Does you attic have ventilation? If it does then you be trying to dehumidify the outdoors. If it doesn't then adding ventilation will should lower the humidity and attic temperature.

Hi Mike! I have thought about a fan ... currently it is not purposely ventilated, but it certainly is not airtight. I do not have an attic fan. Considered just doing that as well, but not sure how effective they are. I am also concerned about operating a dehumidifer in a hot attic and wondering if this is actually a fire hazard.

Thanks all!

You have to make sure that your rafters can hold the weight of what you are proposing to store. .

Store your items in a plastic container that is sealed. And then put them in the attic if they can take the heat. You will not have moisture problems.

If you put plywood on the insulation it will just pack it down and defeat the purpose unless your rafters are tall enough to support the plywood.

You will be dehumidifying the outside if you put a dehumidifier in there.

It will be cheaper for you to rent a humidity controlled storage unit in the long run.

@Kathi ... I do need to go up there again and check how exactly the roof was constructed to see how much load I can put up there. This is a 1921 home and my air handler is already up there. I was probably going to put down a riser so that I can not impact the insulation. I also wont plywood the entire attic ...mainly looking to put some plywood down in an area with easy access to the attic ladder for some basic storage.

When we built our Florida home about 15 years ago, we installed a radiant heat barrier.

It's like foil that is put up on the roof of the home (inside) that reflects the heat.

See the attached you tube video. Perhaps this would help your cause.

https://www.youtube.com/watch?v=N0-YD32ujYY

You can have passive ventilation with a ridge vent and soffits. An attic fan can cause more harm than good if you don't have adequate intakes.

Soffit vents are the first step, a lot more of them are almost always needed. Measure the actual openings behind the grills, not the grills. Here's a web site that can help: https://www.owenscorning.com/roofing/components/vent-calculator

The positioning of attic vents is also a bit complicated, in that a pair of vents staggered can end up acting as a paired intake/exhaust and not do squat for yuor attic venting needs. If you have sufficient linear feet of ridge, ridge vents are great...if not, you have to position vents carefully.

In a warm humid environment, totally air sealing the attic and placing the insulation at the roof deck plane is the better option.

https://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation

https://www.buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates

https://www.energy.gov/sites/prod/files/2015/02/f19/ba_webinar_2-12-15_lstiburek.pdf

https://www.dean-ac.com/newsite/wp-content/uploads/2014/12/4-Understanding_Attic_Ventilation.pdf