Tag Archives: vinyl vapor barrier

How to Reduce Condensation in Post Frame Buildings

How to Reduce Condensation in Post Frame Buildings

Condensation occurs when excessive atmospheric water vapor comes into contact with a cold surface. Post frame building condensation will be particularly common in winter time, in regions where temperatures reach dramatic lows, and also in spring and early summer when ground temperatures are still cool but humidity increases. Post frame building condensation can be a serious problem, as excess moisture can create an uncomfortable environment and even contribute to mold and mildew growth.

Heat Building

For condensation to build up, temperature of building floors, wall and other solid surfaces must be lower than dew point (temperature where water condenses). So if you want to keep condensation away, maintain a warm post frame building. Avoid using propane heaters, because combustion process creates water vapor. Electric heaters can effectively keep temperature and condensation under control.

Use Vapor Barriers

Vapor barriers can help to keep condensation under control if installed in right places. Ceiling level vapor barriers are a bad idea, because they keep water vapor trapped inside the building, rather than allowing it to exhaust through a continuous ridge vent. Wall vapor barriers, can prevent condensation from penetrating your building’s drywall and insulation. Look for an insulation product with a built-in vapor barrier (e.g. fiberglass batts with a kraft paper facing), or consider installing plastic vapor barrier sheets directly over your existing unfaced insulation.

Keep Water Out

If vehicles or equipment become covered in rain or snow, and you then park them in your post frame building, this added moisture can contribute to condensation. If you must park something wet inside, try drying it as best possible before moving it inside. Also, if you have water seeping into your post frame building from rain or snow melt, try installing a drain outside to keep water issues in check. Put simply, do not let water in.

Seal Floor

A garage floor coating, or epoxy, can help to dramatically reduce condensation by limiting water vapor passing through your building’s concrete slab.

Other Solutions

Remove anything from your post frame building containing or requiring water. This can include houseplants, drying laundry, and even bags of trash containing moisture. Installing continuous ridge vents (in combination with vented eave soffits) can also reduce condensation by drawing out warm moist air containing water vapor. In some cases, a dehumidifier can help to remove light to moderate condensation, because dehumidifiers are designed to attract stray water vapor onto specialized coils, trapping it and draining resulting liquid into a reservoir.


And Now…Insulation Crime!

If you didn’t read yesterday’s blog – is good to catch up as a lead-in for today – well worth the time.  In it I discussed a problem a reader had asked for tech support about an insulation issue.

So today – yet another reader has written….

“I am in the process of finishing a pole building. The building will be used as my workshop and it will be heated, I live in Washington State. The contractor that put up the exterior placed R-23 Kraft Faced fiberglass insulation between the 2 X 6 rafters with the facing against the metal corrugated roof. This means that the vapor barrier is facing the roof, not the inside of my building. I plan to install sheetrock on the ceiling. It is not uncommon for the temperature to dip below zero here, and in the summer reach 100 for a month or more. My question is can I place a 4 mil poly vapor barrier on the interior side of the roof thereby wrapping the fiberglass insulation in two vapor barriers?”

What this building owner has is a pole building with 2×6 roof purlins on edge. Condensation on the inside of steel roofing applied directly on top of purlins can be an issue. This particular builder errantly installed batt insulation with the vapor barrier towards the steel, in efforts to reduce or eliminate the condensation problem.

If the builder would have properly installed the insulation between the purlins, with the Kraft facing towards the climate controlled area, making sure all seams were sealed, it would have been both effective as insulation and the vapor barrier would have kept the warm moist air inside the building, from condensing on the underside of the roof steel.

Why do I call this scenario “insulation crime”?  Because the builder took his client’s hard earned money and in return, gave him nothing but a problem to be solved.

Nearly every jurisdiction in the state of Washington requires both a Building Permit as well as the inspection of new buildings under construction. If this was a permitted building, the Building Inspector should have noticed the improper insulation installation and issued a correction notice – rather than signing off on a final inspection.

Metal Building Insulation in Pole Buildings Part I

It was a cold morning….and I was working on one of the first pole barns I had ever built. With the roof all framed up, it was time to install the roof steel, or so I thought.

In a pile, on the ground, were bags of something white, about as large as an oversized water heater. Metal Building Insulation (in the industry also known as “MBI”). This not being my first rodeo (and me being young and cocky), I went over to pick up a bag and found it not only was heavier than Hades, but it was also soft and squishy, not the easiest thing to maneuver and I was going to somehow get it up onto the roof?

MBI is a thin fiberglass blanket (as thin as an inch), glued to a white vinyl vapor barrier. The fiberglass is usually six feet in width, and the vinyl is slightly wider, so as to create a tab on each side. Under ideal circumstances, with no punctures in the vinyl facing and the seams tightly sealed, it can be a very effective vapor barrier. What it is NOT, is a very cost effective method of insulating a pole building.

Back at the building site, I’m doing my best to alligator wrestle a bag of this stuff up a ladder and onto the top of the roof purlins. Winning the battle, I slice open the bag and find out this stuff smells bad, really bad….rather reminded me of when our male cat staked out his territory when we were kids. Ugh!

Once out of the bag, it took several of us to stretch it across the roof and get it into place to be able to install the roof steel over it. Into place involved unrolling these gargantuan rolls with the itchy fiberglass side up. To properly install, the lead edge needs to have several inches of fiberglass removed, the vinyl facing is then folded over and staples are put through into the top of the eave purlin. The roll is run up over the ridge, down to the eave on the opposite side, and the “remove-fold-staple” process is then repeated.

Failure to start a roll properly leaves bare fiberglass at the edge of the building. Strangely enough, when the roof is wet, water droplets can get to the edge of the roof steel and actually cling to the underside at the edge, rather than dripping off the roof. Exposed fiberglass can cause these droplets to be wicked up into the insulation – causing moisture problems inside the building.

The first roof steel panel was then placed on top of the fiberglass and screwed on. First thing I noticed is the thickness of the fiberglass caused the steel to bow up in between each of the roof purlins, rather than laying smooth. My thought was it looked rather like Bibendum (aka the “Michelin Man”) from the tire commercials.

When it was time to lay the next roll of insulation in place, I asked what I was to do with the tabs on the edges and was quickly admonished, “don’t worry about them”….so I didn’t. Only years later did I find out the true purpose of the tabs was to keep any warm moist air, from inside the building, getting through the seam and contacting the underside of the roof steel and condensing. Without an absolutely tight seal, moisture will form and now be trapped in the insulation between the roof steel and the vinyl vapor barrier – potentially causing deterioration of the roof steel from the inside.

In order to properly seal the tabs, they are to be held together, folded over once, and then stapled with stainless steel staples along the full length of the seam. I truthfully know of a total of zero instances where this has actually been done.

I believe I had mentioned before, it was cold at that jobsite. It had also been cold when the insulation rolls were delivered and thrown off the back of the delivery truck. Below 40 degrees, the vinyl facing becomes brittle and will crack – which is exactly what had happened in this case. After we had the roof done from the outside, we had to use insulation tape to patch literally a hundred or more cracks and tears in the vinyl facing on the inside!

From an installation standpoint, nothing involving MBI could be thought of as being fun. Or, worse yet, profitable.  Come back tomorrow to hear the “rest of my story” on metal building insulation….