A while back I scored quite a bit of industrial 6"x6'x12' insulation while bottomfeeding. Theres a reflective white vapor barrier on one side and close to enough to insulate the ceiling/roof, North, east and western partition wall of the proposed 30x40' shop area in the 30x70 pole bldg. I'd like to insulate the roof, rather than the ceiling which would require additional structure between the "ceiling" joist on 10' centers, because it will be easier and require fewer materials, however I'm concerned about condensate developing between the unsurfaced fiberglass and the metal roof. Is this a legitimate concern? If so, what can I do about it? As yet there are no ridge vents but there will be before winter. Thanks

-- john leake (natlivent@pcpros.net), May 22, 2000

Answers

Mostly you're intended to put the waterproof (or near it) side of insulation up, so that condenstation or leaks don't soak into it. Alternatively, I'd get some cheap plastic sheeting and do the job with that.

-- Don Armstrong (darmst@yahoo.com.au), May 22, 2000.

John, If you install the vapor barrier toward the HEATED side and DONT put any plastic between the fiberglass and the roof panels you will have no problems.Do a good job of sealing the joints ( plenty of overlap)The company I work for installs dozens of pre engineered metal buildings each year. These are typically steel framed buildings with either screwed down or standing seam metal roof panels and this is how it is alwys done.The vapor barrier will keep the condensation from infiltrating the insulation.See the thread about the mobile home with the vapor lock problem that resulted in rotting wood and you will see that plastic on both sides would cause rather than solve the problem.

-- mike (mstydale@aeroinc.net), May 22, 2000.

I see. Sorry, we're more used to insulation for keeping heat OUT, or for minor cold. R-factors from as low as 2.5 or so are generally adequate (just) here. I was thinking of insulation which has built-in sarking to keep it dry from water dripping off the roof, either from leaks or condensation. Of course insulation filled with drip water is useless, but even in winter we don't face the major problem with condensation of water vapour from inside which you must be facing. Sorry.

-- Don Armstrong (darmst@yahoo.com.au), May 23, 2000.