Not every greenhouse is a shed with a ridge. The picture above is a bird-groove shaped house - a curved shell whose roof and wall run together as one continuous surface over a round base. The effect diagram is the first thing a client sees, and it is also where the form, the drainage, the structure and the covering have to agree. This page deals with that curved-shell form itself: how it drains, how frame and cover are matched, where such a shape is worth building, why it costs more than a standard span, and what an effect diagram can and cannot tell you. Other projects are listed in the greenhouse project gallery.

The Bird-Groove Form: One Curved Shell, No Ridge

A bird-groove or bird-nest greenhouse is a dome, not a pitched house. Its frame is a lattice of short straight members bolted into triangles that together approximate a hemisphere - a grid shell. There is no ridge or eave; the covering follows the curve from ground to crown. The effect diagram shows the usual result: a triangular steel grid, a single front door and a circular apron around the foot. The building looks the same from every side, so it works as a landmark rather than a row of bays. And with no long straight roof run, every element - members, nodes and cover units - varies with its position on the curve. For the opposite extreme, the sawtooth greenhouse, with its straight repeated daylighting runs, sits at the other end of the range.

Drainage on a Curved Shell

A pitched roof has a clear fall line; a dome has none - it sheds in all directions at once. Rain runs down the slope of each facet and arrives at the base all round the perimeter, so drainage depends on a ring gutter at the foot of the shell rather than a single eave gutter. That gutter is sized for the whole roof area, and the number of downpipes follows the perimeter length and the local rainfall intensity. Where a dome meets a rectangular building, or two domes are joined, the junctions form internal valleys, and those overflow first if the outlet is undersized. Snow behaves differently again: a smooth curve sheds snow readily, but the lower band is flatter, so ice lingers around the base and can block a ring gutter set at ground level, which is why apron and gutter are kept clear. Structural and snow-loading guidance for agricultural buildings is published by the United States Department of Agriculture, and it is the reference used when the shell span and the base ring are fixed.

Matching the Grid Structure to the Covering

On a dome the frame decides the cover. The triangular grid breaks the envelope into many small facets, so the covering goes on as small units that follow the grid, their shape set by the structure rather than by the material. Rigid glass can be used, but every pane is cut to a different shape, waste rises and the weight the grid carries rises with it. Polycarbonate board tolerates the geometry better and holds more insulation. Film is the easiest material to make follow a curve and the least costly to install, but its life is shorter and its insulation lower than a rigid cover. Whichever is chosen, the cover is fixed into glazing profiles or clamped on the grid, with gaskets and sealed joints. The frame is steel; where steel is used, corrosion protection is specified against ISO 9223 and BS EN ISO 14713-1 at class C2 to C5 for the site, with cut ends and drilled holes treated on site. Two points are peculiar to the form. The dome carries load mainly in compression and pushes outward at its foot, so it needs a ring beam or a continuous foundation - a pad under each post is not enough. And a dome has no ridge to vent, so openings go in the upper band, at a crown lantern, or through the doors. Covering options for more conventional houses are set out in the film greenhouse series and the commercial poly tunnel film covering.

Where an Irregular Greenhouse Earns Its Place

A dome is chosen for what it says, not for what it yields. Its natural home is where the building itself is the attraction: a visitor centre, exhibition pavilion, theme park zone, garden showpiece, entrance hall, or a cafe under glass. There the shell carries a brand and draws footfall, and the round plan suits a central display or a gathering space. What it does not suit is high-throughput growing. A curved shell wastes the volume between benches and cover, rectangular benches cannot tile a circle without odd corners, and light in the lower band is uneven because the surface tilts away from the sky there. So build one when experience, landmark value or display matters more than the cover area the same footprint of straight spans would give. Leisure and display greenhouses are followed by Hortidaily, and the wider spread of commercial structures sits in our commercial greenhouse range.

Cost Drivers, and Reading the Effect Diagram

An irregular shell costs more than a standard span for reasons traceable to the geometry. Almost nothing repeats: members are cut to length, connection plates are made for a particular node, and cover units are cut to shape, so material waste and workshop labour both rise. On site the shell is assembled and lifted or propped while the grid closes, needing a crane and temporary supports a simple gable does not. None of this argues against the form - it argues for fixing it early. That is where the effect diagram helps: it shows proportion, the transparency of the covering, the colour and the general look, so a client can agree the shape before steel is cut. What it does not show is the engineering behind it - member sizes, snow and wind loads, gutter capacity, condensation, how the space will be used, or the final cost. Drawing and engineering are read together, and the client is best served by confirming span and base ring, cover type, vent locations, access and services while approving the picture. Our own record goes back a long way: in 2009 we moved our research and development into full production and delivered the large tropical-rain breeding base at ZiGong, which drew praise from the client and the local water conservancy bureau. To discuss a bird-groove project, send the site plan and the intended use to sales@cngreenhouses.com or call +86 191 5068 3942. Bozong Greenhouse has manufactured commercial greenhouse structures for above 35 years.

Frequently Asked Questions

Q: What is a bird-groove or bird-nest shaped greenhouse?

It is a dome: a grid shell of short steel members bolted into triangles forming a curved envelope, with no ridge or eave. Roof and wall run as one surface over a round base, so it looks the same from every side.

Q: How does a domed greenhouse drain rainwater if it has no ridge or eave?

It sheds in all directions at once, so water reaches the base all round the perimeter and is collected in a ring gutter sized for the whole roof area, with downpipes set by the perimeter and local rainfall.

Q: Why does an irregular greenhouse cost more than a standard span?

Almost nothing repeats. Members, connection plates and cover units are all cut for a position on the curve, so waste and workshop labour rise, and on site the shell needs a crane and temporary support.

Q: Can glass be used on a geodesic greenhouse?

Yes, but each pane is cut to a different shape and the weight the grid carries rises, so cost goes up. Polycarbonate board tolerates the geometry better; film is easiest to bend but has a shorter life.

Q: Is a bird-groove greenhouse suitable for commercial crop production?

Only in particular cases. The curved shell wastes volume between benches and cover, rectangular benches cannot tile a circle, and light in the lower band is uneven, so it suits display and visitor use.

Q: What should be settled before an effect diagram becomes a built project?

Span and base ring, cover type, vent locations, access, services and drainage outlets. A drawing shows proportion and look, not member sizes, snow and wind loads or cost, so picture and engineering are agreed together.