Why Seal the Top of the Drywall and Three Ways to Accomplish this Task

by tracy on May 18, 2012

Energy Star Version 3 requires sealing the top of the drywall to the framing top plate below an unconditioned space. But even if you aren’t building an Energy Star home, this step is worth taking. Why? Strapping and wood variations allow leakage between conditioned living space and unconditioned attic space as shown in this thermal image.

 

Leakage between conditioned and unconditioned space

The most basic ‘fix’ is to have the drywall guys add a simple line of caulk or adhesive across the top plate, as pictured here.

Caulk or adhesive applied to top plate

However, this method brings up two concerns:

  • Can you be sure it was done?
  • Can you be sure the caulk was applied to a thickness that will accomplish the seal? This is particularly important when pursuing and Energy Star certification due to limited air leakage requirements.

Two companies have created products designed to overcome these issues.

  • Owens Corning’s, EnergyComplete™ is a spray-on foam that creates a compressible gasket once set. When the drywall is installed, the gasket fills any gaps between it and the framing top plate.

Owens Corning EnergyComplete drywall gasket

  • Knauf’s EcoSeal™ product is a water-based, elastomeric latex caulk. It is not compressible. In order to seal the gap between the partition top plates and drywall, Knauf advises contractors to spray the gap from the attic after the drywall is installed. This method probably means the air-sealing contractor will need to make two trips to the job site: one before and one after drywall.

Both products are part of hybrid insulation systems where building assembly seams are sealed prior to batt insulation installation, thereby providing both an air barrier and thermal barrier less expensively than spray foam.

Knauf EcoSeal applied prior to batt insulation

Although created for the same reasons, there are definite differences between the two products with pros and cons for both. The following table provides a comparison (click to enlarge). The safety and crack sealing details are the same for both but that’s where the similarities end. For example, the cost of equipment and training is significantly higher for the Owens Corning EnergyComplete product and due to overspray, windows, tubs, etc. need to be protected.

Comparison of EcoSeal and EnergyComplete

I was able to witness the installation of the Owens Corning product during the green certification process for a production builder in my area. In spite of the cost difference, they felt that the combination of being able to spray EnergyComplete on the top plate with the compressible nature of the product offered superior sealing capabilities.

While I haven’t seen the Knauf product installed first hand, I’ve seen many positive builder comments online.

Both of these products contribute to best building practices for creating an energy-efficient, green and healthy home and are worth considering for your next project.

As always, The Difference is in the Details .

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spray in insulation January 27, 2014 at 10:57 pm

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Wow! I wish I remembered how I found it, but I am glad I did.
Keep the info-nuggets coming. You have a new reader.

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