Who knows about pole barns?

Rob_Red

New Member
Feb 2, 2021
75
Southern New England
Hey guys what about the roof? Right now its the typical metal roof nailed right to perlins. What if I wanted something more weather tight? should I pull the metal and the purlins an replace with decking, underlayment, then either shingle or go with metal again? Could I do the decking with sawmill lumber for aesthetics?

Would just a simple ridge vent be sufficient for venting? It has a Gambrel roof.
 

Seasoned Oak

Minister of Fire
Oct 17, 2008
7,210
Eastern Central PA
The post will definitely rot is if they were not treated. I once used landscape timbers for fence posts ,big mistake. They are treated for ground contact but not direct burial. They lasted 10 yrs and rotted completely off where the post meets the ground but not underground. Had to replace every one.
 
  • Like
Reactions: GENECOP

SpaceBus

Minister of Fire
Nov 18, 2018
5,601
Downeast Maine
The wood should not rot if there is no oxygen present and usually posts don't rot in the ground but in the loam that forms at the top. Microorganisms oxygenate the soil at the top and give an environment for mold to form. Without oxygen and water the mold cannot destroy the wood. Above the ground level the rot is not caused by mold but instead by mosses and other microorganisms that need light.
 

SpaceBus

Minister of Fire
Nov 18, 2018
5,601
Downeast Maine
The posts are solid because they see little to no moisture. The barn has a french drain around the perimeter and the roof has a decent overhang.
Keep any soil from accumulating near/on the posts or other wood and you will never have rot issues. Sand, gravel, and clay do not harbor mold and other microbes like soil will.
 

GENECOP

Minister of Fire
Jan 31, 2014
734
Ny
Hey guys what about the roof? Right now its the typical metal roof nailed right to perlins. What if I wanted something more weather tight? should I pull the metal and the purlins an replace with decking, underlayment, then either shingle or go with metal again? Could I do the decking with sawmill lumber for aesthetics?

Would just a simple ridge vent be sufficient for venting? It has a Gambrel roof.
Is the roof leaking?
 

Rob_Red

New Member
Feb 2, 2021
75
Southern New England
Is the roof leaking?

Only in one spot where I know I have a flashing issue. I plan to get up there to address this once the snow is gone

Would there be any down side to spray foaming with metal roofing and perlins in place and then make a ceiling from wood from the saw mill? I was thinking I could run the boards through my planer and rout lap joints. This would allow it to breath some and when the wood dries out it wont open up enough to see the insulation.

Also what would you guys do with rusty corrugated roofing? leave it because the rustic looks is cool? Paint it some how? replace it and use it for covering wood piles?
 

GENECOP

Minister of Fire
Jan 31, 2014
734
Ny
Really depends on the condition of the roof, and the size of your budget. One thing I know would be a mistake , don’t consider spray foam to the underside of that roof unless your confident of the condition, the last thing you want to do is have to rip the roof off a few years after you foamed it..
 

SpaceBus

Minister of Fire
Nov 18, 2018
5,601
Downeast Maine
Only in one spot where I know I have a flashing issue. I plan to get up there to address this once the snow is gone

Would there be any down side to spray foaming with metal roofing and perlins in place and then make a ceiling from wood from the saw mill? I was thinking I could run the boards through my planer and rout lap joints. This would allow it to breath some and when the wood dries out it wont open up enough to see the insulation.

Also what would you guys do with rusty corrugated roofing? leave it because the rustic looks is cool? Paint it some how? replace it and use it for covering wood piles?
If you foam in the roof you will need to allow some kind of ventilation between the metal and the spray foam, usually 1-2" air gap. Otherwise you end up with a "hot roof" which becomes a problem if you want to make it a conditioned space.
 

SpaceBus

Minister of Fire
Nov 18, 2018
5,601
Downeast Maine
Can you elaborate on what a "hot roof" is?
A "hot roof" is simply an unventilated roof. Allegedly this can cause condensation to form between the roofing material and the deck (insulation in your case). I've read that spray foam is actually the only product you can use to make a functional hot roof that won't have condensation issues, but it is a relatively recent building practice.
 

Rob_Red

New Member
Feb 2, 2021
75
Southern New England
A "hot roof" is simply an unventilated roof. Allegedly this can cause condensation to form between the roofing material and the deck (insulation in your case). I've read that spray foam is actually the only product you can use to make a functional hot roof that won't have condensation issues, but it is a relatively recent building practice.
Ah ok. So far I've seen two schools of thought. One being that sprayfoam will NOT cause condensation when applied directly to the metal roof. The other is use some kind of pre-engineered baffle.

The baffle idea is intriguing because it seems like the roof would still be easily replaceable.
 
  • Like
Reactions: SpaceBus

SpaceBus

Minister of Fire
Nov 18, 2018
5,601
Downeast Maine
Ah ok. So far I've seen two schools of thought. One being that sprayfoam will NOT cause condensation when applied directly to the metal roof. The other is use some kind of pre-engineered baffle.

The baffle idea is intriguing because it seems like the roof would still be easily replaceable.
I would go with the baffles and create an air gap between the roof and insulation.
 

sloeffle

Minister of Fire
Mar 1, 2012
799
Central Ohio
When you put a layer of rigid foam on the outside of the house under the siding, does that not create a vapor barrier on the cold side in addition to the vapor barrier on the warm side to trap vapors in the middle? Selfishly asking because I want to reside my home and foam is really easy for more R value than the R5 fiberglass currently in the wall!
A few years ago I worked on a couple Habitat For Humanity homes. I was jealous on how well the house was insulated. I'd of opted for 2x6 vs 2x4 walls if I was building the house for myself, but Habitat uses 2x4 exterior walls. The walls were 1/2 drywall -> 2x4 with R13 batt insulation -> 1/2 plywood -> tyvek / moisture barrier -> 4x8 sheets of 2" foam insulation board -> siding.

I've seen hundred of houses in the building stage in Ohio and I've never seen plastic used on the inside of a house. Personally, I'd opt for the moisture to migrate through the walls and out of the house vs trapping it in the house.

EDIT: This seems to be about the best guide I can find online about vapor barriers.
 
Last edited:
Dec 14, 2020
134
Lisburn, PA
Hey guys what about the roof? Right now its the typical metal roof nailed right to perlins. What if I wanted something more weather tight? should I pull the metal and the purlins an replace with decking, underlayment, then either shingle or go with metal again? Could I do the decking with sawmill lumber for aesthetics?

Would just a simple ridge vent be sufficient for venting? It has a Gambrel roof.
Is the metal steel or aluminum? Is it actually nailed or screwed? A properly screwed metal roof can be coated.
You don't need decking or underlayment with metal and it's easy to take off the metal and replace it.
The decking/ceiling with sawmill lumber would be perfect.
Insulate with fiberglass batt. I've seen a lot of problems with spray foam in wood structures.
And I stand by my recommendation for plastic as interior vapor barrier in a pole barn.
Keep the batt insulation to roofing gap the same as the thickness of the purlin.
Your insulation should be the same thickness as the depth of rafters.
Different animal in a residence, and I'm not convinced the "breathable" wraps are that great in a residence.
You have a pole barn that I'm guessing will be heated occasionally.
Same situation with the walls with board and batten on the outside.
You get plenty of ventilation in the wall from the outside.
But what do I know, only been doing this since '85...
 

SpaceBus

Minister of Fire
Nov 18, 2018
5,601
Downeast Maine
Doing something for a long time does not make you an expert. It means you have done it for a while. I've met many a man who did something wrong for their whole life.
 

Highbeam

Minister of Fire
Dec 28, 2006
18,704
Mt. Rainier Foothills, WA
Doing something for a long time does not make you an expert. It means you have done it for a while. I've met many a man who did something wrong for their whole life.
Not speaking about PAMM of course but,

I’ve worked in construction for 20 some years (engineer)and since day 1 I’ve had people try that line when called out for not following the plan. The best contractors are the experienced ones that are willing to learn. Those guys are usually not as angry at the world either as a result of their different outlook.
 
Last edited:

mcdougy

Minister of Fire
Apr 15, 2014
635
ontario
Here's my take on what could be done. FwIw I have 28 years in construction, including building 75+ pole buildings over my years thus far. These include simple uninsulated drive sheds, to fully insulated gorgeous shops, and some may have even been used for living quarters after we left??

Your floor around the posts. I would suggest pour your floor around the post and do nothing. Your saying the posts appear very solid and that is all you need. The rot everyone speaks of is generally caused from a repetitive freeze thaw cycle. The post wicks the moisture from the soil and the moisture exits above grade. The typical rot zone is 4" below grade. This is where the moisture level changes from wet to drying and when the freeze cycle enters the situation it becomes prime for rot to start. A pole thats set in a wet location (wet heavy soil) is a scenario that's not going to work out very often for very long.
The soil your showing in your pictures is a GREAT scenario for pole longevity imo.

Insulation: my suggestion for your attic would be install 6mil vapor barrier to the underside of bottom chord, apply your ceiling finish (metal, wood, drywall, velvet etc) then blow your attic with your required r value with CELLULOSE.

Walls: in the perfect world your building would have been wrapped with a air barrier, then insulate, then vapor barrier, then interior finish.
Since your exterior cladding is already installed and I'm guessing your not interested in removing it then I would propose this idea if budget allows...
A flash and fill.....strap between the posts with 2x6 on the horizontal plane, spray 2" closed cell spray foam directly to the backside of your wood cladding , then get the same CELLULOSE installer to blow the remainder of the cavity with dense packed cellulose, then your interior finish.

Roof...leave the sheet metal roof alone and address the flashing problem. A sheet metal roof is perfect imo, and surely no good reason to remove it to add shingles or anything else. What you have is low cost replacement and extremely easy to maintain roof. If installed correctly you should have zero issues until the paint deteriorates

if there is not any ventilation currently in the roof I would suggest installing a continuous ridge vent with soffit ventilation as well. If the current soffits are finished and unvented, you could remove and replace them with a vented version.
All of this is assuming you have a standard roof truss system, im now thinking you said gambrel roof and if thats the case then there is a entire different scenario for that....
Maybe post a picture of the outside of your building so we can get a look at what your dealing with.
 
Feb 2, 2013
11
south eastern MA
I live in a post style barn, well the part that is the house was the garage and the barn is now my garage and work shop. but it is all held up by post that are pressure treated. I have replace 3 post so far. keeping the water away is key. I put gutters on the barn part and two of the other posts i have cemented in the bases, with plates and brackets because they are an exposed porch roof.

the structure has a typical plywood roof with two layers of shingles. one three tab and the top coat is architectural grade shingles. the next roof is going to cost big bucks to strip and reinstall.

my advise would to do it right, so you don't have to deal with it again. the price of steel has gone way up, but done right it should last a good long time. If i had to do it again, i would have gone with steel years ago.