One of the questions LP® Building Solutions gets from builders often is about burying ducts in attic insulation and whether combining radiant barrier sheathing with blown insulation over ductwork can benefit homeowners. As with most technical situations, the outcome depends on a nuanced approach. Let's dig in and explore this question.
For optimum HVAC performance, the ductwork system should be installed in a basement or conditioned space. However, as builders are well aware, digging a basement or adding bulkheads may not be realistic or feasible. It's particularly challenging in certain house designs like slab-on-grade or two-story structures with an open floor plan. Therefore, the solution to this common problem-especially in the southern region-is to install HVAC ducts in the attic.
However, this presents a new set of problems as it exposes the ductwork and air handler to extreme temperatures and humidity, which can result in heat losses between 10 % and 45 %.
Burying ducts in attic insulation can be easily done and does not require special tools or materials. Revisions in the 2018 International Residential Code (IRC) and the 2018 International Energy Conservation Code (IECC) allow new provisions for partially and deeply buried ducts as a way to construct an energy-efficient option in vented attics.
Before the IECC adopted buried ducts, previous code editions didn't forbid it; they simply didn't specify the conditions for performance and compliance. Whether or not your state has adopted 2018 IECC standards or you wish to achieve net zero building performance, it’s best practice to follow the requirements, which include using the proper R-value of the duct insulation by climate zone and the minimum attic insulation for burying ducts.
There are several insulation methods based on attic design, but ducts placed over the bottom of truss chords and buried under insulation in a vented attic is a popular builder option.
The 2018 provision offers specifications for two different options:
Not only does this buried ductwork improve performance, but it also helps reduce condensation, which is a common disadvantage in high-humidity climate zones. Therefore, the 2018 IECC offers these guidelines:
LP recommends using LP® TechShield® Radiant Barrier Sheathing when installing deeply buried ducts. Installing LP TechShield sheathing helps offer impressive energy efficiency by blocking radiant heat in the roof panel from emitting into the attic, reducing attic temperatures by up to 30 degrees.
The combination of deeply buried ducts and LP TechShield Radiant Barrier further reduces attic temperature fluctuations and helps keep ducts cooler. In addition to having the opportunity to "right-size" the HVAC for reduced costs, this performance combination also allows you to build a more comfortable and energy-efficient home for your client.
Buried ductwork has been approved by California Energy Code Title 24 and the DOE Zero Energy Ready Home program. The 2022 Inflation Reduction Act extends ENERGY STAR tax credits for your clients who purchase energy-efficient HVAC systems and duct insulation.
Not sure how to explain all the benefits of LP TechShield Radiant Barriers to your homeowners? Keep this list of top benefits on hand to guide you.
Business Solutions4 min
There’s a lot to consider when it comes to building an energy-efficient home for your clients and the many nuances that change with each build—including its orientation to the sun.Continue Reading
Sustainability Solutions8 min
Every jobsite has a ton of moving parts, from product shipments, supplies, and schedules to subcontractors and homeowners. It's no wonder that many project teams can struggle to maintain quality jobsite communication and collaboration throughout the building process.
Sustainability Solutions6 min
In an era where environmental responsibility is paramount, we are proud to announce a remarkable achievement: the LP® Structural Solutions portfolio has been officially designated as carbon negative. This milestone is a testament to our unwavering commitment to redefining construction materials for the better with a focus on sustainability, resiliency and groundbreaking advancements.
Sustainability Solutions8 min
In our pursuit of sustainable and environmentally friendly products, we completed five LCAs and EPDs for our LP® Structural Solutions portfolio. Along with LP® SmartSide® Trim & Siding, these EPDs demonstrate the carbon negativity of our products. That means that our products store more carbon than is released during their entire life cycle, making us a meaningful part of the climate solution.