Strategies for Code-Compliant Continuous Insulation 2018 Edition

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.

Installation Failures

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)

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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)

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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)

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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.

4. Mineral or Rock Wool

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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. 

5. Spray Foam

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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.

6. Bautex Wall System

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.

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