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Preparing the Rough Opening


The most critical point to remember when planning your ThermalBuck installation, is to oversize the rough opening on all 4 sides to accommodate the 1/2″ tongue of ThermalBuck.

The unique “L” shape is an important design element that helps handle the compressive and shear loads, and support the weight of the window.

Review the rough opening preparation from the window manufacturer, then add an additional 1″ overall to their rough opening recommendation to accommodate ThermalBuck.

Window Width Rough Opening Width
per Window Manufacturer
NEW Rough Opening Width
with ThermalBuck Installation
35.5″ 36″ 37″
Window Height Rough Opening Height
per Window Manufacturer
NEW Rough Opening Height
with ThermalBuck Installation
59.5″ 60″ 61″

Choosing a Sealant 

ThermalBuck installed with DAP Dynaflex 800 modified polymer sealant

The right sealant is essential in achieving a good air & water seal with ThermalBuck.

You’ll use three 3/8″ beads on every piece of ThermalBuck, on the mitered ends, and around the perimeter where it meets the sheathing. Also, on the nail flange of the window. In the interior, sealant is needed at the transition of ThermalBuck to the window, and where ThermalBuck meets the framing. 

We recommend installing ThermalBuck with sealants specifically designed for window flashing and fenestration materials. They’re durable, flexible, UV resistant, and adhere without priming. 

To estimate how much sealant you’ll need to install ThermalBuck (including the window), we recommend planning 1.75 oz of sealant per linear foot of ThermalBuck. 

Dow Corning 758 Silicone Sealant

This is a commercial grade sealant, packaged in sausage tubes to minimize waste. It requires a sausage sealant gun for use. For more information, please visit dow.com.  

DAP Dynaflex 800 Premium Polymer Sealant  

This is a residential grade sealant. Packaged in traditional sealant tubes, it requires a standard sealant gun for use. For more information, please visit dapspecline.com.  

  • Available at Home Depot & other retail locations across the U.S. Check with your local building materials supplier.

Choosing Fasteners


ThermalBuck is installed not only with sealant, but secured through the 1/2″ tongue into the structure with 2″ galvanized roofing nails, in order to exceed the minimum 1-1/4″ structural penetration requirement

Use nail gun, or hand nail.



Screws are recommended for installing the window. They must penetrate into the structure a minimum of 1-1/4″. #10 diameter are preferred.

If you’re using a thicker depth of ThermalBuck, and want to use a low profile screw, you might need to order ahead. Helpful links: