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Is bubble insulation as good as rigid foam?

I am having a home built. I want to install insulation on the outside of the home. I live in Southern Illinois, which according to BuildingScience.com is a mixed-humid location like Louisville, Kentucky.

I was planning to have 0.5 inch rigid foam insulation installed, but my framer stated he can get bubble insulation. He said he normally installs this under metal roofs, but it would be as good as R value wise as 0.5 inch rigid foam. Is this true? Are there any issues with using it as an outside wall insulation method? The walls are OSB with house wrap, and we will have vinyl siding.

Asked by Chris Johnston
Posted Sun, 06/06/2010 - 12:15

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43 Answers

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1.
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While a half-inch of foam won't offer much thermal protection, it is still far superior to bubble foil which has an R-value of about 1 per inch and is effective as a radiant barrier only with an adjacent air space.

Answered by Riversong
Posted Sun, 06/06/2010 - 13:05

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Chris,
The cost of bubble wrap is much higher (in terms of R-value per dollar) than any type of rigid foam.

You are in Climate zone 4. If you want to install insulation on the exterior side of your wall sheathing, you'll need at least R-2.5 for a 2x4 wall or R-3.75 for a 2x6 wall to avoid the dangers of condensation in your wall cavity. You can't achieve these minimums with bubble wrap. For a 2x4 wall, you'll need at least 1/2 inch of XPS; for a 2x6 wall, you'll need at least 3/4 inch of XPS. More would be better.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 06/07/2010 - 09:08

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Thank you very much for the information. I plan to use 0.75-inch. Now my buidling supplier is saying I don't need XPS because I have house wrap and OSB walls, and he also says I don't need to tape the joints. I am assuming he is wrong. Any comments appreciated!

Answered by Chris Johnston
Posted Wed, 06/09/2010 - 16:19

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And his reasoning is what?

OSB is for shear strength and a nailbase.

WRB is for a secondary weather barrier and drainage plane.

XPS is for thermal protection.

They have three distinct functions, though taped XPS can double as a WRB (as long as the tape holds forever).

If the WRB is over the XPS, then you don't have to tape the seams of the foam board, though it will improve its performance. And 3/4 inch XPS is still not much thermal protection. I would suggest using a minimum of 1".

Answered by Riversong
Posted Wed, 06/09/2010 - 16:25

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Thanks again. The housewrap (WRB) is already up and over the OSB. I am definitely, regardless of supplier or framer's opinions, installing the insulation (rigid foam) on the outside of the home - even if I have to do it myself. I will also tape the insulation joints. Siding will go over this.
Is XPS rigid foam required, or are there other types that are acceptable, such as EPS? Sorry, I am new to all this.

Answered by Chris Johnston
Posted Wed, 06/09/2010 - 16:47

6.
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Chris,
You can choose XPS, EPS, or polyisocyanurate (polyiso). The current consensus is that polyisocyanurate is the most environmentally friendly -- (ozone-friendly blowing agents and low greenhouse-gas potential).

Unless your foam is very thin -- and I think it should be as thick as you can afford -- you will want to install vertical 1x3 or 1x4 strapping, screwed through the foam to the studs. This will create a rainscreen gap between your siding and the foam, and will give you something to attach your siding to.

Be sure that your windows, doors, and other penetrations are carefully flashed, and that all flashing is integrated with your WRB.

Answered by Martin Holladay, GBA Advisor
Posted Wed, 06/09/2010 - 17:01

7.
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Chris,

If there is an interior vapor barrier, you certainly shouldn't use a second vapor barrier, like foil-faced polyiso foam, on the exterior.

And vinyl siding cannot be installed on a rainscreen. It requires solid sheathing for support.

Answered by Riversong
Posted Wed, 06/09/2010 - 17:06

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Robert,
You wrote, "Vinyl siding cannot be installed on a rainscreen." I disagree.

I often tell builders that vinyl siding doesn't need a rainscreen. But it's certainly possible to install a rainscreen behind vinyl siding. In fact, rainscreen strapping is the best approach when installing vinyl siding over thick foam.

According to the Vinyl Siding Institute (http://www.vinylsiding.org/publications/0804_VSI_2007Manual.pdf), "Space the fasteners [used for attaching vinyl siding] a maximum of 16” apart for the horizontal siding panels, every 12” for the vertical siding panels, and every 8” to 12” for the accessories. These distances may be increased if the manufacturer permits greater spacing based on windload testing."

A standard rainscreen resource ("A Reference Guide of Typical Rainscreen Wall and Window Details") developed by a coalition of British Columbia warranty providers in response to the "leaky condo" crisis includes details for vinyl siding installed over rainscreen strapping:
http://www.nationalhomewarranty.com/NewPDF/ACCEPTED_RAINSCREEN%20DETAILS...

Finally, at least one company (Vision Building Products) has developed a rainscreen strapping product (SidingMaster strapping) that was originally developed specifically for vinyl siding:
http://www.sidingmaster.com/productinformation.shtml

Answered by Martin Holladay, GBA Advisor
Posted Thu, 06/10/2010 - 04:54

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Martin,

Double check your sources. The Vinyl Siding Institute quote you pulled is only about fastener spacing, not substrate. That same document also states: "Take appropriate actions to ensure a smooth and continuous surface...Keep in mind that siding can only be as straight and stable as what lies under it."

The BC Rainscreen Guide starts with this disclaimer: "The drawings and text are intended as a general reference guide only…These details are not intended to replace professional advice…Ensure that materials used in conjunction with one and another are compatible."

And the Building Vision rainscreen uses a very thin ¼" metal strap and a high-density foam-backed vinyl to minimize deflection and warpage. They also advocate the use of a modified bubble-foil WRB behind their system - a product you have sharply criticized.

Can you use a rainscreen behind a cladding material that is designed, by itself, to be a breathable rainscreen? Sure. Is it best practice? That would be very hard to justify.

As you know, I've often installed wooden siding directly over framing and WRB with no sheathing, but I will use only 3/4" horizontal siding and never clapboards, which are too flimsy to span between studs without distortion or impact damage.

Answered by Riversong
Posted Thu, 06/10/2010 - 12:12

10.
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Robert,
I stand by my references and my interpretation of those references.

Answered by Martin Holladay, GBA Advisor
Posted Thu, 06/10/2010 - 12:46

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Robert,
I have further researched this question by interviewing David S. Johnston, the senior technical director at the Vinyl Siding Institute in Washington, DC. Here's what Johnston said:

“The installation of vinyl siding on vertical furring strips has always been an accepted option: for instance, over masonry walls. In many cases, using furring strips is actually the only possible way to install vinyl siding. Another example is a re-siding application, where the installer wants to install new siding without tearing off the existing siding. So the installation of vinyl siding over furring strips is not new or controversial.

"In the case of an installation on a house with foam sheathing over advanced framing, there is an ongoing discussion over how best to determine the overall wind-load resistance of the wall assembly. But obviously, the vinyl siding will be just as well attached to the furring strips as it would be with any other installation.”

Answered by Martin Holladay, GBA Advisor
Posted Thu, 06/10/2010 - 14:46

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Martin,

An industry trade organization is almost always NOT the most reliable source for objective information. Their mission is to encourage the use of the least durable, most environmentally-destructive siding material.

Answered by Riversong
Posted Thu, 06/10/2010 - 14:53

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Hello Martin, good stuff you found. It has been a while. How are you?

You know I am a believer in rain screens for vinyl and all types of cladding. Robert are you saying that my siding master only works with my new foam back panel. This is incorrect. It works with all types of vinyl ( hollow back as well). I have installations that are installed with a .042 Certainteed panel and it is a 7 year old installation and it looks straighter than most nailed siding installations with thicker panels. As far as needing a smooth surface. This is exactly what a furring strip does. It does not say (Put foam in between furring) The V.S. I. also states to nail the siding into the sheathing and into solid framing members (Studs) but very few vinyl siding installers ever do this.
Other manufactures like ABTCO suggest furring on resides like all of the manufactures do but nobody does it. Instead they use fan fold insulation that will follow every curve in a wall and you end up with wavy looking siding anyway?

Between nailing to tight, too loose, not adding enough nails or too many nails added causes more unsightly looking installations then any furring vinyl siding application ever will because a person who is installing vinyl siding with furring probably cares more.
I have ripped off so many aluminum and old vinyl jobs that I am convinced that the vinyl siding does not allow all the moisture to escape. Are you aware of the 2006 IRC WRB code 703.1 that states that you must provide a means of drainage behind all claddings?
You better get used to the rain screen theory being used a lot more because it just makes common sense. Oregon just passed a state wide rain screen code and this includes vinyl siding.

Greg Albracht
Inventor
Siding Master and Furring Master

Answered by Greg Albracht
Posted Thu, 06/10/2010 - 19:13

14.
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And next we'll hear from the CEO of BP telling us how wonderful and safe deep sea drilling is.

Answered by Riversong
Posted Thu, 06/10/2010 - 19:50

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I am trying to digest all this. May I ask, Mr. Riversong, what the concern is with OSB covered with WRB then foam, then vinyl siding? Is there a risk in moisture accumulating or condensation and mold? I'm just trying to figure out the content of both side of the discussion. Thanks again, I never realized my question would lead to all this :-)

Answered by Chris
Posted Thu, 06/10/2010 - 21:34

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A discussion of the 'right' way to install vinyl siding on a forum devoted to environmentally responsible building? Could someone please tell me what's green about this unfortunate material?

Answered by James Morgan
Posted Thu, 06/10/2010 - 23:19

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Chris,

"What's wrong with it?" is a many-faceted question.

OSB is a cheap alternative to plywood, which itself is a modern alternative to board sheathing. As we know from building and material science, the more we process wood materials, the more vulnerable it becomes to mold and decay organisms. So, if you want a durable structure, avoid OSB.

Rigid foam insulation is a high embodied energy, high global warming potential material that is far less vapor permeable than traditional building materials. It's becoming commonly used exterior to OSB to keep the moisture-vulnerable sheathing above the winter dew point (the "warm sheathing" approach) to minimize condensation potential. But, since it's still possible to get condensation on the inside surface of the outside foam board, builders are resorting to a "wrinkled" drainage membrane between the two. In other words, the exterior foam is used to protect the OSB, but since it can also create another threat to the OSB, an additional material must be used to protect the OSB from what was supposed to protect the OSB.

Additionally, studies have shown that once an exterior leak (which always happens at some time in the life of a house) introduces moisture into the wall framing, the exterior foam board sufficiently interferes with drying potential to the outside to keep the framing wet for far too long, and since it also keeps it warm makes it far more vulnerable to mold and decay.

Of course, vinyl siding is an environmentally destructive material. PVC is the most common plastic in every type of consumer "good", puts deadly dioxins into the environment at both the manufacturing end and the disposal end of its life cycle, and uses phthalates for flexibility (a dangerous VOC) and sometimes cadmium (a dangerous heavy metal).

Answered by Riversong
Posted Thu, 06/10/2010 - 23:55

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Chris,
Many people who post their opinions on this Web site state their positions strongly. Of course, it's up to you to choose the materials that you want to use for your project.

Although Robert believes that vinyl siding can't be installed over vertical furring, such installations are very common and are supported by vinyl siding manufacturers.

While some builders object to the use of vinyl, I don't take an absolutist position on the siding. It's hard to have a vinyl-free house, since vinyl is used to make insulation for Romex cable and is commonly used for drain pipes. (I used to work in a plumbing warehouse, so I know all about cast-iron drain pipe -- so yes, there are alternatives.)

Vinyl siding drains well and performs very well from a moisture-management perspective.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 06/11/2010 - 05:21

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Robert , You are a very unprofessional person who thinks he knows it all. Nobody knows it all in this world. We do not need people like you spouting off their uninformed opinions with no facts.
I bet you nail too tight too on all of your siding installations. And Martin yes vinyl does drain but not all of the moisture. See the demonstration link below.

http://www.youtube.com/user/sidingmaster#p/a/u/1/3jVlk0zlh2k

If vinyl does not hold moisture (Which it does) then why did the state of Oregon go to a statewide rain screen code that requires even vinyl siding to use an 1/8 minimum air gap?

http://sidingmaster.com/mold_problems.shtml

HUD Report
http://sidingmaster.com/hud_report.pdf

Answered by Greg Albracht
Posted Fri, 06/11/2010 - 07:44

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Another thing Robert. I do not spec out a (BUBBLE WRAP) as you call it. It is Low E insulation that is perforated to a perm rating of 5. Bubble wrap should NEVER be used on exteriors walls in certain regions because they are not perforated. They will create a vapor barrier on the wrong side. Low E reflection insulation is perforated and is approved by vinyl siding manufactures like Mastic, Certainteed and others. This Low-e house wrap seals around all of the fasteners unlike regular house wrap that leaves 1000's of holes in the wall. You gain the high R-Factor because with hollow back vinyl and my Siding Master you get approximate 3/4" air gap behind the siding for the reflective insulation to work and achieve this higher R-factor.

Answered by Greg Albracht
Posted Fri, 06/11/2010 - 08:00

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Robert you stated this below:

"As you know, I've often installed wooden siding directly over framing and WRB with no sheathing, but I will use only 3/4" horizontal siding and never clapboards, which are too flimsy to span between studs without distortion or impact damage" Robert Riversong

Wow Robert, you really do not know anything about building science if you install wood siding without a rain screen. If you were installing siding like this in Canada you would have your installation stopped and for good reason. You would be trapping moisture. Have you seen the new NAHB report below. You are very uninformed. I will help educate you if you have an open mind. Wrinkled house wrap does not work very well either. There are reports out about this type of house wrap that is failing.

2008 NAHB Report
http://sidingmaster.com/documents/NAHBRAINSCREENREPORT2009.pdf

Answered by Greg Albracht
Posted Fri, 06/11/2010 - 08:27

22.
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Thanks for all your comments. I really do appreciate.

Answered by Chris
Posted Fri, 06/11/2010 - 09:42

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We do not need people like you spouting off their uninformed opinions with no facts.

"We", I assume, being those who make a living selling environmentally destructive materials and promoting poor building practices and passing them off as "green".

As most of the readers of this forum know, everything I post here is based on an exacting understanding of building science, hygrothermal engineering and best building practices, based on more than 30 years of pioneering design and construction, research and teaching.

As I've stated many times before, the rainscreen approach can be helpful in some situations, but is unnecessary in most. The HUD PATH Best Practices Guide concurs with this.

Using a methodology, like rainscreen, without fully understanding all its implications is foolish. One of the unintended consequences of leaving an air gap, particularly a vertical one, behind cladding is the creation of the same kind of fire channel that our building codes long ago prohibited within the framing. If the rainscreen channel is open to the soffit and roof, then an exterior fire will quickly consume the roof.

In all but the most extreme rain exposure climates, back-sealed wooden cladding over a WRB is a functional and durable and environmentally-sound option.

Greg, what's "unprofessional" is attacking the messenger when one is unable to make a rational critique of the message.

Answered by Riversong
Posted Fri, 06/11/2010 - 10:43

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What HUD report on you reading? It says the total opposite of what you just stated! Look at the map of moisture areas that HUD shows.
I never spec my products to ventilate into a roof or overhangs, so your comment means nothing. You are assuming that all rain screen installations are done this way. Once again you are the uninformed person. .So what you are saying is Robert that you still think that installing wood siding without a rain screen is the best practices approach? You are incorrect. The HUD reports highly recommends the use of an air gap behind cladding in about 3/4 of the US. I highly suggest you keep building the old way. It will keep me in business for decades to come.

Greg Albracht

Answered by Greg Albracht
Posted Fri, 06/11/2010 - 11:21

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Fire blocking mis-information that Robert Riversong is spreading about rain screens. He does not have a clue of what he is talking about.

STATE OF OREGON INTEROFFICE MEMO
BUILDING CODES DIVISION
JANUARY 19, 2006
To: Mark Long, Administrator
From: Ravi Mahajan, Facilities Engineer
Subject: Rainscreen fire hazard concerns

This memo summarizes my research and conclusions in response to concerns from individual task force members regarding the potential fire hazard posed by a drainage cavity behind the exterior cladding.

Research
National standards/testing bodies: I contacted Oregon Masonry Institute, Brick Industry of America, ICC Evaluation Services, and Underwriters Laboratories. None of these organizations were aware of any fire hazards, and they do not have any testing or research data in support or against this issue.

British Columbia: Neither Dave Ricketts, RDH Building Science, Inc., nor Bob Maling, Homeowner Protection Office, were aware of any fire hazards. Mr. Maling indicated that Canadian officials felt that the fire-blocking requirements of the building code for concealed cavities sufficiently addressed this issue.

Oregon State Fire Marshal: John Caul consulted with his colleagues across the state. The general conclusion was that a drainage cavity did not pose an issue provided the existing fireblocking measures in the building code were followed. (I have attached the relevant sections of the building code.) In non-combustible construction, they concluded there would not be enough air flow to create much of a draft. In combustible construction, they felt that the limited increase in risk was warranted given the rising number of mold, mildew, and rot issues.

Conclusion:
Based on the research summarized above, using a drainage cavity behind exterior cladding does not pose a significant fire-hazard. These concerns are adequately addressed by requiring fireblocking for the full depth of the drainage-cavity at each story and every 10'-0" on center horizontally. Furthermore, in the type of high-density construction common in multi-family housing, the exterior walls of the structure are required to be fire-rated, so the exterior wall would provide protection against the fire for the time-period for which it is rated.

Oregon Building Code requirements:
- "Weep holes provided in the outside wythe of masonry walls shall be at a maximum spacing of 33 inches on center. Weep holes shall not be less than 3/16 inches in diameter." (Section 2104.1.8, 2004 OSSC).

- "Flashing shall be installed in such a manner so as to prevent moisture from entering the wall or to redirect it to the exterior. Flashing shall be installed at ... exterior wall intersections with roof ... and similar locations where moisture could enter the wall." (Section 1405.3, 2004 OSSC).

- "Flashing and weepholes shall be located in the first course of masonry above finished ground
level above the foundation wall or slab, and other points of support, including structural floor, ...." (Section 1405.3.2, 2004 OSSC)

- "Fireblocking shall be provided in concealed spaces of stud walls and partitions, including furred spaces, and parallel rows of studs or staggered studs as follows: a. vertically at the ceiling and floor levels, b. Horizontally at intervals not exceeding 10 feet." (Section 717.2.2, 2004 OSSC).

- "Fireblocking shall be provided to cut off all concealed draft openings (both vertical and horizontal) and to form an effective fire barrier between stories, and between a top story and the roof space. ... rest of the section same as OSSC Section 717.2.2." (Section R602.8, ORSC).

Answered by Greg Albracht
Posted Fri, 06/11/2010 - 11:40

26.
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Greg,

The HUD PATH document, "Moisture Resistant Homes: A Best Practice Guide and Plan Review Tool for Builders and Designers" http://www.pathnet.org/si.asp?id=2434 offers an evaluation method to determine appropriate cladding strategies.

This method considers rain/wind exposure levels, moisture index, site exposure, and overhang ratio. The severe rain/wind and MI exposure zones comprise about 15% of the continental US, mostly the Pacific northwest, east coastal areas and the Gulf hurricane/tornado belt. Proper siting and good roof overhangs dramatically lowers a building's exposure risk.

What you (and many others) fail to understand is that extreme systems of rain control, like the vented rainscreen originally created for high-rise metal-clad buildings in Canada, is necessary only when low moisture-tolerant and non-breathable materials are used in the structure of a building.

A building composed of moisture-buffering natural materials with envelopes that breathe well in both directions is highly tolerant of the wetting and drying cycles that are inherent to living on earth. Once moisture-intolerant materials, such as OSB, are employed, then additional barriers and drainage planes become necessary to protect them from normal hygrothermal processes.

And those more complex methods and artificial materials bring an additional set of unintended consequences. It's really quite simple to build an ecologically-sound, healthy and durable house. Those who rely on technology rather than common sense are forced to resort to unnecessary complexities which, almost invariably, become counterproductive.

And I made no assumptions about how "all rainscreens are done" - I said "if the rainscreen channel is open to the soffit", which is a common detail. Deliberately distorting my argument in order to critique it only undermines your own credibility.

Answered by Riversong
Posted Fri, 06/11/2010 - 12:09

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Greg,

Again, you might come across as more credible if you limited yourself to facts and findings rather than ad hominen attacks.

And copying a memo from a Ravi Mahajan, Facilities Engineer (with whom?), does not prove your case. In fact, that memo contradicts it. His sources clearly state that a rainscreen doesn't post a significant fire threat if it's firestopped at every storey and at the roof and at 10' horizontal intervals.

Of course, interrupting the drainage space with firestopping also dramatically reduces its effectiveness as a drainage plane and completely eliminates any convective drying potential. Most rainscreens are vertically-furred, continuous and open at both bottom and top for ventilation. This does create a fire channel which would be a particular hazard in wildfire zones but presents a hazard in any residential fire scenario (I've been a firefighter for 30 years).

Answered by Riversong
Posted Fri, 06/11/2010 - 12:35

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I guess that you do not believe in anything that you do not agree with. First of all. i am done talking with a so called expert who thinks that he knows it all. Second, all installations are referred to local building codes. As far as a fire problem, you did not read the conclusion by the the article I posted. You are assuming a lot here thinking that I recommend venting into the overhangs and roof areas. I do suggest that installers abide by the local codes. If they need to put fire blocking then they should do it. I suggest a belly da in between the floors like is done all the time in construction. This will insure proper drainage and air flow while abiding by the code and offer the benefits of a rain screen system. You are just an expert who likes to make himself feel better by arguing with everybody.
You still have not answered any of my questions such as: if this was such a problem then Oregon and Canada would not have rain screens as code! Ya dummy

Answered by Greg Albracht
Posted Fri, 06/11/2010 - 14:04

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Oh by the way Mr. Expert you are the one that threw the first stone with your unprofessional comments towards myself and Martin's data that he has compiled. I choose to believe a person like Martin who actually does the research. You are the one who has no credibility here. All the reader has to do is read your post and they will come to the same conclusion. You are no friend of the green movement if you do not believe in rain screens. rain screens are as green as it gets my friend

Answered by Greg Albracht
Posted Fri, 06/11/2010 - 14:13

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Greg,

I correctly criticized Martin's sources as either contradicting his premise or from unreliable and biased sources. I correctly criticized your sources for the same reasons and correctly questioned your own credibility because of your financial vested interest in a particular system.

Answered by Riversong
Posted Fri, 06/11/2010 - 15:42

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And, by the way, if you believe a rainscreen can transmute the most environmentally-toxic siding material (vinyl) into a "green" product, then you're hardly in a position to question anyone else's green credentials.

Answered by Riversong
Posted Fri, 06/11/2010 - 16:17

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I believe in rain screens for all types of siding, wood, fiber cement, composites and vinyl. Do you drive a car? It has PVC in it. Do you ever drink milk? Do you ever drink bottled water? It also has PVC . About everything these days has PVC in it. So what are you going to do? Not drive a car, Not drink bottled water? Move out of your home and into a Wood Hut? I agree that PVC is bad but you have to be realistic?

Answered by Greg Albracht
Posted Fri, 06/11/2010 - 18:42

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Mr. Albracht:
As an inventor and manufacturer I am sure you 'believe' in your product. However, green construction is not an issue of faith, it is a matter of information, study and experience. Robert Riversong has contributed a great deal of each to these columns to the benefit of many readers including myself, and your increasingly venomous attacks are not appreciated.

Answered by James Morgan
Posted Fri, 06/11/2010 - 19:06

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Sir Morgan,

I think that Mr. Riversong set the tone for this post when he was the first one to attack me with his unprofessional comment putting me in the likes of BP, then attacking my technology. I do not appreciate you either because you are standing by a person that has a very negative attitude and outlook on life who tries to makes himself feel better by being right all the time. Are you ever wrong Mr River Song?
Martin wrong Mr. Riversong's right?
Greg's wrong Mr. Riversongs right?
I think there is a pattern happening here.

When I get attacked I fight back just like anybody would. He still has not answered any of my questions, such as if the midwest does not need a rain screen on any type of siding then why is there rotten would on homes all over the midwest? Please don't go there and blame it all on OSB. The OSB would have lasted much longer if it had a wrb and an air gap behind the siding and proper flashing done.

Attacks on me first.

14.
And next we'll hear from the CEO of BP telling us how wonderful and safe deep sea drilling is.
ANSWERED BY ROBERT RIVERSONG - Jun 10 10

Here is another one
"We", I assume, being those who make a living selling environmentally destructive materials and promoting poor building practices and passing them off as "green".

I do not sell vinyl siding. I manufacture a steel strip for vinyl siding. I also make a steel strip for fiber cement, wood and composite siding. You were assuming here once again and attacking me with an attitude.

Answered by Greg Albracht
Posted Fri, 06/11/2010 - 20:42

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I think most readers of this forum would find Mr. Abracht's assertion that "rain screens are as green as it gets" to be an obvious piece of unsupported marketing hype, yet I think many may still come away with the notion that incorporating rainscreen technology in their standard wall construction may be the right thing to do. After all, it can't hurt, right?

Well it can. Rain screens are an important item in the tool box for certain situations but as they have to be installed correctly if they are not to make matters worse. Poor detailing at window and door openings is the obvious area of concern - in the UK where rainscreen-supported double-wythe masonry is the standard for residential construction whole sections of the building code and a huge range of proprietary flashing components are required to ensure the system works. Builders in North America have considerably less support. More subtly, builders may develop a false sense of security with rainscreen detailing and may be tempted to take shortcuts with other aspects of moisture control. Robert Riversong has additionally suggested potential concerns with fire safety.

So what are the standard situations where should rainscreen drainage planes SHOULD be deployed, despite these concerns? The HUD document quoted by Mr. Albracht is quite specific:

"This document presents some guidelines for designing and constructing a building enclosure with a “rain screen” where “absorptive” or “reservoir” type exterior claddings may be used over wood frame wall construction with wood-based sheathing. ..... An “absorptive” or “reservoir” cladding can be defined as a cladding made of materials that are semi-porous and may transmit or retain some water. .... Some examples of absorptive claddings include portland cement plaster (stucco), manufactured stone veneer, and brick and traditional stone masonry veneer. ..... This guide is not intended to be used as a standard or minimum requirement and the examples cited in this guide are not meant to be considered the only way to achieve a moisture resistant, durable building enclosure."

Note that last sentence. Note also that wood siding is not included in this list - nor vinyl, for that matter. With both these materials it is assumed that the drainage plane is at the outside surface of the cladding. No one would claim that such an exterior drainage plane is capable of performing perfectly - the same issues of detailing apply as to the interior drainage plane of the rain screen. However the standard wood siding installation has a second line of defense which is formed by the multiple air spaces between the siding material and the WRB-protected sheathing and I have seldom seen moisture-related problems with this approach. Only when the siding lies flat against the substrate (e.g. when a tongue-and-groove or 'German' profile siding is employed) is this space absent and problems may occur. In these situations vertical furring strips are a necessity.

Robert Riversong has mentioned above his concerns over needless complexity in building systems, and is an eloquent proponent of what may be simpler approaches. This is a voice worth listening to, whether or not you agree with his conclusions.

Answered by James Morgan
Posted Sat, 06/12/2010 - 09:31

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I should have mentioned of course that the primary introduction of vertical furring (post #6) was about the need for mechanical fastening of siding over thick nonstructural external insulation installed as a thermal break over studs. The formation of a drainage plane by this technique is more or less incidental. To summarize: traditional lap siding forms its own evaporative and drainage cavity, and absent the external insulation, which is best justified in those areas of the country which experience severe winters and is in any case not the only way to deal with thermal bridge issues, the furring seems to be generally unnecessary.

Answered by James Morgan
Posted Sat, 06/12/2010 - 10:59

38.
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I think most readers would listen to Dr. Joe and not you! I would love to see you and Mr Riversong debate the great Dr. Joe. I will put my money on the Dr.

You forget to mention all of the other benefits that a rain screen can offer. Such as, venting of condensation (Which your suggested construction cannot do)

Venting of heat that is absorbed into the insulation via the heated cladding from hot days.
(Which your suggested construction cannot do)

I guess if someone wants to save a buck or two and install cladding your way, they can but when codes change they will have a house they can sell. Not one that does not even meet code and is rotting away!

Answered by Anonymous
Posted Mon, 06/14/2010 - 07:15

39.
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Chris, going back to your original blog.
I cannot imagine what you expect to achieve by using 0.5 inch rigid foam.
Perhaps you will explain what you think 1/2 inch of foam will do for your new home?
What does your framer mean when saying he normally installs bubble wrap under metal roofs, what on earth does he expect bubble wrap to do?

In your location, you need at least six inches of polystyrene or similar across the roof, probably best as a SIPS product,completely isolating the shingles from the framing of the home.

Note: Most heat is lost or gained by conduction, isolating the roof is the best way to go.

Then a SIPS system of insulation should be used for the walls.

You really need to consider the amount of energy and money you can save over the next 10 to 20 years by insulating to a decent standard now.

Answered by Perry525
Posted Mon, 06/14/2010 - 08:25

40.
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When is this site going to prohibit anonymous posting?

The quality of discourse is dropping dramatically here, and largely due to letting people spout off with no accountability.

And, for those who actually read what Dr. Joe has to say, it's that high-tech "solutions", such as rainscreens and dimple wraps and mesh spacer membranes are necessary only because we commonly use highly moisture-vulnerable materials such as OSB and then seal them on both sides with impermeable insulating materials.

Plywood-sheathed, felt-wrapped, wood lap sided houses with permeable insulation didn't suffer the kinds of moisture damage that "modern" houses do. And board sheathed houses rarely had such problems.

Our high tech "solutions" are only reactions necessary because we're using low-quality materials, insulations with no hygric buffering capability, and assemblies that don't breathe.

Answered by Riversong
Posted Mon, 06/14/2010 - 14:37

41.
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Wow.. harness the hot air in this thread and we'd be done w/ BP and smelling up our coasts. Where is Sara Palln to add to this discussion? No.. wait.. we just need Cheney to shoot off a few accidental rounds.

Answered by Joe the not a a licensed plumber... and quite a bit dumber
Posted Mon, 06/14/2010 - 16:42

42.
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To the anonymous comedian,
Post your real name. You are not funny.

Answered by Brett Moyer
Posted Mon, 06/14/2010 - 16:50

43.
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Brett,
I agree

Answered by John Brooks
Posted Mon, 06/14/2010 - 19:03

44.
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Dear Campers ... please do not feed the bears.
Dear GBA Members....Please.....do not answer questions by anonymous posters.
Dear Anonymous (or Bogus screenname) please register under your real name and ask your question or make your comment again.

Answered by John Brooks
Posted Mon, 06/14/2010 - 19:04

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