Wednesday, March 30, 2016

What is R-value?

Apr 1, 2016 - Added link

If you've been following this blog for awhile, you know that Lazutin's book Beekeeping with a Smile and his emphasis on insulated hives has greatly impacted my thinking regarding hive construction.

My first insulated hive which proved amazingly
productive in the summer and warm in winter.

Why am I sold on insulated hives?

First, there was that original insulated hive that I built last year. I built it as an experiment, hoping to help my bees overwinter in my harsh New England climate. However, what I found was that not only did it over winter beautifully (and ate way less honey than the other non-insulated hives), but it was far more productive in summer because it didn't beard. As a result, I'm working on retrofitting my existing hives one by one. Going forward, any new hives will be built with insulated walls and roofs, too. Yes, it takes more time and $ to build them, but for me, the extra cost is worth it because:
  • It's more natural for bees to live in a well-insulated cavity.
  • The bees are more productive in the spring, summer, fall. 
  • The bees seem better able to move in the hive during winter in order to reach stores. In my climate, sometimes the lateral movement required in a TBH can be more difficult for bees if they're too cold.
  • Bees that are productive/overwinter successfully provide more honey and splits that you can use to multiply your bee yard or sell. Not to mention, an extra $30 in building materials is nothing compared to paying $165 to replace bees that died. That's all money in my pocket!
  • No winter wrapping. To winterize an insulated hive, I add a few screens over the entrances and fill the back of the hive with straw. That's it. 2 minutes and done. BTW, wrapping hives is a task that I truly hate. It's so cold at that time of year my fingers don't work. And if you have to feed them mid-winter, you have to unwrap and rewrap them all. I did that once while trudging through snow up to my thighs. It was the pits.
  • Less work and more peace of mind. In the spring, I don't have to unwrap hives (which I've heard can confuse some of the foragers who left before the hives were unwrapped). I also don't worry about weird cold snaps because I know the bees are snug.
So anyway, I've become a huge advocate for insulated hives. Of course, most people think that I'm just talking about hives with thicker wood walls. I suppose 2" thick wood walls are better than 1", but that's not my point. I'm talking about hives with some serious R-value in the walls and even more R-value above the bars. That's really important, btw. Moist air condenses on the coolest surface first (think of the condensation on a cold drink on a summer day), and you don't want that water condensing over the bees. So keep the roof super warm. Keep the walls nice and warm, but not as warm as the roof. You can leave the ends/bottom, which are furthest from the cluster much colder if you want (i.e., not insulated).

So what is R-value?

Basically R-value is a measure of how well a material resists transferring heat. Higher R-values provide more resistance. In other words, the greater the R-value, the better your material will insulate.

Here is a short video that explains R-value more eloquently than I could.

Given equal thicknesses, do all materials have the same R-value?

No. Every building material has a different R-value. The R-value for glass, wood, brick, drywall, etc. are all completely different. Different thicknesses will also have different R-values.

Let's go back to the idea of thicker wood walls. 1" of wood is rated about R1.5. It's a little lower than that, I believe, but I'm bad with the maths, so I round up to simplify. Anyway, that's not very warm. So if you double that wall to 2", you've got R3. Better, but still not great.

I think feral bees prefer something like 6" of wood in the walls -- that's 6" of punky wood, which has a greater R-value, btw, than the solid wood boards you find at your local dealer. (Don't quote me on the 6". You can read Lazutin's book. It might actually be thicker than that.) In any case, to simplify and compare apples to apples, let's say that 6" of wood in a feral bee tree is about R-9. That's a minimum of 3 times greater insulation than 2" of wood. It's probably starting to make sense now why I'm not advocating simply using thicker walls (at least not for my climate). I'm advocating adding insulation!

So how do I build more insulation into the hive?

I've taken Lazutin's advice and started building hives that have double walls -- just like you'd build a house. There is an exterior wall and and interior wall. The space in between those walls is filled with foam board insulation. (I like foam board in the walls because it's really easy to work.)

A hive in the process of being retrofitted with insulated walls

I also like hinged roofs that are full of insulation. I prefer the fluffy roll type insulation in roofs because you can get higher R-values for less money. The minimum R-value I would use in the roofs is R-13.

Batting type insulation made from recycled denim in roof

How do I calculate R-value?

If you do a Google search, you can find lists of R-values for different materials. Here is a portion of one such list. It's important to pay attention to the thickness of the material being rated.

Insulation will have the R-value printed right on them. Here are a couple of examples.

1 1/2" thick purple foam board on left has R-value of R-7.5
Recyled denim insulation on right is R-6.7, so I used 2 layers of it in the roof.

Once you know the R-values of all the materials you're using in an area, you can just add them up.

For example, I build my walls like a sandwich. Inner and outer walls are the bread, and insulation is the filling. So I've got a total of 2 wood walls, 1" each (R-1.5 + R-1.5) plus anywhere from 1"-1.5" of purple insulation board (rated R-4, R-7.5 respectively). So let's see how this adds up:

  • R-1.5 + R-1.5 + R-4 = R7
  • R-1.5 + R-1.5 + R-7.5 = R10.5

Do I need that much insulation in my hives?

Maybe not. My hives are well insulated because I live in an area that gets brutally cold. However, if you live someplace warmer, you probably won't need to insulate as much. On the other hand, I still recommend using some insulation, especially above the bars, even in hot weather. Insulation prevents the flow of hot air into a cooler area. In the summer, bees are working hard fanning the hive, and I think it just makes sense to use insulation to keep the bars cool.

Hopefully, this was a helpful explanation of R-value and how it can be incorporated into hive design. 


  1. Thank you, this is great. The pictures and video helps.

    1. Thanks, Mavis! Glad you found it helpful!


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