The gap between crown board and roof- why that big?

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derekm 

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I've measured the gap between the roof and crown board on my Thornes wooden hive. Its 35mm, . Is there reason it would be that large and not say 15mm?
 

Nige.Coll 

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Doesn't an air gap offer some insulation ?
In summer a metal roof can get very hot and cold in winter.
It's handy the size it is you can fit a block of fondant under the roof without an eke.
 

jenkinsbrynmair 

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Doesn't an air gap offer some insulation ?
not when you have two vents in it also

I think it Just happens to be a handy size of timber - inch and a half PAR
No need for anything up there though
 

Newbeeneil 

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I've always assumed it was to allow air to circulate via the porter bee escapes and mesh vents at the sides.
If the roof sat directly on the top it would block both airways! Thank goodness for matchsticks!
 

derekm 

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Doesn't an air gap offer some insulation ?
In summer a metal roof can get very hot and cold in winter.
It's handy the size it is you can fit a block of fondant under the roof without an eke.
that just it! its just that bit too high... it has convection currents in it a bit lower and it wouldnt and would insulate better. People stuffing carpet in there in days of old were probably just making the air gap small enough to insulate despite the carpet being damp and orrible. just seems strange some one picked a thickness of wood just on the wrong side.
 

derekm 

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not when you have two vents in it also

I think it Just happens to be a handy size of timber - inch and a half PAR
No need for anything up there though
quite possibly!
Was there ever an idea of putting fondant or extracted frames up there?
 

pargyle 

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quite possibly!
Was there ever an idea of putting fondant or extracted frames up there?
Who knows ? The strange ideas about beehives have been handed down from generations of mis-informed beekeepers ... probably just as JBM suggests or a measurement taken from a hive roof made in 1912 ...
 
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jenkinsbrynmair 

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when I put together new roofs, I don't even bother putting in those battens - I just put them through the table saw to make rims for new crown boards or Demarree boards
 

Ian123 

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The only real use for the gap is to provide space for fondant, the battens are there I’m sure only to add strength to the roof construction.
 

jenkinsbrynmair 

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the battens are there I’m sure only to add strength to the roof construction.
no - they provide no strength whatsoever and are only tacked in place, I don't have them in any of my roofs and they can take my weight no problem when I use them as a hop up
 

hemo 

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I stick another 40mm PIR in there on top of the 50mm in my polycarb CB's.
 

derekm 

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Who cares? ;)
The size of means its convects and it shows up on the CFD as a pretty pattern called Bernard Convections. So I have to talk about in my thesis, and show I understand the fluid mechanics. I need to put in the Bee keeping why as well. Note: If heat a shallow pan of cooking oil you can see bernard convection patterns.

bernard.png
 

rolande 

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We've bought economy dadant roofs from thornes in the last couple of years made of Russian redwood which don't have those battens at all so even thornes don't think they're a necessity.
 

Newbeeneil 

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We've bought economy dadant roofs from thornes in the last couple of years made of Russian redwood which don't have those battens at all so even thornes don't think they're a necessity.
They certainly are not necessary, as has been said previously they add minimal structural strength. As I said flippantly earlier I am of the opinion that they are there purely to allow the air to circulate within this void and allow air to rise through the Porter bee escapes and exit via the meshed vents.

My roofs are constructed using 150 x 15 cedar screwed and glued onto 12mm ply or OSB with no battens. I've never had one break yet.
 

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