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What Are Insulation Baffles (When You Need Them + Visuals)

If you haven’t heard of insulation baffles before, you aren’t the only one. But, considering they are a key ingredient to home ventilation, I certainly think I should have known about them from the start.

Thankfully, that’s where I make your job a lot easier: I’ve already done the research for you. Not only are baffles easy to understand, but they are also easy to install if you need them. We use these in conjunction with eave vents to maintain the integrity of your attic space.

Insulation baffles are needed for eave vents and contain loose-fill insulation from seeping into different spaces. They come in different materials and attach to the roof deck, allowing air in from intake vents while keeping insulation away. Spray foam needs specific types of baffles.

Location and Function of Baffles

Insulation baffles are part of the attic ventilation system as much as they are part of the insulation system. However, they are only necessary when the ventilation system involves soffit or eave vents.

The baffles create channels or chute-like structures between the roof and the top of the insulation installed between the ceiling joists.

The baffles are installed between the rafters above soffit or eave vents.

SmartBaffle 16 Insulation Baffle for 16" Rafter Bays

Baffles are also referred to as rafter vents, rafter or eave baffles, or insulation stops.

Their function is to ensure that the air entering the attic from the soffit vents has a pathway up to the roof and the ridge (or similar) vents.

This function is necessary because without the baffles, insulation installed between the ceiling joists can easily be pushed to the edge of the roof and block the soffit vents.

Why This Is Important

When the soffit and eave vents are blocked, the amount of air entering the attic is reduced. This prevents hot and humid air from being drawn out by the vents in the upper areas of the attic.

The result is hot air being trapped in the ceiling, which has the potential to affect the temperature of the house, even with the presence of insulation.

In winter, the heat can actually melt snow off the roof, meaning you have to deal with ice damming (the melted snow re-freezes in gutters).

Humidity in the air is not removed, so it can condense onto surfaces in the attic, posing a risk of mold growth, rotting or rusting of structural members, compromising insulation function, and attracting pests.

While the incoming air may not be able to circulate through the attic, it can blow away the insulation nearest the vents. While you might think this is a good thing, there is still every opportunity for the insulation to move back against the vents.

In addition, by moving insulation away from the edges of the attic, it reduces the R-value here. It opens up areas of vulnerability in the building envelope, compromising thermal control.

Appearance of Baffles

Baffles can be made of any material, as long as it’s solid. This is the stipulation found in Section N1102.2.3 of the International Residential Code (IRC).

However, you can typically expect to see baffles made from stiff and waterproof foam (in various colors), PVC, metal, cardboard, or plastic.

Insulation baffles are an interesting item to describe, which is why I will include an image for visual reference.

Air flowing inside the eaves vent to the baffles installed in the attic, attic with fiberglass insulation illustration

They are long, hollow channels. However, often there are large bumps or a ridge that runs intermittently along the inner part of the baffle. These help to catch any insulation fibers that the air is carrying by creating obstacles that the air must move around.

Man wearing a mask installing baffles to the attic with blown in fiberglass insulation illustration

You should be able to see the outside of the baffles running down toward the roof overhang. Because of the ridges inside the channel, there are relatively large pockmarks on the exterior of the baffles.

Baffles installed in the attic with air seal seam illustration
Baffles installed in the attic with air seal seam illustration side view

The baffles are generally stapled into place on the roof deck, so get out your staplegun. You overlap the edges and use caulk to seal these connections. You can also use spray foam or foam blocking to seal the baffles if they extend to the vents. Caulk should do to cover up any gaps on the path down.

Baffles installed in the attic with spray foam as a seal illustration
Baffles installed in the attic with spray foam as a seal side view illustration

Installing Insulation

Your insulation can be installed flush with the baffle to the end of the “floor” of the attic the same way you would have it sit flush with a wall.

Depending on how you are insulating, you can also secure it over the baffles on the roof deck.

Man's hand installing baffle in the attic with insulation illustration
Man's hand installing baffle in the attic with insulation and a fiberglass batt in front of it illustration

However, you need to be aware of what combination you are using. The nature of spray foam insulation means that it will damage cardboard and foam baffles if they cannot take the weight.

Where Are Baffles Required?

Baffles are associated with attic insulation.

They are installed along rafters at the edge of the roof deck when the soffit contains vented panels that can get blocked by insulation and which take in air that must be properly channeled through the attic.

If you have a vented soffit, whether continuous or non-continuous, every rafter requires a baffle.

They must be installed level, and the channel must cover the opening to the vent intakes entirely to keep insulation away from the openings. On the other hand, the baffles must not cover the intake opening.

Because homes come in different shapes and sizes, the number of baffles you will need depends on the specific dimensions of your attic.

When Are Baffles Needed?

According to Section N1102.2.3 of the IRC, eave baffles are required in vented attic spaces with air-permeable insulation (typically what you find in homes).

Where you have non-continuous soffits, you need a continuous baffle installation to make sure that all the air coming in goes through the baffles and that no insulation can bypass the baffles.

As per Section N1102.2.4.1 of the IRC, baffles can also be used around hatches and doors into the attic in order to hold down loose insulation and prevent it from falling into living spaces when the access point is utilized.

However, these baffles must never prevent maintaining (and replacing where necessary) the R-value of loose-fill insulation.

Therefore, baffles are needed wherever you need to contain or create a boundary for insulation, preventing it from moving to places where it can create problems with airflow and temperature regulation.

Baffles | Are They necessary for Batt Insulation?


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