How To: Attic Ventilation

Attic Ventilation

The Do's And Don't of Attic Ventilation

You just had a quote from a roofer who has recommended increasing your attic ventilation. You're wondering, what's that all about?! Doesn't it go against everything you were ever taught about insulating an attic? You probably remember a "This Old House" episode, where they blew insulation into an attic, put up vapor barrier all over, and made that attic TIGHT.

Well, the days of that sort of thinking are over. New science (and a better understanding of thermal properties of roofing) have that theory of tight attics completely overturned. The new science is called "Cool Roofing" systems. Here's how it works:

This is how the air should flow. 

The picture above shows two roofs. The one on the left is a "tight" attic. It has been insulated at the very top, where we all thought it was essential to seal the heat in. What happens is that all the heat in the house rises into the attic, where we insulated like crazy to try to hold all the heat in, and instead - we held in all the moisture, and now the roof is too hot and moist. 

What does that hot attic do? When it rains or snows, and ice forms on the roof, the hot surface melts the ice or snow, and it gathers at the bottom of the roof (called the drip edge) and causes gutter ice dams. What's that, you say? Well, look at this picture: 

That big lump of ice just came out of your gutter. Now imagine how it weighed down you gutter, and eventually tore the gutter down, causing terrible damage to your fascia and soffits. In the meantime, all that ice backed up against your roof, and the ice crept up under the shingles at the roof's edge, slowly prying up all the bottom shingles. Have you ever seen a house with shingle damage from ice dams? Here's what it looks like: 

Ice Dam Damage

Yep, that's what ice can do. But - how does that work, exactly? Okay, check the infographic below, and I'll explain further. 

The hottest area of your roof will be the highest area. This has all the heat trapped in it, and when the sun does shine in winter, it will likely hit only the top portions of your roof. The ice melts there, and slides down the roof, hitting the bottom which is ice cold. The ice forms a dam in your gutter. Then on a warm day, it melts, but instead of going down the gutter (which is still clogged with ice) the water creeps up under the shingles (called capillary action) and then freezes under the shingles at night. When water freezes, it expands. This slowly pries up the shingles, usually in the corners, causing a wave-like effect, and curling shingles. 

Right! Now you know why a hot attic is not desirable. On to the info-graphic again: 

So now we'll look at the right side of this graphic, which shows air flowing in from the bottom (the soffit), rising up, and exiting the roof at the very top, or "ridge".  Why is it doing that? Well, in this graphic the owners installed soffit and ridge vents. Some roofs will have attics that we can ventilate completely, and some have only the space between the sheetrock and the roof, but either way, soffit or even small vents made for "open, cathedral ceilings" can be installed to create air flow. The goal is to get air circulation throughout the roof, keeping cool air flowing and any hot air escaping. The ceiling above the rooms in the house is the area that gets the insulation, NOT the roof. 

How Does The Work?!

The air outside rises into your soffits, circulates as it warms, and rises to the ridge vent, which lets the hot air OUT. 

What does attic ventilation do? 

It keeps the ice from forming ice dams at the bottom of your roof, keeps snow and ice from melting too quickly, and keeps ice from forming under your shingles. Not only does it regulate your roof's temperature in the winter, but it also keep it steady in the summer. 

What can attic ventilation do for you?

It will undoubtedly reduce your roof maintenance bills by preventing leaks, 

It will reduce your energy bills, saving you money and time!

Want to know more? 

See my next blog on types of attic ventilation!

Questions? 

Call me: 631-281-9100

See my website: http://www.bestqualityroofingchimney.com