Hello to All!

I have a question regarding the "best" design for a cost conscious, energy efficient duplex. I currently own a 3 unit apartment building and have space to build another 2 units. I would like some suggestions on what the best way to do this would be. The duplex will be no more than 2000sq ft total, 1000sq ft max per unit with 2 Br and 1.5 Bth, and will be two stories high. There will be no basement and no garage and the property is located in Northern Vermont. Since these are rental units aesthetics are not important, cost is. I am considering ICF's, SIP's, dense pack cellulose in a Larsen Truss, or regular 2x6 construction with 6" of spray foam for the exterior walls. Which will be the most effcient for the lowest cost? I feel that the most cost effective way to build the roof will be trusses with 24" of blown in cellulose. If there is a less expensive, more efficient way I am open to input. I would like to keep the total cost under $200k using the most efficient technology I can afford. Is this realistic or am I totally nuts? Thanks for your time.

First off, realistically, you're nuts (that's what you were looking for, right? :-) ) I'm not sure even standard construction would end up coming in under $100/ft^2 in your neighborhood, (or would it?) But higher-efficiency buildings don't have to come at a huge cost as long as you keep the design simple-simple-simple- a right-rectangular prism with a gable-ended truss roof, no dormers, etc.

The 24" of cellulose is well-north of R75- is super-insulation on a budget a design goal?

There are no obvious answers as to the methods- a lot depends on your budget, location, and design goals. If high R-value/very-low heating load structures are what you're looking for, start reading here for some hints as to price/performance:

http://www.buildingscience.com/documents/reports/RR-0903_High-R_Value_Walls.pdf

Standard 2x6 alone doesn't cut it for high-R no matter what you fill the stud-cavities with, but you can do a lot with non-structural foam sheathing. (Interior, exterior, or both.) 2x6" using advanced framing techniques with spray-cellulose between the studs and 3" of exterior panelized iso will yield a whole-wall R-value in the R35 range, (about the same as an 11" thick SIP) but the same wall with a half inch of XPS sheathing comes in at only ~R18. With that approach you can pick the R-value that meets your budget by the thickness of the insulating sheathing, or price it against SIPs of equal R-value.

Framing it with an "energy heel" to accomodate thicker attic-floor insulation is always cost effective. 24" of cellulose is going to weigh something though- 1000 square feet of attic floor with 24" of cellulose adds up to a coupla tons- be sure that's factored into the structural analysis. (You may have to go with heavier ceiling joists or tighter spacing on the upper floor, etc.)

In any high efficiency building air-sealing is critical to thermal performance, and that requires a lot of attention to detail by all trades (electricians & plumbers who carry foam guns, and aren't afraid to use 'em.) If you can design it without wiring or plumbing in exterior walls the magnitude your air-sealing mission goes down dramatically. (This may require placing electrical outlets on the floor rather than walls in places to meet code for outlet spacing.)

If you're thinking about recessed lighting- don't- air sealing & insulating over them is a PITA. But you're not stuck with center-room surface mount ceiling fixtures either. Cove lighting/light-valances using dimmable T5 or T8 fluorescents aren't a huge cost adder but add a lot of functional non-glare very-high efficiency light without promoting stack-effect air infiltration. (If you go that route, be at least a little picky about the tubes. The color-temperature should not be over 3000K in kitchen/dining areas, nothing over 3500K in living/bedrooms. The CRI, or color-rendering-index should be at least 80 on any fluorescent used in a dwelling.)

When you end up with a very tight building, you'll have to design in active ventilation (in VT it could be as simple as a continuously or timer/humidistat operated exhaust-only low-volume bathroom fan.) Any fire-breathing mechanicals (boilers, furnaces, hot-water heaters, clothes-dryers) need to be sealed-combustion (using outdoor air, not room air to support the flame), preferably with combined water/space heating using the same burner.

Keep the number and size of the windows to a minimum, but still allow for reasonable daylighting in every room. Avoid double-hungs. Awning & casement windows are simpler/cheaper, leak less and are lower maintenance. In very well insulated buildings take care not to overdo south facing windows or you'll be overheating on sunny days even in the shoulder-seasons.

Slab on grade or crawlspace?

Thank you so much for the response! You have kept me busy for the last 4 hours or so looking into some of the stuff you brought up. The link you provided was very useful. Anyway, the duplex will be an insulated frost protected shallow slab on grade with a simple stained concrete 1st floor (to save money).

I am considering radiant heat but I am thinking maybe a small propane Rinnai unit may do the job for the first floor heating (since the first floor is an open floor plan with no walls). I am a little stumped as to what to do on the second floor (where there are walls) if I go this route. Since the house will be superinsulated I will make sure to have an engineer familiar with energy efficient building figure out the proper heating loads. Propane will be used for the cooking, clothes dryers, and heat.

As for the walls I am leaning towards a Larsen Truss design with 12" of dense pack cellulose. I think I have found a contractor in my area that can build it for me, I just need to contact him to see if he is available. I will definately use casement windows and keep them to a minimum. I want to use the airtight drywall method as well. If you are familiar with the Larsen Truss can I put prefabed trusses on top of them or do I have to build them onsite? Thanks again for taking the time to answer and supplying me with a lot of useful information!

I have more questions than answers for you.  Sorry, but I just have to ask.  I've had a few rentals in the past.  Return on investment (ROI) was my goal with them.  Also, it was clear that most renters think a bit differently than home owners.

 

What is your goal in providing super insulated rental units?

 

Are renters more likely to pay more for the unit because it is super insulated?  This is proving to be a difficult sell for the average home buyer.  The shortsighted buyer is looking for the showy granite countertops rather than the boring not to be seen insulation.  Usually, the renter has much shorter time horizons than the buyer.  Why would a renter pay more for better insulation?

 

Are you providing the heating and cooling in your rental cost?  If so, I presume your rent would be based on a normal insulated house and you make more money because your fuel costs are way lower than the normal building.  The renter knows no difference since they've only lived in normally or under insulated buildings.  This may be a good strategy since long term energy costs are likely to go higher.  Your ROI would likely improve over time.  However, remember that renters are different than owners.  The renter is more likely to open a window in the winter when they are too warm.  They'll say, "the landlord is paying for the heat.  Why should I care I'm wasting heat?"

 

I can see your plan working out in the long run if you are in the right area and are very good at picking tenants.  Good luck.  I'll be interested in hearing more as your plans are implemented.

 

Thanks,

Bruce

 

Radiant heat is usually something of an expensive waste in super-insulated houses, since with a heat load so low the water temps are correspondingly low, and the floor temps never reach that cushy "cruising in yer socks" temperature.  If your ventilation scheme uses an HRV, a small hydronic coil or electric element in the supply air stream is enough.  If you want to zone it, a single small low-temp radiator panel per room is cushy enough and will be far less expensive than radiant.  On the open floor plan unit, using spot-radiant only heating certain parts of the floor where one might be walking or lying down can be pretty nice, but again, a few tiny low-profile low-temperature panels will be nearly as cushy at lower cost.

Something like a 150KBTU-out Rinnai is WAY overkill for a heat source on heat loads as small. (Your "design day" heat load is likely to come in well under 10KBTU for a 2000ft^2 superinsulated structure.  Although in a somewhat warmer climate than yours, the 1200ft^2 Urban IL PassiveHouse with 1-foot blown fiberglass insulated I-beam truss walls used a 1kw element in the ventilation air supply stream as the heater. 1kw=3414btus per hour. See:http://www.e-colab.org/ecolab/SmithHouse.html and http://www.e-colab.org/ecolab/SmithHouse_files/EnergyDesignUpdate%20Article1.pdf )  If you can get your heat load down that low, that may be the "right" solution for you too.  For more money a solar heat & hot-water system with electric element backup, using a heat exchanger for the aforementioned hydronic radiator may be viable.

Prefab roof trusses can be used with Larsen Truss designs.  It is common to define one side or the other of the Larsen Truss as the load-bearing wall, but sometimes both are.  This is a detail to be worked out by the structural designer.

Do not skimp on under-slab insulation either or the slab may become the largest fraction of the heat loss.  The PassiveHouse designs all use more foundation insulation than most other heat loss models seem to recommend, but their track record is good. The also limit the wall penetrations for everything, even drawing earth-tempered ventilation air from buried ducts, as well as routing all electrical, drain, water etc from well below the frost line, entering the structure from below.  If you can find a designer with their software package you can probably tweak the price-performance issues to the level you want.  See: http://www.passivehouse.us/passiveHouse/PHIUSHome.html

Dana1, thank again for the great info! I have to improve my websurfing abilities. I have found a lot but the stuff you have is great! Ok, so the Rinnai is out, I guess I need to keep studying and learn more about heat loads etc. Here is what I have so far:

shallow frost protected slab on grade foundation with a minimum of 6" EPS board under and around the slab. The first floor will be stained concrete.

1800 sq ft two story, two unit structure. Open floor plan on the 1st floor with kitchen/dining, laundry/half bath, and living room. Second floor consists of two bedrooms and a full bath.

12" Larsen Truss walls 24" o.c. 2x4 interior structural framing with 2x3 inch external balloon frame attached with 1x4" gussets. The exterior walls will be wrapped in tyvek and the airtight drywall technique will be used on the interior walls. Dense pack cellulose will be blown in from above.

The roof will consist of prefab trusses 24"o.c. with a 18" energy heel. The ceiling insulation will be blown in cellulose 24" deep.

I will minimize the cuts on the exterior walls and in the ceilings. Radiant is out, Rinnai is out. Do I need an HRV or can I get away with exhaust fans in the baths, the kitchen hood, and the dryer vent? How much do these cost?  I would love to use a solar hot water heater but I am not sure if it will fit in the budget, how much do these typically run? The lot is on town water and sewer so I don't have to worry about paying for a septic or drilling a well. I am leaning towards a propane powered dryer, range, h/w and heating. I know this isn't "energy independence" but that won't be attainable within my cost structure. I will also try to keep the units as VOC free as possible, so I can advertise that these apartments will work for people with allergies or chemical sensitivity. I know that this is just the tip of the iceberg and there is a lot more to look at but how does it look so far?

Thanks again for taking the time to help out an EE "newb"!

~Graham

Windows will be casement and used sparingly. Not too sure on pricing of these so I don't know what glazing or how many panes yet.

Graham,

 

Check out http://www.energywisestructures.com/index.html.  On the site they seem to indicate that an ERV or HRV isn't required.  While that seems to go against a lot of recommendations, I haven't seen any bad press on Energy Wise Structures.  Just eliminating the need for the ERV/HRV would pay for their engineering services.

 

What are other people's thoughts on this?

Thanks,

Bruce

How do you prevent renters from wasting all the "free" utilities?

In the ~8000HDD climate of northern VT an HRV isn't an unreasonable expense, with decent payback in most cases.  For small apartments (particularly the one with an open floor plan)  the amount of duct work is negligible.  The Energy Wise Structures folks' case studies all have heating seasons half that or less- what might be reasonable in TN, MO, TX or OK isn't always the case in VT or MN  (and conversely.)

The size and duty-cycle of systems for dealing with 900ft^2 apartments is quite small, and one might get away with an exhaust-only (no heat exchange) type of ventilation scheme to save a few thousand up front.  But ventilation air IS necessary for tight homes, or the humidity levels tend to creep up to intolerable levels, creating both human health and construction-material problems, no matter HOW you filter/sterilize the air otherwise (which is the approach they seem to be hyping on the EnergyWise site.)

If you're designing this yourself it might be worth springing for a decent heat-loss modeling package like the PassiveHouse software, 

or the DOE's EnergyPlus:

http://apps1.eere.energy.gov/buildings/energyplus/

or at least the DOE2 freeware:

http://doe2.com/DOE2/index.html

There are also other DOE options :

http://www1.eere.energy.gov/buildings/commercial_initiative/modeling_software.html

http://www.sbicouncil.org/displaycommon.cfm?an=1&subarticlenbr=112

There's a pretty good suite of Canadian freebies out there too:

http://canmetenergy-canmetenergie.nrcan-rncan.gc.ca/eng/software_tools.html

(Better to simulate it at the design phase than find all of your "coulda-shouldas" later...)

My thoughts:

Your goal should be to build as tight and predictable a building shell as you can, and this is perhaps less about energy in a rental situation than keeping moisture out of places it shouldn't go, and keeping your tenants healthy. Healthy comfortable tenants stay longer and have less churn, which means more profitability. Dry walls mean a longer lasting, lower maintenance building.

You should absolutely have an automatic, simple and tough ventilation system that can't be disabled by someone trying to save a few $ / month on electricity which instead leads to air quality and moisture issues. You will know your tenants better than anyone, so game this one out. We're putting HRV's in all our well sealed low-energy buildings these days (<1.0 ACH50), but you might want to go with exhaust only for simplicity. Take a look at what Austin Design and Steven Winter Associates are doing with RDI in their Solar Village duplexes. They are thinking about all the same issues you are:

http://www.ruraldevelopmentinc.org/index-wwsv.htm

12" double stud walls, cold attics, Panasonic WhisperGreen fans in baths, and their innovation, a WhisperGreen in the first floor ceiling to spread the heated air to the upstairs bedrooms in a very simple, low-energy way.

In general, we've found 2x4 double stud walls to be a much easier way to construct and verify the exterior air barrier than Larson Truss walls. You've got one layer to watch, simple penetrations, and a construction system every framer is familiar with (build a 2x4 house, put an extra interior partition wall to the inside...).

Main construction process change: blower door test your shell with windows and doors installed, no insulation. Seal all leaks. Do it again after insulation, before drywall. If you find your air leaks, you've got a good chance of finding water leaks as well before closing in. It exposes many of the secrets that wold otherwise been hidden.

Once you get your loads down (<20,000 BTU/HR peak), start looking at Mitsubishi and Daikin air-source heat pumps. Very affordable, free cooling with your heating, decent COP even at cold temps in a low load situation. No combustion either...

You're on the right track. Don't worry about payback, worry about cash flow. If anything drastic happens to energy prices, you'll have the most desirable rental units in town.

Excellent recommendations Jesse! (I'd read elsewhere about the Larsen Truss vs. double-studwall constructabity issues.)

I particularly like the bits about air-tightness verification & remediation during the construction process (talk about "coulda-shouldas"!) Finding & correcting the issues is much much easier before it's closed in.

I'll be keeping an eye out for performance reports on those units in Greenfield- sounds like a great project!

If you are using cellulose, use only the all borate product.

Doesn't that go without saying these days? (OK, maybe it doesn't but...)

Ammonium sulfate fire retardent (commonly used in dry-blow cellulose insulation in the US) is hell on metal- particularly copper & brass should it  ever get damp.  Borates work both as fire-retardent and to some extent ant/termite control- definitely the better way to go. (In heavy termite risk areas there are even higher-borate formula cellulose products available.)

In some countries (Australia comes to mind) sulfate fire retardents in cellulose are banned.

If you're not sure the stuff you have conatains sulfate fire retardent,  mix a teaspoon of crystal sodium hydroxide drain cleaner (Drano, etc) in about a pint of water, mix in a half-cup or so of the insulation.  If the slurry then stinks of ammonia, it's not a borate-only product.

Almost all vendors have borate only product- but for some it's only the wet-spray version.   Probably the all-borate dry-blow version most widely distributed in the US (and thus available through distribution almost anywhere in the lower 48) is GreenFiber's Cocoon2 Stabilized Borate Formula. (It's not typically sold in box-stores. If it's doesn't say "Stabilzed Borate Formula"  on the bag it's likely one of the ~10% ammonium sulfate versions.)  But there are literally dozens of smaller local/regional manufacturers with borate-only goods too (or has Greenfiber bought them all up by now? :-) ). I tend to use National Fiber's Cel-Pak but only 'cuz they're local to me, as is their distributor- none of their products contain sulfates so I don't have to think about it, but there are plenty of others.  If you specify "borate only"  or "sulfate free" to the insulation contractor, they'll know what you're talking about.  The difference in price is miniscule "in the noise".

That said, there's not really not a HUGE worry with sulfated versions as long as you keep them dry.  If you smell ammonia it means it's wet & reacting with something- then and only then should you bother vaccuuming it out.  In an open-blow attic situation, if you have a roof leak, scoop the wet & water-damaged stuff out and replace with sulfate-free goods, but don't waste time worry and money replacing the rest.  Proper air-barrier methods, and vapor retarders where appropriate are good enough to keep it dry and non-reactive, and the cellulose in wall cavites wicks & redistrbutes small amounts of moisture, limiting damage from the random once/year or less minor wetting events.  (But this is one of those things that I wish there was an industry self-administered regulation on, lest we go the route of Australia with a regulatory ban.)

Thanks for all of your input! Sounds like if I want to be safe then I should use a HRV system. Should I use one system for both units? It seems that this would save money to do. How much do these typically cost?

I think that your blower door before the buildings sealed idea is a great one.

In regards to the Larsen Truss vs double 2x4 wouldn't a Larsen truss use much less lumber and therefore be less expensive? Having read one of the links Dana provided earlier it showed a Larsen Truss outperforming a double stud 2x4 wall. I found the following info regarding a modified Larsen Truss (http://www.builditsolar.com/Projects/SolarHomes/LarsenTruss/LarsenTruss.htm) and the man who wrote the article actually lives an hour away from here! I am thinking about giving him a call.

Last question for Jesse: Would having an architect help design this project be affordable? I know it is kind of like asking a salesman if I should buy his product. I also know that someone with more experience could make things go easier and avoid some pitfalls but I just have this feeling that getting an architect involved would add $10,000++. For a project like this that can be the difference between making money and losing it. Anyway, thanks for the info from everyone, I am learning a ton!

Graham

Great info on this post. I would install two HRV's one for each unit. I don't particularly like the ventilation only approach of some, using a bathroom fan for ventilation. If the house is sealed up tight enough you won't get the correct exchange and create negative pressure in the house. Drawing in unwanted cold, heat and humidity. With an HRV you can control the exchange much better and some have really nice controls that make that possible. I particularly like the Fantech units, there controls are great and you can add a boost switch in the bathrooms and if sized correctly you won't need an additional bathroom fan/vent. I also put a boost switch in the kitchen so that you can ventilate the kitchen better when cooking. Although HRV's are not designed to control humidity thay can do it when used correctly. If it's dryer outside and your house is humid, turn the HRV up a notch or two. So with one HRV you can do bathroom ventilation, kitchen ventilation and whole house ventilation. Some even have a recirculating mode where you can draw warm air from one part of the house and circulate it through the system to redistribute the heat trapped in, say a cathedral ceiling area. This system costs about $2,500 installed well worth the money for comfort and air quality. I have seen the results from well sealed buildings with inadequate ventilation, not a pretty site.
I agree that awning and casement windows are much more energy efficient but they are much more costly as well. Windows are always the tough one, is it better to upgrade and get the more energy efficient one? or can you spend that money elsewhere with better results in energy performance? Do you intend to use some passive solar design? If so chekc out these thermal mass windows, that store the suns energy in the window, pretty cool. http://www.eebt.org/Trombe.html
Cooling is probalaby not a big consdieration in Northern Vermont, but with a little shading and correct window placement you probably won't need any cooling system at all.
Before bringing in a blower door try this. Place a large fan, I use an industrial floor fan. infront of a window. Make a box, out of cardboard, foam insulation or even plywood that fits fairly tight around the fan and tight to the window frame. Now turn it on and find your air leaks, any kind of smoke will help but you should be able to find most of them by feel. Pay particular attention to the windows, doors, sills, and especially electrical outlets, they seem to be my nemisis. As you continue to seal up leaks you will find more as the house gets tighter and tighter. once you done now call for the blower door test, typically costs from $300-$500 for testing, but Enery star should pay for it if your in the right location. Not all locations are covered under the energy star program and you may have to pay for this yourself. Talk to you local utility to find out if they are part of the Energy star program and if they are you shouldn't have to pay this service. You may even get some money back if you make the house efficient enough. Builders can recieve a $2,000 tax credit if the house reaches a certain level of efficiency. You can also get some rebates for appliances but you don't get the rebates for energy efficient windows, you can get this on an exsisting house but not on a new one, go figure.
Someone mentioned the Mitsubishi or Daikan air source heat pumps as a method of heating and cooling, I'm not sure if they work well in Northern Vermont but Hallowell makes a cold climate one, designed in Bangor ME for very cold climates.
I have never tried the Larsen truss design, sounds interesting but how much of a learning curve is neede to make building it cost effective? I have found SIP's to be a good method to get decent R-value, good air sealing and cost effective when it comes to building, they go together quickly. Thats just me, always looking for a cost effective approach to get the most bang for the buck. I want high performance buildings with out the high costs and for me the choice keeps coming back to SIP's, when you factor in labor.
Keep posting as you build this it will be great to see the project progress and just what choices you make when it comes down to the $'s.
Tom Pittsley
[email protected]
www.eebt.org

HRV vs. exhaust only is contentious, and there is no easy answer. Factors in your decision should be: how tight your building ends up, how confident you are that supply air will be drawn from healthy places (not crawlspaces, combustion appliances, wet areas, etc.), and how confident you are that ventilation equipment will not be disabled by occupants. This last one is not as much of an issue with owner built houses, but is a real issue for rentals and production building, I recommend you talk to your local HERS rater / energy star inspector about this issue, they have usually seen examples of everything.

Robert Riversong builds in a thoughtful and unique but non-conventional way. His methods won't work as well without him guiding the process. The labor to build a Larsen truss can easily be much more expensive than double stud construction, it all depends on the experience of who is building, and what they have done before. The construction system the link shows is basically an inside out double stud wall, which trades some increased framing complexity for reduced difficulty in insulating and air-sealing the rim joist area.

Air-tight drywall is more difficult to inspect, verify and build tightly than an exterior air barrier system (taped and sealed sheathing, like Huber ZIP), but it allows vapor drying to the outside. The Germans build similarly, but with an interior OSB air-sealed layer instead of air-tight drywall.

As to architects, it all depends on your goals. Some might be able to make a project more affordable, most can make a project more beautiful, some can help chase out technical issues early before you start spending big money on construction. It's like every profession, some are helpful and some will take you in a direction contrary to where you want to go. If $10k is the difference between profitability or not, you're on a very thin margin, and everything will have to go right for you, including design, permitting and construction. We're working hard on cost-effectively designing buildings like you are describing, but I won't claim success every time. The perfect architect helps an owner from getting tunnel vision on any one area by being the generalist on a project, but a skilled builder, developer or owner can often meet that same challenge as well.

The two biggest values are to buy the EEBA Cold Climate Guide ( http://www.eeba.org/bookstore/prod-Builder_s_Guide_to_Cold_Climates-3.aspx ) and hire a local Energy Star / HERS rater who can build you an energy model so you can work through your construction options, especially concerning Peak Heat Loss and get small affordable equipment sized early. That's the true trick to affordable, low-energy construction.

Know though that their Federal mandates don't let them downgrade conventional construction performance as much as reality shows, and they tend to get stuck on simple payback financial models, which drastically under-estimate the true historic fuel price increases and discount financing and cash flow financials.