What the airflow is for
The attic should stay cold in winter and shed its heat in summer. The same airflow does both, and on shingle roofing it counts as much as the flashings or the underlayment.
The path, from the overhang to the top
Air enters through the soffits, under the roof overhang. It rises along the deck, between the rafters, and exits at the top through roof vents or a continuous vent installed on the ridge.
This path can be cut at the entrance, along the way or at the exit.
- At the entrance. A perforated soffit is useless if it is covered with paint, blocked by insulation or installed over an old wooden soffit.
- Along the way. At the bottom of the slope, insulation can fill the space under the deck. Baffles fastened between the rafters keep a channel for the air.
- At the exit. The vents must be near the top, where warm air builds up.
The intakes and exhausts must also be balanced. With vents at the top and no air intake at the bottom, the attic draws its air from the house, through leaks in the ceiling.
The damage, season by season
In summer. Heat stays trapped under the roofing. Shingles curl and lose their granules before their time. The top floor becomes hard to cool.
In winter. Humid air from the heated rooms touches the frozen deck and leaves frost on it. In a thaw, this frost melts and soaks the wood and the insulation. Over time, the deck blackens, grows mould and eventually softens.
At the roof edge. Snow melts from underneath over the warm part, then the water freezes again at the colder overhang. An ice dam forms.
What you can safely observe
Besides snow melted in patches, three signs can be noticed without climbing anywhere.
- A band of ice and large icicles along the overhang.
- In summer, an upper floor clearly warmer than the ground floor.
- A stain on the ceiling that appears during a thaw, when it has not rained.
If the attic hatch opens without your having to climb, look at the underside of the wood with a flashlight, staying at the hatch. Frost, black stains, rusty nails, damp and crushed insulation are all signs of the same problem. In many houses, the hatch is in the ceiling and cannot be reached without a stepladder. In that case, do not climb up: the signs visible from the ground and from inside are enough to request a quote, and we will look ourselves during the visit. Do not enter the attic. If the insulation is made of granules that look like vermiculite, do not touch it: this material can contain asbestos.
What we can correct
When the roof is redone, the deck is exposed, and the airflow is easier to correct. These interventions come up often.
- Clearing the soffits and installing baffles between the rafters.
- Adding vents near the ridge, or changing their model.
- Extending to the outside the duct of a bathroom fan that empties into the attic.
The number and size of vents are calculated from the attic area, according to the building code and the manufacturer's instructions. Our quote states what we plan to install, and why.
Frequently asked questions
Can vents be added without limit?
No. Too many exhausts, or exhausts of different models, can work against each other: air enters through one and exits through the other, without sweeping the attic. The attic needs a continuous path from the soffit to the ridge.
Is good ventilation enough against frost?
Not always. Ventilation carries away the moisture that reaches the attic, but it does not make the ceiling airtight. When the house sends a lot of warm, humid air up there, the ceiling leaks are sealed first.
Does the shingle warranty depend on ventilation?
Manufacturers generally attach conditions on attic ventilation to their warranty. Read the one for the product line chosen, and ask us to confirm that our work meets it.