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How to Air Seal an Attic “Right and Tight” – Part 2

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In the first part of this article, we shared how Attic Systems contractors air seal all the gaps, holes, cracks and other openings between the attic floor and the living space that the framers, electricians, plumbers and HVAC workers created when a home was built.  We showed how all the pipe and wire penetrations, can lights, chimney chases, top plates, drop down stairs and other gaps and cracks in the attic floor where the air your customers paid to heat in winter can leak into the attic can be air sealed.  In part 2, we’ll cover a few of the less common problem building assemblies that can be found in and around attics that also need to be fixed to provide homeowners with a complete and comprehensive solution to their comfort issues.

Multi-level attics – Attics can be 30˚ in the winter, and 150˚ in the summer! When one room under the attic has a higher ceiling than another room it leaves a short section of interior wall exposed in the freezing cold/baking hot attic. Since this wall is an interior wall, it’s not insulated. Even if the short exposed wall is insulated above the ceiling, fiberglass batts do nothing to stop air flow. This leaves cold air from your vented attic to descend down into the interior wall between the two rooms, and warm interior air to leak up into the vented attic. You have a major air leak and a cold wall bisecting the middle of your home!

To solve this, Attic Systems installs SilverGlo™ insulation board on any exposed wall in the attic and sealed with expanding foam to stop air leaks.  SilverGlo™ is an Attic Systems™ exclusive. It is expanded polystyrene foam with graphite infused into the foam to increase the R-value by 24% over standard EPS foam. In addition, SilverGlo™ has a radiant barrier on the face to reflect heat, adding to the insulation value.  SilverGlo™ is also used as blocking between floor joists as needed.  This makes rooms adjacent to the wall warmer in the winter and cooler in the summer, less drafts, more comfort, and lower heating and cooling costs.



Whole House Fans – Before most homes had air conditioning, whole house fans mounted in the upper floor ceiling were popular. These fans would suck out a very high volume of warm air from the house, which would be replaced by incoming outside air entering open windows. Of course there was no control over how hot, cold, humid or dusty the incoming air was, but without a properly insulated house with air conditioning, there was little choice. Today, most of these whole house fans are obsolete, and never or seldom used. The problem is that the fan louvers leak a lot of air even when the fan is off (all year long) – and for every cubic foot of air that leaks out the top of the house, a new cubic foot of cold or hot/humid outside air is sucked into the bottom of the house to replace it. In addition, the fan/louver area represents a big gap in the ceiling insulation. These fans contribute to cold, drafty rooms that are hard to heat, and higher fuel and electric bills.

This is fixed by installing our exclusive “David Lewis Whole House Fan Cover™” over the fan assembly and sealed airtight with expanding foam. It stops air leakage and insulates over the fan. Made of lightweight, high-tech SilverGlo™ foam insulation with a radiant barrier (foil) on the flat top to reflect heat back in during winter and out in the summer, so the insulation isn’t doing all the work by itself. Most homeowners will never want to use their fan again, especially after other comfort improvements are installed.  But if the customer wants to use the fan in the future, simply “pumpkin cut” a removable lid in the top of the cover.  This treatment results in a tighter, more comfortable, less drafty home with rooms that are easier to heat, and lower fuel and electric bills.



Kneewall Spaces – A kneewall space is created when a finished room is built within a sloped roof. A short wall called a “kneewall” forms a triangular space which may or may not be accessible with a short door or access panel. The floor of the kneewall space forms the ceiling of the room below it. The floor and kneewall itself are open to the kneewall space side with exposed fiberglass batts. Since fiberglass does not stop air flow, the insulation does next to nothing to air seal and insulate. The floor of the upper level, the ceiling of the lower level and the kneewall are all cold in winter and hot (from radiant roof heat) in the summer. These kneewall spaces are not suitable for storage since it is dusty and very cold or hot.

Blocks of SilverGlo™ foam insulation are installed between the ceiling joist bays. Outside the blocks, the surface of the ceiling is sealed with sprayed foam or SilverGlo™ foam. (Fiberglass insulation may be installed on top). SilverGlo™ foam insulation is installed under the rafters up to the kneewall and sealed at the top with foam sealant.

SilverGlo™ has a radiant barrier on both sides to reflect roof heat out in the summer and house heat back in during the winter. The addition of this radiant barrier gives a thermal benefit so the insulation isn’t left alone to do all the work. After installation, inside air can’t get out of the house through the kneewall spaces and outside air can’t get in. Insulation is added, with integrity, to the correct surfaces. This results in significantly warmer upstairs rooms in the winter, cooler rooms upstairs in the hot weather, more comfort, less dust.  And now the kneewall space is suitable for clean storage.

Bathroom Fans –Bathrooms have lots of destructive moisture when the shower is running. That’s why bathrooms have fans to get the moisture out. But out to where? Often plumbers and electricians leave these fans dumping into the attic. But when warm humid air hits cold attic surfaces, it condenses into water. And this can result in mold all over your roof deck, rafters, and ceiling joists – and even rot.

It’s vitally important to get the moisture carried in the air from the bathroom where it’s supposed to be – safely outside of the attic.  The bath fan will be ducted with insulated (northern climates) duct work through the gable end wall of your attic, with a vent hood on the outside. Uninsulated duct such as PVC pipe may be used if the duct is to be buried in cellulose insulation.

The result is that the bath fan no longer feeds moisture to mold in your attic, and mold and rot from this source stops.

Once all the attic is well air sealed, it’s time to blow in a thick blanket of cellulose.  We like to blow in 17” – 18” inches of TruSoft™, our exclusive pest and mold resistant cellulose to provide an R-value of R60 – the best level of resistance to heat flow to and from the living area and the attic.

For more information on how Attic Systems contractors are fixing these and other comfort and energy wasting issues in homes, visit

Marc Tannenbaum

Posted In: Building Performance

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