Matter of Spec

Category Archives: Matter of Spec

Updating values for polyiso

The January issue of The Construction Specifier included the article, “Impact of Advancements in Model Energy Codes,” by Jared O. Blum. We received the following letter to the editor from Tim Merchant of the EPS Industry Alliance, an organization representing those in the expanded polystyrene community.

The EPS Industry Alliance has always supported informative articles that advance the knowledge, proper use, and application of foam insulation. That said, the article makes some inaccurate claims regarding R-value of polyisocyanurate (polyiso) insulation that we would like to address.
The chart on page 68 lists the R-values of several foam insulations, including polyiso, which it says has an R-value of 6. This is in alignment with ASTM C1289-13, Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board, and Underwriters Laboratories of Canada (CAN/ULC) S770-09, Standard Test Method for Determination of Long-term Thermal Resistance of Closed-cell Thermal Insulating Foams as of your publication. However, new testing methods developed in 2013 have shown the R-value of 25 mm (1 in.) of polyiso is 5.6—seven percent less than the measure of previous standards.
Last June, the Polyisocyanurate Insulation Manufacturers Association (PIMA) announced it would be updating its QualityMark-certified R-value program to reflect the new data, which was determined using a new test method for finding long-term thermal resistance (LTTR). The new 5.6 R-value rating was to be incorporated in Canadian and U.S. standards as of January 1, 2014. Please keep this in mind for future articles related to the R-value of polyiso insulation.

We asked the article’s author to respond:

ASTM C1289-13 was updated last year, and features important improvements regarding the prediction of long-term thermal resistance value (i.e. R-value) for various polyiso insulation boards. The article published in this issue of The Construction Specifier was originally written before PIMA and its members began reporting LTTR values in accordance with the standard on January 1, 2014 as part the PIMA’s QualityMark program.
To participate in PIMA’s QualityMark certification program, a Class 1 roof is suggested to have a design R-value of 5.7 per inch. It should be noted polyiso is unique in the R-value increases with the thickness of the foam, so 76 mm (3 in.) of polyiso has a higher R-value per inch than 50 mm (2 in.).
Since its founding, PIMA has been active in the harmonization of relevant standards to provide greater continuity in the reporting of polyiso roof insulation thermal values throughout North America. This is why the association implemented the industry-wide QualityMark certified R-value program for rigid polyiso roof insulation in 2004. The update to this standard provides more data to aid in the prediction of long-term thermal performance of North America’s most popular rigid roof insulation.

Sounding Off on Acoustic Sealants

In the February issue of The Construction Specifier, we published the article, “Using Gypsum Wallboard for Acoustical Control,” by Ashwin L. Himat. The piece dealt with new drywall products designed to reduce noise. However, one reader was concerned there was a bigger picture to keep in mind. Steven Zalben, AIA, NCARB, LEED AP, wrote:

The use of acoustical sealant to reduce sound transmission was only cursorily mentioned. Using an appropriate sealant on both top and bottom plates, and sealing all perimeter joints of all layers, is as important—possibly, more important—than the mass. The mass primarily addresses the structure-borne sound, while sealing primarily addresses airborne sound.

We asked the article’s author to respond.

Mr. Zalben’s feedback on the use of acoustic sealants along wall and ceiling edges for dampening airborne sound transmission is quite valid. It is important to incorporate these sealants into all aspects of the gypsum-board-finishing process, and also to apply acoustical putty around all electrical boxes to prevent similar airborne sound transmission.
The function of gypsum board sealant is similar to that of the viscoelastic polymer used as the middle layer in laminated noise-reducing gypsum boards—both convert sound energy into thermal energy. The image below helps illustrate the sound transmission paths that could be present in most buildings.

SoundTransmissionI would further like to emphasize adding mass with layers of drywall to dampen airborne sound has its disadvantages. For instance, it is not as effective for improving the sound transmission class (STC) rating of the wall system, and it reduces the footprint of the usable space. Decoupling methods using resilient channels also have their limitations, as they are easy to short-circuit during installation. The newer concept of a laminated noise-reducing gypsum board achieves high STC ratings without any of the limitations that often result from adding extra layers of drywall or using resilient channels.

XPS, EPS, and Dock Flotation

After the feature, “Out of Sight, Not Out of Mind: Specifying Thermal Insulation Below-grade and Under-slab” ran in our December 2013 issue, we received a letter from retired architect, Joseph S. Bond. Mr. Bond wrote that the article in question “seems to reverse the findings” from both his personal and professional experience with expanded and extruded polystyrene (EPS and XPS):

I am a retired architect, and may not have the best current information on EPS and XPS, but when these two products were mistakenly used as ‘flotation’ for lake docks and later removed, the XPS bales were like new and had no water soakage beyond the first (1/8 in.). Continue reading

Re-examining Paver Performance

In the November 2013 issue of The Construction Specifier, we published the article, “Controlling Stormwater at the Source,” by Katie McKain, ASLA, MLA, MUD.  David R. Smith, CSI, of the Interlocking Concrete Pavement Institute (ICPI), wrote in about what he felt were some inaccuracies; we then shared his comments with the author.

I read with interest Ms. McKain’s article. She made some inaccurate statements about permeable interlocking concrete pavement (PICP) that require correction. This includes misstating PICP longevity at seven to 15 years. Continue reading

A Light Discrepancy?

We received an e-mail from a reader regarding an article that appeared in our November 2013 issue:

I read the article titled “Rethinking Cool Roofing: Evaluating Effectiveness of White Roofs in Northern Climates,” by Craig A. Tyler, AIA, CSI, CDT, LEED AP. Although I agree with what I think is the article’s concept, the author repeatedly states ultraviolet (UV) absorption into the roof system contributes to heat gain in a building or that UV reflection helps to keep the roof cool. UV is not only not responsible for heat gain through absorption into the roof system, but it is also entirely the opposite end of the spectrum from the infrared (IR). UV exposure has long been known as a contributor to the breakdown of roofing materials.

When the author was contacted, he responded:

The reader brings up a valid point about infrared being at work here as well. Sunlight consists of infrared, visible, and UV electromagnetic radiation, known as ‘solar radiant exposure.’ Infrared, while commonly associated with heat radiation, is not the only component of sunlight that contributes to temperature rise. All sunlight will heat surfaces that absorb the solar radiation. Infrared consists of 49 to 53 percent of sunlight, with the remainder being mostly visible and UV light. UV exposure from sunlight reaching the earth’s surface can cause degradation to many types of construction materials, as well as people. Degradation can be observed as a reduction in physical properties, cracking/crazing, loss of gloss, and discoloration.