costs rose, home owners started to pay much closer attention about their heating bills. As we all know, heat (or hot air rather) rises, so, to avoid too much heat to escape into our attics, we insulate the attic floor to save as much money as possible. But, no matter what we do, some heat will transfer through the attic floor -- from the living quarters' ceiling into the attic. This heat will (naturally) rise to the point where it can rise no further, to the ridge (or the topmost section) of the attic -- the peak of the "triangle". Because the hot air (or "the heat that rose from the living quarters") is now trapped in the attic, it will accumulate more and more in a downward direction until it can leave the attic through the roof vents (those mushroom-like formations on most roofs). But, because there are only a few (MUCH TOO FEW) roof vents installed on most roofs, the majority of the heat is still trapped in the attic... heating (or baking) the roof!
In the summer time the attic becomes a virtual "oven", baking the shingles. When you see shingles (on many roofs) with curled-up corners, that's a clear indication that the shingles have been "baked". In the winter when you see icicles hanging down from the eaves of many houses, that's a clear indication of the fact that those roofs have insufficient attic (or roof) ventilation. Let's talk about this a little more:
When the roof is being heated from below, the bottom layer of the snow sitting on the roof will be melted and it will start (naturally) drizzle down all the way to the eaves-trough where there is no more heat from below... so it freezes. More and more of this melted snow will flow down until the eaves-trough will fill up completely (WITH ICE), and at that point the ice will build upwards, i.e. ice dam is being created! When water becomes ice, it expands in volume... and when it expands, it will naturally push anything in its way, so the shingles on the roof slope get pushed up slightly, and some of the ice will continue to form UNDER those shingles, and in the worst cases the ice gets to the tar-paper and/or the rubber membrane under those bottom shingles. Over time, no matter whether it's just tar-paper or rubber membrane, they will all get ripped by the ice and the plywood sheathing underneath will give in to all that ice and when it melts, the water will find its way into the attic and then into the living quarters. Does this sound horrible? Keep reading...

In this explanation (above) you can visualize how the built-up heat, over time, will literally destroy your roof.
In the early days of shingle-roofing, the roofing contractors had no better way to protect the roofs but to install as much roof protection as possible, including tar-paper, rubber membrane or even steel sheathing under the shingles! Then some roofers recognized the importance of proper attic ventilation, so they added more roof vents... it's true, the more vents, the merrier! But, no roof will look pleasing when you see a row of roof-vents all along both sides of the roof ridge, say, every 2 feet... because the roof looks over-crowded with nothing but roof-vents.

It's important to make sure that there is plenty of air-intake as well, through the soffit vents. The more soffit venting, the better... just like the more air-output (roof venting), the merrier. Many times we find in the attics that when the home owner got more attic insulation blown in, the air-intakes were plugged up when nobody took care of clearing the air-ways for proper amount of air-intake. They should have (first) installed rafter-vents! Anyway, once there is plenty of incoming air and plenty of roof venting (air-output), the attic will "breathe" well and it won't become hot.
It's also important to mention that the lack of proper ventilation can bring moisture problems into the attic of your house that inadvertently can cause problems with the integrity of your house's structure: the trusses, rafters and support beams will get wet and start to rot. You don't want any danger of your house collapsing!

Remember reading about the heat being trapped in the peak sections of the attic? If you had RIDGE VENTING installed, the hot air and moisture has no choice but to leave your attic! Ridge venting is absolutely the most efficient ventilation solution!

Each foot of ridge venting equals to approximately 5 traditional roof vents! You should DEMAND to have ridge venting installed when you are getting your roof re-shingled!



Click on the following images to see them larger:

	Rafter vent						Perfect venting		Perfect airflow
	Rolled Ridge Venting		A roll of ridge venting		Why use Ridge Venting (ASF video file!)