Radiant barrier and metal buildings is the greatest, smartest, most energy efficient amalgamation possible. Metal buildings are exceptionally conductive which, creates numerous energy use issues. Applying just thermal insulation (conductive) is inadequate due to the constant and gargantuan heat gain and loss in metal structures.
As stated in our article, Cold Climate (Insulation and Radiant Barrier), thermal insulation does absolutely zero to stop airflow and fiberglass allows max unrestricted airflow. Remember, R = trapped air. If fiberglass is condensed with your hand, the R value becomes negligible. Using just thermal insulation without radiant barrier, decreases the R-value performance and function of the fiberglass. Once the thermal insulation has absorbed as much conduction heat as it can, the stated R-value of that fiberglass decreases 60%. Since these are metal roofs, it is a guess at this point if that could be greater than 60%. That means, the insulation is useless and wasted money.
Since it is a metal building, metal supporting structure, purlins, roof and walls, the conduction of the metal versus typical roofing materials on homes, is extreme because let us say it once again, it IS metal. Inside metal buildings the ceilings and wall surfaces are susceptible to condensation. If enough water vapor condenses on the surface, it will all drip and run back into the building. How do we mitigate this?
First, if the thermal insulation and ventilation is inadequate, this is directly related to an increase in the likelihood of condensation by creating the perfect environment for moisture problems. Installing a vapor barrier alone will not prevent condensation in metal buildings. These are designed to block internal moisture from reaching the metal framework, insulation and siding. Condensation can and will occur on any interior surface including vapor barriers.
Three major factors are responsible for moisture within metal buildings and these are: warmer interior air temperature versus exterior, greater interior humidity levels and lastly, cooler ceiling surface temperatures.
Whenever water forms on ceilings, walls or floors, the moisture originated from inside the building and the source is water vapor from the air inside, not outside. The more water vapor, the greater the humidity. In metal buildings, when the temperature difference is high enough between the opposing sides, the moisture forms and this is always at the ceiling and interior walls.
Interior air at the ceiling is always warmer so when the exterior air temperature falls, the exterior surfaces cool. This causes the interior surfaces to begin cooling but at a slower rate. Thus, the warmer interior air at the ceiling is now in contact with a colder surface. If that ceiling surface temperature drops below the Dew point, the water vapor in the air will condense into liquid water.
How do we reduce this risk? By reducing the interior heat gain. The first step is to use a radiant barrier and best is to use bubble barrier with foil on both sides. We have developed a new product specific for metal buildings eliminating the need for thermal insulation.
This diagram was created for our Tempshield bubble foil without speed tabs to demonstrate how bubble can be used in multi-layers eliminating the need for insulation except in arctic and very cold climates.
By starting with a reflective radiant barrier layer, 3 in fact, with the necessary air space and installing the last layer with foam or wood spacers on the purlins and putting the last layer lengthwise across the purlins, the thermal bridge is broken and you have solved 3 problems with one product.
The radiant barrier will dramatically reduce the radiant heat gain inside the structure and the metal which, will decrease the temperature difference between the interior air and ceiling and walls. When the sun goes down, the metal will begin to cool and the adjacent interior air will also be cooler reducing condensation risk.
As with residential attics and roofs, ventilation is crucial. Keeping the humidity levels low inside is directly proportional to condensation risk. Depending on what activity is happening inside, removing the added heat and humidity is essential. Think again in systems, ventilation, improving air circulation, sealing air gaps, leaks and humidity levels all help reduce temperature. During the winter, if there is humidity and moisture, the whole interior temperature will be colder.
Reflective radiant barrier bubble either the Tempshield or the NEW Premium Stiff Bubble Speed Tab radiant barrier insulation, should be installed under the metal roof with 1-inch airspace. Then a second layer will be installed 1 inch below that to leave a ¾ inch airspace and then the final layer will be under that with a ¾ inch airspace leaving air below that last layer as well. This installation can be done with our regular bubble foil however the new Premium Stiff bubble with tabs for lightning fast installation does not require furring strips for installation like regular bubble foil does and, can be used for both metal building installs and residential.
This article emphasizes metal buildings due to the highly conductive nature of metal however, most of the installation applications would be the same for residential. When using a multi-layer system, air space is critical and just the right amount as well; too much air and the whole R-value system breaks down. Air space = R and with 3 layers properly spaced, there is no need for thermal insulation. Surprised? Not convinced? With the multi-layers, the summed R-value is 48-5- and that is without any thermal insulation! Wow. Soon, the radiant barrier industry will have a calculation tool for determining effective R-value of airspace; most likely will be called the Airspace Tool. We hope to see that early 2021.
In a multi-layer approach the top layer will reflect 95% of the heat back out and the second layer will catch the small percentage that is emitted from the top layer and then the bottom layer in a metal building application should be installed in a long run over multiple purlins with foam or wood spacers to break the recurring thermal bridge of the metal. In the first diagram, you can see that the 3 layers of radiant barrier bubble inside (between the studs) does not break the thermal bridge because the foil is inside the space (the last layer). IF that layer were to run the full length across roof rafters, with appropriate spacers, the thermal bridge would be beautifully broken as well.
Thermal bridging accounts for 30% heat lost (residential) and heat gained in metal buildings which, leads to an overheating of the air closest to the ceiling and walls. With ONE very simple installation application, 3 layer (multi-layer) bubble foil radiant barrier, not only can the thermal insulation be left out of the install but the thermal bridge can be broken when placing the last layer under the purlins attached to the spacers.
Using a thermal bridge-free design is highly beneficial because, the money spent keeping indoor air temperature at a consistent level will defeat the purpose of installing energy efficiency applications. Heat loss and gain will vary depending on severity and occurrence of the bridge. In metal buildings, that thermal bridge would occur at every purlin. Even though the radiant barrier would reflect 95% of the heat back out the roof, the metal skeleton of the building would be hot. This would translate into the building and create a thermal bridge. By installing the radiant barrier under and across or between the purlins, using spacers on the purlins, the radiant barrier incorporates the metal into its reflectivity protection so whatever heat is coming off the metal will cross the air space, hit the barrier to reflect back up into the whole insulation assembly. With the first layer close to the roofing material reflecting 95% back out, the second layer capturing what is left over, those purlins are not as hot as they would be without the barrier and they are cooler than they would be if thermal insulation were installed.
With 3 layers (remembering R = trapped non-moving air), the three layers sum to an R value, in the first diagram, to R-48. That is without thermal insulation! Wow. That value will increase slightly on the metal installation application because of the spacers placed on the purlins for the last layer. There will be more air between the second and last layer and that will all sum to a high R-value. We do know that radiant barrier in metal buildings will add at least a 20% savings in heating and cooling costs and greatly increase interior comfort. No studies are out, yet, about how great the savings would be with the three-layer system.
If thermal insulation is used in a metal building and there is excess moisture, the moisture will reduce the effective R-value performance of the insulation and if ventilation is inadequate, and the thermal bridge is not broken and the intense heat from the metal is not managed, the thermal insulation is rendered completely useless and a waste.
Thermal bridges cause interstitial moisture which, is the invisible enemy because it cannot be seen and will cause rust, rot, mold and so much more. Even when the metal is treated and is in constant contact with water it will suffer corrosion and building structure fallibility.
Continuous insulation is indispensable in metal buildings because that pesky thermal bridge must be blown to pieces. Placing radiant barrier between the purlins in 3 layers, ignoring the thermal bridge, will create water vapor accumulation between the panels.
Radiant barrier bubble is a vapor barrier and when air leaks, windows, doors, foundation, sills and side or end flaps are sealed and the thermal bridge has been broken and the heat is not conducting through to the interior, the temperature difference and changes will be minimal and the condensation risk will be under control. Humidity control would be one last issue to review depending on location and building use.
An extraordinary example of a multi-layer application using our Tempshield bubble radiant barrier use was for a large cold-storage facility. During the design phase they were told they would need two cooling towers however, the multi-layered bubble foil insulation application was so efficient, the second cooling tower has never been used and there is no thermal insulation. Yes, let me repeat that, no thermal insulation and only ONE cooling tower is being utilized. They reported this application has cut air conditioning cost buy 50% over just using the same R-Value of fiberglass. Adding 99% reflectivity to the building envelope is the reason. When applying a Radiant Barrier to the structure, you are directly addressing radiation.
The energy savings has been tremendous and will continue for this client. The application is such a success, it should and could be adopted industry wide.