00:00:01.960 [Music] 00:00:04.57000:00:04.580 it looks like I'm coming to you from CIA 00:00:07.51900:00:07.529 headquarters but in fact we're recording 00:00:10.87900:00:10.889 at our underground building science 00:00:12.74000:00:12.750 earlier all right guys 00:00:16.22000:00:16.230 hard topic today we're talking about 00:00:17.99000:00:18.000 vapor barriers and I was trying to 00:00:19.73000:00:19.740 figure out how I could shoot this at a 00:00:21.08000:00:21.090 job site but I'm just not using any 00:00:23.33000:00:23.340 vapors on jobs these days so I thought 00:00:26.00000:00:26.010 we'd record this here at the office 00:00:28.07000:00:28.080 where I can have access to the computer 00:00:29.72000:00:29.730 and show you some images both in the 00:00:32.15000:00:32.160 past and from a few places around the 00:00:33.92000:00:33.930 web on this important topic specifically 00:00:37.25000:00:37.260 what's happening is I'm seeing vapor 00:00:39.02000:00:39.030 barriers being used incorrectly on jobs 00:00:41.60000:00:41.610 all the time and I'm getting builders 00:00:43.97000:00:43.980 asking me when do I use them when do I 00:00:46.16000:00:46.170 not now when I say vapor barrier most 00:00:48.79900:00:48.809 builders are looking at this image right 00:00:50.69000:00:50.700 here this is some rockwool unphased bats 00:00:53.90000:00:53.910 that's how they're coming and then the 00:00:55.72900:00:55.739 Builder whether it was the inspector or 00:00:57.65000:00:57.660 the Builder said hey let's cover those 00:00:59.72000:00:59.730 with polyethylene six mil poly is 00:01:02.33000:01:02.340 typically what's being used out there 00:01:04.07000:01:04.080 that I'm seeing and when I was a builder 00:01:06.14000:01:06.150 in the 90s we were told on the warm side 00:01:08.53900:01:08.549 and the winter is where we're gonna put 00:01:11.00000:01:11.010 that that polyethylene vapor barrier 00:01:13.82000:01:13.830 poly vapor barrier and so that's where 00:01:15.74000:01:15.750 you're seeing it right here now let's go 00:01:18.53000:01:18.540 to a couple places in the web that I 00:01:20.57000:01:20.580 uses some trusted sources find home 00:01:22.91000:01:22.920 building comm you know this is a great 00:01:24.92000:01:24.930 image from their web site talking about 00:01:26.71900:01:26.729 vapor barriers if you look here we've 00:01:28.85000:01:28.860 got a house here's the cold outside 00:01:31.13000:01:31.140 that's you know maybe under ten degrees 00:01:32.87000:01:32.880 outside here's the inside of the house 00:01:35.48000:01:35.490 and the heaters on or maybe sixty eight 00:01:37.81900:01:37.829 degrees outside and this blue right here 00:01:40.42900:01:40.439 you're seeing that's some vapor that's 00:01:42.31900:01:42.329 been diffused on the inside air inside 00:01:45.44000:01:45.450 our houses were breathing we're cooking 00:01:47.56900:01:47.579 we're showering we're boiling pasta and 00:01:49.78900:01:49.799 so the humidity typically in our houses 00:01:51.80000:01:51.810 in the wintertime is much much higher 00:01:53.89900:01:53.909 than it is outside cold air can't hold a 00:01:56.12000:01:56.130 lot of humidity so if you look at this 00:01:58.16000:01:58.170 diagram here they've got a sheet of 00:01:59.69000:01:59.700 drywall in that water vapor is diffusing 00:02:02.81000:02:02.820 through the drywall that's the process 00:02:04.81900:02:04.829 where basically those small water 00:02:06.42900:02:06.439 molecules that are in the air floating 00:02:09.68000:02:09.690 we can't see them are able to actually 00:02:11.54000:02:11.550 go from places of high humidity to 00:02:14.03000:02:14.040 humidity from warm to cold and so it's 00:02:17.33000:02:17.340 diffusing through the drywall you can 00:02:19.72900:02:19.739 see it's even wetting somewhere in the 00:02:21.22900:02:21.239 insulation there and on the back of the 00:02:23.42000:02:23.430 sheathing that's cold it's condensing 00:02:25.28000:02:25.290 and if you look to this diagram you 00:02:26.50900:02:26.519 think oh my gosh without a vapor barrier 00:02:28.91000:02:28.920 this walls gonna get drenched there's 00:02:30.89000:02:30.900 just gonna be liquid water all over the 00:02:32.75000:02:32.760 place I don't want to get into this 00:02:34.36900:02:34.379 article in particular but I do want to 00:02:36.50000:02:36.510 jump over to Wikipedia I was curious to 00:02:39.22900:02:39.239 see what they had to say on the matter 00:02:41.11900:02:41.129 check out this Wikipedia page right here 00:02:43.78900:02:43.799 we're talking about vapor barriers 00:02:46.03900:02:46.049 specifically here and it defines a vapor 00:02:48.86000:02:48.870 barrier it says a vapor barrier is 00:02:50.05900:02:50.069 something that's point one perms or less 00:02:53.24000:02:53.250 basically plastic sheeting and then 00:02:55.49000:02:55.500 interesting where they show where you 00:02:57.11000:02:57.120 need it based on the geography here 00:02:59.47900:02:59.489 really the only place where you need an 00:03:03.30900:03:03.319 exterior vapor barrier they're saying is 00:03:05.59900:03:05.609 in Florida and maybe a few parts of 00:03:07.25000:03:07.260 Texas and then where you need an 00:03:09.41000:03:09.420 interior vapor barrier is basically from 00:03:11.18000:03:11.190 there on north everywhere north of this 00:03:13.36900:03:13.379 kind of line right here on Wikipedia is 00:03:15.34900:03:15.359 saying we need a vapor barrier on the 00:03:17.21000:03:17.220 inside very interesting now let's move 00:03:20.56900:03:20.579 over to a friend of Mines website this 00:03:23.21000:03:23.220 is Allison bales who runs a blog called 00:03:25.25000:03:25.260 energy Vanguard fantastic blog you 00:03:27.92000:03:27.930 should subscribe to his feed for sure 00:03:30.68000:03:30.690 but he wrote an article a couple years 00:03:33.43900:03:33.449 ago called you don't need a vapor 00:03:34.78900:03:34.799 barrier probably and this is a great 00:03:37.33900:03:37.349 article I'm gonna summarize it briefly 00:03:39.02000:03:39.030 he basically says that the act of 00:03:41.53900:03:41.549 diffusion that water vapor going through 00:03:44.36000:03:44.370 the sheet rock and potentially 00:03:46.24000:03:46.250 condensing on the inside that act of 00:03:49.30900:03:49.319 diffusion is a pretty slow process and 00:03:51.83000:03:51.840 it's not gonna move a lot of water in 00:03:54.11000:03:54.120 fact through the whole heating season 00:03:56.03000:03:56.040 this article says that you're gonna 00:03:58.69900:03:58.709 diffuse at most a third of a quart of 00:04:01.72900:04:01.739 water through a four by eight sheet of 00:04:03.61900:04:03.629 drywall now on the other hand most the 00:04:06.55900:04:06.569 time when walls are getting wet it's not 00:04:08.96000:04:08.970 diffusion but it's actually air movement 00:04:11.53900:04:11.549 which is depositing that water look at 00:04:14.14900:04:14.159 this right here again 4-byte sheet if we 00:04:16.67000:04:16.680 had a small hole in the drywall and our 00:04:19.37000:04:19.380 interiors being heated and we've got 00:04:20.75000:04:20.760 forty percent relative humidity air 00:04:22.94000:04:22.950 leaking into that cavity could bring 00:04:24.98000:04:24.990 with it as much as thirty quarts of 00:04:27.05000:04:27.060 water 00:04:28.01000:04:28.020 now that's a big deal that's also a big 00:04:30.55900:04:30.569 deal for me in the hot humid south 00:04:32.18000:04:32.190 because air could be leaking from the 00:04:33.92000:04:33.930 outside in and doing the same thing 00:04:36.55900:04:36.569 depositing on the back of the sheetrock 00:04:38.24000:04:38.250 where I've got a cold condensing surface 00:04:41.08900:04:41.099 so basically Allison says on this 00:04:43.21900:04:43.229 article there's very few places if any 00:04:45.89000:04:45.900 in the u.s. that you really need a vapor 00:04:47.68900:04:47.699 barrier the big deal that we need to 00:04:49.49000:04:49.500 think about is air barriers now let's go 00:04:52.58000:04:52.590 over to my friend Martin Holliday who 00:04:54.95000:04:54.960 writes for green building advisor great 00:04:57.83000:04:57.840 source of information on building 00:04:59.05900:04:59.069 science and his article here I'll link 00:05:01.58000:05:01.590 to this below do I need a vapor retarder 00:05:04.07000:05:04.080 read this great article but the summary 00:05:06.86000:05:06.870 at the bottom here if we go all the way 00:05:08.33000:05:08.340 to the bottom the very last line has 00:05:10.01000:05:10.020 what's the short version here's a couple 00:05:12.14000:05:12.150 rules most buildings don't need 00:05:14.89900:05:14.909 polyethylene anywhere except underneath 00:05:18.14000:05:18.150 a concrete slab or in your crawlspace 00:05:20.14900:05:20.159 floor this goes really for the whole US 00:05:22.64000:05:22.650 and the main reason you might use an 00:05:25.82000:05:25.830 interior vapor barrier or a vapor 00:05:27.35000:05:27.360 retarder rather is to keep your building 00:05:29.65900:05:29.669 inspector happy now instead of using 00:05:32.08900:05:32.099 polyethylene martin says what we should 00:05:34.49000:05:34.500 consider using is a vapor retarding 00:05:36.86000:05:36.870 paint that means a paint on the outside 00:05:38.30000:05:38.310 of the gypsum sheetrock which is gonna 00:05:40.93900:05:40.949 slow that diffusion down or a smart 00:05:44.02900:05:44.039 retarder for instance here's a couple 00:05:45.95000:05:45.960 brand names right here quoted but the 00:05:48.86000:05:48.870 point of this article is that there's 00:05:51.20000:05:51.210 multiple different building zones in 00:05:53.51000:05:53.520 America and we really need to be 00:05:55.49000:05:55.500 cautious about putting that polyethylene 00:05:57.86000:05:57.870 up now here's a direct example from from 00:06:00.80000:06:00.810 me down here in Texas I did a remodel in 00:06:02.57000:06:02.580 this house that was less than ten years 00:06:04.10000:06:04.110 old and this has happened to me on 00:06:05.65900:06:05.669 multiple occasions where we found on a 00:06:07.58000:06:07.590 very young house polyethylene sheeting 00:06:10.12900:06:10.139 on the inside and it's a little hard to 00:06:12.80000:06:12.810 tell in this photo maybe but there's a 00:06:14.24000:06:14.250 little bit of some moisture it looks 00:06:16.99900:06:17.009 like depositing in the backside of that 00:06:18.76900:06:18.779 and then look who we found on the inside 00:06:20.54000:06:20.550 of that sheetrock in several locations 00:06:22.58000:06:22.590 not good not good at all if you're in 00:06:27.29000:06:27.300 climate zone one two or three you don't 00:06:31.21900:06:31.229 want any kind of vapor retarder on the 00:06:33.83000:06:33.840 inside of the house whatsoever on the 00:06:36.74000:06:36.750 outside of the house you might have a 00:06:38.89900:06:38.909 low perm house rap 00:06:41.18000:06:41.190 or something that's gonna stop both 00:06:43.16000:06:43.170 water and vapor on the outside but on 00:06:46.28000:06:46.290 the inside of the walls you want nothing 00:06:48.71000:06:48.720 now there this is the climate zone from 00:06:51.17000:06:51.180 climate zones from the do-e so this is 00:06:53.54000:06:53.550 basically a map of all the different 00:06:55.10000:06:55.110 zones in America and if you're in 00:06:57.56000:06:57.570 climate zone four and above it actually 00:07:00.77000:07:00.780 you might actually use some amount of 00:07:02.60000:07:02.610 retarding of that moisture from getting 00:07:04.99000:07:05.000 into those walls but it's really only if 00:07:08.09000:07:08.100 you get into the very coldest zone in 00:07:10.19000:07:10.200 America which is climate zone seven up 00:07:12.14000:07:12.150 there where you might actually use a 00:07:14.00000:07:14.010 vapor retarder pretty much every other 00:07:16.52000:07:16.530 climate zone you don't need one on the 00:07:18.50000:07:18.510 inside and certainly you don't want to 00:07:20.84000:07:20.850 be using a plastic sheet okay last thing 00:07:23.45000:07:23.460 I want to mention going back to the web 00:07:24.74000:07:24.750 here go to building science comm and 00:07:27.41000:07:27.420 they have a bookstore and there's 00:07:29.45000:07:29.460 different climate zones as I mentioned 00:07:31.49000:07:31.500 and there's different ways to build and 00:07:33.23000:07:33.240 there's different zones the same house 00:07:35.24000:07:35.250 that you're gonna build in Minnesota is 00:07:36.86000:07:36.870 not going to work if you build that 00:07:38.42000:07:38.430 house down in Florida and so you 00:07:40.25000:07:40.260 actually want to buy the climate zone 00:07:42.02000:07:42.030 guide for your specific area this is 00:07:44.78000:07:44.790 your Bible from a building science 00:07:46.25000:07:46.260 perspective and there's of course 00:07:47.90000:07:47.910 there's a million different assemblies 00:07:49.43000:07:49.440 some people are using exterior 00:07:51.02000:07:51.030 insulation others are not you really 00:07:53.48000:07:53.490 want to get this book for your climate 00:07:55.13000:07:55.140 zone and figure out what's right for you 00:07:56.84000:07:56.850 but the long and short of this video is 00:07:59.00000:07:59.010 if you're in America you don't need a 00:08:01.07000:08:01.080 plastic sheet on the inside of your 00:08:02.48000:08:02.490 walls you don't need to worry about it 00:08:04.37000:08:04.380 the chances of a perm failure or a 00:08:07.10000:08:07.110 diffusion Ferrier failure are very very 00:08:09.95000:08:09.960 low most of the time if you have a 00:08:11.87000:08:11.880 problem it's because of air leakage 00:08:13.52000:08:13.530 through that cavity or bulk water that 00:08:15.74000:08:15.750 got in from the outside guys super geeky 00:08:18.56000:08:18.570 topic thanks for putting up with me 00:08:20.33000:08:20.340 doing a slightly different video from 00:08:21.98000:08:21.990 the office here comment below if you've 00:08:24.02000:08:24.030 got any comments on this if you like 00:08:25.55000:08:25.560 this format - I'd love to hear that 00:08:27.23000:08:27.240 otherwise follow me on Twitter Instagram 00:08:29.33000:08:29.340 or ever see you next time on the build 00:08:31.88000:08:31.890 show 00:08:47.65000:08:47.660
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