The following covers most everything about green building in just 30 questions, including many for which there is much misleading information available.   Click on the + or the question to show the answer, and click on it again to hide it.


How Much Insulation do I need?
More than most people would assume, but of course it depends on your climate and your assumption about future energy prices and how often your power goes out.  The recommendation for moderate climates is R30 walls and R50 ceilings, while colder climates would be R40 and R60.   Hot climates can get away with R19 walls, but still want at least an R40 ceiling.

In the case of new construction the payback is quite short, and for remodels where the siding & windows are being replaced anyhow, its usually good.  Other remodels won't pay until the price of energy truly skyrockets.  In all cases, there is a point of diminishing return where energy use starts being dominated by loss thru infiltration and window.  In the long run, insulation is generally the best place to put your money since it lasts a long time.  Putting in a lot of insulation will allow for smaller/heating cooling systems, and the potential to eliminate central heating completely in sunnier climates.

If your concern is only avoiding fuel use, then any kind of insulation is good.  If you care about climate change, then avoid stuff with HCFCs.

The limitation is fitting it all in, and to get to the high levels some thought is required.  Walls ought to be double 2x4s, 2x6 sheathed in foam board or equivalent;  floors and ceilings need 12" TGIs or the equivalent.

One nitpick: The reason there is more insulation in the roof than in the walls is NOT because heat rises.  Heat moves from warm to cold in all directions, although warm air rises.  The roof will typically experience greater temperature differences than walls: colder in winter and warmer in summer.  Plus any warm air that rises indoors during winter will exasperate the situation.  Of course that fact that it easier to more in up there means that even if these things weren't true, roofs would still probably have more insulation.

Read more about keeping heat in here, or about energy in general here.

How tight should it be?
Much tighter than most houses are built.  Most people think they're house should "breath", but the way it works is that cold, windy winter days you get far more air leakage than on moderate, calm spring or fall ones, so in order to get enough on those moderate days, you're getting far too much in the winter (hot climate people don't have to worry about this very much). The alternative is to build tighter and combine mechanical ventilation with the heating system.

How tight should you build?  No looser than 2.5ACH50, depending on climate. Depending on the size of the house, you can probably get away with little or no mechanical ventilation if you're no tighter than 1.5ACH50: as you get tighter you'll have to live cleaner (ie keep the toxics out) and be more careful about using spot ventilation to keep the humidity down. The issue generally isn't getting enough fresh air (you only need like 5CFM/occupant for that), it keeping the air clean enough.

For more on infiltration, and what ACH50 means see Infiltration/Ventilation.

What about Windows?
The bottom line is that compared to a well insulated wall, even the best windows are effectively just holes for heat to escape (ballpark R5 versus R30).  If not properly placed and protected by shading, they're all the source of excess air-conditioning load, although this can be substantially mitigated by using a low-E glass that blocks solar heat gain, which currently (2013) is most of them.

When done right, they provide daylight, let in heat when needed and don't let it in otherwise.  Windows with Low-E coatings that provide heat gain are currently (2013) hard to find.

The sad state of affairs is that from the energy perspective the windows in many (maybe even most) houses are a much greater liability than they should be--often its not even the window itself, but its size, placement, or lack of overhang.

The best performing windows are generally foam filled fiberglass frames with triple or even quad panes of glass (the middle panes are actually often plastic) with a whole unit R-value of around 5.  Some windows are better than this, but in either case, there are only a handful of manufacturers who make them, and most of them are not in the US.  The good news is that the vanilla double-glaze windows are much better than they used to be.

Everything you wanted to know about windows is here.

Choosing a heating systems & fuel
Now that air-source heat pumps (usually called mini-splits) work at lower temperatures than they used to, their the best choice in climates where it rarely goes below somewhere around 10F (depending on the unit, maybe as low as 0F).  Ground-source heat pumps aren't affected by air temperature, but they're typically much more expensive.  In either case, these options only really make financial sense if the house is well insulated--otherwise you're installing quite a few of them since they don't put out a lot of heat.

The current fuel of choice for most people is natural gas, but environmentally there is really nothing to like about it, other than maybe its not as bad as coal.  Bio fuels currently don't seem promising-they either take too much land, or the technology to extract them isn't ready.

If the house is small enough, and the insulation is large enough, it might not matter much what fuel is used, since it uses very little of it, but then using a mini-split would reduce that amount typically in half, so its hard not to want go this route.  The main drawback is that most of them are really ugly.

Distributing the heat via an hydronic system is somewhat more efficient, and generally more pleasant (eg no hot or lukewarm blowing air), but there are few heat-pumps that produce hot water instead of hot air, so most hydronic systems burn gas.

Read more about heating systems here.

Radiant heat: hype & reality
The heating system commonly called "Radiant heat" is supposedly accomplished mainly by radiation, but in fact heats the floor (or whatever surface it is placed in), which in turn heats the air (largely by conduction), and heats the other materials by a combination of conduction & convection from the warm air, and some radiant transfer directly from the floor. It will not however heat your body, because the floor temperature is typically below body temperature.  However, a warm floor does raise the room's mean radiant temperature, which reduces your body's heat loss to the room (see the comfort section).  Keep in mind also that in a superinsulated home, the heat will not run all day long, hence the floor will tend to sink back to room temperature, reducing any radiant effects. 

The only true radiant heater are those portable quartz heaters that you point at yourself.

The hydronic heat industry makes a lot of claims about energy savings that I'm pretty convinced are false, but it is still probably the best heat distribution system, particularly for super-insulated homes.  The problem with forced air heat is that air holds very little heat, so you have to move a lot of it and/or make it quiet hot to heat the house.  When you do make it hot, some of the dust ends up getting 'cooked' creating potentially toxic byproducts (it isn't clear how much of a problem this is, other than a tight house clearly makes is worse).  The alternative, the hydronic fan-coil, heats the house very slowly and uses a significant amount of electric moving air while its at it.

The claim that radiant heat (the in-floor kind) saves energy is based on the assumption that the floor is warm and that as a result people will lower the thermostat (since much of your perception of warmth is based on floor temp).  However, in a super insulated home, the floor will not be that warm because it doesn't need much heat, and further at least one study found that people didn't turn the thermostat down at all.  The reality is that climate, insulation and air infiltration are the major factors governing energy use.

There is a claim that radiant avoids temperature stratification in rooms, but this doesn't typically happen in super-insulated homes anyway, since those that don't use in-floor heat use min-splits whose output is much cooler than standard forced-air systems.

The bottom line is that if you want to save energy, super-insulate your house.  Once you do, hydronic heat is the best choice, but not for the exaggerated reasons they say.  Its because its the most efficient way to move heat around the house.

For a complete discussion on heating systems, click here.

Does On-demand hot water really save energy?
Tankless hot water has been a popular (and in my view very over hyped) product, although conceptually a good idea.  The idea of avoiding "standby losses" (the heat that escapes from the tank), is a good one, but not as simple as it would seem.  What your actual loss is depends on your climate, and whether the tank is inside the house or not.  Complicating it further is that the  standby loss is less significant if you use a lot of hot water and if the tankless unit has a pilot light.

There are various technical limitations with them (random example: you typically have to run at least 3/4Gal/minute to get them to turn on), but the biggest problem environmentally is that they all run on gas.  There are electric ones, but they use so much electric that they often need a special panel.

This is another industry that has made some fairly outrageous savings claims: in most cases your savings will be small, particularly if you doing a fair comparison, which would be to a well insulated tank with an additional blanket on it.

A possible better alternative would be a heat pump water heater (but not in cold climates).

Assuming you're trying to be as sustainable as possible, the biggest impact you can have (without changing use habits) is to install solar hot water. 

For a complete discussion on hot water options, click here.

Why you should think about Passive solar
If you haven't bought property yet, keep in mind that a simple passive solar design will supply 25-50% of your heating (and a lot more with more design effort and some additional cost).  All that free heat could add up to a lot of money over time.

Assuming your location gets sun, then all you have to do is put the right amount of windows on the south side of your house (the area of the windows should be about 7% of the floor area), make sure the windows have a proper sized overhang for your latitude and climate and enjoy your free heat.  Of course there are a few little caveats, but what free thing doesn't come with a few strings attached?

In many climates you can get as much as 90% of your heat from passive solar by adding additional windows, water walls or other collection area and having some thermal mass to store the heat for 12-48 hours.

If you live in a cooling climate like Phoenix or Miami, then obviously you mostly want to hide from the sun instead. In this case, passive solar design shows how to keep the sun out of the windows most of the year.

Read more about solar energy here.

Should I consider Solar hot water?
After you've insulated and upgraded your appliances, and still have $4-8,000 to spare, solar hot water is a great way to use less energy and reduce your carbon footprint.  Obviously the more sun your location gets, the more hot water you'll get out of it.   The only downside to these units is that they do require a small amount of maintenance--the collector loop fluid has to be replaced every few years.  It used to be that solar hot water was a much better deal than solar electric, but since solar panel prices have come down dramatically, its a much tougher call.

Read more about hot water here.

Should I consider Solar electric?
Costs have come down quite a bit, and microinverters are making installs simpler and somewhat more tolerant of shade. Photovoltaic (PV) or solar electric is the one source of renewable electric generation that is available to most urban dwellers--all you need is a sunny spot to put up the panels and a way to run a wire to feed the power back into your service panel. Keep in mind that a small amount of shading will reduce your output as much as a lot of shading, so look for locations that aren't in the shadow of trees, buildings or other obstructions. Systems with battery backup suffer 10% (or more) efficiency losses keeping the batteries charged and require inverters that are about twice as expensive, but without batteries you have no power when the grid is down, even if the sun is shining.

PV prices had been dropping steadily until demand exceeded capacity around 2006.  Recently the prices of panels has dropped precipitously due to a glut of supply, mostly from China.  While large utility-scale projects install for under $4/watt (now closer to $2/watt), residential ones are still more like $5/watt  (SEIA data as of 1Q 2013) with a wide variation from state to state (most are from $4 to $8), and prices have become somewhat volatile, so expect prices to keep changing. Larger systems (5kw+) are less per watt than smaller systems (2kw and smaller). 

Understanding costs: Since panel prices are approximately the same everywhere (currently ballpark $1.50/watt), the remaining cost is in inverters, hardware, wire and "soft costs" (permits, labor, overhead, profit)  Germany has significantly lower residential install costs, mostly due to lower soft costs, so prices could come down in the US even if the hardware costs stay the same.

Power purchase agreements: There are now companies who will sell you fixed rate PV power from your roof with no upfront cost to you--the rate is locked in, and sometimes lower than the current rate.  Alas, not all states allow this.

Payback: On a straight financial basis, payback depends heavily on assumptions about future electric prices, the availability of incentives, and of course how much sun your site has. However, most things people buy have no payback at all, so the choice also depends on how much you like having your meter spin backwards.

Read more about solar energy (including solar electric) here.

Do Set back Thermostats really save energy?

In houses with mediocre insulation, the answer is yes, but in super-insulated houses the answer is probably not.  They only work if the house reaches the setback temperature well before the heating system is turned back on in the morning--otherwise the extra heat to warm the house back up negates the heat saved when it cooled down.

Lighting: do I really need those CFL bulbs?
It depends. Compact fluorescent lighting (CFL) are more mainstream than ever and are now fairly inexpensive. However, their environmental impact in manufacture & disposal is greater than incandescents, so there is not really a reason to use them for bulbs that are rarely turned on (example: a bulb on 5 min/day is on 30hrs/year at a savings rate of 40watts, saves 1.2kwh/year which is about 1/10% of what the average house uses, and often rarely used bulbs are on much less than that.)

LEDs are now starting to be both affordable and more efficient than CFLs, but heat is still a problem for them, so their use in any fixture where the hot air around the blub can't easily escape is somewhat dubious.  The big win will be that LEDs are easier to dim, provided you buy the special compatible dimmer.

For the efficiency geeks: looks for bulbs which produce 100 lumens per watt.  New labeling requirements means this info should be on the package now.

Unfortunately, both LEDs and CFL are a more complex product with many components, in CFL one of them being a small amount of mercury, all of which mostly ends up in the landfill.  The individual bulb has very little, but collectively its not a small amount, so they should be recycled.

Because the energy wasted by lighting ends up as heat, more efficient lighting is a bigger advantage in hot climates (reducing air conditioning load) than cold ones. When heat is needed, installing efficient lighting results in the heating system having to put out extra heat to replace the heat that is no longer coming from lighting.

The three top energy users are refrigerators, washer/dryers and dishwashers.  New refrigerators are dramatically better than  old ones, consuming ballpark 1kwh/day versus 2-6kwh/day for older ones, so that old refrigerator in your garage or basement might be costing you a bundle.  Surprisingly most mini-refrigerators use almost as much energy as the full size ones, so beware of that. For washers and dishwashers, much of the energy goes to heating water, so in this case the lower water use models are also the most energy efficient.  Newer washers that automatically adjust water level, and particularly front loading machines are the most efficient; likewise machines that have a high spin speed reduce the energy used for dry--that is if you're not air drying.

Most small appliances aren't used often enough for their efficiency to matter, other than TVs & computers, and unfortunately the market doesn't sell them based on efficiency so its hard to find out how much power they use.

Read more about appliances here.

What's a phantom load, and why do you care?
Many devices use energy even when they're off, including TVs, DVD players, cable boxes, cordless phones, coffee pots, microwaves, the later because there are clocks on them.  Each of those little black boxes that you plug into wall charge stuff also draw a little power even when they're off. In fact if you add up all the power these devices use it can easily be a steady 50-100wats--as if you left a light bulb turned on all day, every day: anywhere from 1 to 2kwh per day, or from 3 to 15% of your total electric usage.

Look for devices with the energy star label.  Consider putting you TV/DVD etc on a plug strip so you can actually turn it off.  Unplug chargers when your not using them.  It's what your grandparent would have done.


How much ventilation is enough?
Now that houses are built tight, mechanical and/or passive ventilation is pretty much a requirement (see tight houses for why leaky houses are a bad idea).  If your lifestyle is toxic free and your house isn't too tight (ie not tighter than 1.5ACH50), you're probably fine using only spot ventilation (on timers), provided you run them every time you generate moisture (cooking, bathing) and for a long enough time, even if your house is quite tight. If this turns out to be not sufficient, then you need whole house ventilation.  Often this amounts to a timer that runs a bath fan for a certain amount of time every day, but the problem with this approach is that it gives you the same amount of fresh air every day, no matter the weather or how much your home. 

Ideally a ventilation controller would give you fresh air only when you need it, but to date the only one that comes close is the aircycler which only works with forced air heating--it runs ventilation for a selectable amount of timer every hour only if the heating system didn't already run.

The amount of air a tight house leaks can be modified simply by opening and closing windows from day to day throughout the periods of milder weather.  This is a low tech solution that is both highly effective and quite easy to do.

Air filtration will remove much dust and potentially much more, but beyond the basic dust filter, removing more will result in an energy penalty.  To make the air significantly cleaner, the fan needs to run for much or all of the day, incurring a large energy cost.  The fundamental problem is that the particles that are the biggest health problem are small and so require a very fine filter to remove them--which also makes the fan work harder.

Read more about ventilation here.

The world is now so full of toxic (or potentially toxic) substances that they are almost difficult to avoid.  Luckily the most egregious ones are either banned or in the process of being banned, so it is getting easier to keep them out of the house.  The most insidious ones are the ones you don't even know are there: flame retardant in bedding, glues in furniture and cabinetry, residual chemicals from the dry-cleaner, VOC in paints and finishes and things of that nature.  For those who read labels, most of the other toxins are easy to avoid, although you might not find a suitable replacement product in the mainstream retail outlets.  My rule is that if it smells bad, it probably is--even though such a subjective measure is bound to be wrong.

Carpeting is often a problem, even if it doesn't off-gas itself (although it typically does), because it absorbs toxins like a sponge and re-emits them over time.  It is also a sponge for dust, and hence often a breeding ground for dust mites.


Before thinking about roofing material, make sure you have an appropriate roof slope for your climate.  Low slope roofs in wet climates are asking for trouble.  The one caveat to this would be for a living (green) roof because the dirt protects the membrane from the ravages of weather and also provides a mechanical barrier to falling debris--the only downside is that if the membrane does eventually fail, its pretty difficult to replace.

Composition (asphalt) roofing is the most common choice largely due to being much cheaper than any other product.  These shingles are theoretically recyclable (although it appears as if they're typically down-cycled into pavement, and now come in 40 & 50 year warranties, significantly reducing the advantage over their expensive competitors.

Tile & metal are probably environmentally preferable.  Standing seam metal on steep roofs can create maintenance difficulties for any activity that involves walking on the roof since it can be very slippery.  In snowy climates, metals slick surface helps shed snowfall.  Tile roofs are very heavy and may require additional structural support.

Read more about materials here.

There is really no environmentally preferred siding product at the moment.  Fiber-cement is durable and does not need to be painted as often as wood, but uses a lot of energy to manufacture.  Wood, when obtained locally from a sustainably harvested source is much more preferable, but not nearly as durable and needs to be painted often, increasing its environmental footprint.  Vinyl, although durable, is toxic to manufacture. Stucco suffers the same energy problem as fiber-cement, and is probably equally durable.

Read more about materials here.

Construction Lumber
Ideally you'd like to use all FSC certified sustainably harvested wood, salvaged wood or finger joined wood, but in reality its not likely you will find all these materials (2013), although FSC wood is getting much more common.  It is especially important to avoid large timbers (say bigger than 6x6) of non FSC origin, since they mostly come from old growth clear-cuts.

SFI lumber is an industry standard that is weaker than FSC, but still better than standard industry practice.  Depending on how you look at it, buying SFI lumber is either encouraging the industry to move toward sustainability, or helping them wipe out FSC as a standard.  If your personality allows for it, the best option is to keep asking for FSC as loudly and often as you can, and only buy SFI after you've finished complaining about the lack of FSC.

Read more about materials here.

Finish Lumber
Ideally you'd like to use all locally sources FSC certified sustainably harvested wood, re-milled salvage, urban salvage or finger jointed wood made from scrap, but it will take vigilance to source all your material that way.  MDF with exterior glue is also acceptable, but interior glue MDF (urea formaldehyde) isn't because it off-gasses for 20 years.

Read more about materials here.

The best choices are local hardwood (finished with a low VOC finish), tile and linoleum, since they are low toxic, easy to clean and long lasting.  Bamboo and cork are renewable resources, but currently are imported from far away.  As the wine industry moves away from cork it makes some sense to use it for other purposes like flooring--otherwise the forests will be cut down. Soft vinyl flooring is toxic to manufacture, contains toxic phthalates and doesn't last very long.  Hard vinyl tile  (VCT) is very durable and doesn't contain phthalates would be a choice of last resort, only when other options won't work.  Laminate flooring (eg, Pergo) may off-gas, depending on what glue is used and what material the surface is made of and is not recyclable nor biodegradable, so isn't a preferred choice.

Note that linoleum, although a natural product, does off-gas, and occasionally people are sensitive to it.

Carpet is generally considered to be a health hazard as well as a poor environmental choice.  The carpet industry has worked hard at instituting recycling programs aimed at reducing how much carpet ends up in the landfill, and also at reducing the level of off-gassing from new carpet.

Read more about materials here.

There are a limited number of truly eco-friendly countertop choices, but new ones are coming out often so it is likely that not every product is covered here.

Paperstone and Richlite and are two similar products that are actively courting the "green" market.  Richlite is made from sustainably harvested paper and standard phenolic resin, while Paperstone offers a product with 100 post consumer paper and water based non-petroleum based resin. Both are very durable and come in a range of solid colors.

Granite counter tops are very durable, but are mined by removing large chunks of some mountain (mostly not in the US). Quartz composite (Caesarstone, Cambria, Silestone) look much like granite, but are made out of 94% quartz particle (the hardest component of granite) and 6% resin.  They are very durable, but their manufactures are not attempting any sustainability claims.  Corian (Avonite etc) are very durable, but use a much larger amount of resin than the quartz composites.

Concrete countertops are also durable, but require a large amount of energy to produce.  In addition, because concrete is porous, most of them are sealed with expoy.  Vetrazzo is a terrazzo like product using recycled glass (reducing the concrete content), but unless you live near Berkley, CA, it might not make sense to ship one.

Tile (including granite tile) is a lower cost alternative which is also very durable, but tends to have mildew problems in the grout around the sink.

Wood (e.g. butcher block) can be a sustainable and fairly durable choice, but needs to be refinished regularly.

Plastic laminate (Formica etc) is often the lowest cost choice, and although they aren't very durable.  On the other hand, there isn't that much to throw away when they're worn out.  A similar alternative is to use linoleum, which is not petroleum based, but is also not very durable.  In both cases, durability is relative: if you're careful, both can last 20 years.

Read more about materials here.

Most cabinets are made with particle board boxes, which typically use urea-formaldehyde resin--which off-gases formaldehyde for around 20 years, and so aren't very good choices.  The one exception to this is for Ikea's cabinet line, which use some modified U-F resin that meets strict European off-gassing standards. Look for strawboard or solid wood boxes, preferably FSC certified.  Likewise look for the wood content to be FSC certified as well.

A low-cost option is to use open shelves instead of cabinets.

Read more about materials here.

Salvage Material/Antiques
The use of salvage materials is limited mostly only by your creativity, and to some degree your determination, since using them is often labor intensive.  The labor pays off in having items that are unique pieces of art, giving your home character that can't be obtained any other way.


A simple way to save energy is to reduce the amount of hot water left in the pipe after you turn the faucet off (which also saves water thrown down the drain waiting for hot).  The best way is to locate all your plumbing fixtures close to the hot water heater, but when that isn't possible, using a "home run" plumbing system is second best, although this system only saves energy if your pattern of use is spread out thru the day and the plumber actually uses 3/8" lines: the savings is because the lines are skinnier and hence hold less water than the standard configuration.  However if there are 2-3 sinks and 2 showers all adjacent and all used at nearly the same time, the standard system with one 3/4" line (versus 4-5 single lines) would save energy.

For cost reasons almost all plumbers are using PEX plastic now.  While the idea of plastic pipe isn't that appealing, copper pipe isn't either, so its not clear which is better from either a health perspective or environmental footprint.

Low flow faucets and shower heads (2.5GPM or less) should be the default choice.  There are now ultra low flow (1.5GPM) shower head as well.  A good compromise option is a shower faucet that has a volume control on it (as well as temperature), allowing you to run at lower volume much of the time and only turning it up when you want a quick rinse.

Low water use toilets (1.6GPM) are now being replaced by ultra low flow (1.3GPM) and dual flush models.  The best choice is a toilet that actually flushes everything first time, every time--consult www.savingwater.org to find the best performing models.

If you have access to municipal water, and its not terribly expensive (most of them aren't), a rainwater system won't make much economic sense.  They can still  make environmental sense in climates with seasonal rainfall (most of the west), since they act as additional storage capacity, saving the impact of building additional storage capacity.  The simplest uses of rainwater are for non-potable use-landscaping, toilets and maybe laundry.

The key to a successful rainwater system is keeping crud out of the tank...which means keeping it out of your gutters or filtering it out before the water gets in the tank.  Unless the water is kept very clean, you will most likely want an additional filter before using it for toilets, and certainly for laundry.

Tanks are typically plastic (polyethylene), metal or concrete, with typically cost ranging from fifty cents a gallon to a dollar a gallon, plus installation cost.  Underground tanks tend to be more expensive than above ground storage.  The necessary size depends on how long the dry season is and how much you need per day: in most cases this will be thousands of gallons.

Unless you can collect the water at least 50' higher than you use it (providing about 20psi), you will need a pump to supply adequate pressure, which means that when the pump dies (which they all inevitably do) or the power goes out, you'll be without water from your tank until the problem is resolved.

On the plus side, you can water your yard guilt free, even when there is a drought!

Storm Water

In areas where there are combined sewers (sewage and storm water), anything that can be done to slow the release of water into the storm sewers during heavy rains helps prevent sewage overflows.  Even when they're not combined, slowing water down is a good idea because it can reducing sudden flooding on area streams.  The solution is simple: try to get the water to go into the ground rather than running off into the street or straight into the sewers.

Turf grass is easily adaptable to industrial maintenance, but is otherwise an environmental disaster: the fertilizers and herbicides applied to lawns pollute groundwater and stream, and the power mowers spew large amount of air pollution, as well as consuming petroleum. In addition, turf grass requires large amounts of water to keep green. If you really want turf grass, use organic fertilizers and consider allowing other plants, like clover and yarrow into the mix, keeping in mind that nature never produces mono-cultures.  A push mower or electric mower will reduce pollution emissions significantly.

Perennials and shrubs make much more interesting landscapes (although admittedly you can't play on them), and when properly selected, will generally use less water and fertilizer than turf grass.

No matter which type of landscaping you use, starting with good soil will make you plants happier and reduce your fertilizer needs.

Read more here.


Why you should be green right from the start
Mostly its because you can't just put windows anywhere and expect a house to be low energy, but you also want to think about plumbing, durability and future use.

If you design for how you'll use the house, you usually find it can be smaller, leaving budget to make it nicer instead.  Plus you don't have to clean, heat or cool the additional space, and living in a smaller space discourages you buying stuff you don't really need anyhow.

Integrated design

Integrated design is a characteristic of green building that should have been done anyhow:  The structural need, plumbing layout, heating needs etc are all factored in as decisions about windows, walls and roof are being made.  Here is where you see how your aesthetic choices affect the energy performance and to some degree material costs (although currently you can't really get material takeoffs from software, at least not for houses, so you still won't have cost info until a builder spends hours doing a budget.

Psychology and comfort
This isn't a topic that comes up often, and isn't even universal in green building, but is worth considering. There is no point building a green home that most people don't want to live in.  This is your opportunity to keep the TV from dominating the household, for keeping social gatherings out of the kitchen (if you want), for putting daylight into the rooms that want it most, and for providing spaces you enjoy being in.  A basic understanding of psychology makes designs more occupant friendly.

Luckily most standard plans do a passable job of this, although its not hard to find ones that don't.  Although there are no hard and fast rules, there are design patterns that will help guide layout; get the full gory details about design here.