Reflective Insulation and Radiant Barriers in Metal Buildings

Published November 9, 2015 by Whirlwind Team

If you know anything at all about metal, you're familiar with rust. While metal buildings are virtually impervious to other traditional building threats, like pests, fire and strong winds, they can succumb to moisture damage without proper planning and design. They are also excellent conductors of heat.

One of the first lines of defense for metal buildings are the protective coatings used to seal the metal panels and components, providing a durable barrier against water, debris and environmental pollutants. A close-second line of defense is the combination of high-quality insulation with a radiant barrier. When these three items are in place, you can rest assured your metal building will be the low-maintenance and long-lived structure it was intended to be.

Don't Forget a Radiant Barrier When Insulating Your Metal Building

Some of the biggest mistakes made by DIYers is they think in terms of traditional wood-framed buildings since wood materials are where most people get their start. So, many first-timers construct their metal building using insulation - sans a radiant barrier.

Radiant barriers are an essential component for attic spaces, and sometimes interior walls, to prevent heat gain/loss and protect structural metal from trapped moisture and condensation.

Also called vapor barriers - are typically made from a foil-like material with a reflective surface. It may be sold on its own, as a separate product, or it may be attached to blanket/batt or other types of insulation to make insulating your building more efficient.

The barrier serves two main purposes in for your metal building:

  1. Prevent heat transference. The laws of thermodynamics state that heat will always move from a warm area, to a colder area. During the winter months, the warm air from your heater and/or wood-burning stove will try anything it can to escape into the cooler outdoors. During the summer months. all that hot, outside air will do its best to infiltrate, undoing your cooling system's hard work. In the latter case, that heat transference is called heat gain.

    Metal buildings are particularly sensitive to heat gain because metal is a wonderful conductor of heat. This is why cool metal roofs originated in the metal building world, as have reflective coatings that increase the exterior structure's emissive qualities. Radiant barriers work to prevent unwanted heat transference.

  2. Mitigate condensation. Whenever there is a notable temperature difference between the interior and exterior of a hard surface, condensation occurs. An example being the condensation that builds up inside your car's windows on a cold day. This same type of condensation can occur on interior metal components that are hidden from view - such as interior wall spaces and, most commonly, the undersides of roof and attic spaces.

    This sitting water can wreak havoc on metal building parts, increasing the rate of rust and corrosion. Additionally, chronic condensation issues will lead to mold and mildew on insulation and other organic materials, which is detrimental to the health of building occupants as well as structural building elements.

Radiant barriers, or vapor barriers, deflect radiant heat from the sun, the atmosphere or the heating system back to where it came from, preventing it from coming in contact with metal surfaces. This simultaneously decreases the amount of heat transference or solar heat gain impacting the building and improves interior temperatures and air quality.

Choose the Right Barrier For the Application & Climate

Not surprisingly, radiant barriers aren't a one-size-fits-all product so choose carefully based on the product's application, as well as your climate. If you aren't sure which product will be best for your building, ask your metal building supplier or a representative at the product supplier's headquarters. The local building department is also a good resource.

  • Foil in or foil out? To gain the benefits these barriers were designed for, the reflective surface needs to face the right direction. If your live in a warm climate and your main impetus is to protect the roof/attic space from solar heat gain, then the reflective side should face outward. If you live in a cold climate, radiant heat is best kept inside the building, so the foil barrier should face towards the interior of the building.
  • In non-conditioned buildings. If you'll be erecting a warehouse, shop or other type of building that won't be conditioned, run the radiant barrier right between the purlins, near the roof. Even without any insulation, this will protect the building from radiant heat gain - or effectively trap radiant heat in cooler climates - which can make a tremendous different in terms of interior comfort.
  • In conditioned buildings. If your building is conditioned, the typical layering of materials from the roof to the interior of the building would be: the roof sheeting, furring strips/battens to provide the required air space, your radiant barrier (foil facing outward if you're mitigating solar heat gain, your insulation product of choice, fabric liner and then the banding/purlin system.
  • Perforated versus solid radiant barriers. In almost all cases, you are better off using a perforated radiant barrier, that allows for better airflow and prevents condensation. Solid radiant barriers are typically reserved for interior wall surfaces in cooler climates, some stucco structures or in high hydrostatic pressure areas along the southern US coast.

Don't undermine the value of quality insulation by neglecting to use a radiant barrier. Work with a metal building manufacturer or experienced metal building contractor to select the best product and application for your building's function.

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