G = g Case Study

Studio Rebus completed a G = g renovation on a home in Minneapolis' Corcoran neighborhood.  The home was built in 1914.  It's a two bedroom, one bath with a full basement.  It has excellent southern exposure for winter time sun and a large maple on the southwest which shades the entire western elevation in the Summertime.  Please click on the link below to download a short Excel spreadsheet which gives an introduction to G = g and demonstrates why Greener is greener.  Then download the insulation diagram.  It'll show which part of the house is investigated by the spreadsheet.

The spreadsheet is looking at three options : in blue, do nothing, maintain the status quo; in green, the G = g option, add insulation; and in blue, add insulation to comply with the Minnesota Energy Code.  This spreadsheet is only looking at adding insulation in the flat part of the attic.  For the G = g renovation, in addition to the attic, the pitched sections of the living space were dense packed with blown in cellulose. 

The first six lines in the spreadsheet are used to calculate how much natural gas will be used for each option.  Tables in construction references provide heat flow values for all elements in a construction assembly.  The first line indicates how much heat is lost per hour on the coldest day in the winter.  Degree days are a way of measuring how cold a climate is for designing a heating system.  The degree days in Minneapolis are 8,322.  In Miami Beach, Florida it's 123 and in Resolute, Northwest Territories, Canada it's 22,600.  

The third line indicates how much heat flows through the ceiling plane of the second floor during the heating season.  The measure is the British thermal unit.  How much is one Btu?  If you light a wooden kitchen match and let it burn completely, that releases one Btu of heat.  Imagine standing on the second floor during the heating season and lighting off nearly 53,000,000 matches.  Also gives a sense of why a modern nation state might use natural gas rather than wood.  A therm is a standard unit of measure for natural gas.  Taking the current price for a therm of gas, there's enough information to calculate how much it costs to apply heat to just that section of the home.  

The house was insulated with Zonolite, a brand of vermiculite.  It was tested and there was not an actionable level of asbestos.  The house still had knob and tube wiring powering the second floor.  The knob and tube can't be buried in insulation.  The insulation contractor vacuumed out the vermiculite.  Then the electrician replaced the knob and tube.  Where possible he used armored cable to reduce electromagnetic pollution.  The costs to remove the old insulation and install cellulose are listed.  The Minnesota Energy Code doesn't require as deep insulation as a G = g approach.  The cost to insulate is lower.

We sought a graphic answer to the question, "How deep should the attic insulation be?"  Open up the third document to see the answer. 

Life cycle cost = installation cost + operating cost + maintenance cost - salvage value.  For insulation there's no maintneance cost and no salavage value.  The most challenging aspect to these studies is choosing a realistic escalation rate, that is, how much more expensive fuel will be this time next year.  The most most powerful tool in life cycle costing is present value.   Life cycle costing assists in answering the question, "What should I do now, in the present, to have a better economic and ecologic outcome in the future?"  Present value determines what a future series of payments would be worth today, the present, if a particular escalation rate is assumed.

There has to be a boundary to these studies.  I chose seven years because that's the average length of time Americans live in their homes before moving.  Adding all the elements the life cycle costs for each option are given.  The prudent course of action is to go with lowest figure.  As you can see the lowest is the G = g option.  Also note that complying with the Minnesota standard is quite Green.  

In our life times price tags will become more sophisticated.  They will list three elements : intial cost, life cycle cost and carbon footprint.  As you can see the G = g option has the smallest carbon footprint.  Using the Kyoto Protocol standards, if the G = g option is implemented 3.3 tons of carbon dioxide are not festooning the planet.  As the years roll on there are greater and greater savings.  Take a look at the last lines with a fourteen year boundary. 

Another tool to assist in planning is simple payback in years.  Simple payback = installation cost divided by yearly savings.  After six years the work has paid for itself and in the seventh year we're making money. . .

In planning your project Studio Rebus would do a life cycle cost study for all the major components.

Studio Rebus will provide a complete analysis on this site when the homeowner has a year of heating bills to compare before and after.

Click filename below to access file

Greener_is_greener_Case_Study_Insulation_Diagram1.pdf

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Greener_is_greener_insulation_and_heat_flow.pdf

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How_Deep_Should_The_Attic_Insulation_Be.pdf

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G_=_g_Life_Cycle_Cost_for_Attic_Insulation.xlsx

Studio Rebus Incorporated 

510 Sibley Street  Suite 503  Saint Paul  Minnesota  55101 

763 412 8070