Why does an attic get so hot under a roof?
The roof surface absorbs the sun and passes heat into the attic below. In a closed or poorly vented attic the heat cannot escape, so the air under the deck gets hotter than the air outside, and the deck and underlayment take that heat all day.
Heat rises, so the hottest air collects at the peak of the attic. Without vents at the top, the air sits there and bakes the deck from below, and the underlayment is pushed against its heat for hours.
The effect is strongest where the roof is dark, where the attic is closed and where the insulation is pushed against the deck at the eave. A crew checks each of these points when it visits a hot attic.
How does attic heat age the roof?
Attic heat ages the roof from below. The underlayment becomes brittle and loses its flexibility, the shingles dry out from the back and the deck boards can warp or split. The shingles on top may still look sound while the layers under them have worn.
Heat and moisture work together. Warm air can carry moisture up into the deck, and when that air meets a cool surface in winter it condenses. Repeated cycles of this kind weaken the boards and the nails that hold the covering.
A crew can judge the heat's effect from the underside of the deck. Staining, blistering and warping are the marks it looks for, and it records them as evidence of how long the attic has been running hot.
Will better attic ventilation lower my cooling costs?
Better ventilation can reduce the heat that reaches the rooms below, but the effect depends on the attic, the insulation and the house. No figure is given here. A crew can say what it expects the change to do for this attic and why.
A ventilated attic lets hot air leave at the top while cooler air enters at the eave. Where the path is clear, the attic runs cooler, and less heat passes into the rooms below.
A crew does not promise a particular saving on a bill. It shows you the vents and the airflow, and it explains what changes it expects, so you can judge the result yourself.
Why does condensation show in the attic in winter?
Warm, moist air from the house rises into the attic and meets the cold deck in winter, and the moisture condenses on the boards. Good ventilation and a sealed ceiling below move that moisture out before it settles on the wood.
Bathroom and kitchen fans that vent into the attic add moisture, as does a dryer vent that ends in the roof space. The crew checks where these exhausts terminate and whether they vent outside.
Condensation on the underside of the deck is a warning that the attic is not clearing its moist air. The crew records it, checks the path for the moisture and recommends the change that is most likely to help.
What affects the scope of an attic ventilation check?
The scope depends on the number and condition of the vents, the attic's size and access, the insulation and whether the deck needs repair. The check is quoted separately from any repair, and the price is explained and approved before work starts.
A small attic with clear vents is a short check. A large attic with several roof levels, poor access and damaged insulation takes longer, and the crew notes what it could not reach.
Where a vent must be added, the crew explains the position and the reason, and it shows how the new vent connects to the airflow path, so the homeowner can see the change before it is made.
