The Roper Solar Greenhouse
215 Maywood Street, Blacksburg, Virginia (37° 16'3.42"N 80° 24'46.24"W)
Located in the Hale-YMCA Community Gardens (Map)

Roper Solar Greenhouse Features

Regularly redisplay this web page to keep up on the progress of the YMCA Solar Greenhouse.

Official ground breaking for the YMCA Solar Greenhouse

Slide Show about the YMCA Solar Greenhouse
Handout about the YMCA Solar Greenhouse

Roanoke Times article about the YMCA Solar Greenhouse
Roanoke Times blog about the YMCA Solar Greenhouse
YMCA Solar Greenhouse in Solaripedia
YMCA Solar Greenhouse article in the Current Real Estate section of The Roanoke Times 11 April 2009
The YSGH was on the 2009 NRV Green Building Tour 25 April 2009
Anderson & Associates Newsletter
Roanoke Times Article about the opening of the Roper Solar Greenhouse
Video about Roper Solar Greenhouse

Blog about Arlean Hale Lambert establishing the Hale-YMCA Community Gardens

A garden set to produce for generations to come

There was a public naming and opening of the YMCA Solar Greenhouse at 10:00 AM on Thursday 15 October.

Example of a backyard solar greenhouse using the SHCS


What is a Solar Greenhouse?

Many people think that any greenhouse is a solar greenhouse. That is not correct. A solar greenhouse has the ability to store much more energy from the Sun than does an ordinary greenhouse. The energy is usually stored in water or rocks inside the greenhouse, taking up floor space. See Solar Greenhouses for more information.

A solar greenhouse (SGH) differs from a standard greenhouse in that energy is collected from the Sun and stored for use when the Sun is not shining. Greenhouses tend to get too hot when the Sun is shining and too cold during winter nights. A SGH stores energy in some medium other than the air and the soil during sunny weather. The best SGH cools the air as needed when the Sun is shining as well as heats the air when needed. This process of cooling and heating needs to be done with a minimum of energy input from external sources other than the Sun.

The YMCA Solar Greenhouse uses a new way to store energy collected from the Sun, in a subterranean heat sink of soil/rocks/water under the planting beds. This system is called the Subterranean Heating and Cooling System (SHCS).

Why Build a Solar Greenhouse?

Global Warming and Peak Oil require that humans acquire their food from local farmers or grow it themselves. In climates with cold winters, such as at Blacksburg, Virginia where Virginia Tech is located, acquiring local food in the winter time requires the existence of solar greenhouses. Of course, one could preserve summer crops by canning and drying, but fresh vegetables in winter months would make a healthy diet more likely.

The YMCA at Virginia Tech Community Gardens

The YMCA at Virginia Tech has managed a community-gardens area on property of the Town of Blacksburg for several years. A 15-acres area at the end of Maywood Street (215 Maywood Street) off of North Main Street in Blacksburg is being developed into a larger YMCA-at-Virginia-Tech Community Gardens. It is called the Hale-YMCA Community Gardens. It has been beautifully designed by Anderson and Associates:

The parking lot and the curved path from the parking lot to the YMCA Solar Greenhouse will be built by UXB International using the KimsRoads technique.

The YMCA at Virginia Tech Solar Greenhouse

An 18'x32' SGH utilizing the Subterranean Heating and Cooling System (SHCS) has ben built as part of the Hale-YMCA Community Gardens. As far as is known, this will be the first large SGH using the SHCS in the United States east of the Mississippi. It is called the YMCA Solar Greenhouse (YMCA SGH or YSGH).

A model of the YMCA SGH, made by Dave Nickerson, is in a display case inside the front door of the YMCA Center at 1000 North Main Street in Blacksburg VA.

YMCA SGH Steering Committee consists of Pat Bixler (chair), Tim Colley (architect), Gail Billingsley (YMCA of VT), Arlean Lambert (land owner), Justin Boyle & Jason Boyle (Green Valley Builders, Inc.) & Dave Roper.

The site plan was made by Anderson & Associates. The design of the YSGH was made by L. David Roper. The architectural drawings were made by Colley Architects. Engineering calculations were done by Truesdell Engineering. The construction is being managed by Green Valley Builders, Inc.

Several businesses have donated time and materials to build the YMCA solar greenhouse.

Back to the top

Some Details about the YMCA Solar Greenhouse


The best orientation is with the glazing toward geographical south. In Blacksburg VA magnetic north is about 6.5 degrees west of geographic north, so magnetic south is about 6.5 degrees east of geographic south.

Computer Model

Not shown are two 2'x2' vent Marvin awning windows high on the east and west ends. They are opened and closed electrically controlled by a thermostat. There is a fan on the west window, controlled by a thermostat, to push air out that is pulled in the east window and the door, if it is open.

The south 45 ° roof is 10-mm thick double walled polycarbonate; the north 60° 10"-thick roof is insulated.

The rows should be planted north-south instead of east-west as shown here, in order to get more equal sunlight on the plants.

The computer model was made by Tim Colley and Travis Rookstool of Colley Architects PC. Anyone wishing to obtain detailed plans for this SGH or a revision for a different size of SGH should contact Colley Architects.

Dave Nickerson made a physical model, which is on display in the YMCA Center at 1000 North Main Street in Blacksburg VA.

Back to the top

End Vent Windows

Marvin Infinity Awning Window:
Infinity Awning

"One word describes Infinity® from Marvin Casements and Awnings -- easy. They are easy to choose, easy to operate and easy to love.The Casement (left or right hinged) and Awning (top hinged) combine beauty and virtually an effortless operation. The standard Easy Wash® hinge is just that--a design that lets you easily clean the window both inside and out. The optional Clear View® hinge provides for an optimal viewing area. Both Casements and Awnings feature folding handles that tuck conveniently out of the way of most window treatments and provide a clean, finished look." The windows used are 2'x2'.

Thermostatically controlled vent-window opener:

It will be opened (at 90° F) and off (at 70° F ) by a thermostat.

Fan for the east vent window:

It will be turned on (at 95° F ) and off (at 75° F ) by a thermostat.
It is 170/145/115 watts and 3560/3120/2510 cfm for fast/medium/slow speed.

Two of these fans failed, probably due to the hot summer temperatures (up to 140° F!).

The replacement fan is:

It came with fins on the outside, which were removed.
It pushes 3000 cfm.

Back to the top

LED/Fluorescent Lights

Three of the light bulbs will be 9.6-watts (300 lumens) LEDs (cool: 6000K; warm: 3000K; GrowLED: 5-watts, 300 lumens, 130 red, 30 blue), others will be compact fluorescent bulbs (CFL). They will cut down greatly the use of electricity for lighting and on the problem of replacing bulbs in the six ceiling lights.


The below-ground walls are made from ICF (Insulated Concrete Form) filled with concrete. The R value is 32 (ft²·°F·hour/Btu). The above ground walls are 2"x6" wood studs on 2' centers filled with 3" of closed-cell foam insulation. The inside and outside finish is a fiber-cement panel (HardiePanel).


The north roof is 2"x10" wood rafters on 2' centers filled with 3" of closed-cell foam insulation; its inside finish is a fiber-cement panel (HardiePanel) and the outside finish is architectural shingles. The south roof is 10-mm x 4' x 20' double-walled polycarbonate on 4"x10" rafters on 4'3/4"-4'1" centers purchased from Sundance Supply. The polycarbonate sheets are attached to the rafters using the Base and Cap system.

The rafters connect at the top to a 34' long 4"x14" beam.

Nine polycarbonate panels (20' long):

Polycarbonate crate:

Back to the top

Ground Water Exclusion

All ground water must be excluded from entering the heat sink. This is done by the following systems:

Ceiling Fans

Two 36" Action-Aire ceiling fans, actuated by a switch and a Ranco adjustable digital thermostat will be hung from the SGH peak centered between the center post and the two walls. Their purpose is to keep hot air from accumulating at the peak.

The thermostat sensor will be placed near the peak, shielded from sunlight. It will be set to turn on at 90° F and off at 70° F. The thermostat could be in the same box as the thermostats for the heat-sink fan, with a long lead to the sensor near the top. The switch for the ceiling fans could be in the same box as the thermostats, out of range of prying eyes.

Electrical Details

Here are some considerations for the electrical wiring of the YSGH:

The estimated power usage is 425 watts for the fans, 400 watts for the water pump and 300 watts for the lighting. The total is about 1125 watts.

Planting Beds

Here are results of the top-soil tests for the SGH site:


P (lb/A)

K (lb/A)

Ca (lb/A)

Mg (lb/A)

Zn (ppm)

Mn (ppm)

Cu (ppm)

Fe (ppm)

B (ppm)



































Soil pH

Buffer Index

Est.-CEC (meq/100g)

Acidity (%)

Base Sat. (%)

Ca Sat. (%)

Mg Sat. (%)

K Sat. (%)

Organic Matter (%)













lb/A = lbs per acre; Sat. = saturation; Est-CEC = estimated cation exchange capacity; g = gram, Suff = sufficient; ppm = parts per million; L = low; M = medium, H = high, meq = millequivalent
Lime recommendations: Apply 2 lbs of agricultural limestone (ground or pulverized) per 100 sq ft.

Fertilizer recommendations: Apply 4 lbs of 5-10-10 per 100 sq ft.

Soluble salts are not high enough to cause salt injury.

The National Sustainable Agriculture Information Service may be of help in preparing the SGH soil for planting:

Hydrologic Soil Group Descriptions:

A planters' committee (Abigail Convery, John Ogburn, Deborah Wiley and Holly Scoggins) are studying what to use for topsoil; e.g., whether it will involve the original topsoil or not. One option is growing mixes by SunGro.

Sun Gro donated 75 bales of Organic #1 Mix in 3.8 ft3 bales (which expands to 7 ft3 for a total of 525 ft3 [~19.5 yd3]). This will be mixed with builders sand (10% or 2.8 yd3) and worm castings or top soil (20% or 5.6 yd3) to make the approximately 28 yd 3 needed for the planting beds. McEnroe Premium Organic Compost was used and a few bags of Azomite were added.

Back to the top


Under the 3'-wide walkway and the 5'x5' turn-around at the west end will be #57 stone (~8.5 tons) from the tarpaulin at the top of the heat sink up to about two inches below the top of the planting bed. It will be installed at the same time as the planting soil is added to the two planting beds on each side of the walkway. On top of the rocks will be a walkway made of 5/4"x6" Trex "boards" with Trex ribs under them to hold them together. (Eight 16' Trex boards.)

Building the walkway:

Cistern for Storing Rain Water for the Plants and Watering

A 2000-gallons concrete septic tankwith their tops 2' below ground on the south side of the southeast corner of the SGH will store rain water that falls on the roof to be used for watering the plants. There will be filters to keep debris from entering the cistern. At the beginning town water will be hauled in to mostly fill the cisterns.

The water will be pumped out of the cisterns by a Commander pump into a pressure tank behind the center post of the SGH.

There are two water faucets, one at each end of the walkway.


See some data collected using the data loggers.

Start-up Procedure for a SGH using Subterranean Heating and Cooling System (SHCS)

The problem is that some water and heat needs to be stored in the heat sink below the planting bed before vegetable greens are planted in the SGH. In normal operation that water and heat comes from the 90% transpiration of water from plant leaves that comes from watering the plants in the soil. So, it is a “chicken and egg” quandary.

Here is a possible procedure to solve the quandary: After water is hauled in to mostly fill the cistern at the start, some of that water is sprayed into the SGH air and placed in pans on several consecutive sunny days, so that the SHCS can start to work by pulling humid air into the heat sink. Then watch the temperature and humidity for some cold days to see if the heat sink is working. Some lettuce starts will be quickly planted.

Also, the heat-sink fan's rheostat needs to be adjusted for the correct air flow in the heat-sink pipes. The HOBO U10-003 temperature and humidity data sensors/loggers at the heat-sink inlet and outlet pipes will be used to determine the correct air flow to yield the biggest difference in temperature and humidity at those two locations on sunny days.

After a week or two of testing, hopefully confidence will be built so that plants can be planted.

Soil heating cables may be used to get plants started.

Back to the top

Time Table and Volunteers

Back to the top

Latest Pictures:

Walkway finished

Control box

Cistern installed

Backful done

YSGH at night
Energy being stored in the heat sink!:

Back to the top

YMCA SGH Steering Committee

YMCA SGH Steering Committee consists of Tim Colley (architect), Pat Bixler (chair), Jason Boyle (Green Valley Builders, Inc.), Arlean Lambert (land owner), Dave Roper, Gail Billingsley (YMCA of VT), ), Justin Boyle (Green Valley Builders, Inc.), in the order left to right in the picture below.

Contributors and Construction Companies

Back to the top


For the remainder of the winter of 2008 the YSGH will be divided into two parts, separated by a north-south line through the center post. The east half will be planted and cared for by students of Blacksburg New School and the west half will be planted by a group of gardeners organized by John Ogburn and Deborah Wiley.


Several data loggers are used to collect data for the YMCA Solar Greenhouse. Here are some data collected by a data logger placed on the south side of the center post.

Data for April 2009 before the heat-sink and the vent fans were installed:

Temperature and humidity (right scale):
The purple points are daily maxima & minima outside temperatures.
Temperature and light intensity (right scale):
Note that temperature slightly lags light intensity.
Look at temperature by itself:
The black curve is the 2-day running mean.

See YMCA Data web page for more information about data.

Solar greenhouses communications

Weather Stations in Blacksburg for Observing Micro-Weather

Roanoke Community Garden Association

Back to the top

L. David Roper,;