Designing a bottom board with a removable screen

Motivation for the removable screened bottom board

I wanted to make a screened bottom board to facilitate mite monitoring and sugar dusting. I also wanted a bottom board design that allowed more space under the hive for winter. My main motivation for designing this variation of the screened bottom board is so I can clean out dead winter bees with greater ease, and worry less about the bottom entrance getting clogged up with dead bees.

The Screen

Screened frame removed A framed screen was created by gluing together a sandwich of 1/8 inch hardware cloth and wooden slats.

Tips. If you can find it, use stainless steel hardware cloth as it will hold up better to any formic acid exposure that may happen while performing mite treatments. Of course, If all you can find is galvanized, removing the screen during treatments is an option.

Rabbets were cut into the side walls of the bottom board structure to support the screen.

bevel on framed screenInspired by the concepts in Walt Wright's propolis Article, a slight bevel was cut into the sides of the framed screen in the hopes of minimizing the accumulation of propolis between it and the frame rest.

The back of the bottom board

back of bottom board with hinged flap opened.The back of the bottom board is comprised of two pieces of wood:

The top piece:

  • Is screwed in place.
  • Blocks the area containing the screen and the space above it.

The bottom piece:

  • Is hinged to the top piece for the purpose of allowing easy access to the tray when performing mite counts.
  • When closed, it prevents bees, mice and wasps. from accessing the area between the screen and the tray.
Caution. Distance between the screen and the tray is two inches to reduce the possibility of varroa climbing back up into the hive. I've seen references to 1 and 5/8 inches being sufficient, but some say to use two inches. I decided to play it safe.

Bottom view of framed screen.The concept is that during the fall, when winterizing the hive, the screened frame can be removed from the bottom board while all the hive boxes remain in place. My hope is that the screened frame can be pried up from the area inside the hinged flap in order to loosen any propolis. The top portion on the bottom board's back can then be unscrewed and removed to allow the framed screen to slide out. Thus converting the hive to a simple solid bottom board.

The Tray

debris on bottom board trayThe tray is just a simple piece of corflute that slides into a groove in the side walls. I run eight frames to a box. The above photo shows the screened area is large enough to allow debris and varroa to fall through from spaces between and around all eight combs.


Entrance with reducers in placeThe framed screen extends above the height of the landing board so that entrance reducers are prevented from being pushed too far back into the hive.

In the winter, when the screen is removed, the entrance becomes taller. changing from 14mm to 21mm tall.

Note: A 14mm entrance height on my modified warré hives works out to a total entrance area around 40cm2. That's about three times the entrance area preferred by swarms looking for a home in the wild, however, 40cm2 is roughly equivalent to the entrance area found on a langstroth hive using a 3/8" high opening. Perhaps the large difference in feral vs managed entrances is based on the fact that it's not unusual for managed hives to reach a volume that is three times greater than that of the typical colony in a tree cavity?

As my intended mouse guard is just a piece of hardware cloth wedged into the entrance, I suspect the 21mm tall winter opening will allow the bees more room to navigate the tiny gaps of the hardware cloth.

Visual patterns

pile of bottom boards
The above photo shows a stack of the first four entrances I built. I painted each landing board with a unique visual pattern in the hopes that it would help the bees in recognizing their own hive and therefore reduce the drifting of bees between different hives. This was inspired by the concepts discussed in Tautz's book The Buzz about Bees: Biology of a Superorganism. The idea is that unique patterns are more useful to bees than simply painting each hive a different solid colour.

Tips. The bees won't care if the designs are as ornate as those in the photo above. Simple variations will do. The key differences, from top to bottom, between the pictured bottom boards are:

  • A horizontal line with lots of vertical lines
  • A small semi-circle on the upper edge with some radial lines
  • A big semi-circle on the lower edge
  • Three circles with a few horizontal, vertical and radial lines

Other uses for the framed screen

The framed screens may also be used to serve other purposes. For example, if I want to over-winter a weaker hive stacked on top of another colony, I can place the framed screens from both colonies between each other like one might ordinarily do with a double-screen board.

Testing it out

I've added these to 5 hives for the 2015 season. I'll update here once I decide if the experiment was a success or a failure.

tray of dead winter bees

One thought on “Designing a bottom board with a removable screen

  1. Thomas Whichard

    Greenville, N.C. USA 3 hives, 2 Lanstroths 1 top bar just finished 48" Long Hive.
    I have used the slide out sbb and it makes spring clean up much easier. The problem I had was I also used oil pans under the screen for mite, SHB, and wax moth control. Bees seem to be curious when you open the door to slide out the oil pan or sbb and they all come out to see what is happening. When I put it all back together they still managed to get into the oil pans and of course die. After 2 seasons of this I rebuilt everything with the sbb secured and just a door to slide out the pans. I have not lost a bee to the oil since, and yes they will put propolis around the sbb if they determine they need to for too much air or critters coming in. Part of the enjoyment of these fantastic creatures is trying new things. What works for one hive may not work somewhere else. I like the idea of the designs to help prevent drifting, I am trying that too. I just found your site and have enjoyed the topics, keep them coming. Happy bee keeping and good luck!


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