Insulating roof with expamding foam.

Beekeeping & Apiculture Forum

Help Support Beekeeping & Apiculture Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


House Bee
Jul 5, 2020
Reaction score
Nairn, Highland
Hive Type
Number of Hives
I picked up on the consensus that a good layer of roof insulation goes hand in hand with the concept of all year round open mesh floor. I could just have picked up some 50mm PIR board but only have one hive and a 2400 x 1200 sheet is awkward for me to transport. A recent DIY project involved some injection of expanding foam which used only a small fraction of the contents of an aerosol. Anyone who has tried to store this stuff for another job will know that unless you use it within a few weeks it's likely to go "off". So, keen not to waste it, I thought it timely to try to use it for the roof.

This is a 50mm deep roof so I wanted to fill the full void. I found an old piece of kitchen unit particle board about 18mm thick and slightly bigger than the square of the roof. I drilled some 10mm holes in it, (they should have been a bit bigger); there were nine of them in the pattern you get on a domino. I greased the side which would face the foam using some silicone pipe lubricant, but could have used anything oily. Then I sprayed the inside of the roof with water which helps the cure of the foam. I think I should have clamped this board in a few places but I simply placed a concrete block on it. Then I injected most of the contents of the canister into the centre hole. I maybe should have used a bit less and if I did it again I think I would spray an equal amount in each of the nine holes. Obviously, foam expanded out of the holes but then cured and blocked them, which lifted the board at one end; better it did that rather than force the roof apart!

Within half an hour I took the board away, sprayed down the fully set foam with more water from the hosepipe and then left it to dry and evaporate any chemical vapours overnight.

I now needed my 50mm overhang back so that the roof would be secure, so after trimming the surplus foam, I effectively made a simple 50mm deep eke which was glued and screwed to the existing roof-lip. When re-painting it I (literally) slapped on a bit of paint over the foam to seal any loose particles. The paint is exterior grade, water-based and is another bit of useful re-purposing of leftovers.

The execution of the job was very rudimentary and the finished article is not pretty. It would have been easier to use an offcut of insulation board. But it was satisfying to do this effectively for nothing and to get the job done right away on a lovely warm day rather than having to wait until the day I had the proper materials.

I left it in bright sunshine on a very windy day to allow it to "air" and hopefully clear of any chemicals. It's now back on the hive and keeping the bees so warm, I'm sure I saw smoke coming out of the entrance this afternoon. ;)


  • roof.jpg
    591.9 KB · Views: 50
I once made a nuc body out of 12mm ply with correx board on the outside with a 25mm void between them. I clamped the correx with some ply offcuts and carefully injected the foam...... unfortunately not carefully enough as the foam expanded and blew any areas of correx, not tightly clamped, up like a balloon :)
I'm sure it was nice and snug but looked more like a badly wrapped parcel....:icon_204-2::icon_204-2::icon_204-2::icon_204-2:
I managed to pick up some cellotex for my hive roof via my local Freecycle group. It was completely free, and there was enough spare to make a solar wax extractor too.
Try skip diving, local DIY shop may have some damaged board, anyone upgrading insulation on their house??

Latest posts