condensation on top of the ply crown board.

[drstitson]

The OP stated that it was a wooden hive, with ply crownboard and 25mm poly in the roof.

Now it has suddenly become a full blown MB poly hive.

STOP MOVING THE GOALPOSTS!!!!!!!

 

[greatbritishhoney]

am I being painfully stupid here or this simply a case of moisture soaking through a thin bit of plywood?
If so, where is the mystery and what is the point of the thread?

Not trying to be offensive to the OP, you understand, it's just - I don't get it

 

[itma]

I'm getting clear condensation through a ply crown board under 25mm polyurethane foam insulated roof in a wooden hive. The condensation shows as a circular damp patch in the middle of the board about 75% of the diameter. there is mold growth at the edges of the board
As I suspected (and as stated in building regs) untreated plywood isnt a vapour barrier

"I suppose that there is too much space in the hive" no its full of bees
" too much ventilation " No, brood box is a"made in Finland" polystyrene foam one with just the supplied open mesh floor and entrance.
...

At least one of us is confused ...

 

[drstitson]

MB poly hives are designed to be used either without a crownboard or with a thin sheet of plastic sheeting.

Jamming a sheet of ply of several mm thickness into the space will allow moisture to creep from the open edge seams and up under the roof. anything over 1-2mm is too much unless you are actually engineering a formal close-fitting framed structure.

DOI: currently planning on making a few custom shallow poly ekes in case of needing to feed fondant in spring.

 

[user 6228]

The OP stated that it was a wooden hive, with ply crownboard and 25mm poly in the roof.

Now it has suddenly become a full blown MB poly hive.

STOP MOVING THE GOALPOSTS!!!!!!!

Only the broodbox and the base is MB poly... the supers and the roof are wood from a thxxnes cedar kit. The only mod to the roof is the insertion of 25mm of kingspan (PU foam)

 

[user 6228]

am I being painfully stupid here or this simply a case of moisture soaking through a thin bit of plywood?
If so, where is the mystery and what is the point of the thread?

Not trying to be offensive to the OP, you understand, it's just - I don't get it

Well done ... Thats it, I was trying to make the simple point that that the cheap plywood and its glue doesnt do anything significant to prevent moisture migration... not a big thing but it should prompt others to change crown board to be non-porous or change the insulation to porous.
I was trying to show that unfortunately The common fix of sticking kingspan in causes condensation on top of the plywood board.

A correx or similar crown board is needed with kingspan or similar.

A thin bit of plywood crown board will need a deep layer of wool on top of it instead of the kingspan.

Seems some have got the wrong end of the stick..

btw the wooden supers, crown and roof are getting retired soon

 

[drstitson]

at last we get to the point and it was worthwhile.

my modified convecting crownboards all now have 2mm perspex sheets between the open chamber below and the insulated block above. That will remove the problem described AND allow inspection of fondant supplies etc.

My simpler insulated pent composite crownboards again will all have correx first line between bees and insulation. only problem with these is you can't inspect as easily.

 

[user 6228]

is your idea with the perspex sheets to have
a flat sheet separating the two chambers.
a second pent roof sheet underneath it with covered slot in the ridge and gaps at the sides?
condensation forms on the first sheet falls and hits the top sloping side of the second sheet and runs off at the side?

 

[itma]

...my modified convecting crownboards all now have 2mm perspex sheets between the open chamber below and the insulated block above. That will remove the problem described AND allow inspection of fondant supplies etc.
...

So, have I got this right, you will have brood/standard crownboard(with feeder hole)/plastic feeding eke±fondant/perspex sealing layer with no holes/(no airgap)kingspan(no special airgap)/roof ? (A visual aid might be appropriate!)

A few handfuls of rockwool in the roofspace above the crownboard (with clearer holes) sounds a whole lot simpler (if the little deevils stay where they belong) even if it has to be moved to check the state of fondant ...

How low do night temps have to go, to make any of this worth worrying about?

 

[drstitson]

derekm - No. basically just an box somewhere between eke and super depth. Inside, from bottom up - pent correx followed by 1-2 blocks of insulation. no air gaps. In this design the condensation will run down the inside of the correx to the outer walls of the hive.

itma - my original more complex engineered design features 2 components. lower half is an eke with ply sheet base. the base has a central hole, two long lateral slots and tapered channels joining the 3 (dead space insulated). above this (close coupled with hive fasteners) is a ply and pine wooden box with block of knaufboard inside. New version/modification is the sandwiched 2mm clear perspex between the two components. In this design moist air rises from the cluster and then heads towards the sides of the hive before condensation occurs. This version just modifies the natural convection currents that occur in hives, forcing condensation away from the cluster.

will dig out photos if possible - unfortunately the videos i took of proof of principle using a large cardboard prototype and smoke column didn't come out well.

 

[Finman]

"I suppose that there is too much space in the hive" no its full of bees
" too much ventilation " No, brood box is a"made in Finland" polystyrene foam one with just the supplied open mesh floor and entrance.

"the hive is cold" No,the top of the brood frame is between 39C and 41C

Condensation does not require cold Weather or Winter, only a surface below the dew point temperature.

Being Finnish I trust have you seen the condensation on the door window of a Sauna

i surely understand better insulation and condensation better than the wholr brittish gang in this forum


RULE 1 : CONDENSTATION HAPPENS IN THE COLDEST PART OF THE HIVE.

Polystyre hives are 3 cm thick. Their insulation value is better than styrofoam board because of smaller air bubbles.

Add thickness of the inner cover that walls are colder than cover.

Put the mesh floor smaller. make no sense that the hive has good insulation but bottom is missing. Mesh floor is ment to varroa, not for wintering bees. Its name is "varroa floor".

 

[user 6228]

i surely understand better insulation and condensation better than the wholr brittish gang in this forum


RULE 1 : CONDENSTATION HAPPENS IN THE COLDEST PART OF THE HIVE.

Polystyre hives are 3 cm thick. Their insulation value is better than styrofoam board because of smaller air bubbles.

Add thickness of the inner cover that walls are colder than cover.

Put the mesh floor smaller. make no sense that the hive has good insulation but bottom is missing. Mesh floor is ment to varroa, not for wintering bees. Its name is "varroa floor".

You obviously and clearly dont understand condensation and insulation better than at least one of the other persons on this forum.

rule 1 is wrong - go read up on dew point. Condensation occurs at any point where there is a surface below the dew point temperature of the surrounding air.
The top of the hive can be at 38C with a dewpoint of 34C and a roof surface at 32C and condensation occuring while the floor air is at 20C with a dew point of 10C. with the floor surfaces at 17C.

The foam in question in the roof is polyurethane which is better than polystyrene i.e. 0.21W/m versus 0.3W/m. Styrofoam is polystyrene. The conductance of a foam increases with its density so high density polystyrene conducts more not less.



You also appear to have problems with your calendar. you appear to think September is simultaneously winter and summer. Its neither, its Autumn.

you argue its summer "there fore you cant have condensation" and then argue "its winter so the ventilation is wrong".


Your remarks about nationality are irrelevent at best.

 

[Poly Hive]

Ah bless the first winter argument breaks out... and over poly too, wonderfully entertaining.

PH

 

[drstitson]

as promised. pics of mark 1. obviously national hive version (1st & 2nd pics) can be orientated two ways (hot or cold) whilst the dadant ones can potentially come in two flavours (3rd pic).

 

[user 6228]

Ah bless the first winter argument breaks out... and over poly too, wonderfully entertaining.

PH

Over poly? OH NO IT ISNT!!! just getting into the Panto mood a bit early

 

[drstitson]

"Ah bless the first winter argument breaks out... and over poly too, wonderfully entertaining."

I can't wait until we get back onto the correct % oxalic for festive dribbling!!!!!

 

[itma]

... The top of the hive can be at 38C with a dewpoint of 34C and a roof surface at 32C ... while the floor air is at 20C with a dew point of 10C. with the floor surfaces at 17C.
...

While I understand that those values might be possible, that amount of variation would indicate grossly inadequate air movement, wouldn't it?

 

[Finman]

.
Derekm, you have condensation problems, not me.

But a few yars ago I took a photo. There were large water droplets and some "pools" over top bars.
Reason was that I had 2 cm thick polystyrene board as inner cover. My friend engineer told that covers insulation value is smaller than walls'. Yeas it was. The walls were polystyrene and 3 cm thick.

I had 2 cm wooden board as inner cover on poly nuc. boards were totally wet because of condensation..

With 7 cm thick insulation problems has been away. I do not use feeding hole in the centre of cover. Mice loved them.

 

[eric]

Welcome back Finman I missed you

 

[Finman]

.

Condensation I may see every morning on under surface of rain cover.
If insulatig material has contact to rain roof, water returns to the material and it will have some litres water.


Outer cover is metall plate. The heat and moisture rises through the 10 mm wood panel and 70 mm insulation. When it meets a cold outer cover, it makes dropets. Then it must be a good ventilation/ draft in he loft.

I have lids in my outer covers. It keeps the wooden parts dry.

Condensation in the inner roof and wet material means strong mold formation.