A Jungle in the Dining room
The Solarium Addition

When we decided to do an article on additions for this website, 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.

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.

We had never built a solarium. In fact, we had never even heard of a solarium before we took on this project.

The owners were a professor of engineering at the University of Nebraska and his wife who was an avid 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 its 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 connected 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. Then we built up the walls using concrete block reinforced with rebar.

The owners did not want a traditional black rubber liner and elected instead to coat the inside of the pond with a special flexible form of concrete into which fiberglass threads were mixed to provide exceptional strength. The concrete was tinted to look like natural stone and soil.

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. When it was done it was very hard to see where the tinted 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'-6" 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 realized 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 outright 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 undercut the frame around the Filon® a little to create a groove for the silicone 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 through 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.

Rev. 06/15/18