October 17, 2014
Reported R-values and Actual R-values
I've recently been involved in some interesting conversations about polyisocyanurate foam and its insulating performance:
Over the last several decades, reported R-values for polyisocyanurate foam insulation have been declining as the industry has adopted testing and reporting methods that more realistically reflect this material's tendency to decrease in insulating value over time. At one time, R-values as high as R-7.2 were reported for this material. At this time, the Polyisocynuarate Insulation Manufcturers Assocation (PIMA) recommends a Long-Term Thermal Resistance (LTTR) value of R-5.7 for one inch of foam, with the value per inch increasing slightly with greater thicknesses:
|Insulation Thickness||LTTR R-Value per Inch||Total R-Value|
LTTR values are intended to reflect the expected insulation value of the material at 5 years of age, and also its average performance over 15 years (higher in earlier years, lower in later years).
Polyiso insulation also loses insulation value as it gets colder, in some cases by as much as roughly 25 percent. Though it may seem counter-intuitive, most building insulation materials are tested at a mean temperature of 75 degrees F, that is, very close room temperature! (Code of Federal Regulations, Labeling and Advertising of Home Insulation, R-Value Tests.) In the case of polyiso foam insulation, this can lead to overstating its performance at colder temperatures. Tests of polyiso foam samples performed at a mean temperature of 25 degrees F have produced measured R-values ranging from R-3.9 to R5.6 per inch (see Figure 2 in the linked document).
The National Roofing Contractors Association (NRCA), has sponsered tests pf polyiso insulation samples extracted from roofs of various ages and adopted the following recommendations for this material: R-5.0 per inch for heating applications and R-5.6 per inch for cooling, regardless of thickness. These values are intended to account for both aging beyond 15 years and temperature dependent factors.
Polyiso insulation loses insulation value over time as the gasses, or blowing agents, used in its manufacturer gradually diffuse out of the material and are replaced by ordinary atmospheric gasses. The reason that thicker samples retain a higher value longer is because this exchange is slower when it must progress through more material. Impermeable facers, such as aluminum foil, applied to the foam may also slow the diffusion process and loss of r-value to some extent over time, though how much is uncertain.
Extruded polystyrene (XPS) insulation also experiences the same exchange of gasses and loss of insulating value over time, though to a lesser extent than polyiso. The standard value of R-5 per inch reported for this material reflects the results of aged testing. Oddly, a different stanard for determing aged values of XPS foam insulation used in Canada, reports what most agree are slightly inflated values for the performance of this material.
Expanded polystyrene (EPS) insulation is a more gas-permeable material that rapidly exchanges any blowing agents used in its manufacturer with ordinary atmospheric gasses. For this reason its insulation value quickly stabilizes and no aged testing is required. Standard insulation values for this material are in the range of R-3.5 to R-4 per inch.
And one more thing regarding temperature dependency: Fiberglass batts, XPS foam, and EPS foam--unlike polyiso foam insulation--all gain insulating value at lower temperatures.
October 17, 2014 in 07 Interior Finishes for Wood Light Frame Construction, 16 Roofing | Permalink | Comments (0)
June 13, 2014
Wood Foam Insulatoin
Wood foam replaces artificial insulation material (Bine Infomration Service, 3/10/14) describes foam panel insulation made entirely from wood particles. Proposed as a replacement for petroleum based foam panels, wood foam panels have insulation values comparable conventional mineral fiber products.
June 13, 2014 in 07 Interior Finishes for Wood Light Frame Construction | Permalink | Comments (0)
May 28, 2014
Tall Wood Buildings
Interest in tall wood buildings continues to grow. Where current North American building regulations generally restrict wood buildings to approximately 5 or 6 stories in height, upcoming Canadian and U.S. code revisions are likely to open the door to larger and taller wood structures.
Following is a selection of recent news related to the use of wood in tall buildings:
A New Way to Build Tall (Civil and Structural Engineer, April 2014) discusses SOM's Timber Tower Research Project, comparing a hypothetical concrete-jointed timber frame structural system to the traditional concrete frame of the 395-foot tall Dewitt-Chestnut Apartments built in Chicago in 1966. SOM claims that this system can compete technically and financially with conventional concrete frame structures while reducing a building's carbon footprint by 60 percent or more.
A Worthy Wager (structuremag.org, April 2013) provides a detailed account of the the use of innovative composite wood construction in the Federal Center South building, Seattle. The structure relied heavily on the use of reclaimed timbers from an existing 1940's warehouse located on the building site. The story of how composite wood-concrete structural techniques overcame unexpected shortcomings in achieving the proposed building system is a realistic portrayal of the kinds of problems that innovative designers must be prepared to solve.
LCT I (Wood Design & Building Magazine, Winter 2012-13, navigate to p. 25 in the custom reader app) presents the world's first 8-story glulam heavy timber-concrete hybrid building, completed in November 2012. Relying on prefabrication techniques, construction of the structural frame was able to proceed as rapidly as one story per day. The system is claimed to be capable of supporting up to 30 stories with reduction in carbon emissions of up to 90 percent.
Building Tall with Wood in the Future (The Construction Specifier, March 2014, navigate to p.22 in the custom reader app) discusses the various technical aspects of a proposed 40-story office tower relying on wood and concrete construction techniques. In comparison to conventional tall building systems, faster construction and lower environmental impacts are claimed.
Expanding Opportunities with LSL and PSL in Mid-Rise Construction (Wood Design & Building Magazine, Spring 2013, navigate to p. 37 in the custom reader app) discusses potential applications of laminated strand lumber (LSL) panels and parallel strand lumber (PSL) beams and columns in tall building framing systems. While LSL panels are not available in as broad a range of sizes as cross-laminated timber (CLT) panels, they can be produced with higher design strengths than CLTs making them well-suited for shear walls, roof decking, and composite floor systems.
Large Wood Structures (naturallywood.com) is a short video illustrating state of the art composite structural techniques combining large wood members, concrete, and steel, suitable for use in larger wood structures. An important concept discussed in this piece is the reliance on steel as the weakest link in the composite systems, thus taking advantage of the especially forgiving and predictable failure characteristics of that material.
April 18, 2014
Odds and Ends
Self-Repairing Concrete Could Be The Future Of Green Building (Forbes 1/6/14) reports on a number of interesting product concepts from the Cradle to Cradle Product Innovation Challenge including:
- Brick made with cement from bacterial byproducts
- Building insulation made from agricultural waste products that can be grown within a mold or the wall cavity
- Self-repairing concrete forumulated with calcuim carbonate producing bacteria
Scrap tires used to boost masonry blocks (Missouri Institute of Technology 2/6/24) describes the development of rubberized block, in which recycled rubber particles from used tires replace approximately 20 percent of the sand in a convention concrete masonry unit, resulting in a block that has a higher insulation value and potentially better performance under seismic loads.
TERMES & Collective Construction (Self-Organizing Systems Research Lab, Harvard University) discusses the modeling of collective termite behavior to produce automonous construction robots. Especially fun is this video:
C.F. Møller and DinnellJohansson’s Wooden Skyscraper Wins International Competition (ArchDaily 12/14/13) reports on this team's winning entry for the HSB Stockholm architectural competition, a 34-story structure consisting of a concrete core and wood structural frame.
For more info about tall wood buildings, see ArchDaily's The Timber Tower Research Product or Michael Green presents ‘The Case for Tall Wood Buildings’.
March 21, 2014
The Politics of Sustainability
Sustainability and green building are by their nature public policy concerns and, as such, cannot always escape the influence of political process. Environmental Policy Alliance,' PR Firm Front Group, Targets LEED, Green Groups And EPA (Huffington Post, 3/7/14) relates the D.C. public relations firm Berman & Company's targeting of green building standards along with other environmental groups and programs. According to the article, Berman & Co. and its front groups have a history of running campaigns on the behalf of large industry interests.
Berman's recently launched Environmental Policy Alliance is targeting, among other things, the U.S. Environmental Protection Agency and the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED) standards. The Alliance's home page states the organization's mission:
The Environmental Policy Alliance (EPA) is devoted to uncovering the funding and hidden agendas behind environmental activist groups and exploring the intersection between activists and government agencies.
and provides links to projects such as Big Green Radicals, LEEDExposed, and more.
Industry action against LEED and its environmental standards is not new--the lumber and plastics industries being two notable examples of groups with a history of working against environmental standards related to their interests.
And patricularly as green building standards have found their way into jurisdictional regulations, industry activism against such regulations has intensified (GSA gets greenwashed as Green Globes gets approved as building certification system equivalent to LEED, Florida Bill a ‘Backlash’ Against LEED Rules).
February 25, 2014
Portland-Limestone Cement and Environmental Impacts
Following European precedents, evolving changes in cement production standards are allowing increasing amounts of limestone to be blended into Portland cement. By reducing demand for Portland cement itself, Portland-limestone cements (PLCs) reduce the environmental impacts of concrete used in construction, without compromising the performance qualities of the finished product.
Cement production is an energy-intensive process, accounting for 80 percent or more of the total energy required to produce concrete. Cement production is also a major contributer to greenhouse gas emissions, accounting for roughly 5 percent of such emissions worldwide. In North America, traditional, ordinary Portland cement (OPC) is manufactured according to ASTM C150 and CSA 23.1 standards (in the United States and Canada, respectively).
In previous decades, North American standards have been modified to permit the addition of limestone to ordinary Portland cement in quantities not to exceed 5 percent by weight. In the last several years, standards have been further modified allowing concrete production using Portland-limestone cements with limestone content as high as 15 percent. By increasing the proportion of limestone in the cement, the quanity of Portland cement is reduced, as are the various enviromental impacts of Portland cement production.
A recent technical report (An Environmental Life Cycle Assessment of Portland-Limestone and Ordinary Portland Cements in Concrete) by the Athena Institute quantifies the environmental benefits of Portland-limestone cement in concrete production.
The report documents a cradle-to-gate life-cycle analysis comparing concrete produced with both ordinary Portland cement and Portland-limestone cement. The analysis predicts reductions of between 9 and 12 percent for all of the following environmental impacts:
- Global warming
- Energy consumption
- Respiratory effects
- Ozone depletion
February 11, 2014
High-Performance Homes Tested by Cold Winter Temperatures
Cold Snap Tests High-Performance Homes (Journal of Light Construction, 1/27/14) relates the experiences of 3 owners of high-performance homes during the recent North American record-breaking cold waves. Results were promising.
Owners of a Ripton, Vermont Passive House report requiring nothing more than slightly extending the duration of their twice-daily wood stove fires. On nights reaching 20 degrees F below zero (-30 deg C), the house maintained temperatures in the low 60s throughout the night and early monrning, even after the evening fire had burned out.
In Belfast, Maine, homeowners lost power for 5 days and were without any source of home heating. Despite temperatures as low as -15 degrees F (-25 deg C), temperatures in the home remained in the mid- to high-fifties (12-15 deg C).
In Brooklyn, New York, a passive house heat pump came on only once during the week, for about one hour, while home temperatures remained consistantly in the high sixties to low seventies (around 20 deg C).
February 11, 2014 in 07 Interior Finishes for Wood Light Frame Construction | Permalink | Comments (0)
January 28, 2014
Tall Building Trends in 2013
Tall building design and construction is alive and well. 2013 had the second-highest ever rate of completion of buildings 200 m (650 ft) or taller. Since the year 2000, the number of completed 200-m-plus buildings has increased from 261 to 830.
Trends in tall building design over the last several decades are also interesting. Considering the worlds 100 tallest buildings in 1990:
- 80 percent were located in North America.
- Almost 90 percent were exclusively office use.
- More than half were constructed of steel.
In 2013, for the world's 100 tallest buildings:
- The largest share (43 percent) are now in Asia. (Only one new 200-m-plus building was built in North America in 2013, compared to 54 in Asia.)
- Less than 50 percent are exclusively office use. Almost a quarter are mixed-use and 14 percent are residential.
- Almost half were constructed of reinforced concrete and only 14 percent of steel. (The remainder are composite or mixed structural materials.)
Change in regional distribution of tall buildings is a direct reflection of changing world economies. Change in structural materials is a reflection of regional availability of different materials. For example, concrete is the predominate structural material in China, where many of the world's new tall buildings are being constructed. Change in material also relates to change in building use, with residential and hotel buildings favoring the thinner floor plates and lesser floor-to-floor heights possible with concrete in comparison to steel.
November 29, 2013
Highly-Insulated Residential Wall Systems
In Achieving highly insulated buildings, National Research Council Canada reports on its collaboration with industry partners and government agencies to better understand the performance of highly-insulated wall assemblies and to develop effective strategies for achieving improved energy performance in residential buildings.
The article also discusses innovative applications of vacuum insulation panels (VIPs) in foam insulation sandwiches (left), to achieve overall wall insulation values of roughly RSI 12 (R-68).
November 29, 2013 in 07 Interior Finishes for Wood Light Frame Construction | Permalink | Comments (0)
November 15, 2013
State of the art tall building facade treatments
Nearing completion in Sydney is One Central Park, a mixed-use development with two residential towers. A design collaboration by architect Jean Nouvel and botanist Patrick Blanc, the 380-foot tall towers will be support the world's tallest living (green) facades. 190 native Australian and 160 exotic plant species will cover roughly half of the total tower facade area.
A cantilevered heliostat containing motorized mirrors will ensure sunlight also reaches the development's (horizontal) gardens year-round.
South Korea Will Soon Be Home To An Invisible Skyscraper (Forbes, 9/13/13) discusses the Tower Infinity, recently permitted for construction outside of Seoul, Korea. Designed by GDS Architects, the 450-meter tall tower will be equipped with LED recording and projection technology that captures images of the surrounding environs and re-projects these images onto the building facades, providing the capability to make the building appear transparent.
November 01, 2013
Creative Shipping Container Architecture
Outside the box: Celebrating the shipping container in architecture (Gizmag.com, 9/5/13) showcases 10 innovative shipping container structures for single- and multifamily housing, portable hotels, temporary theater, orphanage, Antarctic research station, and drive through coffe shop.
October 18, 2013
Innovative GFRC Skin Clads The BROAD Museum
The Broad contemporary art museum, designed by Diller Scofidio + Renfro and currently under construction in Los Angeles, is being enclosed with an innovative glass fiber reinforced concrete (GFRC) panel skin. 2500 panels, in more than 400 trapezoidal variations, are supported by a network of structural steel framing. This so-called veil is supported at only 3 points, one of which consists of a 32-ton, 57-foot-long beam pivoted to allow for movements during a seismic event. More info:
October 04, 2013
State-of-the-Art Glass Technologies Taking Hold in Building Systems
6 emerging energy-management glazing technologies (www.bdcnetwork.com, 9/19/13) discusses new technologies impacting the use of glass in building systems, such as:
- High-performance insulating units using aerogel or vacuum fills in lieu of heavy gasses such as argon or krypton
- Electrochromic glass with transmittance characteristics adjustable via applied electrical current
- Thin-film building integrated photovoltaics used to generate electrical power directly from sunlight
- Aluminosilicate glass (such as used to protect personal electronic device screens) with very high impact resitsance
- Ethylene tetrafluoroethylene (ETFE) plastic glazing units with very low weight and high thermal resistance properties
A few more interesting glass technologies are described in 14 'extreme' glass systems (http://www.bdcnetwork.com, 10/7/12). These include PVB interlayers for laminated glass that passively lighten and darken with changes in ambient temperature and sunlight and bird-safe etched glass designed to reduce bird collisions without reducing visible light transmittance.
September 20, 2013
Japan Proposes Soil Freezing to Control Water Flows from Fukushima Power Plant
Japan To Fund Ice Wall to Contain Fukushima Reactor Leaks (ENR.com, 9/03/2013) and Fukushima leaks: Japan pledges $470m for 'ice wall' (BBC News, 9/3/2013) discuss that country's plan to apply soil freezing techniques to controlling water flows from the damaged Fukushima nuclear reactor plant.
Unlike the temporary soil freezing applications sometimes used to protect building site excavations, the proposed Fukushima ice walls may need to last 40 years until plant decommissioning is complete. The 1.4 km of walls will extend as much as 30 meters into the ground.
September 06, 2013
Glueless Cross-Laminated Timber
Five story all-wood house built with zero chemicals (Treehugger, 8/21/13) describes the use of adhesive-free CLT panels for construction of a five-story Hamburg apartment building. The lumber pieces from which the CLTs are manufactured are held together with wood dowels. The central lamination of the panels is also made from pressed wood with a higher R-value, allowing the panels to be used without insulation added to one side of the panels or the other.
A similar technology, interlocking cross-laminated timber, is described in a 21 page research report by Ryan E. Smith, University of Utah, Integrated Technology in Architecture Center (ITAC): INTERLOCKING CROSS - LAMINATED TIMBER:
alternative use of waste wood in design and construction.