Vapor barrier

[gnball]

Ok, first post so my apologies. I'm building a shop and have a question about insulating it for heat and air(I want to be able to use it). Since a picture is worth 1000 words, I'll save myself some typing. Basically the metal siding was put on 2x4 lath boards directly. My question is, what are my options for insulating without a vapor barrier, or do I need to put a vapor barrier inside, I'm pretty clueless. I'm hoping that I don't have to take the metal off and put the vapor barrier on the outside, but I have no idea. I'm going to try and talk to an insulation company tomorrow to see what they say, but thought I would get your all's opinion first. Is closed cell spray foam my only option or can I use fiberglass blown in or bat insulation?

 

[Junkman]

Go for the spray foam, it will cost more, but in the end, you will be a lot happier. It will add rigidity to the building, and make it much more comfortable to work in year round. Mice don't get into foam, but they sure can make a mess out of fiberglass.

 

[chrenan]

Vapour barrier goes on the warm side, so inside. If it was me I'd do pink insulation bat between the studs, then a nice thick plastic vapour barrier stapled to the studs and sealed with tuck tape at edges and seams, then whatever wall material you prefer. Make sure you get all your electrical done before you close up the walls.

 

[PCO6]

... I'm going to try and talk to an insulation company tomorrow to see what they say ...

That's probably your best bet because methods vary based on where you are located. chrenan is right though ... "warm side".

 

[chrenan]

That's probably your best bet because methods vary based on where you are located.

Very true, what I suggested is common where I am, northern Canada. If you're in the southern states I have no idea what is common there.

 

[SARG]

Spray foam done by a pro will make you much happier than any other technique.

 

[Junkman]

I believe that we all can agree that energy costs are not going to be going down anytime in the future, unless you happen to have an oil or gas well on your property. For this reason alone, I believe that the best insulation that can be installed, is going to be the most economical in the future. I have a friend that everyone tried to talk him out of using foam in his home, and it was double the cost of the pink fiberglass. The foam made his home so energy efficient, that he doesn't need to have it air conditioned in the hottest of days. His heating costs are half of what his neighbors spend on homes of smaller size, and newer construction using fiberglass insulation. There are always gaps in the fiberglass, no matter how well it is done. Foam doesn't leave gaps, that allow cold air to get into the warmed space.
Go into the attic of any home that has fiberglass insulation on the ceiling joists, and look at the edges where the outside walls are. You will see that the pink fiberglass is dirty. This is because of the movement of the air at these edges. You won't get that with foam. Unless he is planning on moving to another location in a few years, the foam will be the better value for his money over the long haul.

 

[gnball]

I suppose it would help to say that I am in Arkansas, so the warm side definitely varies. I would love to do closed-cell foam, but $1.25 a board foot based on estimates that I have seen online makes the insulation cost like $12,000 for 3 inches of foam to get R-20. That's like 10 times the cost of fiberglass. The shop is 30x50x12 with 2 10x10 doors and a walk door, so I have roughly 1720 sq. ft. of wall space to insulate and then the roof as well which I think I would just do the ceiling instead of the entire roof, so that's another 1500 sq. ft. for a total of 3220 sq. ft. area to insulate. Multiplied by 3 for 3" of foam and that's 9660 board feet of foam. Another thought I had was doing like 1" of cc foam for a vapor barrier and then doing fiberglass rolls on top of that, or maybe blown in fiberglass on top of that or maybe oc foam on top of that. This would get me close to or over the r-20 mark. Still hoping to be able to talk to the insulation folks today at some point if I don't get too busy at work.

 

[70C-10]

I recently read about hybrid insulating. 1" of foam & fiberglass over that. I'm no expert but I think that's the best value. Foam for a complete vapor barrier & fiberglass for added R-value. YMMV

 

[gnball]

Left messages with several places around here that do foam and got to talk to one of them. He recommended that I do 3.5" of open cell foam. I did ask about doing 1" of closed cell for a vapor barrier and then doing fiberglass or OC foam on top of that and he said that it would likely be more expensive and that I didn't really need to do that if I did all OC, since it would be a vapor retarder at 3.5" anyway. Basically it would still allow vapor through still, but it would not be able to condense, if that makes sense. I'm thinking that it would actually likely be the same cost or cheaper to do the 1" of CC and then fiberglass on top of that. His estimate was 4600-4700 for the 3.5" of OC. I am going to ask him what 1" of CC would cost hopefully tomorrow or Monday. Then I'll know for sure which is cheaper since I can do blown in the attic and fiberglass bats in the walls for around 1000-1200. I am assuming that the 1" of CC would be around 3200-3700 which would put it about the same price as the 3.5" of OC and have a higher r-value, so it seems like the hybrid CC and FG would give a lower $/r-value and give an actual vapor barrier, but I'm going to try and verify that. Opinions/thoughts?

 

[CNGsaves]

Any insulation guru's out there to explain WHY that foam insulation has not been dropping in price with more acceptance??

Seems crazy that it's double or triple of fiberglass with all the extra labor dollars it takes to install bat insulation.

When will the "China effect" hit for foam insulation ?? . . . . that IS something we wouldn't mind happening !! . . . . ie the cost dropping 50% every year for a while !!

 

[sideways]

Hey there...not sure if anyone's still following this post or not, but I'll pose my question anyway. What is considered the "warm" side? In the summer, wouldn't the warm side be the "top" of the ceiling joists due to the fact that any ceiling insulation should make the work space somewhat cooler than the space above the ceiling....and vice versa in the fall/winter months? Therefore...where should the vapor barrier go? Based on previous advice, I finished my ceiling as follows; I stapled 6mil plastic to the bottom of my ceiling joists and tried as best I could to tape up the seams. I then screwed my metal/corrugated ceiling over the plastic. My floor joists were 4' centers so I layed 2 rolls of 2' R30 insulation inside them. The roof tops are vented. I did the same on the outer walls...layed R19 bats inside 16" center 2x4 studs. Hung 6mil plastic from top to bottom covering the insulation and taped the seams, and then screwed OCB sheathing over the plastic. I'm hoping I did this correctly....but now have some doubts since I'm not quite sure what the "warm" side of the insulation is....seems it can change with the seasons...