A Jungle in the Dining Room: The Solarium Addition

Please excuse the photos. Thirty years ago we were documenting our work with a Polaroid-Land camera, so the resolution is not fantastic, nor is the clarity.

When we decided to do an article on additions for this web site, we reviewed lots of our past work, and found that one of the most inte­resting jobs we had ever done was one of our first, over 30 years ago: A solarium addition.
We had never built a solarium. In fact, before we took on this project, we had never even heard of a solarium. The owners were a professor of engineering at the University of Nebraska and his wife who was quite the gardener. There did not seem to be any tropical plant she could not make prosper. What she wanted was to grow a tropical forest in her house. For this she needed a solarium.
A solarium, it turns out, is a sunroom that has no floor — essentially a greenhouse. Plants are grown right in the ground in as close to their natural habitat as possible. The "floor" is dirt, just like a garden, with, in this case a path and patio on which the owners can sit and enjoy their indoor tropical jungle.
The site chosen for the solarium was just about perfect. Right outside the owners' dining room, it would be entered through existing French doors that at the time opened to a small patio. It would have ample southern exposure.
The structure would be 16' x 16' and 16' high at it peak. The mass of soil, rock and water inside the solarium would do double duty as a growing medium for plants and as a solar mass to collect heat. The collected heat would be dissipated at night to keep the solarium warm. In winter, excess heat, which would naturally rise to the top of the structure, could be distributed throughout the house by a blower connect to a thermostat that activated when the temperature at the top of the solarium reached 70 degrees. It was an ingenious idea, and we were very curious to see if it would work.
The plan called for a brick knee wall 3 feet high. This wall is actually two walls with a cavity in the middle filled with blocks of XPS foam block insulation. Essentially waterproof and not affected by moisture. XPS was the ideal choice. The knee wall rests on a foundation of 10" concrete block which in turn sits on a solid 16" footer buried 3-1/2 feet below the graded surface. This footer is more than ample for the weight of the walls and roof it supports. The foundation was insulated with 4" XPS foam sheets applied to the outside below ground level.
Once the knee wall was finished, we were able to begin framing the upper walls and roof. This was more or less conventional framing. The spacing between studs was altered to fit the 24" glazing material. The roof framing was a little unusual. The roof was to be insulated with 12" of fiberglass insulation. To allow room for the insulation we built what were essentially site-made trusses for the roof using 2" x 4" lumber and 1/2" plywood. When the framing was finished, it was given a coat of mildew-resistant primer before the glazing was installed.
Finally we could get to what we like to do best — interior finishing. But this was like no other finishing any of us had ever done. The room was to have a 3-foot double entry door to permit moving large plants in and out. Opposite the door was to be a pond. A brick path was to extend around the pond from the door to the dining room French doors. Everything else was just to remain dirt. Not just any dirt, however. We dug out the entire area down to two feet and replaced all the clay with a blend of soil provided by the owners. This was more like landscaping than carpentry.
The pond is in a heated area and not going to be exposed to winter so we did not have to worry about the effects of the normal Nebraska freeze-thaw cycle. We built it by digging down three feet and laying a concrete floor. The we built up the walls using concrete block reinforced with rebar. Finally we coated the inside of the pond with a special concrete mix containing very small PVC fibers. These make the concrete very strong and somewhat flexible to resist cracking. Finally the pond was topped off with stone designed to look like a natural outcrop. A waterfall was built into the stone outcrop and connected to an external pump and filter very much like those used for swimming pools. We had tinted the final coat of concrete to match the rocks. When it was done it was very hard to see where the concrete ended and the rocks began. The two blended seamlessly.
The next step was to test everything to extremes of temperature. The glazing material is a special fiberglass called Filon® that admits more light than glass, but is obscure enough to allow privacy. It is used primarily in commercial greenhouses. Frosted glass would have cut down on light, which was something the owners nixed right away. Filon®, however, is not as stable as glass and reacts to changes in temperature by expanding and contracting. We were not concerned with contracting, but we wanted to ensure that when it got very hot, the material would not bind or buckle. We used every portable heater we owned to heat the room to over 110 degrees. The glazing groaned a little but neither bound nor buckled, so we were in good shape.
The double doors are taller than normal, 7' instead of the 6'-8" that is the usual door height. The extra height was to allow for tall plants. We had always intended to use a pair of factory-made wood entry doors designed for glass — just replacing the glass with Filon®. However, by reading the specifications for Filon®, we found out that doors designed for glass will not work. The spacing between outer and inner sheets of double-glazed Filon® needs to be larger than the spacing for glass, and the shelf on which the glass is installed needs to be wider for Filon® because it has more movement than glass. We suggested just using glass instead of Filon® to eliminate the problem. The owners weren't having any of that. We begged, we pleaded, we even tried bribery. Nothing worked. So we designed and made our own doors.
To allow enough spacing for the double glazed Filon®, we made the door a full 2" thick rather than the standard 1-3/4" entry-door thickness. We milled in an extra wide shelf for the glazing to rest against, and under cut the frame around the Filon® a little to create a groove for the silicon sealant to sit in. Then we had to figure out how to get the latch and lockset designed for a 1-3/4" door to work with a 2" custom door. With the help of a local locksmith we were able to adapt commercial hardware to the thicker doors.
Now just a few finishing touches and we were done. The brick walk was laid on well-tamped soil over a bed of sand. A mixture of sand and the same tinted concrete we had used for the pond was dry-brushed into the seams between the bricks and then wetted with a fine mist of water. When fully cured it made a very solid walkway with what looked like soil in the seams between the brick instead of concrete, but it really is concrete.
We covered the existing concrete patio with brick pavers to match the full bricks in the walkway. All of the brick used was purchased at Yankee Hill brick in Lincoln, so we were certain of a good match. The brick was designed to look like used brick, and it certainly does look used — complete with rounded-over edges and what looks like little bits of old concrete stuck to it here and there.
Somewhere in the process, but after we had built all the walls, the owners decided that the solarium needed a supplemental heat source for those really cold winter nights. So we removed a panel to the left of the door, next to the house, and called in a plumber to install a wall-mounted gas heater. The heater vents though the wall so we did not have to run a stack through our new roof.
Our final act was to permanently install pendant globe lamps in the solarium from boxes already wired by an electrician. These had been hung from temporary wiring during the construction. The lamps are rated for exterior use, very corrosion resistant. The amount of humidity produced by the plants required that all fixtures and electrical switches and outlets in the room be exterior rated for both safety and durability.
Then we helped the owners carry in all the tropical plants and took a break while they planted their jungle. In the process we learned a bit about cultivating tropical plants. We were most amazed when Mrs. Owner whipped up a concoction of moss, buttermilk, fertilizer and water in her blender and used this slurry to paint our new walkway. It's a medium for quickly growing moss, and it works. A month later it looked like our new brick walk had been there a hundred years. And, in a hundred years, I suspect it will indeed still be there.
Need to know more about designing, planning and building an addition? Try these articles

  • Building by Design: The Design-Builder Concept
    A design-builder is a modern form of an ancient approach to building structures — that of the master builder. A master builder of old was a combination architect, engineer and builder, responsible for every phase of building a structure from initial concept to completion. Design-building firms such as StarCraft Custom Builders continue this oldest of building traditions.
  • Building Your Addition
    We don't build the old-fashioned way when new technology works better. Learn about the new foundation and framing technologies we use to build your super-insulated addition at the lowest possible cost.
  • The Construction Process
    Once your blueprints are completed, the real work begins. Your project manager works with you to develop a construction process that minimizes disruption to your household while work is in progress.
  • The Design & Planning Process
    If your plans include substantial changes to your kitchen or bath, or another room, or you are contemplating an addition; then a construction plan is required. Learn how your ideas are turned into a concept plan and then a construction blueprint in a three-step process using computer-assisted design.
  • Finding Some More Kitchen Space
    In many cases, existing kitchens are just too small for any real improvement in space management. Learn where to get more space, or at least the illusion of more space for your new kitchen.
  • Getting More Bathroom Space
    Our fondness of open spaces within the home doesn't end at the bathroom door. Unfortunately the acreage needed to create that spacious feeling just is not available in many older bathrooms. Often the key to updating a bath is creating more space — or at least the illusion of more space. This article examines where additional space can be found both outside and inside your existing bathroom.
  • Insulating Your Old Housenew
    Is your old house drafty in winter, swampy in summer? Almost impossible to heat and cool? That's because when your house was built a half-century or more ago, no one thought insulation was necessary — or, better said, experts believed that the 4" of dead air space inside the stud cavities of your walls was adequate insulation. Now we know better, and in an age of declining energy resources, adequate insulation in your old house has become a critical requirement. Learn how insulation works, and when and wear you should insulate your old house.
  • James Hoban: Master Builder (Sidebar)
    An Irishman designed and built the most famous house in American: The White House. Learn about this little known master builder.
  • Living Through Remodeling: A Homeowner Survival Guide
    Remodeling will disrupt just about every routine you have; including some you are not aware of having. But this noisy, gritty process doesn't necessarily mean you will be tearing out your hair. With a little advance planning, it is possible to live through even major renovations with your sanity and good nature largely intact. Check out our remodeling survivors guide.
  • Planning Your Addition
    Here are the basic rules for designing an addition that is as functional as it is beautiful.
  • Whole Wall Insulation (Sidebar)
    The R-12 insulation in your walls may be providing only R-8 thermal protection. The Oak Ridge National Laboratory has come up with a new technique for measuring actual R-value that is a lot more accurate than the current methods. Which materials are winners and which are losers in the R-value rating game? Find out.
  • Your Old Windowsnew
    If the fine craftsmanship and charm of your old windows is quickly being eroded by cold drafts and frost on the panes, it may be time to consider doing something about them. Can your old windows be saved? If they are saved, can they be made as energy efficient as modern windows? The answer is "yes" and "yes". Most heritage windows can be restored and upgraded to rival the performance of a standard replacement window, and usually at a fraction of the cost.
Rev: 10/18/14