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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″


Product Dimensions

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.

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* 

Use our online ThermalBuck calculator to estimate your order total.  Don’t forget to add in the measurements for your doors, too. 

*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.

Miter cut at the correct 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.

Compatible Sealants


ThermalBuck installed with DAP Dynaflex 800 modified polymer sealant Compatible 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 and interior seal), we recommend approximately 1 oz of sealant per linear foot of ThermalBuck.

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

BASF MasterSeal NP1 High-Performance Polyurethane Sealant

MasterSeal NP1 high performance polyurethane sealant
Photo sourced from basf.us Master Builder Solutions NP1 brochure

This is a single-component, non-priming, elastomeric polyurethane sealant. Cure times varies with temperature and humidity. Skin cure time 24 hours, full cure up to 1 week. Available in bulk packaging, sausage tubes, or traditional sealant tubes.

  • Adheres without priming to most common building materials, including concrete & masonry
  • Excellent bonding & flexibility: Joint movement capability ± 35% (ASTM C 719
  • Superior holding power
  • Suitable for long-term water immersion
  • Extreme temperature use – 0°F to 120°F
  • Meets VOC requirements in all 50 states
  • Minimizes sound transmission

For more information, please visit basf.us.

ThermalBuck high-performance window buck with Dap Dynaflex 800 sealantDAP Dynaflex 800* Premium Modified Polymer Sealant

This residential grade sealant provides a durable, 100% waterproof & weatherproof seal around windows & doors. Working time = 30 minutes. Tack free in 2 hours. Complete cure in 24 hours. Packaged in traditional sealant tubes, it requires a standard sealant gun for use.

  • Adheres to most common building materials
  • Excellent flexibility
  • Adheres to wet surfaces
  • Extreme temperature use – 0°F to 120°F
  • ASTM C719 +/-25% joint movement capability
  • Low VOC
  • Meets AAMA 803 & 808, ASTM C920

For more information, please visit dapspecline.com. *For ThermalBuck installations in CANADA, use DAP 3.0 Window, Door, Trim & Siding High Performance Sealant. 

DAP Dynaflex 800 can be purchased directly from BRINC Building Products. Inc with ThermalBuck. Call #888.814.2825 for pricing.

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.

  • 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

For more information, please visit dapspecline.com.

DAP Draftstop 812 can be also be purchased directly from BRINC Building Products. Inc with ThermalBuck. Call 888.814.2825 for pricing. 

DowSil 758 Silicone Weather Barrier 

This is a commercial grade, neutral one part RTV (room temperature vulcanization), neutral-cure silicone sealant. It has excellent adhesion to a wide range of building materials, including polymeric surfaces, and offers primerless adhesion. DowSil 758 can be used over a wide temperature range, and begins curing immediately by reaction to moisture in the air. Working time = 15 minutes. Complete cure time 24 hours. Packaged in sausage sealant tubes to minimize waste, it requires a sausage sealant gun for use.

  • Long-term silicone durability
  • Excellent durability, remains flexible
  • Sealant Waterproofing Restoration Institute Approved (SWRI)
  • ASTM C719 +/- 25% joint movement capability
  • ASTM C920 Type S, Grade NS, Class 25
  • Low VOC
  • UV Resistant

For more information, please visit dow.com.

Henry AIR-BLOC LF® Liquid Flashing 

Henry AIR BLOC LF® liquid applied flashing is a fast curing, single-component elastomeric flashing using a silyl-terminated polyether (STPE). This sealant can be used both for ThermalBuck attachment, and as flashing once the window goes in. 

This moisture-cure sealant provides a heavy-duty, rubber-like membrane with excellent weather and water resistance. Available in 20 oz. sausage tubes to minimize packaging waste. Achieves full cure in 24 hours.

  • Seamless and self-gasketing
  • Mold resistant
  • Bonds and cures in wet weather,
    surfaces must by dry
  • Application temperature 20°F to 110°F
  • Vapor permeable
  • Low VOC

For more information, please visit henry.com.

Henry Fortifiber Moistop® Sealant & Liquid Flashing 

Photo sourced from smallplanetsupply.com

This hybrid product can be used as both a sealant and a flashing agent. Combining silicone and polyurethane technologies, Moistop® offers the elasticity, moisture resistance, and long-term durability of silicone, with the excellent bonding ability of a polyurethane. Full cure time 24 hours.

Moistop® can also be used as a liquid flashing, and exceeds AAMA 714 standards. It is available in 20 oz. sausage tubes to minimize packaging waste.

  • Adheres to most common building materials
  • Fills joints up to 1/2″ thick
  • Adheres to wet surfaces
  • Application temperature 40°F to 110°F
  • ASTM C719 +/- 25% joint movement capability
  • Low VOC
  • Exceeds AAMA 808.3, ASTM C920

For more information, please visit henry.com.


Prosoco AirDam Air & Weather Barrier Sealant

AirDam waterproofing sealant is a single component, silyl-terminated polymer (STP). It combines the best properties of both silicone and polyurethane, to create a long-lasting, weather-tight seal around windows & doors. AirDam is a moisture-cured sealant – achieving full cure within 4-6 hours to produce a durable, high-movement elastomeric sealant. one of the greenest sealants, AirDam is packaged in traditional sealant tubes or sausage tubes to minimize waste. It requires standard caulking tools for use, and is easy to gun and tool in all weather conditions.

For more information, please visit prosoco.com.

  • Adheres to all types of window & door frame material
  • Extremely flexible
  • Bonds & cures in wet weather, and on damp substrates
  • Breathable – allows damp surfaces to dry
  • Sealant Waterproofing Restoration Institute Verified (SWRI)
  • LEED Ready, Living Building Challenge Ready, Red List Compliant, CAL Green Ready
  • Meets ASTM D4541 adhesion tests, ASTM D412 – 1,000%, ASTM C719 – PASS
  • UV Stable

For detailed installation instructions on how to incorporate ThermalBuck with Prosoco FastFlash liquid flashing membrane and Spray Wrap MVP fluid-applied air & water resistive barrier, please contact us at thermalbuck@brincbp.com.

ZIP System™️ Liquid Flash

Photo sourced from Huber ZIP System™️ Liquid Flash brochure

With silyl-terminated-polyether technology (STPE), ZIP System™️ Liquid Flash gets its durability from silicones, toughness from urethanes. Becoming quickly waterproof after installation, ZIP System™️ Liquid Flash bonds and cures in wet weather, at temps from 35° F to 110° F. Available in 10.3 or 29 oz cartridges, as well as 20 oz. sausage tubes, Liquid Flash achieves complete cure in 4 hours.

For more information, please visit huberwood.com.

  • Liquid Flash is ideal for both installing ThermalBuck, and flashing the window.
  • 180 day UV exposure
  • Bonds & cures in wet weather, and on damp substrates
  • Passes ASTM E331, and E2357


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. We’re big fans of these Grip Deck screws from the experts at Rodenhouse.


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 under the sill plate of the rough opening. Many window manufacturers recommend this so that the window is completely supported on the sill. 

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

Place one square inch of shim material for every 40 lbs. window weight (example 120lb. window one shim at each corner 1.5” x 1”) on top of the ThermalBuck. 

Consult the window manufacturer for their recommended shim placement.

“Innie” or Flangeless Windows
Installation featuring ThermalBuck, Yaro windows, and Rockwool Comfortboard exterior insulation submitted by 377 Builders, Massachusetts.

Inset Windows 

ThermalBuck was originally designed for nail flange window installation. Our performance testing, and installation steps were developed using nail flange windows, attached to the structure through the outermost part of ThermalBuck.

However, many architects and builders who prefer inset or flangeless windows have seen enough value in the thermal break provided by ThermalBuck, that they have developed their own installation techniques.

Here are some example details for inset windows using ThermalBuck.

Download Example 1

Download Example 2 – Subsill

Download Example 3 – Anchor Straps

Arched Windows


Arched Windows 

Plato said that “necessity is the mother of invention”. If you try to use ThermalBuck in an arched rough opening, you’ll agree with Plato wholeheartedly.

Some of our more industrious customers have developed unique methods to approach arches, such as this builder in Oregon. 

He cut the lengths of ThermalBuck in half lengthwise, then into smaller blocks. He seamed them back together as a “top” and “bottom” piece on either side of the arch. 

If you’re going to “step outside of the box” with ThermalBuck, we’d suggest plenty of sealant, and a layer of flashing tape. No matter what method you use, making sure it’s airtight & watertight is the goal. 

If you’ve tried something unusual with ThermalBuck, we’re interested. Send us your photos and testing to thermalbuck@brincbp.com . Maybe we’ll learn a thing or two.  

Energy-efficient custom home build in Eastern Oregon featuring 2.5″ ThermalBuck, R-Max Polyiso exterior insulation and Andersen Architectural Collection.