Insulating a pole barn that already has vinyl-faced insulation?

[Stryfe]

I recently framed bookshelf girts in between the posts in my shop (wish I did this from the start), in order to put up interior sheathing. When I had the building built, I had them install the standard pole barn type insulation which is sandwiched between the metal siding and girts. This is vinyl-faced fiberglass insulation, much like this product from Menards.

Now I want to put some insulation into the new cavities that have been created by framing the bookshelf girts. Picture below, that was an "in-progress" shot. I want to use r19 fiberglass batts. I am in SW Idaho - hot summers, cold winters.

My question is, do I need to install an interior vapor barrier? I'm under the impression this could create a moisture trap and maybe the best way to go about this would be like this (exterior to interior):

- Metal siding
- Fiberglass blanket with vinyl face (acts as vapor barrier)
- Girts
- ~6in deep cavity from new interior bookshelf girts
- R19 fiberglass batts in cavities
- Plywood interior sheathing

I'm thinking unfaced might be the best option here? There will be a small (1.5") gap between the new insulation and existing insulation due to the exterior girts. I do not want to cut out, puncture, or modify the existing insulation...building is a year old.

Thoughts?

 

[billconner]

If you're in a heating climate, I would take a knife to existing vinyl, install batts, and install a poly vapor barrier on interior. If you put up in faces and leave vinyl where it is, almost assured of condensation on that vinyl when moist interior air hits the below dew point vinyl, which it's sure to be on colder days. If you don't slice existing vinyl, some moist air will get into cavity - at least higher up where the interior pressure is positive - and condense and not be able to dry out.

 

[Stryfe]

If you're in a heating climate, I would take a knife to existing vinyl, install batts, and install a poly vapor barrier on interior. If you put up in faces and leave vinyl where it is, almost assured of condensation on that vinyl when moist interior air hits the below dew point vinyl, which it's sure to be on colder days. If you don't slice existing vinyl, some moist air will get into cavity - at least higher up where the interior pressure is positive - and condense and not be able to dry out.

Do you mean if I were to heat the shop? If so, I’m thinking I will have some source of heat, yes. May also cool it. Wouldn’t piercing the existing barrier cause potential issues with moisture on the metal siding?

 

[Youngandfree]

Do you mean if I were to heat the shop? If so, I’m thinking I will have some source of heat, yes. May also cool it. Wouldn’t piercing the existing barrier cause potential issues with moisture on the metal siding?

I think he's saying pierce it, put additional insulation up with a new vapor barrier.

 

[Stryfe]

I think he's saying pierce it, put additional insulation up with a new vapor barrier.

I know, but what's confusing me is won't a moisture issue be presented either way? Doesn't hot vs cold weather change the dynamics of how moisture vapor wants to move? (Vapor barrier on the interior wall vs vapor barrier on the exterior wall where it already is) ... and doesn't metal siding also change things compared to OSB or sheathing you'd see on a house?

Here's my dilemma.

WITHOUT interior vapor-barrier, keep existing vinyl barrier

• Cold weather scenario: Warm air in the shop may find its way through interior sheathing, through insulation, and cause moisture on the existing vinyl face which is much colder than the shop air
• Hot weather scenario: The air outside the shop is hot, the metal siding becomes hot, and it cannot penetrate through the existing vinyl barrier and then cause moisture with the new insulation which is cooler since it's interior facing (I am unsure of this?)

WITH interior vapor-barrier, slice/puncture existing vinyl barrier

• Cold weather scenario: Warm air in the shop may find its way through interior sheathing, but cannot penetrate interior vapor-barrier and cause moisture between cold exterior metal siding and warm interior wall
• Hot weather scenario: The air outside the shop is hot, the metal siding becomes hot, and now it can penetrate since the vinyl face is punctured, contact the cooler interior insulation, and introduce moisture between the exterior and interior walls? (also unsure of this)

This assumes that there is a source of heat in winter and source of cold in summer...mini split...wood stove...etc... I'm probably massively overcomplicating this. I am in climate zone 5B (cool dry).


My house is done the way that you'd expect from exterior to interior: Siding, sheathing, insulation, vapor barrier...but this is a pole barn, not a house. Maybe I just replicate this like @billconner is saying because obviously the house is built the way it should be done. No moisture issues in here.

Is it simply because of where I live (cold, dry) that the temperature difference between a heated inside area vs the outside cold air is so dramatically different that the vapor barrier would make more sense to go on the interior side? The difference can be great...could be -10F outside and even heated to 60F inside would present a 70 degree difference. There would never be such a large temp difference in the summer.

 

[billconner]

Is it simply because of where I live (cold, dry) that the temperature difference between a heated inside area vs the outside cold air is so dramatically different that the vapor barrier would make more sense to go on the interior side? The difference can be great...could be -10F outside and even heated to 60F inside would present a 70 degree difference. There would never be such a large temp difference in the summer.

Based on my learnings, yes.

 

[Youngandfree]

I know, but what's confusing me is won't a moisture issue be presented either way? Doesn't hot vs cold weather change the dynamics of how moisture vapor wants to move? (Vapor barrier on the interior wall vs vapor barrier on the exterior wall where it already is) ... and doesn't metal siding also change things compared to OSB or sheathing you'd see on a house?

Here's my dilemma.

WITHOUT interior vapor-barrier, keep existing vinyl barrier

• Cold weather scenario: Warm air in the shop may find its way through interior sheathing, through insulation, and cause moisture on the existing vinyl face which is much colder than the shop air
• Hot weather scenario: The air outside the shop is hot, the metal siding becomes hot, and it cannot penetrate through the existing vinyl barrier and then cause moisture with the new insulation which is cooler since it's interior facing (I am unsure of this?)

WITH interior vapor-barrier, slice/puncture existing vinyl barrier

• Cold weather scenario: Warm air in the shop may find its way through interior sheathing, but cannot penetrate interior vapor-barrier and cause moisture between cold exterior metal siding and warm interior wall
• Hot weather scenario: The air outside the shop is hot, the metal siding becomes hot, and now it can penetrate since the vinyl face is punctured, contact the cooler interior insulation, and introduce moisture between the exterior and interior walls? (also unsure of this)

This assumes that there is a source of heat in winter and source of cold in summer...mini split...wood stove...etc... I'm probably massively overcomplicating this. I am in climate zone 5B (cool dry).


My house is done the way that you'd expect from exterior to interior: Siding, sheathing, insulation, vapor barrier...but this is a pole barn, not a house. Maybe I just replicate this like @billconner is saying because obviously the house is built the way it should be done. No moisture issues in here.

Is it simply because of where I live (cold, dry) that the temperature difference between a heated inside area vs the outside cold air is so dramatically different that the vapor barrier would make more sense to go on the interior side? The difference can be great...could be -10F outside and even heated to 60F inside would present a 70 degree difference. There would never be such a large temp difference in the summer.

The existing vapor barrier is against the interior wall, not exterior.

 

[firebirdparts]

I'll say, for what it's worth, air doesn't become moist in the winter by magic. It takes effort. If you heat the shop and melt snow off the car every day, then maybe you could get it humidified if it's tight enough. You could invite 100 people over and have ballroom dancing in there. That might do it. For most people heating a shop, the interior of the shop is going to be very dry. FWIW.

We have a whole house humidifier on the house, and I sure wish "warm moist air" would just happen, but it doesn't. Typing it doesn't make it happen.

 

[jonnyboy]

I recently framed bookshelf girts in between the posts in my shop (wish I did this from the start), in order to put up interior sheathing. When I had the building built, I had them install the standard pole barn type insulation which is sandwiched between the metal siding and girts. This is vinyl-faced fiberglass insulation, much like this product from Menards.

Now I want to put some insulation into the new cavities that have been created by framing the bookshelf girts. Picture below, that was an "in-progress" shot. I want to use r19 fiberglass batts. I am in SW Idaho - hot summers, cold winters.

My question is, do I need to install an interior vapor barrier? I'm under the impression this could create a moisture trap and maybe the best way to go about this would be like this (exterior to interior):

- Metal siding
- Fiberglass blanket with vinyl face (acts as vapor barrier)
- Girts
- ~6in deep cavity from new interior bookshelf girts
- R19 fiberglass batts in cavities
- Plywood interior sheathing

I'm thinking unfaced might be the best option here? There will be a small (1.5") gap between the new insulation and existing insulation due to the exterior girts. I do not want to cut out, puncture, or modify the existing insulation...building is a year old.

Thoughts?

I know this post is a few months old but I am currently in the exact same predicament. I have 2” Vinyl Back installed between metal and hurts but want to add additional insulation such as R19 batts. What did you end up doing?

 

[Stryfe]

I know this post is a few months old but I am currently in the exact same predicament. I have 2” Vinyl Back installed between metal and hurts but want to add additional insulation such as R19 batts. What did you end up doing?

I framed the shop with bookshelf style girts as seen above, I sliced/cut small slits in the white vinyl, and then installed unfaced fiberglass batts in the framing voids. Then I used poly sheeting as a vapor barrier inside, put up OSB, and called it good.

 

[jonnyboy]

I framed the shop with bookshelf style girts as seen above, I sliced/cut small slits in the white vinyl, and then installed unfaced fiberglass batts in the framing voids. Then I used poly sheeting as a vapor barrier inside, put up OSB, and called it good.

That’s what I’m leaning towards… it’s just hard since I just had the thing built and regret my decision of having the vinyl back installed. Hard to cut into that insulation since it’s brand new. Lol

 

[billconner]

I know this post is a few months old but I am currently in the exact same predicament. I have 2” Vinyl Back installed between metal and hurts but want to add additional insulation such as R19 batts. What did you end up doing?

Where are you climate wise?

 

[jonnyboy]

Where are you climate wise?

Southern VA, about 15 minutes from NC line. Zone 4.

 

[billconner]

If you can live with a permeable interior sheathing, like drywall, do the same as Styrfe. Add girts or studs as required.

 

[jonnyboy]

If you can live with a permeable interior sheathing, like drywall, do the same as Styrfe. Add girts or studs as required.

I’m leaning towards plywood or metal. Would you still do the same thing as Stryfe? Slash vinyl back, install unfaced, and then add a plastic vapor barrier? What are your thoughts on just unfaced, no slashing of existing and then plywood and/or metal wall covering? That would leave me with just vapor barrier on exterior.

 

[dcg9381]

You already have a vapor barrier. Why add another?
I just thew up regular old OSB on the girts. No problems 3 years later. In your case, I'd fill the voids with bat insulation....

 

[jonnyboy]

You already have a vapor barrier. Why add another?
I just thew up regular old OSB on the girts. No problems 3 years later. In your case, I'd fill the voids with bat insulation....

I guess just from what I’ve read it seems to be more common to have a vapor barrier on the interior when heating for any decent amount of time to prevent moisture from getting trapped in the wall cavity. I honestly have no idea what’s right or wrong. Just trying to figure out the best solution for my situation to prevent problems down the road.

 

[dcg9381]

I guess just from what I’ve read it seems to be more common to have a vapor barrier on the interior when heating for any decent amount of time to prevent moisture from getting trapped in the wall cavity. I honestly have no idea what’s right or wrong. Just trying to figure out the best solution for my situation to prevent problems down the road.

You get moisture when you cool moist air. If you're planning on insulating the space between the outside vapor barrier and inside wall, I'd say that you don't need an additional vapor barrier as it's in the insulation layer. That space becomes part of your insulated envelope. It might be different if you had empty space in there... We've built structures up north with vapor barrier -> Zip-R -> closed cell foam -> bat insulation -> drywall. No problems (up north). But if someone else suggests a double barrier, I'll defer to their reasoning.

The other way you can get moisture is by heating with something like propane that creates moisture. In those cases, moisture is then controlled on the inside by an ERV or HRV.

To some degree, what works depends on if you're mainly heating or cooling and your climate zone.

 

[billconner]

I’m leaning towards plywood or metal. Would you still do the same thing as Stryfe? Slash vinyl back, install unfaced, and then add a plastic vapor barrier? What are your thoughts on just unfaced, no slashing of existing and then plywood and/or metal wall covering? That would leave me with just vapor barrier on exterior.

I think in your climate I would risk leaving vinyl as is and using unfaced batts behind a permeable surface (plywood is permeable, OSB not so much) so any moisture can dry inward. Board interior - like t&g or my favorite rough sawn pine - lots around here - is also super oermeable. Slashing vinyl, I faces, and poly would be fine as well, with any wall sheathing.

 

[billconner]

Just on the existing vapor barrier derp in wall, the problem is if the insulation behind it is enough to keep that surface above the dew point temperature. 2" of rigid foam or spray foam probably is in your climate, not sure about that fiberglass. As I said, I'd risk unless you're washing cars or doing other wet stuff or have an invented fossil fuel heater or even stacking fire wood. Do a good job of tight fit with added batts and avoid gaps.

 

[jonnyboy]

Just on the existing vapor barrier derp in wall, the problem is if the insulation behind it is enough to keep that surface above the dew point temperature. 2" of rigid foam or spray foam probably is in your climate, not sure about that fiberglass. As I said, I'd risk unless you're washing cars or doing other wet stuff or have an invented fossil fuel heater or even stacking fire wood. Do a good job of tight fit with added batts and avoid gaps.

Thanks for your input Bill. I planned on heating with a wood stove.

 

[billconner]

Morula bent it should be fine but firewood usually is not real dry and can put a lot of moisture I to the air. Keep most outside?