Pole Barn Insulation

[jcook5003]

I'm finally about to start construction on my 24x30 shop with 24x20 equipment shed attached.

The plan is to use perma-columns and steel pole barn style trusses from a local builder. Like these:

24x30 of the area will be totally enclosed with a concrete floor for a shop.

My question is, upfront how do I set myself up for success as far as condensation and insulation goes.

I'd like to know what you all are doing to stop the roof from "raining". Where if anywhere should I put tyvek? As far as roof insulation goes how would you do it in this style of building? I'm just trying to make it as good as I can from the beginning.

I know spray foam might be the very best but it's probably too expensive for me. All suggestion welcome and appreciated.

 

[EddieWalker]

Your right about spray foam being best. Closed cell spray foam a couple inches thick is really the only thing that will accomplish this. Open cell will hold moisture and cause the metal roof to rust, so don't even consider using that, even though it's a lot cheaper. You can use open cell over a layer of closed cell, but if your main goal is just to stop condensation, there isn't any real need for that additional expense.

Before installing the metal roof, you can put down a layer of plastic/foil type insulation. This really doesn't stop the condensation from forming, but it's a cheap way to deal with it. You will have less moisture, and what does form will either dry quickly from air flowing from your eaves to your ridge peak vent, or drip onto the plastic and either evaporate from that air flow, or flow down to the outside of your building.

With that style of metal truss, be sure to ask your supplier about how much weight you can add to it if you decide to insulate with fiberglass. Those are great trusses for spanning big distances for minimum money, but they are not able to support a lot of extra weight.

 

[Snobdds]

I don't like seeing metal right on top of the perlins. I always like to see OSB on top of the perlins, then another set of perlins on top of the OSB then the metal roofing. This creates a air way under the metal roofing and it keeps the bottom and top of the metal roofing in the same climate, thus eliminating the condensation.

Usually the added expense of OSB is cheaper than closed cell foam.

Foam is best because it gives you some insulation as well, but get it done fast and cheap...OSB the roof.

 

[jack707]

My pole barn has 2 1/2" of spray foam on all walls and I have R13 under the roof because they used 2nd not 2.6 or I could of used R 19

 

[AGRIMAN]

I'm finally about to start construction on my 24x30 shop with 24x20 equipment shed attached.

The plan is to use perma-columns and steel pole barn style trusses from a local builder. Like these:

24x30 of the area will be totally enclosed with a concrete floor for a shop.

My question is, upfront how do I set myself up for success as far as condensation and insulation goes.

I'd like to know what you all are doing to stop the roof from "raining". Where if anywhere should I put tyvek? As far as roof insulation goes how would you do it in this style of building? I'm just trying to make it as good as I can from the beginning.

I know spray foam might be the very best but it's probably too expensive for me. All suggestion welcome and appreciated.

I would suggest that you at least get a few quotes from some of your local spray foam contractors. Where are you locate?

 

[Creamer]

It makes a lot of difference what climate you are in. Most buildings around here use a wide fiberglass bat with a vinyl back trapped between the purlins and the steel. that keeps the moisture from getting up to the steel.

 

[brown40]

If you aren't heating it, and you keep plenty of air flow at the eaves and gable ends that will help keep your temperature/vapor differentials closer and alleviate condensation issues. I used double bubble foil and also a cellular foil product called prodex over my purlins and on the walls behind the plywood... ideally it would be under the purlins on the roof, but so long as its draped down, the gable ends can still breath over its surface. I did an aftermarket installation on my roll-up doors with contact cement using the double bubble, and that was a big help with heat transfer when the sun is on the southern door. A side benefit was it helps the doors roll easier. They aren't the cheapest products, but are tough, air & water tight, keep the radiant heat transfer downand easy to cut and handle. I have had no troubles with either.
I don't particularly like handling fiberglass--plus it can hold moisture, and is an attractive nest material for all the vermin you don't want in your barn.
If money wasn't an issue, the closed cell spray foam would definitely be the ticket.

 

[POC]

What about putting 1/2" foam board on the bottom of the purlins? That will leave an air space.

 

[FF110]

Just seeing what insulation you decided to go with. I am about to start construction on my shop using that same truss system and am trying to decide the best insulation to go with.