The Key to Continuous Insulation - Mind The Details

By Frances "J.R." Babineau

Continuous insulation (CI) has quickly become the rule when it comes to meeting the higher efficiency requirements mandated by the most recent International Energy Conservation Code. As exterior foam sheathing becomes a more common means to achieve CI, it is important to understand the details that can detract from CI’s effectiveness.

Here are five considerations:

Avoid using just one insulating material While traditional cavity insulation is great, batts and rolls alone cannot prevent thermal bridging. Solution: A combination of exterior foam sheathing and interior cavity insulation ensures a seamless thermal barrier across the structure, making a great CI solution.

Properly install cavity insulation Cutting corners on the cavity insulation will decrease the overall effectiveness of the entire wall system. Batts and rolls, or spray foam are good options, but standard installation best practices must be followed. Solution: If installing batts and exterior sheathing, ensure the batts are trimmed properly and aren’t compressed into tight spaces. Interior cavity insulation should touch all six faces of the structure — the front, back and all four sides. If using spray foam, fill the full depth of the cavity to ensure proper R-value – but don’t overspray. If cavities are overfilled, contractors must trim or grind down the foam prior to gypsum board installation.

Choose the right sheathing material Not all materials are created equal: Be sure to use the material that will lead to minimum complications and maximum performance Solution: Of foam sheathing options, XPS and polyiso are the two most popular. XPS foams are durable, are less permeable and offer an R-value of about 5 per inch. At an R-value of about 6 per inch, polyiso foam is one of the most thermally efficient insulations on the market. Polyiso also contributes to a more fire-safe structure as it will not melt even at very high temperatures.  This makes for a great solution for commercial building.

Right-size and air-seal windows Window frames and panes are very conducive. Accounting for 25 percent (or more) of the total area in commercial buildings, they can constitute up to half the energy loss. Solution: Consider reducing the window-to-wall ratio and avoid floor-to-ceiling windows. Instead, design window locations and selection to maximize effective daylighting and views. It’s win-win: people still benefit from the sunlight and the view but the thermal bridges between the sill and the floor can be reduced with insulation. Also, note that gaps around windows should be air-sealed with foam, not fiberglass.

Make balconies energy smart Balconies are a high-demand element in commercial buildings, but they can be a thermal nightmare. Solution: Don’t create the balcony simply by extending the floor slab to project off the side of the building. Instead, create a balcony that is separated from the building structure using steel connectors and foam blocks to secure the balcony to the building. Or, consider using a less conductive material such as wood or wood-plastic composites or a standalone balcony connected to ground.  

As a building scientist for Johns Manville, Frances "J.R." Babineau is responsible for research and technology development of building products and applications, with an emphasis on indoor environmental quality and energy efficiency.  He has been with Johns Manville for 16 years and is actively involved in standards development through ASHRAE and the Building Performance Institute (BPI).  

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