With respect to hive insulation, this is what I do.
I certainly don't have all the answers and very likely few. I can offer help in sharing how I do my best to cut cold related losses. I went to Lowes and purchased a 10 sheet bundle of Johns Manville R-9.3 1.5-INX4-FTX8-FT AP FOILSHT:
https://www.lowes.com/pd/Johns-Manvi...x-8-ft/3851109and cut it up into various sized smaller pieces that were 18.25" x 14.6875" for 10 frame boxes and 18.25" x 7.75" for nucleus colony boxes. This size allows on my hive boxes a perfect fit for the sheet of insulation to slide into the inside of the box and create and insulation layer on top of the hive. Since it is still not too cold to feed sugar syrup at my latitude, I use 1 gallon syrup feeder buckets on top of the inner cover. I place an empty deep box around the feeder buckets on top of the inner cover and then place 1 or 2 sheets of the cut to fit insulation board inside the deep box around the feeder buckets on top of the buckets. This creates a nice air pocket under the insulation boards that aids in limiting heat loss through the top of the hive. I do the same thing with my nucleus colonies with the only difference being that I use 2 half gallon glass jars with the punched hole lid to feed through the top of the nuc using a feeder box made out of a medium nuc box. I try to give each hive 2 sheets of this insulation which in theory provides nearly R-19 insulation. Nucs I applied this insulation to demonstrated more and earlier activity as compared to those that got none.
You can cut a half inch hole in the foam board for ventilation of moisture or install an Immerie Shim under the inner cover for the same thing.
The outsides of the hives I use either a Bee Cozy, on some I am experimenting with the Easy-On Beehive cover, and the nucs get pushed together and wrapped with layers of Reflectix bubble wrap insulation.
I have Broodminders is a number of my hives and I noticed an immediate stabilization and a gradual increase of about 10 - 20 degrees of the daily temperatures inside my hives once I added the above insulation.
Something to consider when treating for varroa mites in the Fall.......as a precaution, I treat my bees for tracheal mites as well with Mitathol. Although tracheal mites are not near the problem varroa mites are, they can cause a hive crash during the Winter if left untreated in more than a few cases. According to our state Apiarist Mike Studer, tracheal mites accounted for a significant percentage of hive losses last Winter.
Another option to consider depending upon how many hives you have is to move them inside an insulated storage building to get them out of the wind, rain, and bad weather. During really cold snaps, you can close the building up but onces the temps begin to get into the 40's you will need to open the building up so the bees can get out to do their purging flights and forage. This what another beekeeper who raises nucs does that lives not far from me.
The above methods are typically NOT taught in beekeeping books and courses. You will have to judge for yourself what is best to maintain the health of your bee colonies. I have long tried conventional measures beekeeping and grew VERY disaffected with losing so many hives. I CAN say that I have been able to significantly cut my hive loses but not entirely. Some years I have gotten through Winter with NO losses, other seasons not so much. Be prepared to start making splits like a mad man in Spring to make up your losses and increase your hive numbers. In early Spring the bees have a tremendous reproductive urge which is perfect for making walk away splits from as many hives as you can. Once mid to early Summer arrives, you will have to raise queens to make splits that reliably are queen right. Last season, I have very good results experimenting with a batch of 50 Saskatraz queens I made nucs with.
One thing is for sure......I am ALWAYS seeking to learn more, keep and open point of view, and adapt with what I learned.
Again, sorry to hear of your hive losses and hope this helps.
