Comments on: What Happens When You Put a Plastic Vapor Barrier in Your Wall?

By: John Wilson

John Wilson — Mon, 01 Jun 2015 18:06:48 +0000

do I need to put poly in the
do I need to put poly in the ceiling of a drywalled unheated garage before I blow in insulation?

By: Richard Lyders

Richard Lyders — Wed, 08 Apr 2015 14:18:15 +0000

Any chance you could help us
Any chance you could help us with our dilemma? Our 1930's wood-framed brick-veneer house in hot, humid Houston is being gutted and remodeled. We had spray foam insulation (open cell, I recall) sprayed on all walls, the underside of the roof and the underside of the floor in the crawlspace under the house of pier and beam foundation. (NOTE there is one 25'X15' room that sits on a slab foundation ... interestingly, we also have a 10'x12' basement that filled up with water during Tropical Storm Allison.)

There is no vapor barrier between the brick and the wood framed walls. In fact, the original tar paper against the wood frame is probably rotted away based on what I've seen from the spots where we have done brick work in the past. I'm being told that our walls will rot in 20 years if we don't install a vapor barrier because the spray foam will cause moisture to collect in the wood keeping the wood wet without any proper method of drying out. We didn't plan on tearing off all the brick to install a vapor barrier, but we don't want our walls to rot or be fodder for termites. Any chance you have some good advice for us to help keep our home energy efficient, comfortable, and not slowly rotting away? Thanks so much for your help.

Regards,
Rich

By: ivin boren

ivin boren — Wed, 01 Apr 2015 21:46:52 +0000

Vent under the house.Poly 6
Vent under the house.Poly 6 mil. over dirt.Direct roof and ground water away from and around house.Do these first.

By: Londi Dennis

Londi Dennis — Sat, 14 Mar 2015 02:34:23 +0000

I purchased a home that's 130
I purchased a home that's 130 year old. It has cypress throughout all of the walls. I love the house my only problem is that the walls sweat... The home doesn't have a basement and it sit on piers off of the ground, can you please advise me what I may do to help with removing the water out of the walls

By: Jared Davis

Jared Davis — Tue, 15 Jul 2014 22:22:35 +0000

Although I am a Mechanical
Although I am a Mechanical Engineer, I don't do residential construction so the understanding in this area wasn't totally there until reading your article. Thank you for lining out the overall picture of utility of vapor barriers. I came to the same conclusion as you, but like you mentioned at the beginning was quite confused by the dearth of common sense fact based information (there is a huge amount of information, but most of it does not justify their conclusions). It is nice to hear that you and other professionals are coming around to the same conclusion that I came to (although obviously my mind wasn't made up as to whether or not I had come up with the correct conclusion until now).

I have to say, I live in super-high humidity (South-east Iowa) and have an old house with a basement full of clay dirt/mud which brings in huge amounts of humidity due to the high temperatures in the basement. So this gives me the understanding that I need to control that year round source of moisture from the ground by first redirecting as much moisture away from the basement as possible, AND THEN seal off the ground to the basement environment as good as I can to retard the vapor from getting in there in the first place. Then obviously I need to control the humidity with a dehumidifier so I can apply some polyethylene to the floors of my home. Thanks again!

By: mathew braun

mathew braun — Fri, 25 Apr 2014 02:53:29 +0000

what is your take on the
what is your take on the inside in a rain screen wall type in a wet to colder climate?

By: John Proctor, P.E.

John Proctor, P.E. — Fri, 25 Apr 2014 00:54:18 +0000

Digressing again to the ducts
Digressing again to the ducts!! So people still like flex duct. The linked 1995 study for EPRI showed that in residential new construction in a dry climate, only two builders out of 10 had appropriate AC airflow for the climate. One of the builders used oversized air handlers to accomplish this (with massive watt draw penalties) and the other used rigid duct. All the rest of the inappropriate airflows were using flex duct (see figure 2-5). Has nothing changed?

By: David Butler

David Butler — Thu, 24 Apr 2014 22:13:52 +0000

In mixed humid climates (most
In mixed humid climates (most of eastern US), it's best to have vapor retarder in middle of the thermal sandwich. This can easily be accomplished with continuous foam boards on the exterior, fibrous insulation on the inside and a couple of layers of inexpensive building felt on the wood sheathing. This also mitigates thermal bridging.

By: Sean @ SLS

Sean @ SLS — Thu, 24 Apr 2014 21:19:52 +0000

Allison – as an FYI, blue
Allison – as an FYI, blue board in this case is actually a specially coated drywall sheet specifically meant for plaster
Jack – the materials still allow for drying both ways

By: Allison Bailes

Allison Bailes — Thu, 24 Apr 2014 20:20:32 +0000

A Hyde: Oh
A Hyde: Oh, but you should have seen the sauna, the great room, and the billiards parlor!

Bob K: Good idea! I did write about that house a year ago. It's one that Martin Holladay and I discovered when he was here in Atlanta: The Energy Nerd's Tour of Green Homes in Georgia.

Charles: My friend Mike Barcik has a good description for a wall where you put poly on both sides: a terrarium. It's a stupid idea.

jack: By blueboard, you probably mean extruded polystyrene (XPS). It's a class II or class III vapor retarder and can work fine, even with plaster on the outside, as long as you allow for moisture that gets behind it to drain away. A drainable housewrap behind the XPS works for that purpose.

Darrel T.: It does indeed look like it could be condensation behind the poly, but it wasn't. The material is translucent, and that's what makes it look like it may be fogged up with condensation. I wouldn't be surprised if it does fog up sometimes, though.