The Kenyan top bar hive is a trough-shaped hive that originated in Kenya under the direction of Canadian bee researcher Dr.Maurice V. Smith, sponsored by the Canadian International Development Agency under an initial four year project begun in 1971. The Kenyan TBH is differentiated from the other common design, the Tanzania Top Bar Hive, by having sloped sides (intended to minimize attachment of the comb). Reports vary as to how well this end is achieved in practice, but it is worth noting that this design appears to be preferred among top bar hive builders and designers in the USA and Europe, including Les Crowder, Marty Hardiman, Michael Bush and Phil Chandler and Wyatt A Mangum. The degree of slope varies, but 30 to 40 degrees from the vertical seems to be most common.
Because of its sloping sides, the Kenyan hive conforms more closely than the Tanzanian in its trapezoidal cross section to the shape that bees will build their comb in an unrestricted space, i.e. a catenary curve. This, it is claimed, makes for better use of space and more efficient warming of air in winter than is the case with a rectangular cross section.
Entrances may be arranged at the ends (Hardiman, Bush, Mangum) or the sides (Crowder, Chandler). Like all things in beekeeping, there are and always will be arguments for and against, but bees are adaptable and will make use of whatever is provided.
Top bars are wooden, usually 1 3/8" (35mm) wide and anything from about 15" to as much as 24" long, although the average is 17" - 19". Some form of guide is usually provided to encourage bees to build straight combs - a big help to the beekeeper, but not necessarily the first choice of the bees. This can be a simple groove cut in the underside of the bar and filled with wax, or a thin strip of wood fixed to the bar. Some beekeepers incorporate vertical guides to help support comb, although this is more common in the Tanzanian pattern, where a wide, rectangular slab of comb would otherwise be unstable. Mangum cuts a groove in the top bar and glues with beeswax a 1.5 inch strip of foundation as a guide or uses some old comb
Left to their own devices, bees tend to build comb in a series of catenary curves, similar to the shape made by a heavy rope or chain, which is suspended by its ends. Because of this, the 'V' shape of the Kenyan hive is a better approximation to the shape of natural comb than a simple, vertical-sided box. Hence the Kenyan hive enables bees to build in a way that is close to their natural preference and reduces their need to build 'spurs' to attach the comb to the sides of the box.
There exist several arguments for differing angles of the slope that the side of the hive follows.
The argument for 30° follows that in a perfectly formed hive, the comb cells will be built parallel to the bottoms of the Top Bars. It can be observed that each side following build out of the top bar would be 30°. More specifically, a two dimensional 360° geometric object is divided into 6 equal angles (360° / 6sides = 60°), because a flat surface of the cell is parallel to the top bar, by dividing that angle equally for each side of the comb would dictate 30° on either side of the buildup. Therefore if the walls are built at 30° (or slightly less), when the bees are building comb, the bees will tend to keep the edge of cell walls straight and not attach them to the sides of the hive.
A slope of 90° would actually be a Tanzania Top Bar Hive.
Some beekeepers who use Top Bar Hives claim that they see no real difference in the functionality of the angle of the side walls of the hive. All that is important is that the opening of the top bar hive in relation to the trough is not convex.