Green Roof - "The Devil is in the Details"

“The Devil is in the Detail” best describes the lessons learned regarding the design, construction and maintenance of the Green Roof for this project.

The intent of including the green roof in our project was to experience first hand the benefits and challenges of this roofing system. The proclaimed benefits of a green roof as follows:

• They return the biomass that was lost during the development of the project
• They moderate the surrounding and internal temperatures of the building
• They provide a place in urban areas that allow for growing of crops & visual appeal
• They help to manage the required on-site storm water retention regulations
• They have a high degree of aesthetic appeal
  
  During the process of including a green roof in the design I discovered the following challenges:
  
• The soil science of growing plants on a roof is extremely complicated and needs to be simplified to help owners make informed decisions.
• Green Roofs have only recently been third party tested to verify that they indeed manage on-site storm water retention. EB News (Environmental Building News) Volume 17 Number 10, shared the results of the recent findings on this subject.
• They found that while all the tested roofs in the study were capable of significant thermal moderations, some held water well while others were barely better than conventional roofs at preventing or slowing runoff. When the roof was designed to include larger planting-medium retention cups, low drainage-hole area in the drainage layer, and a high proportion of perlite or soil absorption material in the planting mix it correlated with high water retention.
• This same article verify that indeed the green roofs do a good job of reducing the roof temperature of the building in lieu of a black or even white roof. This can greatly affect the possible benefits of large commercial buildings that are attempting to cool their buildings or reduce urban heat island effects.
• The embodied energy of Hydrotech’s Green Roof growing medium needs to be improved. The production of intensive energy using material included in their soil media seems to be counter productive to the sustainable doctrine.
• The recommended hot applied water proof membrane system for the Green Roof is not that much different than a high quality hot applied built-up roof system normally specified for commercial buildings. The main difference I found was that the recovery board that goes over the hot applied water proofing has a root inhibitor included in it. Two types of hot applied systems seem to be the main ones on the market, one has more recycled material included and the other has less but is more cost competitive. The less costly one also has fewer features that make the quality control of the application of the product more reliable.
  
  We had a bit of trouble on our project, the contractors selected for the project seemed to have had a communication breakdown and the product installed was not the Hydrotech 6125, Hydroflex RB II, associated water retainage cups, (GR 15 Garden Drain), and the root barrier filter fabric that was specified. So after a couple of weeks of steady conversations with the contractor and product representative for Hydrotech we added the correct material over the originally applied material and now have over 400 mils of roofing material on our roofs in lieu of the 210 mils intended. Which for those not familiar with the unit measure of mils 400 mils is nearly ½ inch of material.
  
  One of the best outcomes of going through the process of selection and constructing a green roof was the introduction of product called GaiaSoils. This is largely credited to my sister-in-law, Mem, sending me an earth day news article from the NY times that I am attaching for your readingpleasure. GaiaSoil is an amazing soil, it will be replacing Hydrotec’s suggested soils mixture with a soil that is made from non-toxic recycled expanded polystyrene foam, coated with organic pectin, mixed with high quality finished compost. Here is the comment from the Hydrotech’s soils scientist after reviewing the GiaiSoil specifications:
  
  “Technically for plant survivability there is no issue with the soil. They do recognize that there may situation where this soil can be utilized but with strong cautions.
  
  The draw back;
  
  "American Hydrotech has looked into this soil and similar soils on the market place and they have chosen to not use or recommend the soil. The issue that we have is with wind uplift on roofs and wind erosion. When the soil is dry there is too little weight holding the system in place. I would recommend using a permanent erosion control mat to hold the soil in place to prevent the soils and insulation from blowing off the roof. The Garden Roof is a Protected Roof Membrane Assembly and there are guidelines stating the minimum weight or ballast that is required to secure a roof in place. In American Hydrotech’s Binder under the insulation section there is Dow Chemical’s Tech Note 508 that covers most of the conditions for wind uplift.
  
  The last draw back on the soil is the moisture retention will be less than our soil or typical green roof engineered soil.”
  
  I decided after looking through the data regarding moisture retention that the amounts differed so little and since our site had very little exposure to heavy winds the use of a more environmentally sound soil was worth the small risk we would be taking. Thus, for our situation I determined that the use of a recycled sytrofoam from New York Cities fish market was a better soil medium component than the use of Hydrotech’s recommended shale type soil mixtures that need to go under tremendous heat to create the “cat litter” type substance that they use.
  
  Finally, I need to thank Nathan Salo for building a overflow drainage system for our green roof that will be admired by this architect for years to come.
  
  From the wood plywood deck up is the assemble used for the green roof:
  
  # 8 & 7 -- Hydrotech 6125 EV-FR– Monolithic Membrane is seamless, fully reinforced rubberized asphalt membrane. It consists of one coat of membrane at 90 mils into which Hydrotechs Flex Falsh F (a spunbonded polyester fabric) is embedded. A second coat of membrane is then installed a 125 mils. The total membrane thickness is 215 mils.
  
  In our case since they installed a Carlisle Coatings and Waterproofing CCW-500 hot applied Liquid Membrane 305364 in lieu of the Hydrotech 6125 we put the MM6125 over the Carlisle product for a 400 mil application.
  
  #5 -- Hydrotech RB II – a heavy-duty, granular-surfaced, modified asphalt sheet with an integral root inhibitor blended in. It is used when intensive applications or whenever aggressive root structures are anticipated. It is also used in sloped applications, as the granular surfacing provides additional slip resistance.
  
  #4 -- Drainage/Water Retention Component GR15 – These are water storage troughs, or cups, on the top side of the panels that retain additional water for use by the vegetation. Diffusion holes through the panels allow air circulation and water vapor to move up into the root zone.
  
  #3 -- Filter Fabric - This helps to prevent soil particles from washing through the system and potentially causing drainage layers and drains to become clogged.
  
  #2 -- 6” GaiaSoil – This is the growning medium for the plants, the portion of the soil that both retains and drains water as well as provide the minerals to the plants.
  
  Walking trellis -- Recycled content garden trellis’s that will be installed horizontally over the GaiaSoil prior to the final lay of local compost. This will assist with the erosions control and compaction of the soil as you walk on it to maintain the plants.
  
  1 ½” Compost -- This will be continually applied to the soil over the years as the need occurs to keep the plants healthy and growing properly. Similar to what you would do for your own garden plants in your yard.
  
  Plants will be selected with help of Gus Blumer the Landscape Architect for this project and Allyz Kraemer my friend the boreal forest biologist.
  
  We will be providing rainwater collect water to irrigate the green roofs through hose bibs and drip lines provided on the roof.

Window & Door Installation

The delivery of the infamous Mueller doors and windows occurred around Labor day of 2008. It felt similar to having a newly adopted child show up in your life. The windows and doors took a big trip on a ship from German to Montreal and then trucked to Minneapolis and finally driven to Isabella. Miraculously they arrived in one piece. They were big, beautiful, heavy and amazingly engineered.

Only a visit to the ecohome can do these works of art justice, plan a trip to Isabella to experience the integrity of these castle worthy doors and windows.

Nathan, Jose and Nick, the contractors, key to installation of these doors preformed no less than a miracle in the effort to install these 2000 lbs window units. It took 20 guys to unload them from the containerized truck.

Exterior Stone Collection & Installation

One of the lasting memories John and I will have of this project is the experience we had selecting and collecting the stone for the exterior finish of the ecohome. With 1,600 sq ft and about 1 ½ ton per 30 sq ft. we collected 90 ton of stone, which is why we will hold on to this memory for years to come.

The two types of stone we considered using for the project included the iron ore waste rock from Cliffs Natural Stone Company in Hoyt Lakes and the hand picked natural field stone that came from the site and near by gravel pits.

While the waste rock at the nearby iron ore mines were extremely appealing due to its intriguing story and shear beauty, (oldest fossils in the world & 35 miles of waste rock from previous years of mining ore at Cleveland Cliffs Mining Operation), the cost and hauling of the rock were just not meant for this project.

Instead, John, Nancy and Danny Two Otters, (Danny is a tribal member of the Bois Forte Band of Ojibwa Indians), spent five days hand picking rocks from our site, the neighboring site owned by Dan Spina and a site about 10 miles away. We are extremely pleased with the workmanship that Keith Johnson of Mesabi Masonry Inc,andhis crew performed installing these local stones.

Danny was the piece of the stone picking experience that made it all worth it, for those interested in the commentary that he added to the process, corner me someday and I will share it with you.

Solar Thermal Storage System - Zero Energy Home Challenge

I am updating this portion of the blog to give you the latest information regarding the Solar Heat Storage and Delivery System. One of the updates that may be of interest is the diagrammatic drawing of the system, created by Mike LeBeau, it most definitely helps to understand how we are building the system. The controls for the system will be added to the drawing in the near future.

Additionally, I applied for an Innovation Credit for this system through the LEED for Homes rating system program and have receive notification that it will be allowed for an additional credit. I had applied for several others, but have learned through this process that only extraordinary energy saving or environmental improvements are being accepted, it was communicated to me that of the 2000 + requests received as of March 2008 only 4 or 5 had been approved. This was one of the approved Innovative Credits.

Solar Heat Storage & Heat Delivery System – Innovation Credit Request Documentation:

There are 92 solar heat collector vacuum tubes planned for the roof that will be collecting an average of 172,500 BTU’s per day that that there is full sun. We have assumed that there will be at least 120 days worth of full sun available for producing heat available for long-term storage, outside of the times when it would go directly to either short-term storage or to an end use. This will mean that we can put around 20.7 million BTU’s into storage per year. We estimate that approximately 2 million BTU’s per year will be needed for heating of domestic hot water.

The energy model that we ran for this home indicates that we will need 9.7 million BTU’s annually for space heating. This is 4.6 kBTU/sq-ft. or 15 kWh/m2

We have 9,000 cubic feet of a sand and taconite mix (approximately 50:50) under the foot print of the main portion of the house which is insulated with 16 inches of expanded polystyrene (EPS) on all six sides and has cross-linked polyethylene (PEX) tubing running horizontally at every 9 inches vertically through the sand and taconite. The taconite bed is on the top and the sand bed on the bottom with 2 inches of extruded polystyrene (XPS) separating them. The 2 inches of XPS between the two beds was installed only for testing purposes so the heat storage performance of the taconite and sand beds could be evaluated more-or-less independently. Sensors will be installed at various locations in each bed to monitor performance and fine tune the control strategy.

Heat storage capacity for the space under conditioned space is estimated as follows:

Energy density of water = 4,190 kJ/m3 oC (www.engineeringtoolbox.com)
Energy density of taconite = 2,560 kJ/m3 oC (www.engineeringtoolbox.com)

Specific heat of sand = 830 J/kg oC (www.engineeringtoolbox.com)
Density of packed dry sand = 1,682 kg/ m3 (www.simetric.co.uk)
Energy density of packed dry sand = 1,682 kg/ m3 x 830 J/kg oC = 1,396 kJ/m3 oC

950 sq-ft x 3 feet= 2,850 cu-ft total volume of sand
950 sq-ft x 3 feet= 2,850 cu-ft total volume of taconite

2,850 cu-ft x 7.5 gal/cu-ft = 21,375 gal

Assuming that the energy density of sand is about 0.333 that of water:
21,375 gal x 0.333 = 7,118 gal of water storage gal equivalent

Assuming that the energy density of taconite is 0.611 that of water:
21,375 gal x 0.611 = 13,060 gal of water heat storage equivalent

Combined total heat storage = 20,178 gal water heat storage equivalents

20,178 gal water x 8.34 lb/gal = 168,285 lb water heat storage equivalent

Assuming that an 80 oF maximum usable temperature range is available, the total heat that can be stored in the sand and taconite beds combined = 13,462,762 BTU

A closed loop heat transfer circuit will transport the heat from the roof top solar collector to a flat plate heat exchangers and a pair of insulated water storage tanks in the utility room basement. A heat transfer fluid, consisting of propylene glycol and water, will be directed first through a heat exchanger coil in the bottom of an 80 gallon indirect fired hot water tank. During the non heating season, once the 80 gallon tank reaches a desired maximum temperature of 150-160 degrees the heat transfer fluid is redirected to a flat plate heat exchanger that will direct the excess heat into the sand/taconite thermal storage area. During the heating season the heat transfer fluid will be directed to a coil in a 400 gallon bulk thermal storage tank. When that larger tank reaches a desired operating temperature any surplus energy will be transferred from the tank and into the closed loops of PEX tubing going through the sand and taconite beds via a separate closed loop that is common with the space heating distribution system. Energy will move to the storage bed when there is a surplus and be removed from it when need for space or water heating. The 400 gallon tank will be used to create the desired temperature needed for space heating by calling for heat from the heat transfer fluid coming from either the sand/tanconite thermal storage area or directly from the heat transfer fluid coming from the solar collectors.

Since the heat will only flow from hot to cold, water in the PEX tubing in the floor slab will have to be somewhat above the desired slab temperature. If a slab temperature of 75 oF is desired, water at 80 oF or above should be sufficiently hot. To supply water at this temperature, the sand and taconite beds will need to be somewhat above this temperature, perhaps 90 oF at a minimum. Based on the heat capacity storage calculations, if the sand and taconite beds were to reach 170 oF by late fall, the two beds combined could release about 13.5 million BTU without their temperature not going below 90 oF. Assuming that one third of the approximately 21 million BTU of heat that is anticipated from the solar collector vacuum tubes is lost through the 16 inches of EPS around the sand and taconite beds and elsewhere in the system, there should still be about 14 million BTU available for space heating and domestic hot water, which is about 2 to 3 million BTU more than the energy models predicts for the total annual space heating and domestic hot water needs of the house. Should there be any excess heat, to prevent overheating of the sand and taconite beds, the heat can be diverted into the garage floor slab, which has PEX tubing in it to keep the garage warm and its floor ice-free in winter.

A small electric boiler will be integral with the solar heat collection system and will supplement and back-up the solar thermal system. The location will be next to the water storage tanks. This boiler will back up the domestic hot water tank, if ever needed, by heating the 80 gallon tank via a second heat exchanger coil suspended near the top. It will also back up the space heating system by working in parallel with energy from the solar thermal system either from the larger storage tank or from the sand and taconite long term storage bed. The electric boiler will be connected to a 8kw propane powered generator for the rare situation when the power is out for a long period of time and the system is not capable of keeping up with the electric loads for the ecohome. An electric boiler was selected because of the ability for electric boilers to be size in smaller increments than propane boilers, making it more appropriate for the small loads needed for this project.

The electric boiler will be controlled by the Sunny Island device to allow it to switch into operating mode should the battery backup or grid power go down.

The 400 gallon water solar storage tank is also important for heating the home during the shoulder heating seasons, spring and fall. Installing a system that allows the heat collected to go directly into the 400 gallon tank and then into the floor heating coils was important to allow quick access to the heat when the sand/taconite is likely to be loosing capacity during the spring and the sun is gaining its strength. And conversely, when the sun is loosing its strength in the fall and the taconite/sand thermal storage is at capacity, the solar heat is more efficiently sent right to the in-floor heating system.