Stirling Board or Plywood for tops of Roofs

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NoBBy

New Bee
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Preston UK
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National
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I was wondering if Stirling Board is better for the top of roofs than Plywood. I have several shop bought roofs that use Stirling Board and they never seem to have any condensation issues. However my home made ones using plywood seem to get black mold on the underside. The ventilation on my home made roofs is routed exactly the same as the shop bought ones.
 
Moist warm air hits a cool surface and condensation forms.

I have filled in the cavity of my rooves with insulation and it seems to work well and a help for weak and small colonies, large ones on the other hand they perhaps don’t need it.

So for me its ply top with metal covering then 25mm baton around the inside, 25mm insulation, 6mm ply over insulation and then a 7mm baton to give a bee space if needed and to ensure the roof makes contact with the frame of the crown board.
 
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Moist warm air hits a cool surface and condensation forms.

I have filled in the cavity of my rooves with insulation and it seems to work well and a help for weak and small colonies, large ones on the other hand they perhaps don’t need it.

So for me its ply top with metal covering then 25mm baton around the inside, 25mm insulation, 6mm ply over insulation and then a 7mm baton to give a bee space if needed and to ensure the roof makes contact with the frame of the crown board.

My Nuc roof is pallet boards glued and screwed together with cross battens, 30mm HD polystyrene and then lined with 5mm plywood. Covered outside with Shed roofing felt. Enough space under them for a rapid feeder and about 150mm Kingspan if there's any bees in it this winter. Batten round inside rests on crown board as per ...
 
I was wondering if Stirling Board is better for the top of roofs than Plywood. I have several shop bought roofs that use Stirling Board and they never seem to have any condensation issues. However my home made ones using plywood seem to get black mold on the underside. The ventilation on my home made roofs is routed exactly the same as the shop bought ones.

First thing - you don't mention your crown/coverboard.
Does it have holes in it?
Using a vapour-impermeable (and no holes) coverboard keeps the warm (and moist) air within the hive.
Using insulation above the coverboard (even in summer) means that there is going to be little temperature difference between the top and underside of the roof - making the underside of the roof an unlikely spot for condensation.



What I expect you are seeing (or rather NOT seeing) is that, with the vapour-permeable fibreboard, the condensation is actually occurring on the underside of the tin, and the rot is hidden on the top surface of the roof board.
With your relatively impermeable ply, the condensation and consequent rot is going to be in a visible place.

Close off the coverboard, and stop the flow of vapour, rather than trying to deal with its consequences!
 
I have been using a Crown Board with 7mm on one side and 30mm on the other. This can be inverted for treatment or to hold insulation. This year I've left the kingspan on the hives so this has effectively closed the feed hole.

one consequence of the insulation is that the bees' have been filling the top super first. I put 2 or sometimes 3 supers on when they require them.
 

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