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Old 12-16-13, 05:09 AM   #391
Mikesolar
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Dudes,
I have been into at least 20 houses where people have bought into the bubblewrap scam for use under slabs IN PLACE OF PROPER XPS and the under performance has been very noticeable, and in many cases, the slab has had to be either ripped out or major work around the perimeter had to be done to fix it.

For 20 years I used radiant barriers (foil faced building paper, not bubblewrap) behind walls. It is with an appropriate air space, usually 1.5" min because it allows for plumbing, electrical to be placed without breaking the barrier which is also the vapour barrier so it was properly caulked.

Foil faced insulation :: NRCan :: Advisory paper

Attic placement is iffy and especially below radiant tubing under the subfloor, I think, is a waste of materials and effort. I don't like suspended radiant tubing anyway, so i would never do it anyway.

I'm still looking for the report done many years ago about using the radiant barriers directly under the slabs. It doesn't paint a good picture.


IMO, the wall is the best place for the radiant barrier to be used.

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Old 12-16-13, 11:00 AM   #392
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Originally Posted by jeff5may View Post
The radiant barrier and airspace would still work, but would have less radiation at a lower gradient to contend with.
Less? How much less?

In this thread, I keep hearing words like "negligible" and "less".

What do they mean? No one has offered any analysis, or found any studies to shed any light on what is meant.

What may be a negligible loss when using an oil fire boiler, may be enough, that when systematically dealt with, can make a design completely successful when working from a low exergy point of view.

When you say less, do you mean 1% less, do you mean 95% less?

When you say "less" exactly how much less?

That's one thing I really respect about the Passive House design approach. They didn't disregard 'negligible' losses or 'insignificant' gains... they don't throw away 'less'.

And you know what? All these disregardable quantities that conventional thinking brushes aside, have added up to a revolution in thinking, and a whole new approach in house construction.

-AC
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Old 12-16-13, 11:44 AM   #393
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Originally Posted by AC_Hacker View Post
Less? How much less?

In this thread, I keep hearing words like "negligible" and "less".

When you say less, do you mean 1% less, do you mean 95% less?

When you say "less" exactly how much less?

That's one thing I really respect about the Passive House design approach. They didn't disregard 'negligible' losses or 'insignificant' gains... they don't throw away 'less'.

And you know what? All these disregardable quantities that conventional thinking brushes aside, have added up to a revolution in thinking, and a whole new approach in house construction.

-AC
The correct answer here is:

Not everyone wants to invest the time, labor, and money to do the best job possible. There is usually a point where the return on investment diminishes beyond design goals or a target is hit (or missed). A "Take no prisoners" approach, such as the passive house standards employ, is a noble cause (which I and many others here subscribe to) that many of intermediate skill level doubt they can accomplish.

This is especially true in the renovation/remodel/retrofit arena. Many homeowners completely neglect energy efficient building methods when planning DIY projects. Those that consider air sealing and insulating weigh the cost vs. benefit aspect heavily. In the hydronic heating realm, the extra money is not always spent in the right place with respect to the overall efficiency of the system. Given a choice, the average DIY installer will oversize the capacity of the system to cover 99.9% of the existing heat load rather than to insulate enough that a smaller capacity system would do the same job.

Other well-intending home improvers are swayed by the lofty claims of previously mentioned manufacturers and integrate these products into their design, relying on these high-performance values to "pull their weight". After commissioning and operating the system for some time, the DIY'er realizes the system is not as efficient as it should be on paper and begins to hunt for answers why. More often than not, the individual must bring in third parties to get a grip on the situation and dispel the mythology. By then, most, if not all of the budget has been spent. The remediation is then either done at great pain, or not done at great pain.

Anyone who has much experience in building projects knows that you nearly always experience problems and run over budget. One day you're golden, the next it's doom and gloom. It takes a good amount of diligence and patience to stay on track. It's much easier to delete a step or three along the way rather than to dig in and do it right the first time.

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Old 12-16-13, 01:48 PM   #394
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Not everyone wants to invest the time, labor, and money to do the best job possible. There is usually a point where the return on investment diminishes beyond design goals or a target is hit (or missed). A "Take no prisoners" approach, such as the passive house standards employ, is a noble cause (which I and many others here subscribe to) that many of intermediate skill level doubt they can accomplish.
OK, this is swell.

But the Internet is awash with forums, and blogs, and commercial builders' conventional advice. They tell you exactly how to do a conventional job.

Shouldn't we be taking the "Eco" part of EcoRenovator more seriously? I mean, have you been paying attention to what Daox is up to? He is doing a full-on, no compromise effort on an office remodel... that should be a hint to us.

We're in a minority here. I think we should be a minority of excellence, clarity and DIY creativity rather than a minority of conventional thinking.

We should ask more of ourselves. We should expect that our readers will ask more of themselves, too.

* * *

BTW, I did a tiny experiment just now, to see what "not much" might look like...

I happened to have a 1/2" sheet of polyisocyanurate foam leaning up against the wall in the room I am in the process of insulating and remodeling, and I also happened to have an IR thermometer in my pocket.

I held my arm out to the side and took a reading of the polyiso with the IR thermometer. Here's what it read:


...this was within a degree of the ambient temperature, measured with a very reliable thermometer.

Then, I stood square on to the foil-covered polyiso, and measured again and this was the reading I got:


Why was the reading higher when I stood directly in front of the polyiso and read it square on?

To get my answer, I turned the IR at myself and took another reading:


So what this tells me is that yes, radiant energy exists, and that it reflects not so differently from light, and finally that even at lower temperatures such as the radiated heat from my suited-up body in a cold room, it is radiating enough to make a difference.

Heat radiates down from a radiant floor, too.

It is true that 6.7 degrees F is not a huge number, but having thermal reflectivity working for you over the life of a house is certainly worth considering, especially when a radiant floor during the heating season would be such a large area and would be the hottest surface that a cold, heat-sucking winter night would see.


-AC
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Old 12-16-13, 07:41 PM   #395
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That's what I've been trying to do here! Together, we are strong.

In particular, Michael and Daox are both in the process of self-installing fabulous hydronic heating floors of different kinds. The debate started when Michael asked questions regarding the effectiveness of a radiant barrier when combined with between-joist fiberglass insulation underneath. Since then, half a dozen of us or more have chimed in, weighing the pros and cons, as well as dispelling some of the hype that has propagated through the industry. I have taken the position that for best performance, this product should not be relied upon as a "do-all" solution.

AC, you know the deal with sealing and insulation. There are many ways to perform the job as well as a large menu of products to choose from. The end product is only as good as its weakest link, so much contemplation must be done throughout the testing and planning phases to ensure proper product choice as well as execution.

I am a believer that anything worth insulating is worth super-insulating. I hope to sway at least some of our audience in that direction. Much like diamonds, insulation is a one-time investment that just keeps on giving more and more as time goes on. It ain't cheap, but it sure feels good once you have it.

Especially with slab-on grade hydronic installs, that 2 or 4 extra inches of foam board on the ground will only save you money later if you put it in now. After the concrete goes in, it's too late. With the underfloor situation, I don't expect that all readers will decide to generously use aluminum heat spreaders and insulate their joist cavities to R-40 value with spray foam below dubble-bubble radiant barrier, even though that's what I might do. I do, however, expect a reader to check his or her plan and at least consider filling that space with something (rather than nothing). Small steps lead to big journeys.

To answer your question more directly, I believe the reflective bubble wrap, when used in an airtight cavity between joists or studs, placed 1" under a radiant floor or 1" away from interior wallboard, has an R-value of 3.2, and an emissivity of 5%. IMHO, this is not enough insulation, and I would recommend adding at least 4" of foam board or spray foam to fill the cavity under the radiant barrier to increase this value to above r-20. As with any insulation project, if you still have space, fill it in with more insulation for best results.
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Old 12-17-13, 06:49 PM   #396
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Why was the reading higher when I stood directly in front of the polyiso and read it square on?
-AC
What you probably saw was the effect of one of the fudge factors in the Stefan-Boltzmann law of thermal radiation. It is called the view factor function. The maximum perceived radiation will be perpendicular to the surface. Hence, view factor.

I deal with this every day when checking plant machinery. It is particularly noticeable on highly reflective surfaces. With a filthy bearing housing, OTOH, it doesn't seem to matter how you aim your IR gun.
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Old 12-17-13, 07:18 PM   #397
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What you probably saw was the effect of one of the fudge factors in the Stefan-Boltzmann law of thermal radiation. It is called the view factor function. The maximum perceived radiation will be perpendicular to the surface. Hence, view factor...
When I held the IR-thermometer out to the side, I made sure that it was also perpendicular to the surface.

If anything, that measurement was too high, because the heat from my arm was "visible" to the IR-thermometer. Although it occurred to me to do so, I just didn't feel like duct taping the IR device to a stick.

Do you doubt that heat radiated from the body can be reflected from an aluminum surface and measured with an IR-thermometer?

-AC
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Old 12-17-13, 07:35 PM   #398
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....I would recommend adding at least 4" of foam board or spray foam to fill the cavity under the radiant barrier to increase this value to above r-20.
I never thought of spray foam under a floor but it makes sense if you cover the joists. Most people neglect the thermal bridging from studs and joists. I've seen ice form on an "Oregon code insulated" wall at 16" intervals when the temperature in the middle of the room was 70F.

Why heat the upper edge of a joist to 80F when the lower half is exposed to a cold crawl space?
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Old 12-17-13, 08:06 PM   #399
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Dudes,
Attic placement [of radiant barriers] is iffy
Mike, where are you getting this? In a cooling climate a radiant barrier in the attic is not at all iffy. One should always attach a radiant perforated barrier in a cooling or mixed heating/cooling climate to the bottom of the rafters. This does the most good in summer by reflecting much of the heat back up into the roof during the hottest part of the day in summer. Many houses in these climates have the air handler on the roof with the A/C cooling ducts going through the attic. Those ducts will be gaining efficiency by operating in a much cooler attic.

Of course that radiant barrier is not used as insulation. One would use the standard r-60 or so celllulose or fiberglass insulation on top of the ceiling if its not cathedral. It is very economical to use a reflective barrier in this way, in fact it is probably the cheapest way. Similarly one might use insulation batts with reflective foil in a heating climate effectively in the wall, as you said. But in that case the foil side would face the interior of the home to reflect heat back inside in winter.

I wish more people here, including myself sometimes, would quit criticizing techniques that work well in other climates just because they don't work in their own. Conversely I think it is always appropriate to tell people that something that works well for ones own climate may not work well or be the most efficient use of technology for other climates. I wish everyone here would try to keep this very important principle in mind
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Old 12-17-13, 08:38 PM   #400
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Mike, where are you getting this? In a cooling climate a radiant barrier in the attic is not at all iffy. One should always attach a radiant perforated barrier in a cooling or mixed heating/cooling climate to the bottom of the rafters. This does the most good in summer by reflecting much of the heat back up into the roof during the hottest part of the day in summer. Many houses in these climates have the air handler on the roof with the A/C cooling ducts going through the attic. Those ducts will be gaining efficiency by operating in a much cooler attic.

Of course that radiant barrier is not used as insulation. One would use the standard r-60 or so celllulose or fiberglass insulation on top of the ceiling if its not cathedral. It is very economical to use a reflective barrier in this way, in fact it is probably the cheapest way. Similarly one might use insulation batts with reflective foil in a heating climate effectively in the wall, as you said. But in that case the foil side would face the interior of the home to reflect heat back inside in winter.

I wish more people here, including myself sometimes, would quit criticizing techniques that work well in other climates just because they don't work in their own. Conversely I think it is always appropriate to tell people that something that works well for ones own climate may not work well or be the most efficient use of technology for other climates. I wish everyone here would try to keep this very important principle in mind
You are right that I (and others) am concerned with a heating dominated climate and this is why i criticize bubble wrap. We are not used to any heating equipment at all in any attic space in Canada/northern US but I realize that it is quite common in the south. I do scratch my head about its use. I also talk to a lot of heating technicians in the mid and south who are always trying to take a sub-par system (ducts in the attic) and make it better because they get a huge number of complaints with heat loss and condensation in these types of systems. We sometimes have ducts in the attic for cooling only but there is a big trade off between system efficiency and the ability to have cooling in century old hot water heated homes. To my mind, I cannot even conceive of designing a system with ducts in the attic. That said, if you inherit a system like this, you must live with it and try to find ways to make it work better.

I have no problems with radiant barriers where appropriate but the one big problem is when they are misrepresented as having an R value that they simply don't have. I have seen too many very unhappy people who relied on tarps under slabs.

I agree with the use of radiant barriers in attics but, that too, is not used in our climate much. Having it on top of batt insulation is a good idea partly because it will reduce air movement within the batt which reduces its R value a great deal. Having it below the batt, is, in my opinion useless as that air space is still needed for IR reflection.

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