Pole Barn Question - OSB or not for Roof

[PoleBarnGuru]

If you spray foam the interior, for insulation and moisture barrier, there is a polyurethane foam that is rated for fire retardant qualities... and it stops air infiltration....

Dave ~ I'd like to know more about fire rated spray foam, as I am not familiar with it. The Building Code typically requires a barrier such as 5/8" Type X gypsum drywall to cover all SPF products. There is a Code approved spray on barrier available, but it is going to add significantly to the costs.

 

[DaveOmak]

Below is one of the many spray foam outfits... E-85 Fire rating... What ever that is...

Tiger Foam Spray Foam Insulation Kits

 

[EddieWalker]

If you go with OSB on the roof, then you need to have felt paper on top of the OSB, and under the metal. Condensation will still form under the metal and that water will run down the felt paper to your gutters or just out the ends of the metal. OSB has to have rafters or trusses or purlins 24 inches on center.

If you go with the insulation, you can spread your trusses out as far as your purlins will allow. The size of the purlin and strength of the truss will decide this. The insulation will do the same thing that the felt paper does. You will still have condensation, but the insulation will allow the water to exit the roof.

Either way, the amount of water that is created is minimal, but over time, without a place for it to go, can create problems.

Price it both ways, but I think the most cost effective way will be to use the insulation they recommend and spread your trusses out to four feet or more.

Are you putting brick up over the metal siding? Are you using brick on the walls? All the way up?

I don't know of any reason why house wrap would be a bad idea. It's cheap, easy to install and very effective. Are you going to have any windows? House wrap makes it very easy to tape and seal up your windows!!! Do you live in an area with a lot of wind? Cold wind? House wrap will help to keep that wind out.

If you are going to brick up the walls, then I wouldn't use metal under the brick. Use OSB for the walls. Brick needs brick ties attached to the wall. Doing this on metal is simple enough, but a lot easier with OSB. OSB will also make it easier and nicer looking to install windows.

The advantage to metal is that it's all things in one. It gives you your sheer strength and exterior protection in one. OSB has to be covered, so it's more labor and materials. If you want brick, then that's your exterior finish. Brick wont give your walls any sheer strength, so you need something attached to the walls to do this.

Just like the roof, OSB needs to be attached to studs or purlins every 2 feet or less. If you are going to install brick, you should install OSB. If you are going to install OSB, then you need wood studs or a lot more purlins then you would if you are just installing metal siding.

Eddie

 

[PoleBarnGuru]

Below is one of the many spray foam outfits... E-85 Fire rating... What ever that is...

Tiger Foam Spray Foam Insulation Kits

Dave ~ Thank you for the link. This is a case of something sounding really good.

The supplier you mentioned in your prior post has on their website, "We are the ONLY supplier offering E-84 Fire Rating STANDARD in our surface spray product line."

Flame Spread is based on: ASTM E-84/UL 723/NFPA 255: "Test for Surface Burning Characteristics of Building Materials."

Flame-spread, used to describe the surface burning characteristics of building materials. The most widely recognized laboratory test of such fire characteristics is defined in several tests:

Method of Test of Surface Burning Characteristics of Building Materials

NFPA Standard No. 255
Standard ASTM E-84 and
No. 723 of Underwriters Laboratories, Inc.
These are commonly known as the tunnel test or "Method of Test of Surface Burning Characteristics of Building Materials. (NFPA No. 255, ASTM E 84, UL No. 723).

The flame spread is a number, calculated from the results of a test, which indicates the relative rate at which flame will spread over the surface of the material as compared with flame spread on asbestos-cement board, which is rated 0, and on red oak, which is rated 100.

Note this rating is not the rate at which the flame actually spreads along the surface and is not at all an indication of the fire resistance of the material.

The product supplier is not giving the results of the flame spread test, they are just saying the product has been tested!!

If one really digs through the Technical Information on their website, it turns out a two inch thickness has a flame spread rating of 20. This is a low enough rating to get it into Class I, but is not near what is offered by gypsum wallboard (10-15).

Building codes require spray foam needs to be protected (covered) for fire safety with a 15-minute thermal barrier.

In summary - if using spray foam, plan upon covering it.

 

[mojoinco]

Metal Sales has a very good pdf file on how to build a pole barn. It answers a lot of your questions (which some have already answered).
On thing it mentions is using an adhesive strip to seal the overlap bead as you mount the next metal sheet. Most folks don't seem to worry about this, but the devils in the details.

Just a thought, I find that most of the damage done to a wall is along the bottom (mowers, snow removal, bugs, rodents, bumpers, moisture, etc). A short riser wall would be a plus for these 'errors'. And since you already have the brick, plus it would likely look very nice matching your house....

YMMV, but two things to consider (I have a 30x40x12 pole barn). Make it 2' taller and consider high clearance trusses (sometimes called scissor trusses). It makes adding a mezzanine or a lift, etc, easy to do later.

2 Years ago we added on to our home and learned a bit about spray foam insulation. Basically their are two types: open cell and closed cell. Open cell will drain any moisture in it (if there is a place for it to go) potentially limiting mold issues should it be exposed to moisture. Closed cell creates a more sealed surface, but if moisture gets into it, it will hold it until it breaks (mechanically), and may offer more mold/mildew concern. Open cell has less R value per inch than closed cell, but the cost per R value is about the same. Our building codes (National fire code?) required it to be surface sprayed after it dried. Not difficult. The closed cell was vaguely offered as increasing the structural integrity of the house, but no data was supplied.

 

[CentralNC]

Wow. You guys have made some really good suggestions. I do appreciate all the advice. A few responses ...

Mojoinco - I checked out the Metal Sales website. They had some good information. Thank you

PoleBarnGuru - I have been browsing your website for the past hour. I learned a lot. I think I am going to check with the truss supplier and space as you suggested.

Eddie/Mojo - I appreciate the advice. I think I will use the house wrap. I like the idea of using the brick along the bottom 3' and then metal siding the rest of the way up. We have plenty of brick to do this all the way around. The color of the siding (clay) matches the shanker shingle siding we have on our garage. Our house is mostly brick, but we did shaker siding to give some contrast. The problem is that I am not sure how to handle the footing required for brick. If I have to dig down and pour a brick footer it almost seems like I should just go ahead and pour a turndown slab .. then frame up off the slab. I can't see how I would pour the brick ledge with the pole barn. I might need to chat with a brick mason about doing this.

I have a pretty firm budget number as well. It is a matter of trading "wants" vs. "must haves". You guys have given me some good ideas though.

Thanks again to everyone who has given advice.

 

[KennyG]

Check on what is required for a face brick footer in your area. Up north here, we have to have a 42" to 48" footer for any brick, but you may not need as much. Theoretically, you could erect the frame (with poles just set in soil) and then dig a footer trench outside the poles for the footer and pour all the concrete. However, this situation seems tailor made for poles set on embedded plates on the slab. I think I would "bookshelf" the girts in the lower portion of the walls so the OSB sheathing can go directly against the poles and the metal siding would be well out over the brick when you use normal girts above the brick. Maybe even cap the brick with a custom z-strip.

 

[jimgerken]

i can't tell from the thread if you are set on one particular building plan or not, so I will make one more suggestion. When I was at the planning stage of my own building, (also an "ag" building with no particular code to follow, as your situation seems to be), as I was narrowing down the choices, I called the county seat and asked about real estate tax valuation practices. The information I got from them allowed me to fine tune the plan to then build a building that not only was low cost today, but lowest possible cost for tax value for every year it stands on my property. Also, since mine is in MN, energy efficiency was rolled into it too. Again, the plan considers the long-term costs of ownership (heating and cooling for the next 30 years), as well as the construction costs. My 2 cents worth for ya....

Tyvek the walls? Why not. Its cheap and it stops wind and any rain that comes thru whatever siding you choose. My thought is, if the wall is made of wood in any way, you gotta keep it dry, put on a layer of Tyvek on the outside. Infiltration from wind completely short cicuits your insulation function.

Tar paper under steel roofing? Very few metal roof suppliers recommend tar paper under their product. Instead they want a synthetic underlayment that can take the heat and not turn to dust in 15 years as tar paper will. Also, the synthetic will not adhere to the metal with the heat and pressure, as tar paper will. Once it bonds, after that it tears from expansion and contraction.

Radiant layer? Here is a good article discussing the pros and cons, depending on the climate and the structure details...
Radiant Barriers: A Solution in Search of a Problem | GreenBuildingAdvisor.com

Good luck, do the best you can with the money you have to work with, allow for upgrades later, finish first the hard parts that you cannot access later. No building is ever perfect, manage the compromises.

Here is a link to my shop construction project. There are lots of good photos in there if you don't want to read anything...
35X60 shop design in Minnesota

 

[DaveOmak]

One suggestion on the metal..... whether it be siding or roofing, measure the spacing for purlins or what ever and pre-drill the holes for the screws.... makes for a flatter surface for the rubber washers to seat.... You can pre-drill for the overlap also with a little forethought..... I watched the good builders do this trick... amazing how much better stuff fits...... One more thing... install the screws as the manufacturer suggest.... Takes a few more screws and a little more time, but worth it....

 

[EddieWalker]

Tar paper under steel roofing? Very few metal roof suppliers recommend tar paper under their product. Instead they want a synthetic underlayment that can take the heat and not turn to dust in 15 years as tar paper will. Also, the synthetic will not adhere to the metal with the heat and pressure, as tar paper will. Once it bonds, after that it tears from expansion and contraction.

I've never heard this before. While I agree that the paper might attach to the metal and tear with movement over time, I don't know if this really happens or not. I've never seen a synthetic underlayment. What would this be? I have seen quite a few metal roofs on houses with tar paper under the metal and I've seen where the water comes out under the metal panels, on top of the paper. Try finding a leak in one of those roofs!!!!

I've observed, but never been a part of metal rooms going on in commercial buildings, like banks, where they put down tar paper over the OSB, then the metal over the paper quite a few times. Seems pretty standard here, but this is just something I notice while driving by those places.

I wonder just how much movement there is in a metal roof? The gaskets on the screws are the weak link for that type of roofing. If they move around, I'm sure they are going to fail pretty quickly. If the movement is so small and insignificant as to not damage the rubber seals on the screws, then how much damage could be caused to the paper under it?

Eddie