Custom attic baffles and insulating above the top plate

[focusonenergy]

In this video the baffle was installed, but additional cellulose had not yet been added.

Most homes lose a lot of heat through the attic by the top plate of their exterior walls. The primary issue is that there is only about 3-4 inches of space between the top plate and the roof decking.

Typically we see fiberglass insulation rolled out to this point, or pieces tucked into this narrow area. The resulting R-value is at best 1, since the original fiberglass is about R-3, but now it either has air from the soffit moving through it or it has been compressed. With the standard baffle you lose another inch so the total R-value between the top plate and roof deck would probably be only 2 or 3. The result is ice damning as a lot of heat is lost to the adjacent roof deck.

A solution for this problem is to remove the fiberglass and add a sturdy baffle that wont collapse when cellulose is lightly "packed" into this area. In some cases the opening to the soffit (just beyond the top plate) can be sealed with spray foam, or the entire soffit can be packed with cellulose if it is not too large. Spray foam will offer an R-6 or 7 per inch and cellulose an R-4 or 4. The total R-value between the top plate and roof deck would be about 10-12 with packed cellulose or 18-22 with 2-part sprayfoam.

We don't use these sturdy baffles in all of the rafter channels, and we usually reduce the overall number to less than there was before. The reason being that we always air seal an attic, thus greatly reducing the moisture that enters the attic. Air sealing always trumps insulation and ventilation.

[tpatten]

I've made some custom baffles like you suggested. They are each about 60 inches long. The air gap is 2.5" high and the width is 20". I'm going to be putting in 20 inches of insulation. Do you suggest putting them in every other rafter channel or at what frequency? The house is only about 1000 sq ft and the only area lacking for insulation is the attic.

Thanks,

Tom P.

[Jackofalltrades]

The 6' baffles with 20" insulation sounds like very smart choice.

The number of baffles is really dependent on your soffit system, because it can be a limiting factor of air flow into the soffit (and attic). We normally put 2 such custom baffles for every active soffit vent we find outside. If the entire soffit has a perforated aluminum soffit then we usually do every third rafter channel.

Keep in mind that we air seal the entire attic so ventilation requirements go way down because the movement of warm moist air from the conditioned living space no longer gets into the attic.

I hope this helps