Last week we inspected a new build here in the Metro area. The builder used HardieSoffit for his cornice venting.
Net free venting requirements for residential construction states that we should provide a “balanced” air flow for attic ventilation. 50% of the air needed to cool your attic should enter at the edge of the roof…down near the windows. 50% of the required openings should be as high as
possible, preferably at the top of the roof.
For the high part of the venting, we recommend a ridge vent be used. The ridge is the highest peak of the roof-line. Since hot air rises, if you place roof venting at the top you’re more likely to vent ALL the hot air from the attic. Here’s an in-depth booklet on roof ventilation written by the great folks over at Airvent.com.
Care should be taken when using the pre-drilled holes of the HardieSoffit material.
As you can see, newly painted holes and framing/blocking (see lightly shaded area in photo) can “stop up” the vent. Laying down too much paint and adding too much framing behind this product can adversely alter the balance of the attic ventilation.
Run the numbers on your ventilation requirements. If left completely open, the product pictured will allow 5 sq inches of net free venting per lineal foot.
Homeowners, if you have this type venting on your home, take care and don’t allow the painter to clog up the vent holes. It can defeat the purpose and throw the attic air flow out of balance. As a result the attic can overheat and drive hot air downward into the ceiling – the result – higher power bills.
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