Right-sizing Insulation for the Wall Cavity

In the low-hanging-fruit category of energy performance, correctly specifying and installing insulation is near the top of the list. Still, we frequently see insulation thickness that is not in alignment with the size of the wall cavity or an installation that doesn’t fit tightly.  Two big issues to address, both in the construction documents and in the field, are compression and gaps.

Compression reduces R-values

Compression can occur when the thickness of insulation required for the R-value is too large for the size of the studs. Not uncommon, the inconsistency could stem from a change of wall thickness due to plumbing conflicts, structural analysis, product availability, Title 24 requirements, etc. The impacts, though, are significant. For example, R-19 batt insulation that is 5.5” thick fully ‘lofted’ would fit in a nominal 2x6 cavity. Shove that same insulation into a 2x4 wall, and the effective R-value drops to R-12! Compression also occurs when insulation is pushed behind a pipe or conduit instead of cut around it, or when a framing bay is narrower than a nominal 16” space and the installer doesn’t cut the width of the batt.

Gaps could allow convection and condensation

Properly installed wall insulation has contact to all 6 surfaces of the stud cavity: at the header and footer, at the stud on either side, to the outside wall and to the inside wall. We put emphasis on this last surface because we often see insulation that is pushed into the cavity so much that when the sheetrock is installed there could be an inch or more gap between the insulation and the sixth surface. Be sure that batt insulation fully touches the outside wall and is fully lofted to the interior. If there is vertical airgap, convection could occur within the wall cavity, which tremendously reduces the effective R-value.

Gaps can also occur at the top of the cavity, either if insulation isn’t installed correctly or if it slumps over time. The gap at the top of a cavity is concerning as moist interior air could come into contact with a cold exterior wall, causing condensation. Condensation, of course, could lead to mold growth and health concerns.

Tips for getting the best fit

Interested in getting the best performance from your insulation? Here are few tips to consider:

·       Include a Quality Insulation Installation (QII) HERS verification as part of your project. QII applies to residential and non-residential projects, as well as new construction or alterations and covers air sealing as well as insulation.

·       Don’t just leave it to the Title 24 report - add notes to your construction drawing indicating expectations for a QII-level of installation.

·       Whether you are the owner, architect or builder, require a meeting with the insulation subcontractor prior to the start of work and communicate expectations at that time. Trouble-shoot difficult areas and discuss the company’s own quality-control process and employee training program.

·       Consider using a blown-in cellulose or similar product that fills the cavity more easily.

Looking for more information about appropriate insulation implementation? Check out the Quality Insulation Installation (QII) Handbook, developed by CalCERTS,  Questions on energy performance or Title 24 energy compliance? Reach out.

Quick Video Tour of a Local All-Electric ZNE Office

Would you like to see inside an all-electric, Zero Net Energy commercial building, right here on the Central Coast? In this 3-minute video we walk through People’s Self-Help Housing’s new 24,000 SF headquarters located in San Luis Obispo. In the video we highlight the heat pump systems for heating, cooling and hot water, take in a roof-top view of the 115 kW photovoltaic array, and wrap up with lighting and all-electric appliances. Enjoy!

Upcoming Courses on HERS, Envelope Detailing and Energy Code Implementation

We’re pleased to continue offering in-person and online classes through 3C-REN. Here are a few of the upcoming courses:

ENERGY CODE COMPLIANCE: USING HERS MEASURES (PART 2)

Wednesday, March 20th @ 9:30 am – 11:00 am

Elevate the efficiency of your projects with our HERS Integration Series! Join us for Part 2, featuring Jennifer Rennick from In Balance Green Consulting and Paul Dunn from Central Coast Energy Compliance. This session will delve into HVAC and indoor air quality. Learn essential integration strategies and HERS measures tailored for architects and builders. REGISTER

Missed Part 1? Check it out at the 3C-REN On-Demand library.

DETAILING FOR HIGH PERFORMANCE ROOFS AND WALLS

Thursday, March 21 @ 10:00 am - 11:00 am

We know the concepts behind providing a great building envelope – air tight and well-insulated– but how, exactly, do we do that? In this course, we’ll provide ‘sketch-level’ details of high-performance wall and roof assemblies that designers and builders can use as an outline to develop their own project-specific details. REGISTER

ENERGY CODE IMPLEMENTATION SERIES

Accessory Dwelling Units (ADUs) - REGISTER

Wednesday, May 8 @ 9:30 am - 11:00 am

Since the energy code update took effect in January 2023, the industry is adjusting to design, detailing and construction to meet compliance. In this series, we’ll review the code requirements with a focus on what to include in construction documents to streamline the permitting process and tips for construction to ease signoffs and occupancy.

Past courses in the series (available on demand soon)

• Energy Code Implementation: Single Family New Construction

• Energy Code Implementation: Single Family Additions and Alterations

Future offerings

• Energy Code Implementation: Multi-Family (June 12)

• Energy Code Implementation: Non-Residential (TBD August)

High-Impact Strategies to Take on Embodied Carbon

Have you been hearing a lot more about embodied carbon lately and been wondering why it’s becoming so relevant? Around 40% of global carbon emissions are associated with built environment. In building science, we generally think of carbon in two different ways. Operational carbon refers to the greenhouse gas emissions released due to building energy consumption. This is the type of carbon emissions we are more accustomed to thinking about, regarding things like HVAC equipment efficiency and refrigerant types. Embodied carbon (EC) refers to the greenhouse gas emissions arising from the manufacturing, transportation, installation, maintenance, and disposal of building materials, as you can see in the image below. These carbon metrics are measured as Global Warming Potential (GWP) in kgCO2e, a proxy to compare material impacts.

Source: New Buildings Institute

As a whole, we’ve been addressing the lower hanging fruit in understanding the scale of the issue, recognizing hotspots where bigger impacts can be made through easier, more attainable actions. Simultaneously, many organizations have been developing standards and tools for reporting embodied carbon. Now in California, we’re moving towards building LCA (life cycle analysis) code required thresholds and mandatory reporting. Starting July 1, 2024, CALGreen Code for nonresidential projects will require certain projects to comply with an embodied carbon mandatory measure. Look for more detailed information in future blogs.

Where can we look within the buildings we design to find practical ways to reduce embodied carbon? According to Rocky Mountain Institute, around 50-80% of embodied emissions occur in the Product Stage (A1-A3) through raw materials supply, transport, and manufacturing. Certain products have a much higher impact than others, and targeting those specific materials for low-carbon product substitutions can be an efficient strategy for embodied emissions reduction.

Concrete

Source: Ross NW Watergarden, Shoi Sugi Ban: Setting Fire to Portland’s Fences

Concrete is probably the one you’re hearing about the most. With the highest potential for embodied carbon reduction at no to low additional cost, substituting cement with alternative cementitious materials (ACMs) and specifying recycled aggregate are some of the most effective methods for reduction. Reducing the overall amount of concrete in your project is also an effective measure as is thinking a bit outside the box for alternative strategies, like using charred wood instead of concrete for walls in landscaping. Please see our article from last year looking a little deeper into concrete.

Steel

There are many options for rebar and structural steel comprised of higher recycled content. Also consider using wood framing instead of metal framing for both energy efficiency and embodied carbon reasons. Additionally, sourcing sustainable and regenerative materials, like mass timber, instead of steel, and prioritizing local materials helps reduce emissions associated with transport.

Insulation

Source: Hempitecture.com

Insulation provides an interesting opportunity to reduce EC by using materials like mineral wool batt instead of foam insulation. Taking it a step further, there are also alternative carbon-storing insulation materials that sequester carbon like cellulose, hempcrete, and straw bale that will have a net EC reduction. Keep an eye out for emerging technologies, like Mycelium board, for other low-carbon options as they come onto the market.

Mycelium board: Greensulate

Glazing

Glazing options come at a bit higher of a cost premium compared to other targeted areas, but using lower-carbon window frame materials and specifying no more than two panes of glass can be effective carbon reduction strategies. It’s important to consider the tradeoffs between embodied carbon and operational carbon when thinking about how many panes to use. Additional panes of glass will give better window performance and reduce operational carbon emissions, but it will also have more embodied carbon associated as more materials are used.

Finishes

Finish materials are another lower cost category that can have an EC reduction by selecting low-carbon or more durable finish materials. Durable materials that don’t need to be replaced as frequently avoid emissions associated with manufacturing and transportation of new materials.

In addition to targeting specific products, there are some general design strategies that are important to consider in your building design. There’s a well-known quote in the building science world from Carl Elefante that says, “The greenest building is… one that is already built.” Reusing a whole or part of a building, and using salvaged materials reduces emissions associated with new production. When reuse is not an option, it is important to design buildings to use space and materials efficiency, avoiding excess consumption. This can be through designing buildings to be the right-size and avoid unused areas as well as highlighting exposed structure instead of applying additional finishes. We also want to think about the versatility of a building’s design and how a building can be utilized in the future, creating opportunities for reuse or recycling.

The terrain of embodied carbon is changing rapidly as new products become available and mandatory embodied carbon tracking becomes part of our codes. Start getting familiar with embodied carbon now so you can incorporate strategies to address it in your projects.