Tag Archives: insulation R value

Insulation Values Reflect Real-World Energy Performance?

Insulation R Values Reflect Real-World Energy Performance?

Energy efficiency has become huge for post frame building construction. More and more people are discovering post frame buildings as being a cost effective design solution for residential and commercial construction.

Long time readers of this column have seen article after article in this vein, increasing with time. You have also had an opportunity to witness questions from many current post frame building owners who wished they would have designed appropriately to begin with. Proper advance planning can certainly help to achieve desired results.

Let us assume, for a moment, you have created a post frame building with commercial 2×8 bookshelf wall girts and 22 inch high raised heel trusses. In your walls, BIBs https://www.hansenpolebuildings.com/2011/11/bibs/) fiberglass insulation 7-1/4” deep has been used. This will give a laboratory R value somewhere in excess of 30. In attic space, 20 inches of blown in fiberglass will provide a R value of over 60. You have done your work and are happy your decision will give a more than satisfactory end resultant.

Then along I come and poke holes in your investment.

Keep in mind, my very own post frame home has fiberglass insulation very much like our imaginary scenario above.

The most common yardstick for measuring insulation performance will be R value, but there’s a problem. Insulation packaging shows lab analysis of R values, but it’s based upon used testing completely eliminating air movement from results. This matters a lot with fluffy insulation materials because air movement greatly lowers real-world insulation performance. Drafts and air currents often happen within wall cavities and attics and this will be why real-world insulation performance can be significantly lower than advertised values.

Alternatively, insulation products not allowing air movement through them (spray foams and rigid foams, for instance) have real-world insulation values almost identical to what you see printed upon packaging and used in advertising. Their performance doesn’t decline. Air-impervious insulations can be more than twice as effective as air-porous insulations of identical R value under real-world conditions.

Where does all of this leave us as post frame insulation specifiers and building owners?

When I added an exterior elevator shaft to our post frame home two years ago, my insulation choice was closed cell spray foam. I did make an error in that I did not listen to my own inner voice. Our local installer made recommendations for thickness I felt were insufficient, so I had roof and wall sprayed one inch thicker. I should have gone thicker yet as there was plenty of space available to fill. As a result the elevator shaft is cold and drafty into our living space.

Considering closed cell spray foam? Think it may be expensive? Consider its performance will probably be twice as effective as fiberglass and closed cell spray foam suddenly doesn’t seem so costly.


How to Install Fiberglass Batt Insulation

How to Install Fiberglass Batt Insulation in a Post Frame Building Attic
There are times when I overlook things which seem obvious to me, but do not appear to be so to the innocent beginner doing their own construction work. This past week we were contacted by one of our new post frame building kit owners, who had hired a contractor to assemble his building. The contractor was apparently facing some challenges when it came to installing the unfaced fiberglass insulation batts in the attic space.

First step – unless your post frame building has trusses spaced every two feet, chances are good the ceiling joists must be installed between the truss bottom chords.

Exception (and not covered in this article) would be if your building is going to use steel liner panels for a ceiling and the trusses are spaced appropriately to be able to support the liner.

Step two is to install the ceiling material, which in most cases is going to be 5/8” sheetrock (although other materials such as OSB or plywood could be used). Do not install a vapor barrier between the ceiling materials and the ceiling framing.

Step three – lay down boards or plywood sheeting to help you be able to walk safely in the attic space.
When installing fiberglass insulation, observe all safety precautions. Fiberglass can release tiny fibers, which can be harmful if breathed into the lungs and which may irritate the skin. Wear protective gear.

The necessary R-value for the attic will depend upon the manufacturer and style of insulation chosen. Check with the manufacturer’s instructions on the packaging to determine how much insulation thickness is needed to achieve the desired R-value.

Once you’ve determined the amount and type of insulation needed, and the insulation has been purchased, begin staging the rolls in the attic. Place rolls around the perimeter of the attic for easier access during the installation.

Fourth – When laying insulation, it’s a common mistake to cover up the soffit vents. Soffits are part of the overall ventilation scheme, and covering them blocks essential air flow in the attic. With the widely spaced trusses typical of post frame construction, insulation baffles can be created by using rigid insulation boards to maintain a minimum two inch airflow above any insulation.

Fifth – Begin laying in the insulation, starting at an area furthest from the attic access.
When rolling the insulation, cut it to length using a utility knife.

When you reach the end of a line, pull the insulation back slightly, then place it on a joist so there is a solid surface to cut on. Using a straightedge as a guide, make your cut.
After making the first cut, use the remaining portion of the roll and work back in the other direction. When you reach the end of the roll, butt a new roll up to the cut piece and finish the run.

Once the perimeter is reached, cut the end of the roll to fit. Using this technique results in the best use of the insulation and reduces wasted material.
Lay the rows snugly together to prevent undesirable gaps or spacing.
When you run into an obstacle like a cross-brace or pipe, cut a notch in the insulation roll to fit around the obstacle, then continue with the run.

Areas around the perimeter of some attics can be rather tight and confining. Just keep rolling out the insulation, but don’t compress or squeeze it into tight spots, as this can decrease the insulation value.

Rigid Insulation Boards Part II: Foam Board

 Yesterday’s blog featured a discussion of the various foam board products with application for your new pole building.  Used correctly, they provide good thermal resistance. Applied incorrectly can create a huge structural problem with pole buildings, along with safety issues.

Protect all types of foam  insulation from direct sunlight. Over time, the sun’s ultraviolet rays can damage the insulation. For roofs, this is generally done by applying a coating such as tar, acrylic, silicone, or rubberized paint. You can also cover the foam with a rubber or plastic membrane, or a layer of asphalt and roofing felt. Make certain you are using compatible products. The solvents in some coatings dissolve certain plastics.

In cold weather, warm inside air containing water vapor can get past the wall finish and insulation, condensing inside the colder wall cavity. In hot, humid climates the same thing can happen, just in the reverse direction. Humid outdoor air in the summer can condense inside cool, air conditioned wall cavities. If enough of this happens and the water cannot escape, wood rot, mold, and other moisture-related problems can occur. For this reason, building codes often require installing a vapor diffuser retarder on the warmest side of the wall cavity.

Foam board insulation is commonly placed against the steel building siding, between the girts of exterior walls. To prevent air infiltration, place rigid insulation boards tightly together and seal the seams with tape or caulk. This practice may worry some in cold climates since the foam board may act as a second vapor diffusion retarder. Studies have shown, condensation rarely occurs in these areas unless something else is seriously wrong with the wall assembly (like massive uncontrolled air leakage into the walls from the building). If the assembly is constructed correctly, the inside surface of the foam board stays warm enough to keep water vapor in its gaseous state long enough for it to escape.

When insulating a foundation you need to consider, although insects don’t eat foam board, they can easily tunnel through it. Insect burrows reduce the R-value and structural integrity of the insulation. For these reasons, some manufacturers treat their foam products with an insecticide, usually a borate compound. Many building jurisdictions also mandate treating the earth around the building with insecticides. These jurisdictions may also want an inspection area several inches wide and all around the foundation of a house kept bare of insulation board.

A better solution for below-grade walls in need of insulation is to install the foam board over the interior of the basement walls rather than on the exterior, which is more common. Interior applications prevent ground-dwelling insects from finding the foam board at all, and they eliminate the need for the bare inspection area. Insulating interior walls, however, requires careful attention to moisture control.

Most jurisdictions also require installing a fire barrier over the interior foam board. While this adds extra cost, the thermal performance of this method is superior in most cases to the more common exterior foam board application. This equates with a dollar savings in energy which can repay many times over for the additional cost of an interior application. If converting a basement into a living space, there is almost no additional cost.

Foam insulation is relatively hard to ignite, but when it is ignited, it burns readily and emits a dense smoke containing many toxic gases. The combustion characteristics of foam insulation products vary with the combustion temperatures, chemical formulation, and available air.

Because of these characteristics, foams used for construction require a covering as a fire barrier. One half-inch thick gypsum wallboard is one of the most common fire barriers. Some building codes, however, do not require an additional fire barrier for certain metal-faced, laminated foam products. Always check with local building code/fire officials and insurers for specific information on what is permitted.

While rigid insulation boards may afford a relatively high R-value, if installed improperly they can provide less than desired insulating results, structural issues or pose a fire hazard. In many instances, other methods of climate control may be more cost effective.

Thermodynamics and Reflective Radiant Barriers Part II: Application

As I said yesterday, the reflective radiant barrier inhibits heat transfer by thermal radiation. It does not necessarily protect against heat transfer by conduction or convection.  Why do you need to know about reflective radiant barriers?  It could mean thousands of dollars saved over the years for heating/cooling, in what you choose for roofing materials, and what lies beneath them. It might help for you to read yesterday’s blog for background on how I got to this point.

Continuing on….

For installing a reflective radiant barrier under a pole building steel roof, the reflective radiant barrier may be applied directly by draping the reflective radiant barrier over the roof purlins. Even more effective is to install the reflective radiant barrier over the purlins, install 2×4 furring strips on top of the insulation, and then the roof steel. The furring strips ensure the reflective radiant barrier faces into a sufficient air space to be effective. If an air space is not present or is too small, heat may be able to conduct through the reflective radiant barrier. Since the metal in the reflective radiant barrier is highly conductive, the heat transfer would all be through conduction and the heat would not be blocked.

I did this on my huge 3 story gambrel style accessory building I built in South Dakota about 7 years ago.  I put 2×4’s over the reflective radiant barrier, and then applied the roof steel.  My wife chose black steel, and so I added in the 2×4’s both to counteract her color choice and get the most out of the insulating value of the reflective radiant barrier.  Our heating/cooling bills are phenomenally small.  In fact, this 84’ x 60’ x 20’ building is easily a third less expensive to heat/cool than our 30’ x 60’ single story home across the road from it!

For shingled roofs, the reflective radiant barrier may be applied over the rafters or trusses and under the roof decking (usually osb or plywood). This application method has the reflective radiant barrier sheets draped over the trusses of rafters, creating a small air space above with the reflective radiant barrier facing into the entire interior attic space below.

I even used this method in re-roofing our house two summers ago.  The shingles had seen their better use, so we applied 2×4’s right over the shingles, put down the reflective radiant barrier and then applied white roof steel for a “cool roof” solution.  It’s noticeably cooler in summer and much warmer in winter, along with lower energy bills.

Another method of applying a reflective radiant barrier to the roof in new construction would be to use a reflective radiant barrier which is pre-laminated to OSB or roof sheathing. While manufacturers of this installation method often tout the savings in labor costs in using a product which serves as roof decking and a reflective radiant barrier in one, these products are generally considered by most to be “pricey”.

One common misconception regarding reflective radiant barriers is the heat reflecting off the reflective radiant barrier back out the roof has the potential to increase the roof temperature and possibly damage shingles. This is simply not the case. Performance testing by Florida Solar Energy Center conclusively proved the increase in temperature at the hottest part of the day was no more than about 5 degrees F. In fact, this study showed the reflective radiant barrier had the potential to decrease the roof temperature once the sun went down because it was preventing the heat loss through the roof. RIMA (Roofing Insulation Manufacturers Association) International wrote a technical paper on the subject, where they collected statements from the largest roofing manufacturers, and none said a reflective radiant barrier would in any way affect the warranty of the shingles

Wrapping a building’s walls with a reflective radiant barrier can result in a 10% to 20% reduction in the tonnage air conditioning system requirement, and save both energy and construction costs.

Reflective radiant barriers are also quite effective in floor systems above unheated basements and crawl spaces. The reflective radiant barrier may be either stapled below the floor joists, creating a single reflective air space, or between the joists, followed by some type of sheathing. Reflective radiant barriers work extremely well in this application for two reasons. First, a reflective radiant barrier which is not perforated for breathability acts as an excellent vapor barrier. This means ground moisture will not be able to pass through the reflective radiant barrier and enter the living space. Secondly, the floor is the only part of the building where the heat flow is always down, unlike a roof where the heat would be coming down during the summer and rising to escape in the winter. When the heat flow is down, 93% of the heat is radiant heat, which is exactly what the reflective radiant barrier is designed to block.

A reflective radiant barrier actually IS insulation and it DOES have actual R values in tested systems. It IS highly directional, meaning it is better against heat gain, than heat loss. In tests, it rates as high as R-14, depending upon the installation.

However reflective radiant barrier are not the “end all” of insulation. My preference is to use it for what it is great as – an insulated vapor barrier.

There are many commercially available vapor barriers. These include Tyvek® (a registered trademark of the DuPont Corporation) and other similar housewraps. Even polyethylene plastic sheeting (think of British Polythene Industries Limited’s product Visqueen) is a vapor barrier.

While fine vapor barriers, none of these products have insulation bonded to them, so are not an effective method of condensation control. In order to control condensation, a thermal break must be created. It is the layer of air cells sandwiched between the facings of the reflective radiant barrier (most commonly a white inner facing and an aluminum exterior facing) which creates the necessary thermal break.

If the only intention for heating a pole building is to take the chill off for a few hours with light heat (like throwing a space heater on), then the reflective radiant barrier can be an affordable option. For buildings which are to be climate controlled, other options are more practical.

For more information on reflective radiant barriers, I’d recommend visiting https://www.buyreflectiveinsulation.com, which also features a handy calculator to determine the required amounts of insulation for gable roofed buildings.