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FAQ’s – Frequently Asked Questions 

Choosing the Right Depth

Choosing the Right Depth ThermalBuck

ThermalBuck is available in 7 different depths. The one you choose should match the thickness of the exterior insulation, and/or rainscreen.

1.0″, 1.5″, 2.0″, 2.5″, 3.0″, 3.5″, 4.0″

If they don’t match up exactly, and you’re between two sizes of ThermalBuck, in most cases we recommend choosing the smaller of the two sizes.

Product Dimensions

Once you add the sealant behind ThermalBuck, the thickness of the nail flange, and a layer of flashing tape, everything should line up within 1/8″ – 1/16″ for easy attachment of cladding.


Estimating ThermalBuck

Estimating ThermalBuck 

ThermalBuck ships to the job site in 8′ lengths, and is cut to fit on site.

In order to minimize waste, you can use split pieces on some of the jambs, but we do recommend using whole pieces at the head & sill.

Use this formula to best estimate how many linear feet of ThermalBuck you’ll need for your installation. 

Total RO linear feet + 2.0′ per RO + 10% = ThermalBuck* 

Contact us for a simple-to-use spreadsheet for you to use for your estimating. Don’t forget to add in the measurements for your doors, too. thermalbuck@brincbp.com

*Assumes the use of split pieces on some of the the jambs, whole pieces on head and sill. 

Preparing the Rough Opening

Preparing the Rough Opening

You’ll need 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.

Interior shot with window installed. Finish sill with on-site scrap drywall or plywood – cover with trim.


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″

WATCH: ThermalBuck Installation Video Step 2: Verify the Rough Opening   

Minimizing Waste

Minimizing Waste

We recommend using split pieces of ThermalBuck on some of the jambs to use up the smaller pieces you’ll have left over.

They will already be miter cut at the right angle to shed water away from the rough opening. Use plenty of recommended sealant at the joint for a good air & water seal. Insert roofing nails close to each seam. 

Use split pieces of ThermalBuck on the jambs if needed to minimize waste. 

Whole pieces are preferred at the head and sill for good drainage. If it is necessary to seam pieces of ThermalBuck at the head or sill because the opening is larger than 8′ wide, use a butt joint to shed water. Apply  sealant, and wrap flashing tape around the seam (butt joint only) before installing the window.



ThermalBuck installed with DAP Dynaflex 800 modified polymer sealant Choosing Sealants 

The right sealant is essential in achieving a good air & water seal with ThermalBuck. We recommend installing ThermalBuck with sealants specifically designed for window flashing and fenestration materials. They’re durable, flexible, UV resistant, and adhere without priming.

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 it meets the framing.

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.

WATCH: ThermalBuck Installation Video Step 4: Air & Water Seal for details   

DAP Dynaflex 800* Premium Modified 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.

  • Adheres to most common building materials
  • Extremely flexible
  • Adheres to wet surfaces
  • Low VOC
  • Meets AAMA 808, ASTM C920
  • Widely available across the U.S. Check with your local building material supplier.

*For ThermalBuck installations in CANADA, use DAP 3.0 Window, Door, Trim & Siding High Performance Sealant. 

DAP Draftstop 812 Window & Door Foam 

This is a low pressure, single component polyurethane foam designed to fill gaps between windows & doors, and rough openings. It can be used on the interior, between ThermalBuck and the window framing. dapspecline.com

  • airtight seal, non-rigid
  • protects against air, water, and sound intrusion
  • highly elastic – 30% joint movement capability
  • closed cell, will not absorb water
  • meets AAMA Standard 812

DOWSIL 758 Silicone Weather Barrier Sealant

This is a commercial grade, neutral-cure silicone sealant. Packaged in sausage sealant tubes to minimize waste, it requires a sausage sealant gun for use. It has excellent adhesion to a wide range of building materials, ASTM C719 +/- 25% joint movement capability, and is emits low-VOC’s. ASTM C920 Type S, Grade NS, Class 25.

For more information, please visit dow.com.



ThermalBuck insulation in the rough opening - interior shotChoosing 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.

Nails should be placed 10″-12″ apart. Insert nails close to the seams in each corner, and on any split pieces used on jambs. ThermalBuck can easily withstand use of a nail gun.

All fasteners must penetrate into the structure a minimum of 1-1/4″ for structural attachment.

Screws are recommended for installing the window. Install them at angle for better attachment to the stud, since ThermalBuck has moved the window 1/2″ outwards from the stud. 

If you’re using a thicker depth of ThermalBuck and want to use a low profile screw, you might need to order ahead. #10 diameter are preferred. Purchase from your local building material supplier, or direct from manufacturer. 

Side-by-Side Windows


Side-by-Side Window Installation

Home designs often feature several windows side-by-side. Think above the kitchen sink. It’s important to consider the dimensions of ThermalBuck, and how it impacts the amount of space needed between the windows. 

While ThermalBuck comes in 7 different depth to match the continuous insulation and/or rainscreen, the width that extends past the rough opening is consistently 2.0″. If you have side-by-side windows, you’ll need at least 4.0″. Most framers use two studs, and have only 3.0″ to work with between side-by-side windows. It just won’t fit.

When planning side-by-side window installations with ThermalBuck, a minimum of 4.0″ between windows is needed to accommodate the ThermalBuck from each window.

Now that doesn’t always happen in real life, so we’ve figured out a solution if you’re left without enough space between rough openings (see how to solve this challenge below). You’ll make everyone’s day go a lot smoother if you just leave enough room between the windows in the first place. 




Preferred placement of shims is between the jack stud and the sill, on the interior of the rough opening. Many window manufacturers recommend this placement so that the window is completely supported on the sill. 

Place shims on the interior, between the jack stud and sill.






In some instances, the only option will be to shim on top of the sill piece.

If so, ensure one square inch of shim material for every 40 lbs. of window weight (example 120lb. window one shim at each corner 1.5” x 1”).

Consult the window manufacturer for their recommended shim placement.