Ventilation

I have six hives all with mesh floors. Last winter I had an issue with damp in one hive and had to change the comb on 5 frames due to mould. The colony survived and built up ok but obviously had to draw out new comb. Since then I have cut ventilation holes in all of my roofs (with mesh behind) but the consensus seems to be to have a solid crown board with insulation over for winter which will negate their effectiveness. Was I just unlucky or did I do something wrong? The hive in question along with two others were in a very sheltered spot whilst the others were in a field at the local farm,

How high are your hive stands?

Sorry, but holes in the crownboard, with open mesh floors, over winter, is a recipe for disaster, IMHO.

They need to keep up the temperature of the brood, and a fierce draught can only mean huge amounts of energy (and stores) to do that.

Dusty.

there's no need for ventilation in the roof either if they're properly insulated

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Too much ventilation and that is why hive is too cold. Moisture condensates inside in that way.

Perhaps too small cluster in the room.

If the ground is wet under the hive place the stand on a concrete block

http://www.beekeepingforum.co.uk/showthread.php?t=31604
This is a link to a recent similar thread that may help you
E

Not often that I've said this, but there is an article in the BBKA News (that arrived today) that is promoting the right idea. (OK, he mistakenly thinks that old carpet is a decent insulator … so it ain't quite gospel!)

The combination of these elements seems to work well -
- open mesh floor (without its inspection board)
- no-hole coverboard
- insulation above that
- and a watertight roof on top
This prevents both roof-rot and condensation above the bee cluster. Any condensation will be on the walls - where the bees can safely access it as a water source, and excess can freely drain away through the mesh floor.
I must stress that it is the combination that works - change just one element and you spoil the recipe!

The best insulation you are likely to find (if you find Aerogel you wouldn't want to pay for it) is the foil-faced building insulation rigid foam board sold under a variety of brand names including Celotex, Kingspan, Recticel, and Xtratherm.

The hive in question had a crown board with holes for porter bee escapes. I will swap this out tomorrow when I put in the second tray of apiguard.

As for the insulation, any recommended thickness?

The brief explanation:
Bees prosper best if they can create a temperature of 34C and humidities greater than 75% RH. Both the temperature and humidity require the least input from the bees when the hive is heavily insulated and the top of hive cavity is sealed. The bottom of the cavity can be left open because heat and humidity rise.
Low insulation i.e. standard wooden hives make maintaining both heat and humidity difficult and thus take alot of energy and effort
Condensation is a problem if the condensate is cold as this will remove even more heat from the bees. Cold condensate occurrs in low insulation hives
Ventilation may remove the risk of cold condensate in low insulation hives.
Thus ventilation is only relavent if you insist on keeping the bees cold.


The long explanation takes about hour with another hour answering questions

pigletwillie said:

…
As for the insulation, any recommended thickness?

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50mm thick Celotex is OK.
And can be had in small (car back seat size) sheets for about £5 from Wickes.

Thicker is better, but only comes in big (much more expensive and awkward) sheets - and occasionally in skips!

You can put two layers of 50mm thick inside an empty super, and it'll be nearly as good as a 100mm layer …

itma said:

50mm thick Celotex is OK.
And can be had in small (car back seat size) sheets for about £5 from Wickes.
Thicker is better, but only comes in big (much more expensive and awkward) sheets - and occasionally in skips!
You can put two layers of 50mm thick inside an empty super, and it'll be nearly as good as a 100mm layer …

Click to expand...

I recently bought a big sheet. Took a saw with me and cut the sheet into loadable pieces in W....'s car park.

derekm said:

The brief explanation:

... ...

The long explanation takes about hour with another hour answering questions

Click to expand...

Been there and it's really not as painful as it sounds.
I must take this opportunity to thank Derek for the very informative and useful presentation he gave at our BKA last month.
If it had been up to me Derek, I would have let you continue for double the time.

derekm: Bees prosper best if they can create a temperature of 34C.
Surely during winter without brood present ( 2 months up here in the north) they won't need or attempt to maintain 34 C.

Ventilation of the roof is totally different to gaping holes in the crown board. One is required, the other not. There is a huge ventilation area at the bottom of any hive with OMF. The sooner people realise this, the sooner threads like this will be an unnecessary thing of the past.

masterBK said:

derekm: Bees prosper best if they can create a temperature of 34C.
Surely during winter without brood present ( 2 months up here in the north) they won't need or attempt to maintain 34 C.

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Given that studies in Scotland have shown brood present in most hives in February? (coldest month of the year?) and in a significant proportion in January (another not so warm month).

oliver90owner said:

Ventilation of the roof is totally different to gaping holes in the crown board. One is required, the other not. There is a huge ventilation area at the bottom of any hive with OMF. The sooner people realise this, the sooner threads like this will be an unnecessary thing of the past.

Click to expand...

I concur:
the ventilation of the cavity above the hopefully insulated crown board is to stop rotting of the roof.
The OMF certainly stops a pool of water that can trap bees and permits debris to escape when the house keeping bees are in cluster. But as a significant means of ventilation compared to the entrance? I am yet to be convinced, it really does make a significant difference to the air flow. I would like to see some either measurements or simulation work on that aspect. I might be surprised

derekm said:

I concur:
the ventilation of the cavity above the hopefully insulated crown board is to stop rotting of the roof.
The OMF certainly stops a pool of water that can trap bees and permits debris to escape when the house keeping bees are in cluster. But as a significant means of ventilation compared to the entrance? I am yet to be convinced, it really does make a significant difference to the air flow. I would like to see some either measurements or simulation work on that aspect. I might be surprised

Click to expand...

Its harder for folk to follow a discussion when it dives into detail of a single variable as though that was a completely independent variable.


With closed crownboard holes and an OMF there is perfectly adequate (but not excessive) air exchange between inside and outside. The bees have a 'hot air balloon' or 'diving bell' of warmth. But CO2 and damp are not a problem (or easily managed) by the bees.
The proportion of air exchange due to entrance and mesh floor makes for an interesting academic discussion (with lots and lots of new variable factors), but it isn't central to the basic lesson …

… which I take to be that an open-hole crownboard combined with an OMF produces an environment where there is excessive air exchange, causing the bees to lose more heat (ie energy that has to come from honey stores) and the escaping moist air produces condensation in the cold roof space - which commonly results in roof-rot.

itma said:

Its harder for folk to follow a discussion when it dives into detail of a single variable as though that was a completely independent variable.
...

Click to expand...

to return to the bulk of the question.

An experiment for the OP

Open the front door then the hatch to the loft. Stand in hatch and feel the strong up draft.
Notice how quicky the house gets cold with the hatch open.

Do this again on a cold day and feel how clammy it is in the region immediately above the loft hatch.
This is evidence on a larger scale of the convection heat loss and the reduction in water carrying capacty of the air when you reduce the temperature.

Bees by necessity have the front door open, do you really need the loft hatch open as well?

Ever seen a wild colony happily living with anything other than a small opening for getting in and out?....no, neither have I....and I've seen more wild colonies than most.