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Published in: Metal Architecture
Date: January 2009


Simple Retrofit Solutions using a Liner System

The new construction market in 2008 was much slower than recent years however we have seen an substantial increase in the retrofit market. Since new construction numbers have decreased, many firms found themselves keeping active by supplementing revenue with retrofit projects. There has been an enormous increase in energy efficiency/awareness and with the current economy struggling, many owners are looking at ways to reduce their energy expenses and operating costs. In addition, there are numerous incentives that make energy efficient investments more attractive than ever. These wonderful financial opportunities are for owners and designers to capitalize on by motivating them to conserve energy, invest now and take advantage of accelerating payback periods.

The liner system is installed to the bottom of the substructure, encapsulating the conductive purlins and creating the enclosed cavity space for insulation to be installed.

Recently, Congress extended energy tax incentives specifically pertaining to the Commercial Building Tax Deduction. The extension is now valid through 2013 and allows building owners or designers to claim a deduction of up to $1.80 per square foot for upgrading their building envelope, HVAC and lighting system which results in 50% savings over ASHRAE Standard 90.1-2001. Architects and designers should be aware of a special rule for government-owned (Federal, State, or local government) buildings where the owner may allocate the deduction to the person primarily responsible for designing the energy efficient building. In addition, there are many state and local programs that are rewarding individuals who incorporate renewable energy systems and make energy efficiency improvements to their existing buildings by aggressive tax incentives, rebates, loan guarantees and grants.

Metal buildings are excellent construction candidates to reap these rewards because most pre-engineered metal buildings have obsolete energy systems for today's higher energy costs. They are particularly thermally challenged because of the inefficiencies of “traditional” insulation methods which has promoted compressing the  faced fiber glass insulation between the substructure and the roof deck or wall panel. The insulation is not only compressed at the roof/wall fastening points but it is also compressed throughout the entire purlin/girt cavity negating the full effect of the insulation. Traditionally, the vapor retarder is laminated to fiber glass rolls and the installer “seals” the consecutive rolls by aligning, rolling and stapling the tabs together. It is not uncommon for the staples and joints to deteriorate over time, increasing the opportunity for heat transfer. In addition, the vapor retarder is placed between the steel panels and the substructure, consequently leaving the conductive purlins and girts exposed to the conditioned air space. The exposed purlins and girts allow heat to escape during the winter and radiates heat into the building during the summer. This improper placement of the vapor retarder outside of the dew point line commonly results in condensation and corrosion problems. Overall, the typical “installed” R-values are up to 50% less than the package label R-values when it was originally installed. If the existing building's vapor retarder has deteriorated and is damaged by rips, holes or tears, the overall performance could be even lower.

One economical and reliable solution to improve thermal performance and interior appearance is to retrofit with a liner system. The concept is simple, reduce the overall conductive surface area that is exposed to the conditioned space, properly seal the vapor retarder, and add uncompressed un-faced insulation in the existing cavity space.

When retrofitting with a liner system, the existing compressed insulation can be left installed in the roof because a large flexible fabric membrane will cover all existing insulation and conductive purlins. The liner is a continuous vapor retarder that encapsulates the purlins, typically spans entire bays and is sealed to the bottom of the rafter flanges. The liner is supported by a series of evenly spaced steel straps that typically span the building width and are mechanically fastened through the liner, to the bottom of the purlins. Additional cross straps could be specified to create a grid pattern appearance if desired. In most cases, the existing ceiling attachments such as lights, fans, ducts, conduit, fire sprinklers, etc. are temporarily detached to pull the liner throughout the bay. There are a variety of hangers that can be used to preserve the integrity of the vapor retarder and the system manufacturer should be able to provide you and the installer with specific details and specifications. The existing building interior is instantly transformed to a clean finished look making the space much brighter and more pleasant with uniform temperatures. This is also an excellent time to switch the energy consuming metal halides to efficient high bay florescent fixtures that will lower operating costs and energy usage up to 50% while providing the same amount of light. Thermal Design retrofitted one of their manufacturing facilities with a bright white, highly reflective fabric liner system that achieved the designed light levels with approximately 30% fewer fixtures and replaced existing metal halides with new high bay fixtures. We took advantage of a $90 rebate per light fixture through a state funded program and the investment for the new fixtures plus installation should pay for itself in only four months and will save thousands of dollars annually.

Once installed, the liner system creates the enclosed cavity space for uncompressed, un-faced insulation to be installed. Fiber glass batts can be pulled through the cavity or alternatively the cavity can be filled with blown-in insulation depending on preference and desired R-value. As an example, in a typical metal building with 8” purlin depths and existing 6” (R-19) fiber glass insulation compressed above the purlins; an additional 6” of fiber glass batt can be pulled through the cavity space. The liner system and additional insulation can provide up to 250% more in place R-value. Additional uncompressed thicknesses can be achieved if the building is equipped with deeper purlins and/or   bottom purlin stand-offs are used, such as a thermal spacer block. In most cases, we recommend filling the cavity with insulation to assure the highest in place R-values and avoid possible condensation problems.

Payback periods will obviously vary depending upon fuel costs, typical energy consumption, building size and building use. It is not uncommon for owners and facilities managers to realize utility bill reductions up to 50% by simply retrofitting their existing building with a liner system. Moreover, considering the aforementioned government incentives the payback period is further accelerated making the insulation investment even more attractive and profitable. At a time when new construction projects are not as abundant as years past, liner system retrofits are an excellent way to deliver value and continue to build trust with your clients while capitalizing on available tax incentives for themselves.


Brad Rowe
Thermal Design
National Marketing Manager


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