A Jungle in the Dining Room — The Solarium Addition

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. A solarium addition.

The finished solarium. What looks like frosted glass is actually Filon®, a special fiberglass glazing material designed for greenhouses that actually admits more light than glass. The vent at the gable peak opens when the interior gets too warm in summer. 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 greenhouse that has no floor. 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 knee wall going up. The foundation of 10" concrete block rested on 16" footers. 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 waterproof insulation. 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" 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.

The walls above the brick knee wall were framed for double-glazing. Here the roof and marine plywood ceiling are finished and double-sealed and the skylights 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 fed by a waterfall and drained through a hidden skimmer box located under a rock overhang. The concrete used to make the pond was tinted to match the rocks. 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. 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 newly planted "tropical jungle" surrounding the pond already looks pretty authentic. This is the view from the seating area. A wonderful sight in snowy February. The double doors are taller than normal, 7 feet 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.

The site-built solarium doors were designed to work with Filon® glazing instead of glass. 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 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.

No one enjoys the new solarium more than Curtis, the family cat. The finch is not so sure. 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.

End

For more good reading, check out our complete articles index.