This question follows from my previous question about leveling my OSB shed floor. I didn't realize until I received several comments and suggestions that said question actually has two focuses:

  1. How do I level my OSB shed floor?
  2. How do I seal my OSB shed floor against critters, weather, and temperature?

Thus I'm copying my proposed "leveling" fix because it seems that was actually more appropriately a weatherization fix.


  • Pretty sure this OSB is not weatherized or pressure-treated already (it is golden tan, not dark green)
  • I don't think the floor is inusulated, or if it is, not very well.
  • I've spent time in the shed overnight sleeping in the loft. It gets cold relatively quickly in the winter, but takes until about 1 PM to get nicely warmed up.
  • The doors have a tight seal for just 2x4 framing (barn style double doors)
  • The windows are closed tightly and are vinyl, I believe
  • The roof is metal
  • There is no insulation between the rafters

In summary, I know the roof and walls are not insulated and I'm thinking If I can seal the floor and close up all the cracks that will help the situation tremendously. But, maybe I'm wrong. Imagine the whole shed is insulated, but the floor still has these gaps:

Q: Will I have problems with weather and temperature regulation because of those gaps?

Q: If I caulk the seams will I then find out those gaps were on-purpose and necessary for expansion and contraction??

When I was assisting the foreman on a vinyl siding job, he told me something that was NOT INTUITIVE. He said you have to cut the siding about 1/2" shorter than you need so that there is room for expansion. I wouldn't have known that if I was going about doing it in a DIY fashion and I'm concerned there may be some non-intuitive knowledge that I'm missing that is detrimental to me not messing things up in my attempt to fix things.


So, to recap here are my concerns:

  1. I believe that cold air (in Winter) and heat and humidity could find an easy way into my shed while I'm in there through gaps in my floor seams.
  2. I also want to reduce the free access cockroaches, wasps, fire ants, and other tiny pests have to get inside my shed. I believe that caulking the floor with silicone will solve my concerns about the floor and make it airtight.
  3. BUT, I am concerned that I have a knowledge gap and what I don't know about what I plan to do could cause other problems and make things worse. I certainly don't want a buckled floor!

I'm really looking for guidance from those who've "been-there-done-that".

  • Please create the following tags for this question: tiny-homes, sheds, outbuildings, and weatherizing. Thank you. Jan 16, 2021 at 13:59
  • 1
    OSB will obviously vary somewhat (as do all manmade boards) but here it is usually quite tolerant to weather, so much so that it's used outdoors with no added protection and in that context it can hold up quite well for at least a couple of years. So assuming your stuff is roughly similar as a shed floor it's not exactly being put under moisture stress. Assuming the shed is built right, to have airflow underneath, the least of my concerns would be the floor! Other than the levelling issue I'd be much more focussed on the roof, and secondarily the walls if I wanted to ensure weatherproofness.
    – Graphus
    Jan 16, 2021 at 17:07
  • I am transferring this to the DIY stackexchange site where you should get better answers.
    – Ashlar
    Jan 17, 2021 at 3:22
  • @Graphus My neighbor has a shed hes had for 20 years and it has holes in the floor, possibly from motor oil spilling on it, or maybe simply from the high humidity in deep south. I want to seal my floor against ending up like his Jan 17, 2021 at 23:04


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