Recent building code requirement changes and the growing demand for energy-efficient buildings are driving architects to search for a better solutions for continuous insulation.
Continuous insulation is required by the International Energy Conservation Code (IECC), The Energy Standard for Buildings Except Low-Rise Residential Buildings, and, in most cases, ASHRAE 90.1.
Knowing how to best select and specify materials for continuous insulation is key. But it’s also important to understand the methods used to prevent thermal bridging and improper installation of materials: this ensures that you’re able to deliver the most energy efficient and high-performing buildings to clients.
Addressing Thermal Bridging
Thermal bridging occurs when heat passes through the path of least resistance, like through steel or wood studs. It’s the enemy of energy conservation.
Effective continuous insulation stops energy waste and effectively addresses the problem of thermal bridging. Any gaps in the insulating layer are simply unacceptable. Wasted energy also increases carbon emissions, so aggressively attacking the problem is more important than ever before.
Thermal bridging may also allow unwanted moisture flow, resulting in condensation within the wall cavity. Wet insulation can quickly lose R‑value, and moisture inside the wall may lead to mold growth, mildew odors and wood rot.
These are all problems that can compromise the health and comfort of building occupants, and they may also lead to expensive repairs or a structure with a shortened life cycle.
The Problem with Traditional Methods
Of course, insulation batts or spray foam inserted between studs are not continuous. To counter the problem of thermal bridging, steel and wood-frame construction requires the installation of continuous insulation over the studs.
But traditional sheathing and cladding requires fasteners that may create a new threat of thermal bridging, particularly when fasteners are improperly installed.
Any installation failures that create gaps or crevices in the layers of continuous insulation can compromise the integrity of the wall system.
Even when building designs comply with current codes, installation failures may compromise the continuous insulation layer, leading to additional cooling requirements in the summer and heating needs in the winter.
The importance of properly installed continuous insulation in modern building construction can’t be underestimated. Mass air migration in a poorly sealed building envelope wastes energy and increases carbon emissions.
Available Solutions for Continuous Insulation
There are a few products and methods available for achieving continuous insulation. Understanding what each of these products offers can help guide how you choose wall construction solutions in their projects.
1. Polyisocyanurate (Polyiso or ISO)
Polyiso panels are rigid foam panels fabricated from liquid foam. Polyiso rigid foam panels provide an R‑value of about 6.0 per inch, although insulating values can degrade slightly over time. Due to the liquid foam fabrication technique and the need for additional dimensional stability , polyiso panels must be faced with a secondary liner material.
These panels are not vapor permeable — one manufacturer states its product has a 0.05 perm rating. If the breathability of the wall cavity is an issue, polyiso sheathing should be used with caution.
These panels are often considered less “green” than some other exterior sheathing options. They are used more often in roof construction than wall construction.
2. Extruded Polystyrene (XPS)
XPS panels are quite noticeable because they are usually green, pink or blue in color. XPS offers an R‑value of about 5.0 per inch.
XPS is a semi-permeable sheathing with a perm rating of approximately 1.0. As such, even unfaced XPS is more of a vapor retarder than a vapor barrier. In some instances, XPS can absorb moisture over time, which lowers its R‑value.
The manufacturer of one XPS product calculates potential shrinkage of as much as two percent. Undue contraction can leave gaps and put stress on tape along seams, which impacts its effectiveness as an air/moisture barrier.
3. Expanded Polystyrene (EPS)
EPS panels are considered a versatile solution for insulation. With an R‑value of approximately 4.0 per inch, it often outperforms XPS and Polyiso in terms of cost-efficiency, and tends to retain its R‑value over time.
EPS rigid foam panels are usually applied over house wrap or a suitable alternative. EPS is typically the foam of choice for use in structural insulated panels (SIP) and insulated concrete forms (ICF). EPS can also be used for below grade applications and can be treated to resist insects.
EPS is available faced or unfaced. Faced EPS is considered a vapor retardant, and some specialty products are considered vapor barriers.
You can also design walls with a layer of mineral wool, also referred to as rock wool and stone wool.
Roxul® is a rock wool insulation panel fabricated from basalt, an igneous rock. In both commercial and residential construction, Roxul is used in a variety of ways, including as exterior wall insulation.
Since it is a stone-based product, Roxul is very fire-resistant. In fact, it can withstand temperatures up to 1,177 degrees C or 2,150 degrees F. It inhibits the spread of fire, and it does not release toxic gases. Moreover, the non-directional nature of the rock wool fibers effectively absorbs acoustic waves, so it reduces noise and disruptive echo.
Mineral wool is highly water repellent, so the risk of mold, mildew and bacteria growth is effectively eliminated. And Roxul’s vapor-permeability allows water vapor trapped inside a wall cavity to escape.
Unlike some types of rigid foam panels, Roxul retains its essential characteristics over time. It’s not as prone to expansion and contraction when there are local shifts in temperature and humidity.
Spray foam insulation provides an R‑value of 6.0 per inch while both acting as a vapor retarder and offering an air/water barrier. What makes it stand out from other insulation products is the flexibility afforded by its sprayable form.
The spray application is far simpler than conventional continuous insulation methods and entirely eliminates the need for metal fastening. With fewer steps and easy application, spray foam reduces labor costs. This is especially true for curved walls and other similar designs, which are otherwise difficult to achieve and require additional labor hours.
For both commercial and residential structures, a wall system with built-in continuous insulation is an effective solution to thermal bridging. The Bautex Wall System, for example, is a four-hour fire rated load-bearing system that includes the continuous insulation required by modern, updated building codes, so no additional sheathing or insulation is required.
Single-contractor installation reduces the chance of worker errors that can compromise wall integrity. The thermal mass of the wall helps exceed energy code requirements in Texas and climate zones in nearby states. Moreover, with the application of a liquid-applied air and moisture barrier, Bautex exceeds both above-grade moisture protection requirements and air tightness standards.
Safeguarding the Future of Our Buildings
By understanding the solutions and methods available to architects for continuous insulation, we’re one step further to more energy-efficient, successful and safer buildings.
“A continuous insulation barrier is a very big deal,” Carl Weinschenk said in Energy Manager Today. “In addition to saving money by improving insulation, continuous insulation safeguards the health of the people within the structure.”
Building with continuous insulation in mind means architects deliver structures that perform efficiently, save their clients money and protect the people who use it.