Hi! I'm new here, and looking for advice. I would like to build a new very energy efficient house in Atlanta. It is a hot humid type of climate.

We have two children, a granny, three dogs and three cats, plus me and hubby. From reading around, I was thinking about a double framed / double studded design, with dense packed cellulose (if anyone can be found in Georgia to do that).

Also I would like geothermal heating, probably a slab floor assuming a suitable plot of land, and a white metal roof. An energy recover device is also in my plan, and I would like to wire the house for home automation.

I like courtyards, and houses designed around courtyards, but I'm not sure how best to do that while maintaining energy efficiency.

I'd like an insulated, non-vented attic, and a very tight construction.

I would also like a workshop and an elevator as my knees are not what they were. Also, I have a fascination with solar panels, though I understand they are lower priority than making a tight construction.

I would like to do this on a budget of $300k, and there is a separate budget for purchasing a plot.

One thing I was thinking of is that one day Granny and the kiddies will not be here, so I would like their parts of the house to be reasonably self contained, so they can be rented out eventually.

If anyone has suggestions on how to proceed, or would like to rip holes in the Masterplan, now would be a great time! I am reasonably technical, more so than hubby, and my first problem was convincing him that the attic is part of the house and it will not be vented / uninsulated etc. He has previously had a house built to his own design, so there is some experience there, and I am busy learning to use the BeOpt software.

I like ultra modern designs, plantation and mediterranean.

General Contracting the home yourself and the high performance specs your laying out, your looking at a minimum cost starting at about $160 - $175.00 s.f. and up!

It's a bit silly to specify the mechanical systems until the heating & cooling loads are known, and the loads are based on the construction & orientation of the house.

Exterior surface area of the house and the U-factors of the various surface type (be it roof, wall, foundation, window, door) etc comprise the basis of the heat load calculations. U-factors for windows & doors are usually labeled, the rest have to be determined by a careful calculation of the building assembly's materials and structure (including framing, insulation, siding, sheathing, etc.)

The shape of the house has a huge impact on the amount of exterior surface area, and by extension, the heating/cooling loads.  The most efficient shape using standard framing techniques would be a cube- a 2-story square house with a shed, gabled or pyramid roof. That has shape has the lowest,most favorable exterior surface to floor area ratio. When designing the footprint of the house try to limit it to no more than 6-8 corners (an L or T topology.)

Atlanta is in US climate zone 3, which is still a heating dominated climate, but if you don't design & orient the house carefully it's easy to end up with so much solar gain (particularly afternoon gains) to drive the peak cooling load numbers sky-high.  From a cost/benefit point of view on the "whole-wall R" values it's useful to work starting from Table 2 p10 on this document.   You will note that for climate zone 3 they are suggesting R20 as a starting point on wall-R. That doesn't mean 2x6 framing with R20 cellulose, since the thermal bridging of the framing reduces that to an effective R13-R14.  But it doesn't take the complexity and expense of a double studwall to get to R20 and beyond.  A cheap way to hit R20+ would be to start with a 2x6 studwall with dense-packed or wet-sprayed cellulose, and install at least R6 of continuous insulating sheathing between the structural sheathing and the siding.  The insulating sheathing can be either EPS or polyisocyanurate, either of which costs about 10 cents per R per square foot (so R6 would be 60cents per square foot), but if you object to using foam of any type, there is also rigid high-density rock wool panels available for a modest uptick in cost, which has the advantage of being completely fireproof & insect proof.

In any new construction it's useful to consider a simple roof line (easy to air-seal), oriented to be able to add solar PV panels later.  Take this seriously- in 10 years PV will be the cheapest source of electricity of any type, and when the full cost of Georgia Power's new nukes get fully rate-based, electricity prices in GA are primed to rise pretty dramatically.  (You're making a down payment on it every month right now, but that's just the tip of the iceberg.)

For a modern-looking house design a single-plane shed roof of about 1:3-1:4 pitch facing south would be about right for your latitude.  That would also make it fairly cheap & easy to insulate with rigid-foam above the roof deck and cellulose between the rafters, at a ratio that works well enough to not require interior side vapor retarders.  The absolute minimum exterior-R for dew point control in climate zone 3 is  about 12% of the total center-cavity R (cavity-R+ above-deck R) so to get the R-50-ish roof you could blow cellulose into 2 x 12 rafters (about R40), and add about R15-R20 rigid foam as continuous insulation above the roof deck. That's about 3" of 2lb density fiber faced polyiso, or 4" of Type-II (1.5lbs nominal density) EPS.

At an R50 whole-roof the additional benefits of "cool roof" finishes are negligible, and if you're going to be shading the roof with PV panels it's worth even less. It won't hurt, but don't spend any extra on it.

To avoid high summertime solar gains, minimize the east and west facing window area, and design the roof overhangs on the south facing windows to minimize summertime gains while still allowing wintertime gains.  Eliminating west facing glass completely is best, since the sun is low in the sky when coming from the west, and those gains occur when the house is already warmed up from sitting in the sun all day.

In a high-R open floor plan house in your climate you should be thinking about the trade-offs of high-efficiency ductless mini-splits vs. geothermal.  The geothermal gets you room-by-room heat/air conditioning distribution, but it's not dramatically more efficient than mini-splits that cost less than half as much.  In new construction even at TODAY's prices for solar, PV+ mini-splits often pencils out more favorably than geothermal.  There's a lot of napkin math and tweaking of the room-by-room loads to do to get you there, but there are existence proofs of this working well with as few as one mini-split head per floor in climates with much colder design temps than yours.  It's much easier to get point-source heating/cooling to work well when you are designing the house than trying to get there as a retrofit.

Oh Dana thank you!! That was some incredible advice. Exactly what I needed. I expect. I'm going to look up the bits I don't understand, and rewrite the Masterplan about 90%. Your suggestions on the wall materials were especially helpful. I am wary of thermal bridging. Not quite the same thing, but I have done some minor construction, accoustically isolating a floating wooden floor in a sloping building and trying to get it level, so I can sort of visualise the problems.

Personally I love nuclear power. 93 million miles away. I didn't know Georgia was planning on building some NP plants, but I'm from England and new here. You would think the local corruption and the mosquitoes would be enough trouble really.

Minisplits are better for an open floorplan, I think? Where the heat and cool can wend its way about. I was thinking more of getting away from Granny and the kids. In Stepmommy's office. Far far away.. (Wonders how much her own bunker would cost..)

With you on the windows. I don't like windows in general, but the rest of the family will expect some.

The budget isn't set in stone. It is more optimistic, and what I'd like to spend rather than what I will spend. What I really want is to stop paying through the nose for other people to ruin the planet. I'd like to go off grid one day so they can do it on their own dime.

Does anyone know of any nice looking shed design houses? I'll look for myself of course, but if anyone has any favorites.. I need inspiration.

Would be interesting to compare the price of an elevator to building, heating and cooling a single story house.

Posted By jonr on 04 Sep 2014 09:01 PM
Would be interesting to compare the price of an elevator to building, heating and cooling a single story house.

I think it is about $25k for an elevator. But I like two story houses best. I get a roof garden or balcony, and they have more character.

Here's a few suggestions:
There are some great sources for information on high performance building. One online is GREENBUILDINGADVISOR.com. Basically a bunch of HP building geeks talking methods and practicality to each other & homeowners in blogs, pictures, articles and Q&A. Look for nearby building conferences such as the Boston & NY NESEA conferences where all those geeks gather & share knowledge.

Look at DWELL magazine - all contemporary houses.

Houses like the one you are going to build are going up all over the country; people are learning! That's great!

Posted By Rainbow on 04 Sep 2014 08:52 PM

Personally I love nuclear power. 93 million miles away. I didn't know Georgia was planning on building some NP plants, but I'm from England and new here. You would think the local corruption and the mosquitoes would be enough trouble really.

Not planning, actively building some nukes, which are (of course) behind schedule & over budget. The fact that it's a fixed-price contract may protect the ratepayers from the cost over-runs to a degree, but this project is fairly unique in that the state regulators allowed them to add some of the cost into the rates charged years before the project was scheduled to be completed. 

The utility Georgia Power is a state-wide monopoly that actively discourages independently owned generating resource from putting power onto "their" grid, and usually has their way with the regulators, but not always. Private homeowners are allowed to net-meter the PV on their roofs, and attempts to impose excessive fees on those PV owning ratepayers have (for now) been rejected. But unlike most US states, Georgia does not allow third party ownership of rooftop PV, a business model that has worked VERY well for getting large amounts of PV implemented quickly in other parts of the US.

Currently in states with competitive solar installation markets grid-tied small scale rooftop systems cost $3.50-4/watt (half what it was 5 years ago), but that is still more than the $2.50/watt it costs in the red-hot Australian market or the ~$2/watt it costs in Germany.  As the US market continues to expand the average installed price in the US is expected to be in the $1-1.50/watt range by 2020, even though 30% income tax subsidy for rooftop solar is dropping to 10% on 1 January 2017, causing a short-term blip in the market.   At $1.50/watt the net output of the system over it's lifetime is below the retail price of electricity in Georgia, even before the nuclear plant capitalization & operation becomes fully rate-based. With that level of internal rate of return, the rooftop PV should be bankable, and should be able to attract financing on it's own merits with out subsidy, as long as net-metering continues to be the rule.

Net metering will not last forever, since somebody has to pay for the maintenance of the grid. But if the fees for PV owners to remain attached to the grid become too onerous it will only incentivize them to go off-grid. Solar City (a large vertically integrated US solar company)  is currently selling/leasing grid attached PV systems in California with local battery backup. But they also have a stake in Tesla's large lithium ion battery factory (currently under construction in Nevada), that is expected to cut the cost of power storage by more than half by 2020.  The period between now and 2030 is going to be a very distruptive time in the electric utility business, and the utility companies will have to adapt their business models quickly (and the regulations will have do update quickly too.) 

If they screw it up and retail electricity costs go too high, grid defection en-masse will push all of the grid costs onto the remaining rate payers, which will become a vicious cycle.  This is already a very serious risk to the grid operators in West Australia and parts of Hawaii, where there are businesses advertising grid-defection kits.  At Australia's  high electricity rates even new construction built fairly near the grid it's now financially rational to not pay the fees for extending the line even 1000' and simply stay off-grid.  When the cost of storage is halved along with the installed price of PV it will become financially rational for MOST people already running on grid power there to disconnect.

The retail cost of electricity in Georgia is currently less than half that of Australia or Hawaii but this movie will be playing in Atlanta before 2025, count on it.  That's why in a new home design it's useful to design the roof & orientation to be able to take full advantage of that eventuality.  With a high-R house it's not very difficult to get to Net-Zero-Energy in Georgia, but with sufficient roof area going off-grid may even be possible without giving up much in the way of amenities.

But if the fees for PV owners to remain attached to the grid become too onerous it will only incentivize them to go off-grid.

Agreed, although PV owners may either be required to connect (by building codes) or to pay something whether they connect or not (as we do with many other services).

Ah yes, 'amenities'. Like the air conditioning in the vast mansion we are renting right now big enough to house four UK families, and mostly filled with plastic tat, and with so many air leaks it felt like an experimental wind tunnel till I went through it with saran wrap, sticky door insulation strips, bubble wrap and filler.

Everyone thought I was crazy too when I confiscated their incandescent light bulbs and made them use the nice shiny new LED ones I got from China.

After a bit of grumping about the colors of everything not having a strong yellow cast any more, life went on as usual. I never thought of inaccurate color as an amenity, but apparently some people do

I am a bit worried there are nuclear power plants in Georgia. Thank you for letting me know they are already here. I'm not so much worried because they are nuclear power plants, but because they are in Georgia. You just know some good ole boy got the contract for that. I've seen how they run their schools here. (The BEST one in the area has a principal who breaks children's bones and touches them inappropriately and everyone carries on covering right up for him and I'm really not sure why because one of the parents will go postal sooner or later). Am I supposed to think they have more respect for the laws of physics than the laws of people?

Thank you for your comments everybody. Dana, thank you especially. i shall move solar power higher up the priority list, and look for a plot upwind

It doesn't sound like you have a lot yet. You can do quite a bit to make the house more energy efficient simply by proper orientation, and buying wooded land. Deciduous trees have wonderful properties for a climate like Atlanta. We are in upstate SC, in a similar climate. I carefully oriented the house, and we have lots trees, so solar gain in the summer is really quite low. The house has large overhangs, and the garage is on the west side, further shielding the house from hot afternoon sun. We have a big porch on the south side (southwest, really) which also keeps sunlight from streaming in. Our house is small (1400 sq ft) built from ICF, both in the basement and main floor. We are using two small mini-splits, although we only run one at a time. A single 12K head keeps the entire main floor comfortable as long as the interior doors are open (which they always are). We shut off the 12K, and run a 9K in the master suite at night.

I agree that the roof color doesn't make much difference. We went with Galvalume finish because we wanted the old-fashioned tin look. I was planning to use a system that runs PEX tubing through purlins under the tin rood for hot water, but my tin doesn't get hot enough, so I scrapped that plan. I am oriented well for PV, though.

A lot of the danger of nuclear power is not the power generation but storage of the spent fuel. One catatrphic failure of the cooling system and we are all done.

You are correct we don't have a plot yet. Thank you for your advice, I shall bear it in mind.

Thinking about PVs, I have a more fundamental problem. I'm not from the US. I have recently come to realise how many otherwise suitable plots belong to neighborhoods, with covenants. I am not keen on covenants as many of them will prevent solar PVs.

If I do use PVs in a roof, I would like them to cover one whole rectangular roof face so it just looks like a dark blue roof, but even so I am anticipating problems with neighbors, so I would prefer not to have any neighbors.

This clashes with another ambition. I miss London. I miss going out of my front door and having a choice of 50 hangouts within ten minutes walk.

From a quick look online (well.. all day yesterday) I am having trouble finding plots that look like they are close to restaurants or interesting places and are not part of a neighborhood.

Is there an easy way of telling if a plot is part of a neighborhood or part of a planned neighborhood-to-be? I am thinking the right location is 90% of the solution to the problems I will be facing with this whole project, and would like to be able to rule out unsuitable plots from their adverts online.

SFAIK there is no easy way to tell if a particular neighborhood is going to be developing into a walkable village type of community, but that is not the current US suburban paradigm. Locations near public transportation are more likely to have some of that aspect, but there are no guarantees.

The location of a single family house relative to other amenities has a real impact on energy used for transportation as well. In high density urban centers even a code-min dwelling may have a net lower carbon footprint than a remote location where you have to drive everywhere. I know someone who moved her family out of a Net Zero Energy house in a low-density suburb into a 1950s not-so-insulated ranch house, but can now walk to the grocery store rather than drive 10 minutes each way, etc. They're working on reducing the energy use of the older house, but have had no qualms about the decision to move.

Rainbow, I'm currently building a house in Fayetteville. If you want to come see it, pm me! I designed it, and it has separate areas for kids and grannies and a rooftop deck over one wing. It is one story with a walkout basement under part of the house. One wing is built using scip panels, and the rest is 2x6 stick built, with a plan to spray foam insulate. The wall framing is about done, no roof yet. I'm in the process of pricing a Mitsubishi multi-split system and PV panels, and possibly solar hot water. We will see how it prices out.

Rainbow, also look up Serenbe. It is a green community in south Atlanta with a focus on a walkable, live able green community.