Have a 40' cargo container I am fashioning into a photo studio.   I am located in the Pacific Northwest
and the condensation on the ceiling is more or less constant eight months out of the year.  I have a
wood burning fireplace which helps when in use, but it would be impractical to run it 24/7 as a means of
keeping things dry. 

My first thought was the DIY spray foam kits, which the internet tells me might be frustrating, and comparable in cost
to having someone who actually knows what they're doing come out and do it anyway.  (This is what I'm planning on doing
unless someone reads this and tells me it won't work well or there exists a better solution.)

Then I came across the ceramic paints, which I had never heard of.  It seemed cool at first, but the internet is telling
me to be skeptical about some of the claims concerning the effectiveness of these things.

I read a post that (sada1?) replied to concerning a commercial building in Georgia and the investment/return using
E-shield vs. spray foam.  It sounds like it depends on the specific situation.  (In fact, on that one he recommended putting
more effort into sealing up the building than in adding more insulation.)  It also sounds like the coatings are
not highly regarded by the guys that do this for a living in any residential situation? Or do they have their place? (The one
I first ran across was Supertherm). 


Anyway, the container is shaded by trees on the South side, I may or may not insulate the walls as insulating for comfort sake is second
to fixing the condensation problem.  I have to think about the hot area where the single walled stove pipe exits through
the roof. There are vents built into the thing; they are very small and have been covered with tape since I got it.  Someone has
cut a hole in one end of the container and duct taped a decent sized extraction fan in, but it surely draws quite a bit of juice, and I would rather
not leave it on all the time; I don't know how much it would help anyway.

What's my best bet you think?

PS     Why do my walls not "sweat".  I wouldn't expect big crocodile tears to form, but I am surprised that they are bone dry.  Not
even that little dewy layer you hardly notice on the walls of pole barns until you run your hand across the metal.  And they remain
like that even when it's literally raining from the ceiling.
It's odd to me; am I missing something fundamental?

Thanks,
Danny

Danny,

Hot air holds more moisture, rises to the top, without significant air flow it will stagnate in the corrugations long enough to cool against the roof putting the air through condensation. It is then displaced by additional hotter and more humid air. The air on the sides will be drier and be more active as well. Continues air motion in the container would even out some of the condensation.

Is the bottom of the container sealed against moisture?

The entire container needs to be insulated, due to the high conductivity of the corten. Given you only plan on using it occasionally 2 inches of poly foam would probably be adequate. You will have to cover the foam with a UV proof coating as well.
If you use it more often and want to invest in additional efficiency there are other options you should consider. I am in Washington, where are you?

Brian

Firstly I wanted to introduce myself, I am perhaps the biggest fan of Shipping Container Construction in the World.

I am also a general contractor with several years of working in ISBU based construction and today I teach people to build with ISBU's.

I have made a 30 minute video explaining the requirements of insulating Shipping Container homes

The video is here.

Insulating Shipping Container Homes


I appreciate that this is my first posting on the board and so I ask for the forums indulgence in placing an outbound link as a newbie however the content created is hyper focused and I feel adds great value to this thread.

Thank you for your consideration.

Victor

Insulating cermic paints are pure bunk in a heating dominated climate, and some aren't even useful for reducing cooling loads. Of those that CAN reduce cooling loads (some SuperTherm paints qualify), their efficacy over cheaper materials of high solar reflectivity/moderate emissivity isn't necessarily worth paying a premium for. See: http://www.greenbuildingadvisor.com/blogs/dept/musings/insulating-paint-merchants-dupe-gullible-homeowners There are other "cool roof" paints/coatings that can improve summertime heat gain issues that can be less expensive. You can look up the specs for a given product (or look for relevant products) here: http://www.coolroofs.org/products/search.php Some products may be labeled as California Title 24 compliant as cool-roof, which is also a good indicator of efficacy for cooling-season performance.

DIY foam kit's aren't rocket science to use, but if you have more than 1000 board-feet to spray it'll be cheaper & better to let a pro do it.

Outdoor dew points in the PNW are pretty low compared to the Atlantic or Gulf coast states- I'd be surprised to see interior condensation on even an R5-insulated cargo can there unless your ventilation rates are dangerously low. An inch of closed cell applied to the exterior, painted with a UV-opaque paint to protect it should fix any condensation issues, and improve both winter & summer comfort issues.

Since the steel is a strong vapor barrier insulating the exterior is preferable to insulating the interior in a PNW climate or humidity can condense in or behind the insulation layers, the exception being if the insulation is perfectly air-tight (such as spray foam). A combination of spray foam & studwall with fiber insulation can work though, provided the interior of the studwall is air-tight but water-vapor permeable, and the ratio of exterior foam to interior fiber is such that the average January temp at the foam/fiber interface stays above 40F when you're heating the place. An inch of closed cell + 2x3 studs with unfaced R8 batts would deliver ~R13 performance with very low risk of mold on the studs.

See also:

http://www.greenbuildingtalk.com/Forums/tabid/53/aff/21/aft/77471/afv/topic/afpg/1/Default.aspx

Paint the inside wall of the cargo. Paint that has a mixture of insulating additives. While painting make it sure that there is enough ventilation.,because it makes you ill if you are suffocated with the paint smell.

Don't expect a layer of paint (or anything else that thin) to provide any noticeable amount of insulation.

Around here, cargo containers seem to go for around $2500. Not bad given how well they can be secured.

I would expect that spraying the outside with closed cell foam (or glue on EPS) and then applying spray on cementitious stucco (shotcrete) would be durable (and interesting looking). I did something similar to this after having paint over foam fail (in a different application).

jonr has it right- insulating paints and insulating paint additives have pretty much been debunked in both real-world & lab testing.

Some may (or not) make decent protective additives in some applications, others qualify as a CRRC rated "cool roof" material/coatings (others not- check the CRRC website), but none are going to change the condensation issues on the ceiling (at all) or reduce the heating/cooling energy use as much as an inch of foam would.

i'm wondering how this worked out for you? i'm in a similar climate (Occidental, CA) and am going to use a container for storage (of dry things), and am wondering if i should get an insulated container (e.g., a refrigerated container with the cooling unit taken out) or a regular one and then insulate it. any thoughts on this? thanks!

Do you happen to know the typical R-value on a refrigerated cargo can?

If it's >R8 (2"+ of EPS foam) it's probably worth starting there, but it's <=R4, you're probably better off just starting from scratch, since you'll need to add something anyway.

(e.g., a refrigerated container with the cooling unit taken out)

There are all kinds of refer containers. Some of them have VIP (vacuum insulated panels) and it's not too big a stretch to assume they get surplused out when the panels lose effectiveness, so be sure of what you are getting.

Do you happen to know the typical R-value on a refrigerated cargo can?

Typically, About 4" of shell is given over to insulation and air circulation. Foam thicknesses run about 2-1/2" - 3" of that.  These are ones I have experience with; there are many, many different kinds.

Some of them have VIP (vacuum insulated panels)

There's an idea. Weld (or glue?) up a second layer of sheet steel 1/2" inside a non-insulated container, fill the gap with perlite and then apply a vacuum pump to the cavity (will probably need to be redone now and then).

Paint it plaid or grey on the outside?