Foam insulation minimum thickness

[jeremywrags]

Hi All,

So I had contracted a Pole barn in Oklahoma and did not know that I needed to specifically include insulation in the bid, so here I am with my awesome new barn and there is no insulation whatsoever, just metal screwed directly on top of wood.

We have had several storms with high wind and rain and so far the shop is water tight but I gather from reading and asking around that at some point I am going to have an issue with condensation inside my shop. I have a 1969 camaro in the shop and condensation would ****...

So I am trying to understand my options...

1. Take off the metal and have insulation installed.
2. Have spray foam sprayed directly on the metal.

I think both will probably cost similar since for option 1. I have to pay someone to undo what was done, apply insulation and then re apply the metal.

For option two I gather that I can dictate what I want the thickness to be, obviously the thinner the cheaper but that brings me to my main question.

What is the thinnest I can get away with to prevent condensation in my shop?

I don't really care about how hot or cold it is inside the shop I just want to prevent condensation...

I had one contractor tell me that he could do 1/2 inch and that would be enough but I have had others suggest that I would need at least 2 inches. I don't know what's right, 2" is more $$ so perhaps he knows what he's talking about or perhaps he wants more money...

 

[theoldwizard1]

First, put your location in your profile !

Second, you are NEVER going to be able to maintain a LOW humidity unless you install some kind of heat/cooling system. Humidity will enter through window gaps and from opening and closing the doors.

Third, spray foam is the best. The low cost solution is to just do the all the seams and joints and then come back with fiberglass rolls/batts. 1/2" is not enough. 2" nominal. With 2" over everything, you won't need to add more insulation.

 

[matt_i]

Second, you are NEVER going to be able to maintain a LOW humidity unless you install some kind of heat/cooling system. Humidity will enter through window gaps and from opening and closing the doors.

Disagree and offer the dehumidifier as an alternative.

For basic condensation prevention, keeping the outside closed as much as possible and keeping a ceiling fan working at all times will do the job. Note, if said car is bare metal it won't be pristine and rust free for ages with just the fan, but if painted, typical street vehicle, way more than enough.

My bare metal machine tools never rusted in the shops where they lived for 10-15 years with just a fan running.

 

[theoldwizard1]

Disagree and offer the dehumidifier as an alternative.

For basic condensation prevention, keeping the outside closed as much as possible and keeping a ceiling fan working at all times will do the job. Note, if said car is bare metal it won't be pristine and rust free for ages with just the fan, but if painted, typical street vehicle, way more than enough.

My bare metal machine tools never rusted in the shops where they lived for 10-15 years with just a fan running.

I am not disputing your claim. But I would say that a dehumidifier is not very effective below about 50F.

Depending of the size of the building, a mini-split heat pump, along with ceiling fans, would do a very good job of maintaining a reasonable humidity.

This is a case where controls based on humidity versus just temperature would be important. From what I know, OK is hot, but not super humid (like FL) so there is no real reason to maintain 70-75F if the goal is just low humidity.

 

[wfopete]

Well until everyone can make up thier mind on this go with this solution:

http://www.carbag.com/products/carjacket

 

[Antique Engine]

I'm in North Texas and went with my installer's recommendation and had 1" put in. It's absolutely fantastic. Prior to having the shop sprayed, condensation would form on the inside of the steel and run down and drip on everything. The 1" of foam stopped that from happening anymore. It's nice and tight and cozy in there now. I gave the installer every opportunity to upsell me to thicker foam, but he steadfastly insisted that 1" was fully sufficient and I feel he was correct now looking back.

I will never again want a building without spray insulation. And, I have had previous shops with the roll type that is installed between the metal and the structure. It's plenty good, but this is better.

 

[theoldwizard1]

I'm in North Texas and went with my installer's recommendation and had 1" put in. It's absolutely fantastic.

1" of closed cell foam has an R value of about 6.5. That is more than 2" of fiberglass batt. Of course, the real win with foam is sealing the cracks.

 

[Voi]

Hi All,

So I had contracted a Pole barn in Oklahoma...

All of Oklahoma is in Climate Zone 3 except for a very small part in Zone 4.

I don't know specifically of a building science article on pole barns or other steel sheathed buildings but you should need very little R value to meet your goals of keeping condensation off of your steel.

If it were me I'd look for reclaimed 1.5" rigid foam and cut it to fit between the girts. It will be more work but cheaper and will make replacement of damaged steel much easier in the future compared to prying it off of cured spray foam.

Even if you had to pay for new foam it would be much cheaper.

Then a think coat of spray foam over everything for air sealing and you should be fine. Batts over the top of that for cheap R value.

I say this assuming your have standard girts. If you have bookshelf girts then I'd worry less about matching foam thickness to girt thickness.

 

[cajunfirehawk]

Going thru this exact same scenario now my self, my findings are: In my area, since the housing market is almost flat lined, spray foam installers are at a premium since most new construction is spec homes and since price is an issue with spec homes, most all builders are not using spray foam, which means for me in my area the cost will be HIGH! To do my 30x40x12 metal building with 1" of closed cell spray foam, the neighborhood price is upwards of $4k! I have had vendors ask if I wanted my girts sprayed or not and most foam contractors around me want to up sell to 2" or more which almost doubles the cost to like $7k. Never considered just spraying the seams but in the 5mths my building has been up I can tell you the metal gets darn hot on a warm day and I cant imagine how it will be in the summer here on the Mississippi gulf coast. I have already had condensation issues occur in the short time my building has been up too, FWIW. Also considering; fans, dehumidifier, window units, etc. to combat the humidity.

 

[tomroblee]

My pole barn in SW Indiana has 4' x 8' sheets of foil faced (foam) insulation board under the roof metal. It's been up for nearly a decade and I haven't had any condensation "problems" yet. As I recall, it was about 3/4" thick, but my memory fades after a decade.

The barn builders in my area seem to offer a choice between insulation board and varying kinds of fan or roll products for use as a vapor barrier under the roof metal. My builder preferred the insulation board because he thought it was more durable and less likely to be damaged during construction.

As others have said, you will need more than a vapor barrier under the roof metal if you really want/need a very low humidity environment. If you just want to avoid having water dripping on your head, a vapor barrier under the roof metal is all that is needed. Having some moisture condense on the cold metal walls of your building will keep it from condensing on your Camaro.

 

[theoldwizard1]

... If it were me I'd look for reclaimed 1.5" rigid foam ...

You are the first person I have heard to mention reclaimed rigid foam !

My daughter's father-in-law is a certified energy auditor so he is a nut about building "tight" buildings. He was the first person to mention reclaimed foam (specifically poly-iso, the highest R-value per inch). The stuff is CHEAP !

Google is your friend.

The biggest issue is transportation. Rent a car trailer, get a bunch of straps and some tarps and go get it ! Even with that added cost, it is MUCH cheaper than new.

 

[theoldwizard1]

...Never considered just spraying the seams ...

... and edges where any wood contacts the metal (makes a great bond !).

This is really just Step 1 ! You can delay further insulation until funding is available.

Step 2 is more insulation. You could always add more spray foam, but fiberglass batts work well. If you put up scrim or install interior walls from the bottom up, you can actually use loose cellulose of fiberglass.

 

[Dick in Wisconsin]

More information about the building.

Dirt floor? Gravel floor? Concrete floor? If concrete, is there 6mil or greater poly under the concrete?

Good drainage away from the building?

How well sealed is the building? Sliding, bypass door(s)? (lots of leaks) Quality overhead door(s) with good seals? Using Green Hinges?

Condensation occurs when moist air touches a surface which has a temperature less than that of the dew point of the moist air. Which is why insulation (especially spray on in your case) can be so effective.

The second problem you will need to address is to reduce the humidity of the space; actually humidity in your pole building is what is causing the condensation. If you had no humidity in the space, you probably would not have condensation. I believe (and I'm sure if wrong others on the GJF will respectfully correct me) that humidity is real enemy of the car you're trying to protect and the condensation is just a symptom of high humidity.