Follow up: new type of treated wood

Re: The constant blast of "innovations"..

david weaver

...and the little detail that comes with the press releases that the local news is only too happy to go along with has made it so that I no longer watch the first round of things. (the coming ethanol fuel cell cars, baked wood for guitars that is "perfectly stable", the next magical insulation product that will save you 40% of your heating bill....)

I wait for other people to make a big deal about something after it's available and has some kind of significant cost savings that they can show.

For one reason or another torriefied wood is becoming the rage in guitars. The oldest trick in the book is to make a simple guitar (stratocaster or telecaster copy, especially) and glitz it up with some buzz words and fancy hardware and jack up the price. "baked maple" necks don't cost much incrementally vs. anything else, but some of the builders and parts suppliers add an *upcharge* of $250-$300.

I understand the significance of baking maple and that it does stabilize the wood by removing volatiles, but looking at some of the patterns that the upcharge is applied to, it also allows use of less well sawn wood. Much of the market is educated with guitars, but much isn't, and there's a lot of superstition.

I did get a nice billet of curly maple that was baked to a temperature high enough and long enough to do the trick (it stinks and it's hard sawing for a hand tool woodworker) - it cost about 20% more than unbaked maple, or something around $5 per neck.

long way around to the point, when one goes looking for technical documents about baking maple, there's a relatively critical temperature to reach. Not all vendors actually reach it. The documents specifying temperature aren't exactly new publications. At least some of them were from the early 1980s.

Very seldom is the next "new thing" that's decades or centuries old presented as an adaptation of something that's already around.

Re: I had a question about this part ...

Hank Knight

I had a question abut this part in the original posted article:

"The sugars in cellulose are effective emitters of infrared radiation, and they do so in two areas of the spectrum where none of our atmospheric gases is able to reabsorb it."

Really? That sounds like so much mumbo jumbo. What "areas of the spectrum" slip by all of our atmospheric gasses?

Re: I had a question about this part ...

david weaver

Some wavelengths end up going back into space just as some come from space and make it to earth instead of just heating the atmosphere.

How that applies to this wood? I guess the idea that it bounces the light back into space more or less without allowing it to heat the air near the wood?

http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ask_astronomer/faq/radiation.shtml

"Only some (not all) of the IR radiation between 1 and 40 microns makes it to the Earth's surface."

Sounds odd to me, but there is plenty that I don't know. Reminds me of the proposals to fight global warming by painting roofs white.

Re: I had a question about this part ...

Hank Knight

David, there's an awful lot I don't know too, but this sounds a little preposterous to me. I know that many of there shorter wavelengths in the spectrum are not absorbed by the atmosphere; but I imagine most in the IR spectrum are, especially with the era of global warming, with increased CO2 in the atmosphere - assuming one believes in global warming.

Re: I had a question about this part ...

John in NM

There are lots of bands from IR down into the microwave that are not absorbed by the atmosphere. Used to see it commonly at the radio telescope I used to work for. The hardest frequencies to tune there were at the edges of absorption bands because the system would be very noisy. Other frequencies we could observe through a rainstorm with very little negative effect (we still closed for rain, to keep equipment dry).

In the IR it becomes less common if I remember correctly, but it still happens - in theory its part of how greenhouses work, only they have to do with wavelengths that glass emits as heat after absorbing broad mostly visible wavelengths. I've never been fully convinced that the effect was as important as thermal mass in the greenhouse, but in principle I believe it is part of the equation.

Glass also generally blocks UV to some extent, while passing the bulk of visible light. Way back when I was in college, they had some poor slobs living on yams in the Biosphere outside Tucson. They were very pale from the relative lack of UV under the glass, but also a sickly orange from eating all the yams - one of the few food crops they were having much success with. Enough UV does get through glass to fade your woodwork in a sunny room though. Probably it is not spectrally uniform.

So that part of the mostly bunk article didn't surprise me much. I don't know which specific bands they were referring to, but it's not uncommon, even in the IR range. We just don't see such obvious examples around us as we do with visible light.

Nope...that part is correct

Bill Tindall, E.Tn.

Why is a lot more than I am willing to type. It has to do with the quantized vibrations and rotations of the atmospheric gas molecules, primarily water and carbon dioxide. The wavelengths of radiation that have the correct energy are absorbed by these vibrations and those that are not, are not.

We get global warming from water vapor and carbon dioxide because these molecules pass the shorter wavelengths of solar radiation, which hits the earth, warms the earth, the warm earth radiates this energy back to the atmosphere. H2O and CO2 absorb some of the earth radiated energy and re-emit it back the earth.

John Tyndall, famous scientist and mountain climber, was sitting on a mountain top wondering why mountain tops are cooler than lower elevation. He speculated the cause way before the quantum mechanics that explains it was figured out. So we could say that global warming was discovered in about 1850.

search "John Tyndall global warming" in Google to learn more

more....

Bill Tindall, E.Tn.

I traced back the information to the original publication. It was in Science magazine. The article barely mentioned how the material was made. Rather, the article focused on the optical and thermal properties and how they could be used in building construction for energy savings.

You don't get something published in Science without peer review by experts. I am confident they described the optical (which were well known) and thermal properties accurately. I am not so confident these properties are going to lead to more energy efficient buildings.

Re: Follow up: new type of treated wood

Barry Irby

I have been looking at heat flow in buildings for a long time.

Some aspects of it still amaze me. For example, I see rust stains around the roofing nails pocking through the roof sheathing. The explanation I got was that on cold clear nights, the heat radiates to deep space (black), chilling the nails. Water vapor condenses on the cold nails and rusts them and the rust soaks into the wood.

The cure for this is to cut down the amount of moisture arriving in the attic. Install an effective vapor barrier over the surface of the grade in the crawl space and the condensation in the attic will be greatly reduced.

I have also seen foil face plywood made to use as roof sheathing. The foil is placed on the attic side, facing down. Somehow it reflects heat back out into the sky. In hot sunny climates it can reduce the air conditioning cost dramatically. maybe as much as a third. I can't figure out how a shiny surface face down reflects energy up. I wonder if it has something to do with a the statement that a Perfect absorber is also a perfect emitter? Since the shiny face is a poor absorber may its also a poor emitter and the heat radiates out the top side.

Maybe Bill's explanation of the molecular activity explains it as far as this "new" material goes. I remain skeptical. Especially of wild claims.

Remember Paul Harvey? He used to advertise a paint that had micro spheres in it. They were alleged to be shiny on the inside and if you painted the inside of your house with it, they would reflect the heat back out. Turned out to be a snail oil claim.

I am turning into an old fuddy duddy. I don't want to be the first kid on my block to try the new thing.

Re: Follow up: new type of treated wood

John in NM

No, Bill's explanation is exactly correct. It is just a specific example of a broad phenomenon that has many other specific examples across the entire EM spectrum. The annoyingly orange light from sodium lamps in parking lots are also a quantum state change - hence the very specific color of light they emit.

The rusty roofing nails are not what you've been told. That is simply that the nails are better conductors of thermal energy than the wood or plywood around them... Cold outside and the roof will be colder than the attic, the nails will thus be colder than the wood on the inside, so any water vapor in the attic will condense on the nails.

Foil coated osb is a low emissivity surface. The foil's purpose is not to reflect heat, it is to be as inefficient a radiator as possible. Thermal emission is proportional to surface area - shiny foil has minimal surface area - same reason it reflects well. So on a hot day if you're inside the structure and you reach up to touch that roofing material (foil down), you'll notice that the air is not hotter until you get very close to the foil and the foil is quite hot. The roof heats up but it doesn't emit that heat downward into the building at all well. Put it on top of a well ventilated attic with insulation over the ceiling and you have a very cool building (my shop is built this way). The stuff really works.

Not sure about the paint thing though That one could be bunk!

>>more energy efficient buildings

david weaver

Or importantly, an overall net cost savings and one (savings) that's greater than anything else on the market.

When something is more efficient, that's great.

When being more efficient is noticeably (net) cheaper and it's easy to use, then it's popular.

Thanks for the fascinating explanations!

Hank Knight

Wow! Thanks for the fascinating explanations. Once again they prove that us non-physical science guys should keep out opinions about things we know nothing of out of public view!

Re: >>more energy efficient buildings

JohnV

can't forget the energy cost of production of this wonder material in calculating real energy costs.

Re: Follow up: new type of treated wood

Barry Irby

John, I had not intention of saying Bill was wrong. He clearly has a much better understanding of this than I do. I was just broadening the conversation. Building science is much more complex than most of us would think.

The rusty nails are more complex that would be expected. The inner tip of the nails cools faster than the underside of the sheeting because the metal is a better conductor of heat. The nails become the First condensing surface. As moisture drops out and condenses on the nails the air is dehumidified. Condensation readily occurs on a metal surface but less readily on wood. The wood adsorbs the moisture. Under the right conditions I have seen icicles hanging from the nails, but very rarely see frost on the underside of the sheeting. Also, the importance to me as a Home Inspector was that I often saw drip marks on the attic floor. They were there permanently, no matter the season. That was a strong indication the crawl space was too wet. Actually, you could narrow it down a bit. If the splat mark and drips only occurred over the bathrooms, you could attribute it to a poorly ventilated bathroom. If they were on the North side only, it might be a marginal case. If it was above a corner only, you might find water puddled in that corner, under the house.

You mentioned the surface area of the foil. Can you explain? I assume you don't mean the gross area such as the area of the underside of the roof. Are you saying the phenomenon is related to the smoothness and slickness of the foil that makes it shiny? That one square foot of shiny foil has less surface are than a square foot of OSB?

I was told they t the reason the micro spheres did not work was due to scale. That even infra-red light had a wave length of maybe 3/4" and that the micro spheres were don in the micron range, thus the radiation was too long to be affected by the tiny spheres. What do you think?

Re: Follow up: new type of treated wood

John in NM

"Are you saying the phenomenon is related to the smoothness and slickness of the foil that makes it shiny? That one square foot of shiny foil has less surface are than a square foot of OSB?"

Yes, that is it exactly. On a very small scale the fibrous surface of the osb is a much better radiator than is the foil because it has much more surface area from which to radiate. It will feel cooler to the touch, but that is just because it is better at getting rid of its thermal energy by radiating it or emitting it down into the home below.

Other considerations...

david weaver

..does insulating the attic too well and keeping the thermal energy above it cause the roof to be hotter than it would be otherwise?

I recall thinking at one point that I would love to not have an attic that's 140 degrees + in the summer, and felt like (I never came close to following through on this, just pondering) maybe I could put a barrier between the bottom of the 2x6s and the sheathing on the roof. It occurred to me that this is probably the kind of sandwich that manufactured homes have, and then I read elsewhere that roofs isolated so well from the rest of the structure get hotter and the life of the applied roofing material is negatively affected.

The layman's answer (I know little about buildings) is, I'm sure, leaving the attic hot and insulating the top floor of the house from the attic rather than the attic from the roof.

As far as the rusty nails go, they oxidize, the tips become rusty, but is it ever really more than a cosmetic issue? Before reading it here (you can touch the tips of the nails if you have easy access to the attic and find that they're wet sometimes, of course), I never considered that it was really any significant issue to deal with.

Re: Other considerations...

Barry Irby

The water on the nails is evidence the attic has reached the Dew Point, or alt least the nails have. There are two ways to deal with this, raise the temperature or low the humidity. On rare occasions I have seen enough condensation to delaminate the plywood. this house had a sloping ceiling and the rafter bay was filled with insulation and had no effective ventilation in each bay. (plywood above and drywall below). I pointed out the problem to the buyers, but the seller convinced them the plywood was defective and replaced it. Two or three years later the problem became apparent again and they called me back to explain it to them and the new contractor again.

I am not sure there is any definitive proof that not ventilating the underside of the sheathing has any negative affect on the shingles. Installing shingle over an insulated deck does not appear to significantly shorten the roofing life.

The sun can deliver about a 1000 BTU's pr hour per square foot or about a million for a thousand SF of roof. Attic fans are advertised to remove something like 50,000 Btu's per hour. The fans don't cool the underside of the sheeting. Thus t hey don't extend the life of the roofing.

The way around a hot attic...

John in NM

Is to ventilate it. You could do the barrier you're talking about on the underside of the joists, but yo would want to ventilate that space.

Re: Other considerations...

Barry Irby

Ventilating an attic is much more complex than it seems at first glance.

One theory is that venting the heat out will cool the shingles and make them last longer. Back in the 30's tests were done to prove the effect. It was found it took a 30" fan driven by a two horse power motor to pull enough air through the attic to significantly cool it.

If you want to reduce AC costs you have to figure out how the heat gets for the surface of the shingles to the ceiling and into the house. Some of it conducts through the shingles and sheeting and heats the attic air. Some of the hot air leaks into the house. You pay to air condition it back out.

Most of it radiates from the underside of the sheeting deep into the fluffy insulation and into the house. If you reduce the temperature of the underside of the roof surface you reduce the radiation. Installing one of the little gable fans has almost no effect. Drawing air from end to end leaves pools of air up in the rafter spaces that are hot and does almost nothing to cool the underside of the sheeting. The attic seems cooler because the air passes through a "tunnel" in the middle and you experience that. Also, if the hatch or door is leaky the fan may draw conditioned air from the house into the attic. You pay for that too.

Foil barriers work for a while, until they get dirty and stop reflecting effectively. (The business with the foil bonded to the plywood gives me pause here) What I have wanted to try was to install foil faced insulation sheets on the underside of the rafters with them vented from the soffit to a ridge vent. Even considered using the bubble wrap version of the foil thinking the bubbles would keep the foil clean.

If you want to break your brain trying to figure this out, look up Joseph Lstiburek And read some of his stuff. He is the best Building Scientist I know of.

Re: Other considerations...

Larry Clinton At Frankfort, (Central) Indiana

When I built my shop I used trusses for the roof. after the decking and roofing was installed I nailed 1"x 1" boards to each truss running from the eaves to the peak. Then I installed foam board installation against these boards allowing a 1" gap between the roof decking and the foam.

I installed ventilated eaves and sealed them so that the air could flow between the roof decking and the foam boards. At the peak of the roof I installed a full length ridge vent.

It appears to work well as when the sun comes up on cool days usually several birds and sometimes even a squirrel will be setting on the roof vent enjoying the warm air flow!

The shop is built with a knee wall second floor, and behind the walls I blew the entire area full of blow in installation. The ceiling is also insulated with the vented area sealed off, then filled with fiberglass batts, then 2" thick foam board. The entire "room" is lined with 1/4" plywood.

my resolution..

David weaver

Back when I moved into my house, it had soffit and gable vents. They didn't flow. It's also brick, so it would heat during the day and dump the heat into the house in the evening. Overall power use wasn't atypical, but occurs later in the day for us, so we get emails from the utility telling us we have a problem that we don't really have.

Not knowing how changing air temps could create condensation issues and where, I left well enough alone and when the roof was replaced, we had a full length ridge vent installed. I'd rather have it a little hot than have condensation issues. The attic temp after roof replacement is down about 20 degrees. I'm sure the heat offers some offsetting benefit in the fall and winter.

Re: Other considerations...

John in NM

That actually ties in to the foil backed roof sheathing too - I've always used it on houses with metal roofs, but since it reduces heat transfer from the roof to the house, I could easily see its use with a shingle roof causing reduced roofing life. It's going to keep the roof hotter to keep the house cooler.

Ventilating under the sheathing won't necessarily improve shingle life, but it will keep the house cooler. I had always understood the point of attic ventilation to be primarily moisture removal and to a lesser extent cooling efficiency.

Called a cold roof....

Kneale Brownson

...where I used to live. I installed the second deck on 1.5" sleepers on top of a normal deck and created the sealed venting you describe. Helped reduce ice dams in the winter and cooled the inside better. I did this on two houses.