How to insulate a metal shed

I have a 10X12 metal shed I'm converting into a home office. It's a shed, meant to be a shed. It doesn't have ridge or soffit vents. I want to air condition and for a few days I'll heat it as well.  It's a wood frame with metal walls and roof. The building is in SW Florida. I do plan on finishing the interior, probably drywall. Not sure, but I do want a finished look inside.

I have read a lot of info and it seems like the info I'm getting is conflicting and confusing so I'm turning to you folks because there seems to be very little noise, just info.  

What is the best way to insulate the walls and ceiling? Do I have to add venting to avoid condensation, or do I need to use a particular type of insulation? As far as condenstaion, are we talking water against the inside of the metal walls, or on the outside of the finished walls?

Does this make any sense?

I keep coming up with ideas and honestly for a 10x12 it might be easier and maybe cheaper to go with a new wood shed from a box store.   At least they will be decent construction that you just need to insulate.

In reply to Stampie :

If I didn't already have this shed, I would do that. 

In the winter, you will get condensation on the interior walls. If I don't stay on top of the humidity in my shop, it starts raining. 

That shop is insulated with fiberglass insulation. One of the better things I did to keep it cool in the summer was mirror film on the windows and solar panels on the roof - solar gain is a big thing here and the panels shade the roof for me. The AC has to work harder than you'd expect to keep temps under control. 

Ventilation. Spray foam($$$) will alleviate that, but with all the issues Keith mentioned about condensation, a wood framed/sheeted structure is a better bet. 

Most inexpensive metal buildings are pretty "leaky" and let air in/out through seams, gaps, penetrations, etc so you may not need tons and tons of ventilation with traditional building materials, although adding it probably won't hurt anything.

Can you see the backside of the metal when you're standing inside? If you can, there's no vapor barrier installed. That's expected for a shed, but for a conditioned space with high humidity you'll want a vapor barrier between the exterior material and the framing/insulation.

Closed cell foam (either spray foam or rigid panels) can be both insulation and vapor barrier if it's at least 1.5" thick. Spray foam would seal the building up tight, so you'd need some air exchange and a good mini split. Doors and windows of a shed can be difficult to seal up and insulate, so keep that in mind.

Condensation will occur on a cold surface when warm/moist air meets it. The idea to avoid condensation is to keep the moisture on the exterior with the vapor barrier, and then put as much R value between the conditioned space and the exterior so the temp difference is negligible. Dehumidify and condition the air inside and you won't see condensation.

I agree with  Keith that anything you can do on the exterior to minimize solar gain would be beneficial. Shade the building, paint it lighter colors, etc.

This is the inside of my metal building. There are no metal fasteners, etc. that go to the outside with the exception of the insulated garage door frames. (you can't do this now,I know) The only place condensation happens is on those frames. I only notice that when I raise the door. It's dry as a bone in here all year. The key is to have no metal going from inside to outside. It may get humid in a small shed like that from you breathing or making coffee but it won't rain if you insulate it right. Spray foam would be the best but not the cheapest IMHO. Then a small wall mounted window unit or mini-split.

"Condensation will occur on a cold surface when warm/moist air meets it."

About my rain - the problem is that my shop is 30 years old, and the vapor barrier is not perfect. So when I do get condensation, it lands on the backside of the vapor barrier until it finds a place where it's come apart, then it all runs out.  I used to get fairly high humidity in there during the winter due to the IR heater exhaust. I was able to solve it by adding a humidity-controlled fan that triggers at something like 50% humidity. It doesn't run all that often, only when it gets really cold and the heater is working hard.

We have the same kind of heaters in the FM shop and the insulation there is definitely suffering, but it never rains inside. That's probably a function of sheer size.

I don't have a lot of pictures of the interior that show the insulation, but here's one. It used to rain from that split in the tape on the right hand side.

Overall, the insulation is in decent shape - just not perfect. That fan in the background is the one that runs for humidity control, and the log from the controller says it ran for about 2 minutes last night while the heat ran for a couple of hours.

In reply to Keith Tanner :

Atmospheric liquefaction sounds better than rain when one is discussing the inside of one's shop.

So, with the exception of closed-cell foam, I think nothing should come in contact with the inside of the metal skin, correct? Let's say I go with rigid foam (some say it acts as a vapor barrier) does that go against the metal?
Sorry, for some reason I'm having a hard time wrapping my head around this simple concept.

If you plan on conditioning the interior space there is no practical way to prevent condensation. It happens because of temperature and humidity differential interior vs. exterior. I'm guessing this is on a slab which, unless it has a vapor barrier will introduce water into the structure. Unless you intend to really tighten up the structure from a airflow perspective, I'd recommend you steer clear of any material that doesn't suffer moisture well. That would include drywall and fiberglass insulation.

More construction details and I could be more specific. One key is figuring out where your dew point within the wall will be. Different climates will change things.

In reply to DrBoost :

"I think nothing should come in contact with the inside of the metal skin"

It's the warmer inside air carrying the moisture that you don't want touching anything cold in the winter.

My buddy, who is a builder, with the classic cars built 2 storage areas or garages for some cars. They were pole sheds for years. He got his guys to run 2x6's between the posts with studs on the inside , poured concrete inside , put metal siding on, sprayed open cell foam on the ceiling and between the studs against the backside of the metal, and paneled it with OSB.  We are down south also with hellish humidity as you are. That was 5 or 6 years ago. Made a nice climate controlled area for cars.

As far as a vapor barrier goes. I've heard that about closed cell foam. We haven't had an issue doing it like I described. We have wall mounted window units for cool in the summer and they keep the humidity down. I don't think condensation can happen unless you have air exposed to a surface with a lower temperature and a lot of thermal inertia. (thermal inertia) I pulled that outa my a$$.

Maybe SV reX or one of the other builders will chime in.

carbidetooth said:

If you plan on conditioning the interior space there is no practical way to prevent condensation. It happens because of temperature and humidity differential interior vs. exterior. I'm guessing this is on a slab which, unless it has a vapor barrier will introduce water into the structure. Unless you intend to really tighten up the structure from a airflow perspective, I'd recommend you steer clear of any material that doesn't suffer moisture well. That would include drywall and fiberglass insulation.

More construction details and I could be more specific. One key is figuring out where your dew point within the wall will be. Different climates will change things.

The floor is wood, and raised up 6-8" above grade. I'm in SW Florida and will need to keep the interior about 10-13º cooler inside than outside in the summer. In the winter there will probably be a few days I have to keep it that same amount warmer.
I'm going with a mini split due to noise and am planning on planting shade on the east side, the house will shade the south side. I'm kicking around the idea of solar panels to run the lights just to provide shade on the roof. I'm far enough south that it takes a seriously tall tree to shade a roof, unless it overhangs that roof.

In reply to DrBoost :

I've been trying to think about this and how to do it.  I've got two ideas if you insist on keeping the metal shed.  Both assume that any moisture is able to escape at the bottom of the metal panels.

1)  This is the overkill do it as right as possible in the circumstances.  Build a frame inside the metal shed.  2x4's would work but for space you could I guess do it with smaller noting that the insulation space would be limited.  As I built the walls I would sheath them in foam board between the new walls and the metal siding.  That gives you a vapor barier and if taped up keeps drafts down.  Inside the wall cavaties I would insulate with normal fiberglass unless you've gone with thinner walls and then it's maybe limited to cutting the foam board stuff to fit inside them.  Note that building the walls inside and flipping them up would be a huge PITA to where I'd just consider taking the metal building down and then putting it back up afterwards.  But you see how that just doesn't make sense.

2) Let's get some rednecking going.  Slap a 4x4 in each corner vertically.  One layer of foam board against the  metal siding and then firing strips on the inside wall.  Throw up some paneling leaving a gap at the top so that you can blow in insulation from there to fill the walls up.  

In either case do simular for the roof/cieling.  Now for 120 sq ft I think a mini split is totally overkill.  If sealed and insulated I think you'll find that body heat and electronics keeps it warm in winter and for the extremes you can use a space heater.  I would just throw a very small window AC into a framed for it hole and be done.

Thanks all. I have some marching orders now.

DrBoost said:

carbidetooth said:

If you plan on conditioning the interior space there is no practical way to prevent condensation. It happens because of temperature and humidity differential interior vs. exterior. I'm guessing this is on a slab which, unless it has a vapor barrier will introduce water into the structure. Unless you intend to really tighten up the structure from a airflow perspective, I'd recommend you steer clear of any material that doesn't suffer moisture well. That would include drywall and fiberglass insulation.

More construction details and I could be more specific. One key is figuring out where your dew point within the wall will be. Different climates will change things.

The floor is wood, and raised up 6-8" above grade. I'm in SW Florida and will need to keep the interior about 10-13º cooler inside than outside in the summer. In the winter there will probably be a few days I have to keep it that same amount warmer.
I'm going with a mini split due to noise and am planning on planting shade on the east side, the house will shade the south side. I'm kicking around the idea of solar panels to run the lights just to provide shade on the roof. I'm far enough south that it takes a seriously tall tree to shade a roof, unless it overhangs that roof.

If you can get some airspace between metal siding and foam board insulation, I think I would, all things considered. The not so good part is you're potentially putting wood between two vapor barriers which could be problematic. Is the wall constructed like a conventional stick frame? I can think of better solutions, but none that would seem very cost-effective. Some photos if what you have would be helpful.

I meant to post pics but I thought my ability to describe things clearly would outweigh my ability to be lazy. The lazy won out lol.  Here's pics.

Comet hunting for lizards ^^

I would plan on adding a window or skylight.

Just use batt insulation. Already has the vapor barrier.  Cheap, easy, - done.

Batt - Fiberglass Insulation - The Home Depot

In reply to DrBoost :

How about a photo of the inside door view?

I really don't have any answers for how to insulate that except maybe the closed cell spray foam in-between the wood framing and then covering with water resistant drywall. You will need a few more 2x4s in the corners for the drywall. I have seen pole barns spray foamed that way and they where very sealed up.

Definitely would need some fresh air exchange happening.

Normally you would use an air and water barrier (Tyvek or similar) on the outside of the studs behind the steel siding, fiberglass insulation in the stud space, and plastic vapor barrier on the inside of the studs behind the interior drywall. 

(I would consider the roof to be two horizontal walls.)

South FL. That means the warm moist side of the wall is the outside, not the inside. That makes most recommendations in this thread backwards (and most How-To books). 
 

Your goal is to keep the moisture on the exterior of the building from getting absorbed into the insulation or drywall. 
 

Two suggestions...

Opt 1: Create an air gap for ventilation against the metal. I'd use attic insulation baffles glued to the back of the metal. Install a small circular vent at the bottom and top of each bay. Air will circulate from bottom to top. Then fill the rest of the bay with closed cell insulation and cover with moisture resistant drywall. 
 

Opt 2:  Your shed isn't actually a metal shed. It's a wood shed with metal siding. Unscrew the siding from the exterior, add conventional plywood sheathing, install Tyvek on the outside, and reinstall the siding. You will need new larger corner posts.  Then treat the inside like a conventional building. 
 

Thise are my thoughts. Good luck!

In reply to DrBoost :

That's much better than I expected.  Those don't look like full 2x4s.  I'd cut foam board to fill the spaces in between maybe sealing the outer layer with great stuff spray foam on the edges.  Put in some ceiling joist even with top rim of the walls.  Insulate the hell out of the "attic" that you created.  That space where the vent is would become my window AC space.  If you do have full 2x4's then it'd be easier with fiberglass batts.

I wouldn't put standard batts against the metal. The moist air from the outside will meet the cool air from the interior and condensate at the dew point.  Most likely in the middle of the batt, but also possible on the back of the metal or the back of the Kraft vapor barrier. 
 

Could lead to panel rust or wood rot. 

I agree with SV reX. Although it would eat up some interior space you could install foam board on top of studs and the (kinda) purlins and somehow ventilate the space between without making for a water intrusion path. 

Closed cell foam has some possibilities, but around here that's expensive and you could be trying to make a "silk purse out of a sow's ear"

If I had to choose, all things considered, I like the idea of removing siding and doing a proper drainage plane. I'd be inclined to sheet the exterior with CDX or OSB, then house wrap topped with siding. Corrugated metal vertically installed could provide ventilation, but would invite bugs if you didn't screen the open ends somehow.

Just not much structure there to work with, but I'm used to working in northern climate.  I would guess that roof  would be sagging in a couple of years if you add much weight on the bottom side.

Thinking a little further about this...

The challenge with this structure is that you don't have anything that resembles a vapor barrier where you want it- outside the studs, but under the siding. 
 

So, I'm favoring my option 2 above, with a few tweaks...

I's remove the siding. I know that sounds like a lot of work, but it's really not. (I've done it recently). Then install Zip sheathing. It's a little pricey, but you don't need much. Tape the joints, roll them, and reinstall the siding. You'll probably need new corner posts (because the building got a little bigger).  That will give you an excellent building envelope with a proper vapor barrier. 
 

On the interior, you want the building to dry to the inside.  Use unfaced batt insulation, and permeable paint on the drywall.  Don't add foam insulation under the gypsum- it's not permeable  

Your mini-split is likely to be oversized for a building this small  That's fine- it will help keep it dried out.

Good luck!