GUND HALL TEST (April 2006) – The GSD is experimenting with soils and sedum plants on the roof of Gund Hall, to test the feasibility of retrofitting Harvard's gravel roofs with green roofs. The system is 3,000 square feet (20% of roof area) and could potentially absorb 500,000 gallons of water per year. The cost was only $1 per sq. ft., and it will double the roof life span. The project is being led by GSD Professor Katrin Scholz-Barth, an expert in green roof technology. More information can be found in Harvard Gazette article, "Gund Hall Sports a Thick Head of...Sedum."

 

CGIS (2005) – This roof, at ground level and above underground space, is 15,000 square feet. It features grass and maple trees. The soil depth is 2 to 3.5 feet deep. The roof consists of a multi-layered waterproofing membrane integrated with a soil support system. It is irrigated daily in the summer and some fertilizers are used.

 

29 GARDEN STREET (2003) – This extensive 10,000 square foot green roof cost approximately $50/square foot. It covers the previously asphalted roof of a parking garage. The system uses a MM6125-EV waterproofing membrane, and was installed by American Hydrotech who provided a 2 year warranty for plants, 20 years for the roof membrane, and a 2 year maintenance contract. The primary impetus for the roof was to improve residents' views of the roof.

 

The system American Hydrotech provided at 29 Garden St. consists of the following:

· Monolithic Membrane 6125 EV (Environmental Grade) FR (Fabric Reinforced) 215 mils
· Hydroflex BR (Root Barrier) 160 mils
· Hydrodrain 300 drainage course 3/8”
· Floradrain 40 Water Retention/Drainage/Aeration layer 11/2”
· System Filter fabric
· Hydrotech Lite Top growing Medium 4” in the field, 12” in shallow planters, 36” in deeper planters
· Hydrotech concrete pavers and precast curbs & walls

 

60 OXFORD STREET (2004) – Installed by Valley Crest, this roof garden is approximately 900 square feet (stone, sand and gravel: 70%; plants 30%), and constitutes 16% of the total roof area. It consists of soils, crushed granite, pygmy bamboos, and amur maples surrounded by birch mulch, which protects the plant roots from cold and prevents moisture from evaporating. “The roof is actually a combination of intensive and extensive roofing. There is a ‘bathtub’ at the center of the roof that is deep enough to allow for the tree planting(…) an intensive roof. The perimeter of the roof is an extensive roof with a shallow (6”) soil profile” (Jones, R. 2006).

According to Joe Jones, the soil goes down 6 inches around the perimeter and then drops down 4 feet. There are 2 drains: primary and back-up. The remaining water is filtered through the gravel. The entire roof garden consists of the same plant species. The trees are Redbuds, and each volcano is covered with ivy. The 4-foot growing mix added significant weight to the loads and required “special structural solutions to support the weight of the soils and plantings”(Jones, R. 2006).

Maintenance (by FMO) is minimal, and limited to pruning. No irrigation, deweeding or fertilizing is required, and the drainage system is checked regularly.

 

A green roof, also called an "eco roof" or "living roof" is an extension of the existing roof, covered with vegetation. It can be located below, at, or above-grade, but in all cases the plants are never planted directly in the ground. No green roof systems are identical but they all include a synthetic, high quality waterproof membrane, a drainage layer, a soil layer and lightweight to medium plants. Green roofs provide several economic, environmental and social benefits. Reduced rainfall and storm water volume, insulation, reduction of the heat island effect, air purification, increased lifespan of the roof (30 years), are among a few.

There are two main green roofs at Harvard are located at 60 Oxford Street and 29 Garden Street. Their managers are aware of the singularity of their roofs and appreciate their environmental and social benefits. In these two cases, environmental goals pushed the design and creation of the green roofs, which are the only green roofs located above-grade. In other cases, the implementation of the green roofs was driven by either economics or aesthetics, and their managers refer to the roof as “the patio” or “courtyard." Harvard's Graduate School of Design tested a green roof retrofit on Gund Hall.

 

EXTENSIVE: minimal or no-required maintenance with a restricted variety of plants; resistant to frost, wind and drought; sedum, herbs and grasses; located on almost any flat or low slope roof deck that maximizes water retention.

INTENSIVE: regular maintenance required (irrigation, fertilizing, pruning, mowing); greater variety of plants (sod grass lawns, perennial, annual flowers, shrubs, small trees); deeper, heavier and richer soil.

The Advanced Buildings Energy Benchmark, Section 6.3, describes optimal performance criteria for Cool Roofs and Eco Roofs.

 

ECONOMIC CONSIDERATIONS

In Europe, where the green roof market is established and thriving, prices range from $4 to $13 per square foot.  In the U.S., prices are much higher, ranging from $10 to $25 per square foot. Initial costs sometimes discourage consideration of green roofs.  Of course, the total cost varies depending on the type of the roof, its depth and size, types of plants, and maintenance.

In spite of higher initial costs, life cycle costing analysis reveals that green roofs provide a payback over the lifetime of a building through:

• longer material lifespan (the green roof can be expected to last two to three times as long as conventional roofs), which leads to reduced maintenance and replacement costs
• savings on heating and cooling, due to reduced peak energy demand
• potential reduction in stormwater/wastewater charges from the municipality
• potential grants
• potential greenhouse gas emissions trading credits, stemming from energy savings

 

ENVIRONMENTAL BENEFITS

Air

• Carbon Dioxide/Oxygen Exchange: (1.5 m2 (16.15 ft2 ) of uncut grass, produces enough oxygen per year to supply 1 human with their yearly oxygen intake requirement)
• Cleaner air (1 m2 (10.76 ft2) of grass roof can remove between 0.2 kg of airbourne particulates from the air every year)
• Reduction of the ambient air temperature (prevention of the heat-island effect as green roofs do not absorb as much heat as conventional roofs)
  

 

Water

• Cleaner storm-water (removal of approximately 95% of the cadmium, copper and lead)
• Storm water management: reduction of the storm water volume and a slower water flow (runoffs from impervious surfaces can cause overflow in sewage systems) “green roofs absorb between 50-95% of the rainfall on the site”
• Water-proofing capacity (green roofs act as sponges)
• Soil erosion reduction (through mitigation of storm-water volume)

Resource Conservation

• Replacement of an impervious roof surface with a living, breathing and permeable green space
• Reduction of the building’s footprint
• Increased life-span of a roof (2-3 times)
• More habitat for wildlife
• Improved views for neighboring building occupants, as they look at a greenscape instead of asphalt or mechanical equipment

 

Ideally, green roofs include low maintenance and native, hardy plants that require no irrigation, fertilizers or pesticides. The choice of plants depends on geographic and climatic conditions (rainfall, temperature, wind, sun and wind exposure) and on the green roof type (extensive versus intensive). Hardy plants are the best bet as they can survive in atypical conditions. Sedum is the most popular choice. There are approximately 1000 varieties to choose from, and many are hardy and drought-resistant.

A number of planting methods can be used ranging from vegetated mats (which provide drainage and moisture retention), sowing seeds to using containerized plants.

 

Irrigation systems are optional. However, green roofs need additional water during the first few seasons. Sprinklers are the most popular irrigation method but more ecological options are available, such as passive irrigation (a membrane located underneath that stores rainwater) or cisterns used for rainwater catchment.  

 

One Western Ave attempted to count the green vegetated roof of the underground parking garage towards this LEED point. Since this "roof" was actually the ground, the USGBC determined it is not applicable to this credit, though it is applicable to SSc7.1.  One Western Ave still achieved this point because over 75% of the building's roof is covered with highly reflective and emissive surface.

 

- Berlin: Half of the city's new government buildings have green roofs.

- Tokyo: All new construction uses green roofs, and existing buildings must convert 20% of their rooftops.

- Chicago: The city introduced its green roof program in 2001 and now has more than 200 green roofs in some stage of development.

- Portland: In 1994, it became the first American city to pass legislation promoting the use of green roofs.

- Seattle: The city hall and its justice center have rooftop gardens.

- Des Moines: The green roof on the city's newly opened $32 million downtown library can retain as much as 187,500 gallons of rainwater.

 

www.greenroofs.com

www.greenroofs.net

www.cityofchicago.org (search for green roofs)

Green Roofs, by Leslie Hoffman (Foreword), William McDonough (Foreword), Earth Pledge Foundation

Cool Roof Rating Council

Planting Green Roofs and Living Walls, Nigel Dunnett, Noel Kingsbury

Roof Gardens, by Theodore H. Osmundson

Sustainable Landscape Construction, by J. William Thompson, et al.

 

FIVE COWPERTHWAITE AND TEN AKRON STREET, HRES (2007) - Harvard worked with Fibertite to develop a "Cambridge Green" color. This Cambridge green is less reflective than the white roof, but qualifies as a cool roof. The roofs of these buildings will be visible from residents of nearby highrises. The roof was installed by Oak Roofing. The materials of Fibertite are seamed together with hot air, avoiding the need for caulking or adhesives. Life Cycle Costing Analysis was used to determine savings. Both buildings are using the 45 mil product.

MANUFACTURER	ACTUAL EMISSIVITY	SOLAR REFLECTANCE	MIN. SOLAR REFLECTANCE	SIZE	WARRANTY
Fibertite SM Membrane	0.95	0.65	low slope initial: > 0.65 after 3 years: > 0.50	5,594 sq. ft (5 Cowp.)	10 year

 

 

BLACKSTONE (2006) is using an EnergyStar, high albedoVersico Versiweld Reinforced TPO Membrane on a concrete and wooden deck with 4” and 6” continuous insulation above deck (Emissivity 0.0624 allowed by ASHRAE 90.1).

MANUFACTURER	ACTUAL EMISSIVITY	SOLAR REFLECTANCE	MIN. SOLAR REFLECTANCE	SIZE, % of ROOF AREA	WARRANTY
Versico Versiweld Reinforced TPO Membrane	Emittance .92, U values: building 10B: 1.022, building 10B: 0.030, building 7: 0.035 (0.0624 allowed by ASHRAE 90.1)6” = R394” = R26, required = R19	0.65	low slope initial: > 0.65 after 3 years: > 0.50	10, 689 sq. ft., 88.11%	5, 10 and 15-year

 

 

90 MOUNT AUBURN STREET (2006) uses a Siplast, Inc.PC-227 Elastomeric Roof Coating.

MANUFACTURER	ACTUAL EMISSIVITY	SOLAR REFLECTANCE	MIN. SOLAR REFLECTANCE	SIZE, % of ROOF AREA	WARRANTY
Siplast, Inc.PC-227 Elastomeric Roof Coating	0.94	initial: 0.75 after 3 years: 0.65	low slope initial: > 0.65 after 3 years: > 0.50	3900 sq. ft., 100%	5, 10 years

 

 

ZERO ARROW STREET (2006)

MANUFACTURER	ACTUAL EMISSIVITY	SOLAR REFLECTANCE	MIN. SOLAR REFLECTANCE	SIZE, % of ROOF AREA	WARRANTY
Firestone Ultraply TPO	0.90	initial: 0.793 after 3 years: 0.715	low slope initial: > 0.65 after 3 years: > 0.50	7816 sq. ft., 79.37%	20 year

 

 

ONE WESTERN AVENUE (2003)

MANUFACTURER	ACTUAL EMISSIVITY	SOLAR REFLECTANCE	MIN. SOLAR REFLECTANCE	SIZE, % of ROOF AREA	WARRANTY
Sarnafil G410 Roof Membrane, 48 mil	0.92	initial: 0.83, after 3 years: 0 .5-.83	low slope initial: > 0.65, after 3 years: > 0.50	10,689 sq. ft., 88%	Will provide via Authorized Applicator for 5-20 years

 

 

60 OXFORD STREET (2004) has a high albedo white roof covering 78.5% of the roof area. A roof garden covers the remainder.

MANUFACTURER	ACTUAL EMISSIVITY	SOLAR REFLECTANCE	MIN. SOLAR REFLECTANCE	SIZE, % of ROOF AREA	WARRANTY
Sarnafil G410 Roof Membrane, 60 mil	0.92	SRI >104	low slope initial: > 0.65 after 3 years: > 0.50	78.5%	Will provide via Authorized Applicator for 5-20 years

 

 

Exceed ASHRAE 90.1-2004 Building Envelope Requirements for Climate Zone 5 requirements.

The Advanced Buildings Energy Benchmark, Section 6.3, describes optimal performance criteria for Cool Roofs and Ecoroofs. Energy Star Cool Roof Criteria:

1. Low-slope roofs must have an initial solar reflectance of >0.65. After 3 years, the solar reflectance must be >0.50.

2. Steep-slope roofs must have an initial solar reflectance of >0.25. After 3 years, the solar reflectance must be >0.15.

 

See the EPA EnergyStar list of roof products for their solar reflectance. The Cool Roof Rating Council (CRRC) also lists roof products and their emissivity. *NOTE: CRRC uses an emissivity test that does NOT qualify for this LEED point. Their list could be helpful to find a product, but you must find another verification of the emissivity using the ASTM E408 test. Such a test may be supplied by the manufacturer, as it is by Sarnafil.

 

Cool Roof SOLAR REFLECTANCE RECOMMENDATIONS:
Department of Energy (DOE) Federal Energy Management Program (FEMP)

Roof Slope	Recommended Solar Reflectance		Best Available Solar Reflectance
	Initial	3 years after installation	Initial	3 years after installation
Low-Slope(<2:12)	65% or greater	50% or greater	87%	85%
High-Slope(³2:12)	25% or greater	15% or greater	77%	60%
* Recommended emittance levels are 90% or higher

 

The color and material of the roof are the prime determinants of the roof’s reflectance and emittance. To help determine the reflectance and emittance of your roof, the Lawrence Berkeley National Laboratory (LBNL) at the University of California, Berkeley has provided a database listing the reflectance, emittance and solar reflectance index (SRI).

 

SOLAR REFLECTANCE OF DIFFERENT ROOFING MATERIALS (LBNL)

	Material	Total Solar Reflectance	Emittance
Reflective Coatings	Elastomeric coating over asphalt shingle	0.71	0.91
	Aged Elastomeric on plywood	0.73	0.86
	Aluminum pigmented roof coating	0.30 – 0.55	0.42-0.67
	Lo-mit on asphalt shingle	0.54	0.42
White Metal Roofing	Siliconized white	0.59	0.85
Single-Ply Roof Membrane	Black EPDM	0.06	0.86
	Grey EPDM	0.23	0.87
	White EPDM	0.69	0.87
	White T-EPDM	0.81	0.92
	Aluminum Paint	0.80	0.40
Asphalt Shingles	Black	0.03-0.05	0.91
	Dark Brown	0.08-0.10	0.91
	Medium Brown	0.12	0.91
	Light Brown	0.19-.020	0.91
	Green	0.16-0.19	0.91
	Grey	0.08-0.12	0.91
	Light Grey	0.18-0.22	0.91
	White	0.21-0.31	0.91

 

Typical roof surfaces absorb 70% or more of the solar energy striking them, resulting in roof temperatures reaching as high as 160-190°F at midday.  By contrast, cool roofs surfaces absorb less than 35% of the solar energy striking them, resulting in roof temperatures between 100-120°F at midday.  These lower surface temperatures have been proven to reduce building cooling costs 20-70%. While high solar reflectance and emissivity levels are beneficial during the summer, they may increase heating costs in the winter.  However, the energy savings of high summer reflectance outweigh heating energy losses in the winter. Cool roofs are typically white or off-white.

 

Cool roofs lower roof surface temperatures by enhancing two main properties in their materials:

• High Reflectivity is the property of reflecting away the sun’s energy instead of absorbing it. High reflectivity generally corresponds to the color of the roof surface; the lighter the color, the more heat the roof surface will reflect.

• High Emissivity is a property that reduces a roof surface’s ability to absorb heat that has not been reflected away. Most roofing materials have emissivity ratings of 90% or higher. The major exceptions are metal and metallic roof coatings that have emissivity ratings as low as 20-60%. These roof coatings, even with a high solar reflectance, can still heat to temperatures of 140-170°F at midday in the summer.

 

Solar Reflectance Index: The Solar Reflectance Index (SRI) is a measure of a material’s ability to reject heat, and incorporates both reflectivity and emissivity. Materials with the highest SRI values are the coolest choices for roofing. Because of the way SRI is defined, particularly hot materials can take slightly negative values, and particularly cool materials can exceed an SRI of 100.

• Environmental considerations beyond reflectance and emissivity that should be taken into account when choosing a roofing product include:
  • pollutants released during installation
  • toxicity of materials used in manufacturing
  • life-span of the material
  • recyclability of material at the end of its life

There are four basic types of cool roofing materials:

• Single-Ply Roofing for Low-Slope Roofs: Cool single-ply roofing is a catch-all term for any cool roofing product that comes in a single prefabricated sheet and is applied in a single layer. Single-plys come in a variety of materials. (Some single-ply roofing materials may be installed on high-sloped roofs.)

• Liquid-Applied Roof Coatings for Low-Slope Roofs: Liquid-applied cool roof coatings are surface treatments best applied to roofs in good condition. They have the consistency of thick paint, although they have additives to improve their adhesion, durability and resistance to dirt, algae & fungus. "Cementitious" coatings have cement particles, while "elastomeric" coatings contain polymers to improve adhesion and reduce brittleness. Both range in cost from $0.75 to $1.50 per square foot depending on the job and the contractor. Liquid-applied cool roof coatings should be carefully selected so that they are compatible with the underlying substrate. (Some liquid-applied roofing materials may be installed on high-sloped roofs.)

• Cool Roofing Tiles for High-Sloped Roof: Cool roofing tiles are usually made of clay or concrete, and come in a range of colors. 

• Asphalt Shingles for High-Sloped Roof: Asphalt shingles are a common roofing choice for high-sloped houses. Asphalt shingles generally have a low reflectance of about 30%, although some asphalt shingles are available with reflectance up to 77%.  

 

Any roofing material used for a cool roof project should be certified by The Environmental Protection Agency’s (EPA) Energy Star Cool Roof Certification and/or the Cool Roof Rating Council (CCRC). Energy Star and the CCRC both specify minimum solar reflectance requirements. However, while the CCRC specifies emittance levels, the Energy Star program does not list emittance as a certification requirement. Therefore, be sure to specify an emittance rating of at least 90% when choosing an Energy Star Certified roofing material.

Note: Many older buildings at Harvard University have special roofing materials (such as slate) that cannot be retrofitted due to historic preservation requirements. Be sure that roof materials are permitted before proceeding with a cool roofing project.

 

Estimating the cost savings that would result from installing a cool roof requires calculating the properties of the building details, baseline and design roof, heating and cooling systems, and energy costs. To assist in these complex calculations, the Department of Energy has provided an online cool roof calculator: 

• DOE Cool Roof Calculator

The calculator asks for basic information about the building, and provides a basic estimate of energy savings that would result from a roof upgrade. Energy Star has identified and made available a list of vendors that supply cool roofing materials and installation services. 

LEED v2.1 specifically requires that roofing emissivity be tested in accordance to ASTM 408. Both One Western Ave and 60 Oxford St were asked for additional documentation to show that this test was followed, even though they were using a roofing product that had been used to achieve this LEED point for other projects. In future submittals, a product data sheet should be included that shows the emissivity and the test used.

In the past, Harvard LEED projects have referred to the Cool Roof Rating Council's (CRRC) list of certified products. However, CRRC currently uses the ASTM C1371 test to determine emissivity. This test is not accepted by the USGBC (see CIR dated 3/23/2004).

 

Lawrence Berkeley National  Laboratory (LBNL) Heat Island Project: The LBNL Heat Island Research Project analyzes, and implements solutions to the summer warming trends occurring in urban areas, e.g., the "heat island" effect. The project currently concentrates on the study and development of more reflective surfaces for roadways and buildings.

Cool Roof Rating Council: The Cool Roof Rating Council (CRRC) is an independent and non-biased organization that has established a system for providing Building Code Bodies, Energy Service Providers, Architects & Specifiers, Property Owners and Community Planners with accurate radiative property data on roof surfaces that may improve the energy efficiency of buildings while positively impacting our environment.

Florida Solar Energy Research Center: The Florida Solar Energy Center (FSEC) is the largest and most active state-supported renewable energy and energy efficiency research, training, testing and certification institute in the United States. FSEC provides technical publications of the performance of cool roofs. 

 

According to Fibertite, 99% of their roofs installed since their invention in 1979 are still functioning, and their roofs have the lowest warranty claims in the industry. Fibertite's 36 mil products have 10 or 15 year warranties, while the 45 mil products have a 20 year warranty. They are EnergyStar approved, with an 0.83 initial reflectivity, and 0.60 - 0.70 reflectivity after 3 years. They meet LEED criteria for emissivity. Cool roof options include beige (standard), polar white, or Cambridge Green. Fibertite is generally 5%-7% more expensive to install, but is stronger than EPDM and is guaranteed to withstand up to 74 mph winds. They can be installed on flat roofs because the seams can withstand ponding of water.

After 20 years, Fibertite will test a piece of the roof to produce a life expectancy report. They can then clean, coat the roof, and extend the warranty. Fibertite will recycle their roofs at the end of their useful life.

The Fibertite representative noted that the 10 Akron and BCG projects went smoothly because he was involved in the beginning planning stages. As of September 2006, the beige, 45 mil roof is about 67 cents per square foot for contractors. There is about a 3-5 cent premium for other colors. Fibertite will provide life cycle cost analysis for the project's roof. According to the DOE Energy Saving Model, energy cost savings of about 9 cents per square foot in energy savings can be expected in the Boston area.

 

LAW SCHOOL NORTHWEST CORNER (2007) – Under Design: The NW Corner is using double glazed Viracon VE 1-2M argon filled glazing.

BLACKSTONE (2006) – Viracon VE1-2M is an exterior glazing with lower shading coefficient used at Blackstone and One Western Avenue. Life cycle cost analysis demonstrated energy savings at small capital premium, and a payback period of 13 years.  This glazing was specified at all clear glass locations: exterior, double pane, argon-filled low-e glass; skylights and lightslot - translucent 2-3/4” pre-insulated panels; skylight – 2-3/4” sandwich panel with R20 insulation between 2 layers of polycarbonate.

	MANUFACTURER	ACTUAL U FACTOR	ASHRAE U VALUE REQUREMENT	ACTUAL SOLAR HEAT GAIN COEFF.	ASHRAE SOLAR HEAT GAIN COEFF. REQUIRE.
Windows	Viracon VE1-2M	0.25	0.57 fixed   0.67 operable	0.37	0.39 all,    0.49 north
Skylight	Solarban 60	0.05	0.8	0.09	0.77

 

90 MOUNT AUBURN (2006) selected a solar-control, low-e insulating and laminated glass, which was identified in the project’s specifications. Windows – double pane, solar-control, low-e insulated, laminated; Skylight – double pane, solar-control, low-e insulated.

	MANUFACTURER	ACTUAL U FACTOR	ASHRAE U VALUE REQUREMENT	ACTUAL SOLAR HEAT GAIN COEFF.	ASHRAE SOLAR HEAT GAIN COEFF. REQUIRE.
Windows		0.22	0.22	0.38	0.4
Skylights		0.22	0.22	0.29	0.29

 

HAMILTON HALL (2006)

MANUFACTURER	ACTUAL U FACTOR	ASHRAE U VALUE REQUREMENT	ACTUAL SOLAR HEAT GAIN COEFF.	ASHRAE SOLAR HEAT GAIN COEFF. REQUIRE.
Viracon	0.30	0.48

 

ONE WESTERN AVENUE (2003) Viracon VE1-2M is an exterior glazing with lower shading coefficient used at Blackstone and One Western Avenue. Life cycle cost analysis demonstrated energy savings at small capital premium, and a payback period of 13 years.  This glazing was specified at all clear glass locations. 

MANUFACTURER	ACTUAL U FACTOR	ASHRAE U VALUE REQUREMENT	ACTUAL SOLAR HEAT GAIN COEFF.	ASHRAE SOLAR HEAT GAIN COEFF. REQUIRE.
Viracon VE1-2M	0.28	0.67	0.37 all	0.39

 

60 OXFORD (2004)

ACTUAL U FACTOR	ASHRAE U VALUE REQUREMENT	ACTUAL SOLAR HEAT GAIN COEFF.	ASHRAE SOLAR HEAT GAIN COEFF. REQUIRE.
0.29 all	for 0-40% of wall: 0.57	0.43	for 0-40% of wall: 0.41
			for 0-40% of wall, N: 0.55
			for 45%-50% of wall: 0.28
	for 45%-50% of wall: 0.46		for 45%-50% of wall, N: 0.4

 

Exceed ASHRAE 90.1-2004 Building Envelope Requirements for Climate Zone 5 requirements.

ASHRAE 90.1-2004 Table A8.2 (page 105) Assembly U-Factors, Assembly Solar Heat Gain Coefficients (SHGC), and Visitble Light Transmittances

 

		Unlabeled Vertical Fenestration
		Clear Glass			Tinted Glass
Frame Type	Glazing Type	U-Factor	SHGC	VLT	U-Factor	SHGC	VLT
All Frame Types	Single Glazing	1.25	0.82	0.76	1.25	0.70	0.58
	Glass Block	0.60	0.56	0.56	N/A	N/A	N/A
Wood, Vinyl, or Fiberglass Frame	Double Glazing	0.60	0.59	0.64	0.60	0.42	0.39
	Triple Glazing	0.45	0.52	0.57	0.45	0.34	0.21
Metal and other Frame Types	Double Glazing	0.90	0.68	0.66	0.90	0.50	0.40
	Triple Glazing	0.70	0.60	0.59	0.70	0.42	0.22

Glazing should be carefully considered in conjunction with other aspects of the building envelope. The U value measures the glazing's ability to conduct heat. A lower U value is more insulated, while a higher U value will conduct heat. The Solar Heat Gain Coefficient, which is a function of solar radiation through a window, measures glazing's ability to absorb or reflect solar heat. The SHGC is a number between 0 and 1. A low SHGC will block heat, while a higher SHGC will absorb heat. Thus, windows on the south side will not necessarily require the same SHGC as windows on the north side. Consider each elevation. The Advanced Buildings Energy Benchmark, Section 6.2, describes optimal performance criteria for Fenestration Performance. They state that U-factors should be in accordance with NFRC 100-2001 (National Fenestration Rating Council). The Advanced Buildings Energy Benchmark, Section 4.1 Controls for Daylighting, outlines optimal performance criteria for Whole Building Energy Simulation.  

 

ASHRAE Handbook of Fundamentals

 

LAW SCHOOL NORTHWEST CORNER (2007) – Under Design -The NW Corner is using 2" polyiso spray in lieu of 2" rigid insulation, which improves the R value from R12 to R18.

 

BLACKSTONE (2006) – Blackstone was able to reduce the size of its mechanical system by optimizing the insulation. Walls are Icynene Foam insulation – external brick with 2-1/2” continuous foam insulation, metal stud with insulation between studs. Blackstone installed a board-type insulation at foundations, a spray-applied foam insulation (both vapor barrier and vapor permeable) and sprayed-in-place insulation at exterior door frames. The additional cost of the insulation was offset by the reduced operating cost and smaller mechanical equipment required.

AREA	MANUFACTURER	ACTUAL R VALUE	ASHRAE R VALUE REQUIREMENT	ACTUAL U VALUE	MAX U VALUE PER ASHRAE
Walls	Icynene	R12 continuous insulation	R7 continuous insulation	0.063	0.123
Roof, Building 10A		R39, 6” solid insulation above wood deck	R19 continuous insulation above deck	0.022	0.063
Roof, Buildings 7, 10B		R26, 4” solid insulation above wood deck	R19 continuous insulation above deck	0.030	0.063

 

90 MOUNT AUBURN (2006) used a slag-wool/ rock-wool fiber insulation.

AREA	ACTUAL U VALUE	MAX U VALUE PER ASHRAE
Walls	0.08 block walls	0.08 block walls
Roof	0.05 concrete with rigid insulation	0.05 concrete with rigid insulation

 

FOUR-SIX GRANT STREET used building felt rather than Tyvek for the moisture barrier because of its smaller ecological footprint. Building felt breathes better and allows water to escape rather than being trapped on the inside of a plastic membrane. The air filtration that the building felt allows contributes very little to the building’s overall air change rate. Without this slow filtration, buildings can lack sufficient fresh air.

 

Exceed ASHRAE 90.1-2004 Building Envelope Requirements for Climate Zone 5 requirements.

See the Advanced Buildings Benchmark for Minimum Insulation Requirements R-Values, and Maximum Insulation U-factors, C-factors, and F-factors. (pages 55-56 (61-62 of the pdf)).

Like glazing, insulation -as well as the mechanical systems- should be considered in coordination with the rest of the building envelope. The R value of insulation measures the resistance of the insulation to the flow of heat. A higher R value is more effective in reducing heat transfer. The U value measures the insulation's ability to conduct heat. A lower U value is more insulated, while a higher U value will conduct more heat.

[Blackstone perm-a-barrier, courtesy Bruner Cott]

View a larger version of the diagram.