Thread: Vapor Barriers New Construction

New Construction. Builder installed continuous OSB exterior sheathing. 15lb felt in shingle fashion and then concrete fiber board siding. Interior has installed unfaced fiberglass batt insulation in the wall cavities. I haven't visited the home in a week since the pre-drywall inspection. Buyer called and stated the wall between the living space and the garage has a vapor barrier but there is no vapor barrier at any other exterior walls. She is looking for a code reference that requires a vapor barrier at all exterior walls. Chapter 11 discusses insulation but I am not able to find a vapor barrier requirement. Can anyone help? Sorry about lack of formatting. Editor will not recognize carriage returns for some reason.

From the IECC (Energy Code):
- R402.4 Air leakage (Mandatory). - - The building thermal envelope shall be constructed to limit air leakage in accordance with the requirements of Sections R402.4.1 through R402.4.4.
- - R402.4.1 Building thermal envelope.
- - - The building thermal envelope shall comply with Sections R402.4.1.1 and R402.4.1.2. The sealing methods between dissimilar materials shall allow for differential expansion and contraction.
- - - R402.4.1.1 Installation.
- - - - The components of the building thermal envelope as listed in Table R402.4.1.1 shall be installed in accordance with the manufacturer’s instructions and the criteria listed in Table R402.4.1.1, as applicable to the method of construction. Where required by the code official, an approved third party shall inspect all components and verify compliance.
- - - TABLE R402.4.1.1 AIR BARRIER AND INSULATION INSTALLATION
- - - - (see table, does not copy and paste to there)
- - - - - here is the air barrier requirement
- - - - - Air barrier and thermal barrier
- - - - - - A continuous air barrier shall be installed in the building envelope.
- - - - - - Exterior thermal envelope contains a continuous air barrier.
- - - - - - Breaks or joints in the air barrier shall be sealed.
- - - - - - Air-permeable insulation shall not be used as a sealing material.
- From the Definitions in the IECC:
- - AIR BARRIER. Material(s) assembled and joined together to provide a barrier to air leakage through the building envelope. An air barrier may be a single material or a combination of materials.

- From the IRC:
- N1101.1 Scope.
- - This chapter regulates the energy efficiency for the design and construction of buildings regulated by this code.
- - - Note: The text of the following Sections N1101.2 through N1105 is extracted from the 2012 edition of the International Energy Conservation Code—Residential Provisions and has been editorially revised to conform to the scope and application of this code. The section numbers appearing in parenthesis after each section number are the section numbers of the corresponding text in the International Energy Conservation Code—Residential Provisions.

- N1101.9 (R202) Defined terms.
- - The following words and terms shall, for the purposes of this chapter, have the meanings shown herein.
- - AIR BARRIER. Material(s) assembled and joined together to provide a barrier to air leakage through the building envelope. An air barrier may be a single material or a combination of materials.
- N1102.4 (R402.4) Air leakage (Mandatory).
- - The building thermal envelope shall be constructed to limit air leakage in accordance with the requirements of Sections N1102.4.1 through N1102.4.4.
- N1102.4.1.1 (R402.4.1.1) Installation.
- - The components of the building thermal envelope as listed in Table N1102.4.1.1 shall be installed in accordance with the manufacturer’s instructions and the criteria listed in Table N1102.4.1.1, as applicable to the method of construction. Where required by the building official, an approved third party shall inspect all components and verify compliance.
- - TABLE N1102.4.1.1 (R402.4.1.1) AIR BARRIER AND INSULATION INSTALLATION
- - - (Same table as TABLE R402.4.1.1 AIR BARRIER AND INSULATION INSTALLATION in the IECC)

Thanks for the quick response. Its a hour+ drive one way to the building site. Unlikely I will be "just stopping by" to follow up unless client is paying time & travel expenses.

Generic OSB or something like the newer ZIP wall? ZIP wall systems are an air barrier, but probably not in use here. I haven't seen it at all in person, only in magazines so far.

Originally Posted by Jim Robinson

Generic OSB or something like the newer ZIP wall? ZIP wall systems are an air barrier, but probably not in use here. I haven't seen it at all in person, only in magazines so far.

I've seen it and don't like it.

All the seams need to be tape sealed, the nails are to be driven flush but not into the surface coating, if they are the nail heads must be taped sealed over too - I don't recall all the stuff from the installation instructions, but the contractor putting it on hadn't read the installation instructions and didn't like having to do all that it said had to be done, but did it after reviewing the installation instructions.

Seemed like it didn't save that much labor and materials in the end (was his opinion).

To clarify, though, an "air barrier" is not the same as a "vapor retarder" (paper facing is a vapor "retarder", not a vapor "barrier") - and "vapor retarders" are questionable as to being required, not required, located inside ("warm in winter side" as it used to be referred to), or located outside (on the exterior of the wall).

In some geographic locations, the preferred location of the vapor barrier changes with the time of year - of course, it is not possible to relocate where the vapor barrier is after construction - maybe technology can change that in the future, but that is not available now.

Dr Joe L. has this: BSD-106: Understanding Vapor Barriers ? Building Science Information

Vapor and air barriers are different animals. Vapor barriers can restrict a wall's ability to release moisture. I wouldn't want it on my home.

Originally Posted by Eric Barker

Vapor and air barriers are different animals. Vapor barriers can restrict a wall's ability to release moisture. I wouldn't want it on my home.

I would want one (vapor barrier) on the inside of the exterior walls in my house to help reduce the vapors being generated inside the living space from migrating into the wall cavities where the insulation is.

We have ZIP walls and like Jerry, I don't care for them. Anything that depends on a 4"wide of basically fancy duct tape to make the system water resistant had got to eventually fail! Just read the install guidelines and it does not take much of an imagination to see that it is a flemsey system. The biggest flaw I see is that the tape can not be removed and reapplied. It must go down perfect the first time and we all know that is not going to happen.

Originally Posted by Jerry Peck

I've seen it and don't like it.

All the seams need to be tape sealed, the nails are to be driven flush but not into the surface coating, if they are the nail heads must be taped sealed over too -

Jerry,

Even though there are thousands of contractors that install Hardie Siding products it is rare to find them installing to the manufacturer specification. Usually they don't hold nail centers to the spec, gap the sheets (if sheet siding) for expansion and caulking. Whether lap siding or sheet siding the nail heads must be proud and fully driven or flush to the material surface ONLY. I have seen sheet siding with only half the required nails and some that had only three or four "good nails".

Any nails that are under driven must be driven properly (finishing hammer with finesse) and any that are over driven must be sealed and don't count in the nail pattern (breaks the concrete board and has no strength).

In my case the answer was to have a very good pressure regulator on my compressor, a larger air tank reserve, and purchase an extremely high quality (read expensive and well designed) nail gun. I was able to actually produce a quality installation, but not with cheap or average workman grade tools. They must be high quality and very well designed and maintained. My nail gun also has a rubberized protector and wont work well without it on cement boards.

Also, one needs to be sure the siding material is fully pressed to the structure before nailing or the nails will make holes in the concrete board siding (they won't count in the nail pattern). If a remodel be sure and set the depth for new wood and use a hammer to seat the nails flush in the old wood.

The material you are describing seems like it would be very similar to install. Hope this helps others. The expense of excellent tools is less than the learning cost in rework and repair.

Dirk,

Overdriving nails with a nail gun is a common problem with every product, especially roof sheathing and wall sheathing.

I've frequently told contractors that if they get a higher pressure tank with more capacity and set that regulator high, then add another regulator at the gun with a lower setting to control the gun - the gun will be consistent and not lose pressure during use.

It solves the problem without the real expensive equipment.

Originally Posted by Jerry Peck

I would want one (vapor barrier) on the inside of the exterior walls in my house to help reduce the vapors being generated inside the living space from migrating into the wall cavities where the insulation is.

I rarely see houses at the pre-drywall stage, but I've never seen the vapor barrier completely sealed. AHJs here never require it. A few years ago, a Realtor asked me to look at her basement that was being finished. The outside temps were hovering in the zero area. The contractor had some walls completely drywalled and was spraying texture while exterior walls on the walk-out side hadn't been rocked yet. The wet texture had spiked the humidity in the basement. The walls not rocked were sweating so badly inside the vapor barrier that water was running out the bottom of the plastic. It was an eye-opening observation about what can happen when the vapor barrier isn't completely sealed.

Interesting. Original post is asking about IRC requirements for a vapor barrier, then the next few replies are talking about air barriers. Is there some confusion here? In my mind, when you are designing the exterior of a home, you need to consider 3 elements:
- a barrier to keep out the hot or cold wind, the air barrier
- a barrier to keep out water such as rain or snow, the vapor or water barrier
- a barrier to keep out the heat or cold, the thermal barrier
But you also need to consider the climate: is it hot and humid outside so you want to limit the amount of moisture (humidity) migrating into your air conditioned home, or is it cold and dry outside so you want to allow some humid interior air to breath out while also keeping the nasty bitter cold temperatures out?

Notice the different approach taken by two of the prior replies, one from Florida, and one from Colorado? I live in a mixed northern climate, where the relative humidity can change from 54% in the morning to 18% in the afternoon, be 25 degrees below and dry, then damp as hell in the spring, then dry as a desert in August. In my area, I think you have to have a house that can breathe in and out, whether by using semi-permeable barriers, and/or air exchange ventilation systems. Most people, even locals, think of Montana a being a dry state (which is in some areas), but if that is true, then why do I have to deal with a LOT of mold and wood rot problems?

Jerry is correct, the BSC is a great source of information, and we should all read as much as possible. I have become an ardent student of another source, Allison Bailes at the Energy Vanguard. He also has a sense of humor, which makes reading his material easier.
His latest article, "The Gap Between Stupid and Hurt Is Narrowing" is short and simple. Great newsletters, and he challenges some of the concepts about how to handle moisture in the home. Oh, you have to understand that his viewpoint is from living in the southern US, so those of us in the middle or northern latitudes have to adjust a little.

Originally Posted by Terry Beck

3 elements:
- a barrier to keep out the hot or cold wind, the air barrier
- a barrier to keep out water such as rain or snow, the vapor or water barrier
- a barrier to keep out the heat or cold, the thermal barrier

And I forgot to stress that each barrier type has very different requirements, may need very different materials, and somehow need to work together.
I.E. Have you ever seen "flash & dash" insulation (combination of closed cell foam spray with traditional fiberglass batting)? I found one home where there was a lot of condensation in some walls and ceilings with this insulation method because the dew point fell at the layer between the foam and fiberglass. Interesting lesson in vapor barrier vs thermal barrier.

Originally Posted by Terry Beck

I.E. Have you ever seen "flash & dash" insulation (combination of closed cell foam spray with traditional fiberglass batting)? I found one home where there was a lot of condensation in some walls and ceilings with this insulation method because the dew point fell at the layer between the foam and fiberglass. Interesting lesson in vapor barrier vs thermal barrier.

I have never seen that combination, however, I am acutely aware that the dew point can fall inside the wall under various conditions ... and having the dew point fall within the wall space is not something one strives for.

I believe one of the reasons for the development of EIFS was to keep the dew point outside the wall near the exterior surface instead of in the wall cavity. I frequently wonder if some of the rotted out walls behind EIFS is not because of leak but because the dew point is at the sheathing.

http://www.tlpca.org/images/articles_condensation.pdf

BSD-163: Controlling Cold-Weather Condensation Using Insulation ? Building Science Information

BSI-049: Confusion About Diffusion ? Building Science Information

Moisture Management | Whole Building Design Guide

Many treatments for many places and constructions.

BSD-106: Understanding Vapor Barriers ? Building Science Information

Part of the confusion is that some areas have attributes of several climes. Here, we are generally drier with low humidity, but this year was one of the wettest on record.

As home inspectors, we don't open up walls to see what's going on inside (unless you're named Holmes). We only report on what we see on the surfaces. I rarely see stucco, or stone/brick veneers applied to best practices, yet I rarely see problems. Our dry climate lets builders get away with cutting corners that they could never get away with back east or in the south.

The vapor retarder requirements has been moved to section R601.3 in the 2009 IRC. It is the same requirements moved to section R702.7 in the 2012 & 2015 IRC with additional amendments shown below. Apologized for not knowing how to maintain the table format. Codes can be viewed here: ICC FREE RESOURCE
You still refer to Chapter 11 for the climate zone using Class 1 or II vapor retarders or use Table R702.7.1 with Class III vapor that allow more moisture vapor to pass through in the wall systems listed.


R702.7 Vapor retarders. Class I or II vapor retarders are
required on the interior side of frame walls in Climate Zones
5, 6, 7, 8 and Marine 4.
Exceptions:
1. Basement walls.
2. Below grade portion of any wall.
3. Construction where moisture or its freezing will not
damage the materials.
R702.7.1 Class III vapor retarders. Class III vapor
retarders shall be permitted where any one of the conditions
in Table R702.7.1 is met.
TABLE R702.7.1
CLASS III VAPOR RETARDERS
CLIMATE
ZONE CLASS III VAPOR RETARDERS PERMITTED FOR:a
Marine
4
Vented cladding over wood structural panels.
Vented cladding over fiberboard.
Vented cladding over gypsum.
Insulated sheathing with R-value ≥ 2.5 over 2 × 4 wall.
Insulated sheathing with R-value ≥ 3.75 over 2 × 6 wall.
5
Vented cladding over wood structural panels.
Vented cladding over fiberboard.
Vented cladding over gypsum.
Insulated sheathing with R-value ≥ 5 over 2 × 4 wall.
Insulated sheathing with R-value ≥ 7.5 over 2 × 6 wall.
6
Vented cladding over fiberboard.
Vented cladding over gypsum.
Insulated sheathing with R-value ≥ 7.5 over 2 × 4 wall.
Insulated sheathing with R-value ≥ 11.25 over 2 × 6 wall.
7 and 8
Insulated sheathing with R-value ≥ 10 over 2 × 4 wall.
Insulated sheathing with R-value ≥ 15 over 2 × 6 wall
For SI: 1 pound per cubic foot = 16 kg/m3.
a. Spray foam with a minimum density of 2 lb/ft3 applied to the interior
cavity side of wood structural panels, fiberboard, insulating sheathing or
gypsum is deemed to meet the insulating sheathing requirement where the
spray foam R-value meets or exceeds the specified insulating sheathing Rvalue.
R702.7.2 Material vapor retarder class. The vapor
retarder class shall be based on the manufacturer’s certified
testing or a tested assembly.
The following shall be deemed to meet the class specified:
Class I: Sheet polyethylene, unperforated aluminum
foil.
Class II: Kraft-faced fiberglass batts.
Class III: Latex or enamel paint.
R702.7.3 Minimum clear air spaces and vented openings
for vented cladding. For the purposes of this section,
vented cladding shall include the following minimum
clear air spaces. Other openings with the equivalent vent
area shall be permitted.
1. Vinyl lap or horizontal aluminum siding applied
over a weather resistive barrier as specified in Table
R703.4.
2. Brick veneer with a clear airspace as specified in
Table R703.7.4.
3. Other approved vented claddings.

Originally Posted by Terry Beck

And I forgot to stress that each barrier type has very different requirements, may need very different materials, and somehow need to work together.
I.E. Have you ever seen "flash & dash" insulation (combination of closed cell foam spray with traditional fiberglass batting)? I found one home where there was a lot of condensation in some walls and ceilings with this insulation method because the dew point fell at the layer between the foam and fiberglass. Interesting lesson in vapor barrier vs thermal barrier.

I dont like the flash and batt system. What you find is that wall lose a of heat through the sutds. The effective R value of a wall will be about 25-30% lower than r value between the studs. The flash does not stop the thermal bridging.

Depending on your climate you will need and r 5 and above. Try controlling the thickness of spray foam. It is not a uniform depth. In northern climate you are right in that you will have condensation.

Then there is the quality control issue of field applied foam.

I would recommend adding rigid insulation exterior of the sheathing. It would cure the condensation and stop thermal bridging.

Originally Posted by Robert Hronek

I dont like the flash and batt system. What you find is that wall lose a of heat through the sutds. The effective R value of a wall will be about 25-30% lower than r value between the studs. The flash does not stop the thermal bridging.

Depending on your climate you will need and r 5 and above. Try controlling the thickness of spray foam. It is not a uniform depth. In northern climate you are right in that you will have condensation.

Then there is the quality control issue of field applied foam.

I would recommend adding rigid insulation exterior of the sheathing. It would cure the condensation and stop thermal bridging.

Thermal bridging at the studs has been a long conversation. 2"x6" and 24oc being the new way to match energy and material conservation.

I am not a fan of field applied foam. To many things can go wrong.Polyurethane Foam Products Class Action Lawsuit - Home
Extruded board and other forms of manufactured foam products are good.

The bottom wall plate is the most important to get efficient in clod climates.
That is done with foam in my neck of the woods.

As for the framing, thermal bridging will remain an issue. When a building is done effectively it is very good. I inspected a condo yesterday. Minus 20 and everything within the wall assembly was close to 69 degrees. Very little thermal bridging. I will post the images later.