Question

How can I improve my roof's venting?

Asked by Vic

We have a 1978 ranch home with gable roof and medium-size gable vents (one on each end). We are having new asphalt shingles put on with four turbines evenly spaced over the roof and keeping the gable vents. We are also having soffit vent holes cut under the overhang for additional intake ventilation. What if the hole is cut and there is insulation in the opening? It can be pushed back when we cut the hole, but how do we keep the ventilation from falling back over the vent hole?

Answer

Mick Dalrymple

Answered by Mick Dalrymple

Scottsdale, AZ

Eco-Friendly Building Center

March 6, 2008

The simple answer is “yes”.

  • If the insulation is batt insulation, cut it out above the vent.
  • If it is blown in insulation and you can get into the attic, install a ventilation baffle.
  • If you cannot get in from above, try cutting a piece of flashing or wire screen, bend it to get it through the hole and then let it unwind and position it to create your own baffle.

Here’s the rub: Is attic ventilation required by code in your area? Are you in a warm, dry climate or a cold climate?

Consider sealing the attic

If you are in a cold climate and are willing to give up the asphalt shingles for something like an ENERGY STAR-rated metal roof or shingles that are slightly raised off the roof deck, then here's what I would suggest.

  • Seal the attic and use home foam insulation against the underside of the roof deck.
  • This will place your ductwork inside semi-conditioned space, saving you significant amounts of energy.
  • If you are set on asphalt shingles, I would suggest going for the lightest color possible. It will make a significant difference in the amount of heat transmitted into the attic.

If you are in a warm, dry climate, I would again suggest sealing the attic, insulating at the roofline and eliminating the asphalt shingles.

  • The difference is that in a cold climate, warm moist air in the house in the winter may cause “fishmouthing” or cupping of the asphalt shingles as it tries to escape.
  • A dehumidifier can be used to avoid this. In a warm, dry climate, the asphalt shingles could bake and fail faster with no place to transmit the heat. That alone says a lot about the amount of heat asphalt is sending into your attic.

Sticking with the vented attic

So, let’s say you want to stick with the vented attic and don’t have the money to add new insulation or consider anything except asphalt shingles.

  • Make sure that the overall square footage of intake vents matches that of the exhaust turbines.
  • Better yet, use a continuous ridge vent instead of turbines. 
  • Here’s why: Air out equals air in. If there is not enough air in, less hot air will escape OR it will find intake air from somewhere else.

Evacuating air will suck replacement air from the closest, easiest place it can get it. If there happen to be leaks in your ceiling air barrier near one of the turbines, the negative pressure caused by the turbine and air flow is going to suck conditioned air from inside your house through those leaks seven feet away, rather than from a gable vent 20 feet away … or even a soffit vent 11 feet away. The leaks could be around can lights, electrical penetrations, duct penetrations or even hollow walls. You can imagine the losses that can be caused by powered attic exhaust fans.

Make sure your ceiling is completely sealed

The proper solution is to make sure all ceiling penetrations are completely sealed and that any hollow walls are sealed at the top and insulated with the insulation touching that air barrier (not spanned across any gaps, hollow spots or soffits).

You might also consider a full ridge vent and full length soffit vents to evenly distribute and balance the intake and exhaust flow.

Here’s to a cooler attic and cooler home. Cheers!

 

For more information:

Read Danny Kelly's Q&A "How effective are the different attic ventilation methods? I read mixed reviews, and many have a commercial bias."

Tagged In: insulation, attic insulation, attic ventilation

Do you have a question about greening your home? GreenHomeGuide invites you to Ask A Pro. Let our network of experienced green building professionals – architects, designers, contractors, electricians, energy experts, landscapers, tile & stone specialists, and more – help you find the right solution.