Designing with Carbon Dioxide

A wood house that is 100 years old is usaly a pile of junk ready for the scrap heap.[I know because I have remodeled many of them.]A concrete or concrete block building can last many hundreds of years.Also ,ask any firefighter,a wood home burns much better than a concrete one,that is why in the motherlode all of the old towns after they burned down once or twice were rebuilt with stone or brick with and with metal doors.

Very interesting article. I need to study more about the ecology of concrete before making a statement. Right now I have a question about this:

'A cubic meter of wood contains 411 board-feet, or about 100 8' long 2x4s'

Let's look at the math here (rounding up, to help support the theory above):

What is the volume of an 8' long 2x4?
2/12 x 4/12 * 8 = 0.44 cubic feet
(dividing 2 and 4 by 12 to convert into feet)

How much is a cubic meter in cubic feet?
1 cubic meter = 35.32 cubic feet

Ok, so according to the statement above 100 8' longs 2x4 fit in a cubic meter of wood, that means 0.44 cubic feet should fit 100 times in 35.32 cubic feet? let's see:

35.32 / 0.44 = 80.28 oops

It doesn't. Only 80.28 8' long 2x4's fit in a cubic meter of wood. Am I missing something here? These number probably still don't make wood anyways, right?

for conversions from one unit to another, use the convert program at:

http://joshmadison.com/software/convert/

LA: Thanks so much for commenting! I used to have that calculator and lost it on a reformatting and have missed it for years!

I did the math slightly differently, but I think the real difference comes from the fact that a 2x4 is not 2x4 but is in fact a 1.5 x 3.5. lets do it again for accuracy:

1 square meter= 10.763 square feet
1 meter=39.369 inches
1 cubic meter = 10.763*39.369=423.72 board feet (being more accurate here)
8'-2x4=1.5*3.5*96=504 cubic inches or 504/144=3.5 board-feet
473.72 board feet/ 3.5= 135 2x4's. Now why did we bother putting the board feet in there at all and not just divide cubic inches?

After reading Treehugger for a few years now, no building written about, no module home, nothing I've seen on this website is more environmentally friendly then a wooden house. It seems to me the the timber, Liechtlehm of central Europe has the lease impact of all. Proper management of our wood resources, forest and urban, is essential.

So wait a sec, does that mean that using paper plates and paper cups actually reduces CO2?

As far as steel being recycled goes, all structural steel mills in the US use the electric arc furnace process, which requires scrap metal (old cars, old buildings, etc.) as an input. Although the exact figure depends on which mill produced the steel, structural steel will be over 80% recycled material (88%, in fact, if you weight the totals by market share among the various mills).

According to the AISI, in 2004, US structural steel produced 0.51 tons of CO2-equivalent per ton of steel. Canada was at 0.88. The trends are downward -- in 2005, it was 0.46 tons of CO2-equivalent per ton. If the EAF process were to be shifted to a carbon-neutral electrical supply, CO2 per ton of steel would drop considerably.

Remember, however, that one ton of material is not the same as a ton of another material -- they weigh the same, but they're not USED the same. The strength-to-weight ratio for steel is much greater than for concrete; this is why steel buildings weigh less than concrete ones (in two identical structures, the steel building will have fewer tons of steel than the concrete building will have tons of concrete).

Simply comparing CO2 by weight or volume, although useful for some purposes, is not especially handy when it comes to estimating the CO2 impact of a structure being designed. You can't say "well, this uses more CO2 per pound, so I won't use it" -- because you may easily end up using MORE pounds of the "better" material, thereby negating your gain and making things worse.

Similarly, an "impact database" that doesn't contain data for your specific area and supply chain will not be accurate; if your database uses basic-oxygen-furnace data, and your steel is going to be electric-arc-furnace, the database will give you terribly wrong information. Even inside the US the figures vary by region & supplier.

[disclosure: I work for an engineering standards association that's affiliated with the steel industry, which is why I'm not going to comment about the other construction materials shown.]

Reclaiming wood from de-construction steps it up another notch, just like recycled steel.

But no matter what...that board or tree will eventually decompose and release that energy back into the atmosphere, right?

Wood is carbon neutral over it's lifetime, not carbon negative. When you add in how much energy it takes to cut one tree up into boards you will see that wood is not CO2 negative, or neutral...it's costly!

Since it has a postive costly we need to factor in expected lifteime of usage. I would guess wood has a useful lifetime of ~100 years before going on to the scrap pile. Cement probably has a useful lifetime of ~1000 years.

Thus unless wood is more than 10 times less CO2 costly than cement, cement is a viable alternative.

Yeah, but if you would build a log house, the energy used on shaping the wood would be minimal. Also, a well built log house should survive 200 years easily - which cannot be said for a log that would decompose naturally in a forest when its time is due. So in that case, it would be a temporary solution, but maybe keeping that CO2 trapped for 200 years would still do the trick - who knows, Maybe at that time we have actually reduced emissions to acceptable levels.
Of cource one thing to consider is that the logs should be harvested sustainably, meaning that new trees are planted and also some trees are left to produce seedlings. But otherwise I think its an ecological solution to house building (even though it can be costly as hell to the customer)

There are greener versions of concrete (such as Flyash) which use recycled material and release less chemicals during curing. Still, not as green as wood.

Obviously reusing structural wood or steel from previous construction sites is much greener than creating new. Even bricks can be reused. Note that concrete may last a long time, however knocking buildings down and building new is very popular and concrete is not reuseable. Once it's up, it's life time is as long as that building. Other materials may live through several other buildings' lifetimes.

Also, structural wood is softwood, which grows much faster than hardwood. So the concept of cutting down trees for construction may not sound green, softwoods are considered somewhat rapidly renewable resources. In areas where grow naturally, bamboo is used structurally and grows very rapidly.

M.Andersons post is quite right and the original article is relatively useless. The structural properties of those materials must be taken into account for any of those figures to be of any use.

There are no good or bad materials, only good or bad designs. You can't know whether a material is appropriate or not until the house is designed.

having grown up in england, where a builder is taught that concrete, brick, slate & plastic windows are the only external materials and plaster, plastic carpet, plastic formaldehyde enriched 'wood' and token insulation are sufficeient for the insides. it is very refreshing to spend some months in sweden looking at materials and have found that not only are Englands choice of materials more environmentally costly but their houses are only built to the Swedish standards of 1978. this means they require more resources to live in too. many houses here in sweden are built from sustainably managed wood, are built quicker, retain heat better and have to deal with a greater range of temperatures - from -50c to + 35c. yet they feel better in almost every respect. even in concrete apartment blocks they make significant use of wood - partly because its a local material, partly because it's versatile (construction - finishings) and partly because they are recyclable, will rot into soil or can be used for heating.

The critical thing is to improve gov't regulation, make sure it is enforced, make sure all materials, everything from clothes, to houses, roads etc are the best available choices. wood is ideal for a great number of uses, but some applications need the properties of concrete - luckily we have alternatives like grancrete

I am not going to put in question the numbers shown in the article. They seem in correct proportion. What I will mention is that the numbers shown strictly reflect DIRECT embodied energy in terms of CO2. ( I stress direct because it leaves out indirect issues that would be relevant on a case by case basis; for instance, wood from clear-cutting forests does not take into account the negative impacts on global warming of forest ecosystem destruction, and, for instance, there are different types of concrete systems - like AAC - which get only a fraction of the figure shown above for 'normal' concrete). This is only one facet in determining the 'CO2 effect' of that material. It is also very important to consider operational energy demands of homes built of different materials. In my opinion it is much more often the case that operational energy requirements of homes (due in large measure to design and construction material used) have a much greater impact on the 'averaged-annual' CO2 impact of such a home than the embodied energy of the construction materials of that home. Embodied energy is most often a minor component of a homes total life-cycle energy footprint (and CO2 footprint). While embodied energy is important and not to be overlooked, it is not more important than the operational efficiency of a home combined with its lifespan. I don't know if you are aware of this fact or not, but in Japan most homes are typically made of wood. The construction is light and quick. They use a renewable 'green' material - wood - and relatively little of it. Unfortunately, these homes have no resale value because they last only about 30 years. After which time, the house is torn down and a new one built from scratch - whether by the old owners or new owners. Actually, new owners almost always tear down and rebuild. This is so wasteful of energy that the Japanese govt. is trying to implement new guidelines and regulations to force developers to start building homes that last several generations rather than just one. This is what happens when one takes the 'wood is renewable, good and cheap' mentality to extremes - disposable homes that end up wasting much more energy than they save.

In case you are interested, The Economist had an article about Japan starting to implement tougher regulations on the durability of Japanese homes about two months back. Sorry, I don't remember the issue date.

For more information on the inherent environmental credentials of wood, which one concludes after examing the LCA of wood buildings, please have a look at www.corrim.org and www.athenasmi.ca (includes links to the US LCI database).

Giving construction with wood a negitive carbon dioxide rating is rediculus. The assumption being made is that "farmed trees" trap CO2 which would otherwise be in the atmosphere. This fails to take into account that all areas where trees are farmed were once naturally forrested and were the tree farmers not to arrive, they would still be forrested.

Not only that but in the process of preparing a tree in eastern europe, scandanavia (or to be realistic Brazil, Congo or Burma because people who love wood that lasts long, love hardwood) for your 2by4s, doors, cladding or what ever, the tree has to be cut down, dragged out of the forest chopped to pieces and transported around the world to reach you. I somehow doubt the fuel costs involved in this process have been taken into account in your negative CO2 rating.

Also tree farms are not pretty places, where nature thrives. They are ugly dark forests, where half the trees barely get enough light to stand straight and the most wild life your likely to see is a rat. I speak from experience.

I'm not surprised you get flak for promoting building with wood, when you show bogus figures like that. You wouldn't happen to have a personal interest in the timber industry would you?

LA: no, I do not, other than being an architect and being rather fond of wood, from a country that has lots of it and should make better use of it.

Wood CAN be carbon negative under the right conditions. Obviously sustainable production is necessary - wood taken from rain forests or grown on drained peat bogs is an environmental disaster.

Wood can be turned into charcoal (or biochar) at the end of its life in a building. This locks the carbon up for thousands of years. Buried in soil, it enhances agricultural productivity greatly. (See www.biofund.org)

All wooden waste from construction or demolition should be turned into biochar.

I found this web page looking for information on the difference in embodied CO2 between low and tall buildings. Can anybody help?