Ahh, the 80′s …. a time of feathered hair, parachute pants, and a cosmetically unaltered King of Pop. It was also when builders got caught up in the ventilation craze.
Seriously, the benefits of attic ventilation for controlling roof deck temperature and ice dams (in northern climates) has been known and studied for decades. Adding vented soffits is the easy part. The also easy but rarely done part is controlling where that air goes once it enters the house. That’s were attic baffles come in.
Attic baffles, also called channel vents, vent chutes, proper vent (and about 50 other names) help direct air flow from the soffit through the attic. They can reduce roof deck temperature, minimize ice dam issues and can help control attic moisture. They also keep insulation from falling into and clogging up the eaves.
The great thing about installing attic baffles (and sealing them): the project can have a big impact on the effectiveness of your insulation and can be done without any specialized contractor tools. And it’s not expensive. That’s right, it’s an effective, cheap and easy to do home energy project. And three out of three ain’t bad.
Side note: we’re not delving into the almost infinite variations about what can go in attic eaves. We’re assuming a basic modern ventilated attic with fiberglass insulation, dry wall on 2′ x 4′ construction and edge and ridge vent (or gable or mushroom cap vent) that meets code.
How To Install Attic Baffles – Why It’s Important
If a house has vented soffits and a vented roof peak, most people think that does the job. Air ought to flow in the edges and out the peak, right? I mean, the ridge vent is properly installed, it has continuous vented soffits. What could go wrong?
What could go wrong is air and air pressure. Air goes wherever pressure dictates. If there’s a powerful fan (like a blower door) on, it will pull air into the house. If there’s a powerful wind blowing, it will drive air horizontally through and across the house. You can read about the effects of wind washing here and stack effect here. The goal is controlling this rampant air flow so it doesn’t whisk away conditioned interior air.
Wind will whip into buildings through the open soffit. That’s a fairly obvious problem. A less obvious one is the top of the interior drywall. In standard framing, the interior drywall comes up flush against the ceiling floor joists. Look at the wall in your house and imagine the drywall board behind it. Where the top edge of the drywall lays flush against the top plate of the wall framing is one enormous unsealed crack.
Unless the air tight drywall approach has been used (which I ought to write about at some point), conditioned air will leak through every crack and seam on the interior wall, up and out the crack on the drywall’s top edge. There are many different approaches, but the goal is the same: Seal the top of the drywall/top plate and keep air pressure driven wind up and over the attic insulation.
Here’s a photo of an open, unsealed, soffit/eave. The air ought to flow in through the soffit, up (a currently non-existent) attic baffles and out of the roof peak.
How To Install Attic Baffles (and Air Seal)
You’ll Need – Installation Equipment: You will need a staple gun, Great Stuff or a foam sealant gun, A pile of attic baffles (OK, one per eave, two if you’re adding a lot of insulation), 2 foam blocks per eave rough cut to fit (approx 6″ x 14″ depending on the framing).
Safety Equipment: Goggles, a dust mask and if it is particularly dirty, a Tyvek body suit.
Retrofit or New Installation – In retrofit situations, the attic baffles may or may not already be installed. If they are present, examine them and evaluate if any baffles need replacing.
Cardboard vs. Foam Attic Baffles – The two most common attic baffles are made of cardboard or foam. They are manufactured to fit either 16 inch or 24 inch on center construction.
Cardboard baffles are less durable but can be bent and cut to cover the end of the eave. This does a passable job of directing wind up the baffle and nothing to seal the top of the drywall.
Foam baffles are more durable but are a straight section that cannot be bent or cut to fit easily In both cases, we need to seal the eave and top plate.
Install Attic Baffles – If the attic doesn’t have attic baffles, let’s install them. You’ll need to crawl to the end of the eave and staple the baffle against the roof deck.
The outside edge of the baffle should be parallel to the exterior wall sheathing. Staple each side to the roof deck, spaced about every 4 inches. Make sure there is a clear air flow path through the baffle. The end result should look something like this (once we’re done with the foam block…which is next):
Cardboard baffles are normally fastened to the top plate but we’re foregoing that to seal the eave with foam blocks.
Be very careful when working near the soffits/eaves. Make sure you stay on the ceiling joists, preferably on a plywood working platform. The ceiling plaster/drywall will not support your weight.
Air Seal The Attic Baffle – Once the attic baffle is fixed in place, seal the drywall edge against the interior wall with a bead of foam sealant, then fit one of the foam blocks horizontally over it. The foam block should sit flush over the exterior sheathing on the outside and the interior drywall on the inside.
Install the second foam block vertically, flush against the outside edge and the attic baffle. This may require some trimming as the gap between the top plate and roof is rarely uniform. Once fixed in place, foam seal around the attic baffle and all of the foam block seams.
There are many variations of how to install and seal attic eaves. Another option, for example, would involve building a solid, permanent vent from plywood spaced away from the roof deck with furring strips. As long as in the end there is a clean air flow from the soffits and the eaves are sealed.