| Samuel,
The FTC rule on advertised R-values states: "For polyurethane, polyisocyanurate, and extruded
polystyrene, the tests must be done on samples that fully reflect the effect of
aging on the product's R-value."
Pentane-expanded polyurethane foam has an initial R-value of 6.8 and ages to 5.5. CFC/HCFC-expanded polyurethane foam has an initial R-value of 7-8 and ages to 6.25.
Just as importantly, those high initial R-values depend on precise control of mixing ratios, application rate, temperature and humidity. It's impossible to control those variables with field-applied spray foams, so there's no way to
determine what kind of performance you might get.
Additionally, when foam is applied on cold substrates, or on green timbers that are still shrinking (even KD lumber loses considerable moisture as it equilibrates to the indoor environment), or too thickly in each pass it can lose adhesion to the substrate or overheat and fail to properly cure. These defects can effect the foam's insulative qualities or its air-sealing performance. And filling framing cavities does nothing to air seal between framing assemblies where most leakage occurs.
There are also many examples of toxic responses to the outgassing of expanding agents, with some home-owners having to abandon their homes permanently or developing multiple chemical sensitivity.
Foam is a petrochemical, with all the inherent environmental liabilities of such products. As a plastic, it removes health-sustaining negative ions from the living space. It is hardly a cost-effective solution, since it is the most costly insulation alternative in the closed-cell variety, and it fails to deal with thermal bridging, which is one of
the greatest heat loss vectors in conventionally-built homes.
Do the math. The higher the cavity R-value, the higher the percentage of degradation in whole wall R-value by thermal bridging. And, as I stated before and you apparently failed to understand, since expensive closed-cell foam is rarely applied to fill the stud cavities completely, the sides of the studs as well as the inside edge are exposed to indoor temperatures and hence thermal conduction (which is 3 dimensional) is significantly increased through the framing. The same, of course, is true of spray foamed rafter bays or floor joists, except typically even more wood is left exposed.
As a non-hygroscopic material, closed-cell foam forces any leakage or condensation into the hygroscopic wood framing, increasing the moisture content and the probability of mold or rot. Because it is impermeable to liquid water, roof leaks over sprayed cathedral ceilings go undetected until the roof sheathing rots.
There are so many liabilities, in terms of structural durability, thermal integrity, site control of application, deleterious health
impacts, and cost - that sprayed foam insulation is one of the least sensible options for the thermal envelope. But, like so many "modern", and "high-tech" and over-hyped building products (including polymeric housewraps and self-adhering bituminous or butyl membranes), poorly-informed professionals over-use it and ditto the commercial claims in spite of significant evidence to the contrary.
One such piece of evidence is a 10 year simulation study of vented and unvented cathedral ceilings by the Florida Solar Energy Center which concluded that, in either hot or cold climates, the worst performing and least durable roof was one with a self-adhering membrane above the sheathing and
unvented closed-cell spray foam below.
- Robert Riversong master housewright, instructor in building science and hygro-thermal engineering
--- On Thu, 3/11/10, Samuel Robins <[log in to unmask]> wrote:
From: Samuel Robins <[log in to unmask]>
Subject: Re: Suggestions on Insulation retrofits
To: [log in to unmask]
Date: Thursday, March 11, 2010, 10:39 PM
Robert,
Attached are a few sites, which claim urethane R-Values between 7 & 8, including The US Department of Energy. I mentioned 6.8, which was the manufacturer's stated R-value on our last house. In any case spray foam is the most effective 'single step' means to achieving a maximized thermal barrier, by it's high R-Value combined with unparalled air sealing characteristics (as you know - this is the Holy Grail) . If you are correct that the industry average R-Value is only 5.9, I would suggest that you not use those products that compromise the average with their low/inferior values. I have never read anything regarding the nature of urethane
spray foam or any other material to have the ability to affect the thermal conductivity characteristics of a wood stud - just ^T changes. I may be misunderstanding your comment. Either way, maybe you could elaborate - I'm interested to learn more.
Admitedly, 'outsulating' is extremely effective in mitigating thermal bridging. If labor is cheap and there is plenty of time to spend, why not do everything possible.
If you have to draw the line without compromising too much, foam is a superior choice. Foam is more expensive and does degrade slightly, but the combination of fast installation, high R, excellent air sealing, significant structural reinforcement and pretty good sound abatement are qualities that at least deserve consideration.
Lastly, if your not a fan of vapor barriers - good news! If you use foam, you don't even need to consider the
topic. It's already built in, just seal the un-foamed framing joints and then focus on air change. Just so you know, I have nothing to do with the foam industry. Foam isn't perfect by any means, but overall, I believe it to be the most cost effective choice. Every job IS different.
A couple of foam sites at the top of Google search:
Dave Robins SDR & Associates 131 Cedar Street. East Hampton, NY. 11937 (631) 324-8868 (631) 324-0900 ~ fax | The average installed R-value for closed-cell sprayed urethane is 5.9, not 6.8 (only foil-faced polyisocyanurate approaches that level). Additionally, the higher the cavity R-value the more significant, in terms of % degredation, become the thermal bridging of the framing. Also, because spray foam rarely fills the entire stud cavity, there is more 3-D thermal transfer through the studs.
With dense-pack cellulose, either damp or dry, all manufacturer's recommend (some even require) that no vapor barrier be installed. One of the many advantages of cellulose insulation is its hygroscopicity - it can buffer indoor RH by safely absorbing and releasing excess humidity (if the wall can breathe) and it protects wood framing by drawing moisture away (unlike foams which concentrate all moisture in the wood
framing).
A
cellulose-insulated envelope requires a good air barrier, but should not have a vapor barrier (vapor retarder latex primer is OK, but nothing more restrictive).
- Robert Riversong master housewright --- On Thu, 3/11/10, Samuel Robins <[log in to unmask]">[log in to unmask]> wrote:
From: Samuel Robins <[log in to unmask]">[log in to unmask]>
Subject: Re: Suggestions on Insulation retrofits
To: [log in to unmask]">[log in to unmask]">[log in to unmask]
Date: Thursday, March 11, 2010, 9:05 AM
Tim, Seems like R- 6.8 closed cell urethane foam would be a better / (over all) less expensive option, allowing you to forget the extra expenses involved with wrapping the exterior. If you choose the cellulose & exterior wrap option, you probably should also include the expense of an interior vapor barrier,
which would eliminate air infiltration and interior moisture escaping and becoming trapped within the cellulose filled cavities. Just a thought. Dave Robins SDR & Associates 131 Cedar Street East Hampton, NY. 11937 (631) 324-8868 (631) 324-0900 ~ fax On Mar 10, 2010, at 11:47 PM, Ben Graham < [log in to unmask]"> [log in to unmask]> wrote: > Tim, > Not sure if you have seen the Building Science Corp. method for this deep > energy retrofit method, but I would check it out, they have it down pretty > good. Furring strips are utilized to secure the siding. I don't think they > would recommend polyiso or house wrap. Essentially, if you seal the foam > well, you don't need the wrap. > > Ben Graham >
> > On 3/10/10 8:29 PM, "Tim Yandow"
< [log in to unmask]"> [log in to unmask]> wrote: > >> Hello all, >> >> On the subject of green building, I am soon beginning renovation work on a >> 1960's home in Burlington. We are adding an addition to the south and west >> sides of the house. The new envelope will be 2x6 with damp spray >> cellulose. The existing house is 2x4 with fiberglass and the owners would >> like to bottom up the house more, so we are thinking about adding a layer >> of insulation to the outside of the house since all the old vinyl siding >> is coming down and the windows all replaced (most of them have broken >> seals). I am trying to figure out the best way to insulate from the >> outside and make provisions for new corner boards and
hardi-plank siding. >> With polyisocyanurate,
for instance, there is the problem of not being >> able to add house wrap and needing to use longer fasteners for siding and >> to secure window flanges. Or can strapping be used over that? Then there >> is the issue of extension jams either inside or outside...I would love to >> know if anyone has worked out a good solid system to do this. What I have >> read and seen so far does not satisfy me. Thanks. >> >> Tim Yandow > > Those who give up freedom for safety, deserve neither. > Benjamin Franklin > __________________________________________________________ > > Ben Graham > www.naturaldesignbuild.us> Natural building/design services/workshops/consulting > > Integrating
Culture and Nature > 802.454.1167
|
| The average installed R-value for closed-cell sprayed urethane is 5.9, not 6.8 (only foil-faced polyisocyanurate approaches that level). Additionally, the higher the cavity R-value the more significant, in terms of % degredation, become the thermal bridging of the framing. Also, because spray foam rarely fills the entire stud cavity, there is more 3-D thermal transfer through the studs.
With dense-pack cellulose, either damp or dry, all manufacturer's recommend (some even require) that no vapor barrier be installed. One of the many advantages of cellulose insulation is its hygroscopicity - it can buffer indoor RH by safely absorbing and releasing excess humidity (if the wall can breathe) and it protects wood framing by drawing moisture away (unlike foams which concentrate all
moisture in the wood framing).
A
cellulose-insulated envelope requires a good air barrier, but should not have a vapor barrier (vapor retarder latex primer is OK, but nothing more restrictive).
- Robert Riversong master housewright --- On Thu, 3/11/10, Samuel Robins <[log in to unmask]">[log in to unmask]> wrote:
From: Samuel Robins <[log in to unmask]">[log in to unmask]>
Subject: Re: Suggestions on Insulation retrofits
To: [log in to unmask]">[log in to unmask]">[log in to unmask]
Date: Thursday, March 11, 2010, 9:05 AM
Tim, Seems like R- 6.8 closed cell urethane foam would be a better / (over all) less expensive option, allowing you to forget the extra expenses involved with wrapping the exterior. If you choose the cellulose & exterior wrap option, you probably should also include the expense of an interior vapor barrier,
which would eliminate air infiltration and interior moisture escaping and becoming trapped within the cellulose filled cavities. Just a thought. Dave Robins SDR & Associates 131 Cedar Street East Hampton, NY. 11937 (631) 324-8868 (631) 324-0900 ~ fax On Mar 10, 2010, at 11:47 PM, Ben Graham < [log in to unmask]"> [log in to unmask]> wrote: > Tim, > Not sure if you have seen the Building Science Corp. method for this deep > energy retrofit method, but I would check it out, they have it down pretty > good. Furring strips are utilized to secure the siding. I don't think they > would recommend polyiso or house wrap. Essentially, if you seal the foam > well, you don't need the wrap. > > Ben Graham >
> > On 3/10/10 8:29 PM, "Tim Yandow"
< [log in to unmask]"> [log in to unmask]> wrote: > >> Hello all, >> >> On the subject of green building, I am soon beginning renovation work on a >> 1960's home in Burlington. We are adding an addition to the south and west >> sides of the house. The new envelope will be 2x6 with damp spray >> cellulose. The existing house is 2x4 with fiberglass and the owners would >> like to bottom up the house more, so we are thinking about adding a layer >> of insulation to the outside of the house since all the old vinyl siding >> is coming down and the windows all replaced (most of them have broken >> seals). I am trying to figure out the best way to insulate from the >> outside and make provisions for new corner boards and
hardi-plank siding. >> With polyisocyanurate,
for instance, there is the problem of not being >> able to add house wrap and needing to use longer fasteners for siding and >> to secure window flanges. Or can strapping be used over that? Then there >> is the issue of extension jams either inside or outside...I would love to >> know if anyone has worked out a good solid system to do this. What I have >> read and seen so far does not satisfy me. Thanks. >> >> Tim Yandow > > Those who give up freedom for safety, deserve neither. > Benjamin Franklin > __________________________________________________________ > > Ben Graham > www.naturaldesignbuild.us> Natural building/design services/workshops/consulting > > Integrating
Culture and Nature > 802.454.1167
|
|