Building my own home in North Dakota
Hello, I’ve been lurking on this website for a few months and have found the information to be invaluable. I live in central North Dakota (technically Zone 7 and about ~9500 HDD) and am currently building my own house. My family and I plan on living here for many decades, so I’m very focused on building an efficient and comfortable home. I am also trying to keep a reasonable budget and simple design. The house will be split entry (lower level is half underground and half above ground) with approximately 1200sq ft. per level. The foundation has already been poured using ICFs. Basement slab will be poured in the next few months. We are heating using a condensing natural gas water heater which we will use for in-slab PEX and also stapled up PEX for upper floor. The roof will used a raised-heel truss and I’m planning for at least 18″ of blown cellulose for approximately R-60.
What I’m struggling with right now is wall construction. I’m leaning toward a REMOTE system, using either EPS or XPS. I can get EPS at almost 1/3 cost of XPS from local Menards store. I’ve done the calculations and I need approximately 2/3 of my wall insulation on out outside to keep sheathing dry. If I go with this system, do you think 2 layers of 2″ foam would be a good setup with r-11 fiberglass in the walls? I’ve found plenty of information about window details for thick walls, but details for doors seems to be more elusive. What options do I have for framing/finishing a door for a thick wall? Haven’t decided on windows yet. I will have approximately 70 square feet of south facing windows and 30 square feet of north facing windows, so it’s not alot, but I’m leaning toward a quality Canadian fiberglass window (Duxton or Accurate Dorwin look nice so far.)
I’m not trying to be a trendsetter, but from my research in this area, there are virtually no builders who are using building science in regards to green building and super insulation. Since I am providing almost 100% of the labor for this project, I want to take the time to get as many details right as possible. Any tips would be greatly appreciated! If you have any questions or need more specifics, please let me know.
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Hi Adam, I am looking to build a similar home in zone 7, northern Minnesota. I too was considering hot water in slab heat. From what I have been hearing, if you have an airtight super-insulated envelope, with that sized home, you would be better served by installing an ductless min-split heat pump of some sort. Cheaper and it will supply air conditioning also. Since you haven't poured your slab, you may want to investigate this option soon. Type mini-split in the search at the top of the page, and voila!
Adam,
Here is a link to an article that gives useful hints for installing doors in thick walls: Windows and Doors in Double-Stud Walls.
Adam and Steve .
I would suggest you contact someone who is familiar with very tight houses and radiant for assistance . Steve , Eric Aune ( Aune Plumbing ) in Zimmerman Minnesota may be able to help you . These homes both sound as if they will certainly require mechanical ventilation and in fact HRVs . Don't eliminate an option without the right information , radiant can be done and done well . You may want to visit heatinghelp.com and post your situations and concerns in the main wall or radiant areas . You will get all you need to make your decision and feel comfortable with it .
By using the water heater as Adam has mentioned to do space heating also is a great start since that equipment is being used anyway you can effectively eliminate several thousand dollars off of the price of a radiant system since you are eliminating the boiler , flue and some other costly things .
You can virtually eliminate what some would call standby loss because the heater would be active more often than idle . Very low water temps also expected in these homes at design temps and outdoor reset makes it all the better . ECM circs using less than 30 watts are the norm now and is is not as complicated as it is portrayed amongst people whom are not current with whats possible now and the fact that there are designers and installers familiar with this type of home , that used to not be the case .
This is what is being worked on at present to make our technology even more in line price wise however there are presently easily installed and enabled controls , this would just be much better . If you would like to ask some questions or get referrals to someone near you to assist with radiant and do it properly feel free to contact me privately . [email protected]
http://www.pmmag.com/articles/97088-year-round-radiant
In very cold climates like both you gentleman are building in there are variables at play with winter weather that would be very unpleasant to find out about using outdoor equipment .
Thanks for your info, guys. Regarding the radiant heat, that's one thing that has been pretty much decided already. I forgot to mention that I already have a 30x40 garage built that we are living in while the house in under construction. I have the water heater (Polaris) installed in the garage and am heating that with in-slab PEX. It works beautifully and the heater is incredibly efficient. I am an Open Direct system, so there is no mechanical separation between radiant heat and domestic hot water. I have been working with Radiantec out of Vermont to design the system and so far it is just fantastic.
Richard, I'm planning to install an ERV with HEPA filtration in the house due to the tight construction and family allergies.
I have considered a mini-split system for quick heat on those shoulder season days when you wake up and it's a bit chilly in the house. We also have need for Air Conditioning for approximately 30 days per year when the humidity and temps are high enough. Not sure whether I should spend the extra on the split or just go with a 15K BTU through-the-wall AC unit.
Of course there is alot of information on keeping a house warm in the winter, but I'm wondering how much effect superinsulation like I am doing will have on keeping the house cooler in the summer. Here in ND we regularly see -30 in the winter and 90+ and high humidity in the summer, so we have incredible temperature swings.
Keeping cool in the summer is less about insulation and more about shading and humidity control. Managing moisture with a dehumidifier is cheaper than AC for the times when you don't need temperature control. Low-E windows help a lot, as do wide roof overhangs designed to keep sunlight off the walls and windows during the peak summer heat. Porches, trees, etc are all good. A ground-coupled slab can help too, though obviously that's not on the menu because of how cold it can get. Since virtually all the intense heat is coming from sunlight, and most of the sun is shining on the roof, having a well-insulated attic is important, and having a reflective metal roof helps a lot, too.
Nathaniel,
Adam is planning to install R-60 insulation in his attic. With that kind of insulation, having a "reflective metal roof" or any other kind of roofing won't make any difference at all. The choice of roofing becomes irrelevant if you have R-60 insulation.
I disagree. A light metal roof will reflect much of the solar heat, reducing the temperature of the attic. That lowers the delta-T between the conditioned house space and the unconditioned attic space. Regardless of insulation level, a lower delta T results in less heat transfer.
Here's an example: 140 degree attic temperature, 70 degree interior temperature setpoint, an R-60 attic, and a 1200 sf attic: (120-70)/60*1200 = 1,000 BTU cooling load.
If you reduce the temperature of the attic even 20 degrees through solar heat reflection from the roofing material, here's the result: (100-70)/60*1200 = 600 BTU cooling load
To get down to a 600 BTU cooling load in this example with extra insulation alone but no reflective roofing, you would have to get to R-100: (120-70)/100*1200 = 600 BTU cooling load.
A metal roof also gives you the opportunity to install it over simple ridge-to-eave ventilation channels, which helps with ice damming, turns the roofing into an effective radiant barrier, and uses the stack effect to carry away heated air under the roof, further helping your cooling loads.
Nathaniel,
First, there are a few math errors in your comment. For example, in your first calculation, you describe a 70 degree delta-T, but your formula calculates for a 50 degree delta-T.
It also appears as if you have confused your units -- writing BTU instead of BTU/h.
Leaving those issues aside, you show a 400 BTU/h difference between the two scenarios. For a house with a 2-ton cooling load (24,000 BTU/h), that difference amounts to 1.7% of the cooling load.
In a 9500 HDD heating dominated climate the additional heat load of the cooler winter & shoulder season leads to more overall energy use than the cooling seasons savings, but it's barely even worth calculating.
Entire 1000 BTU/hr load in Nathaniel's example is about the cooling load equivalent of three standing (but not active) adult humans- truly "in the noise" of the total cooling load. The 400 BTU/hr difference in cooling load between 1000 BTU & 600 BTU is the cooling load equivalent of one adult human doing yoga. It takes about 20-25 watts of mini-split power to remove that much heat.
There's plenty of good reasons for going with a metal roof in that climate, but neither peak cooling load nor total energy use is among those reasons.
From a dew-point control POV in zone 7 you really only need about 40% of the center-cavity R to be on the exterior of the sheathing to protect the sheathing. If you use an interior-side smart vapor retarder and build-in back ventilation behind the siding (or use vinyl, which is inherently back-ventilated) you can even cheat that a bit.
Using a mini-split to bring the house temperature up quickly during the shoulder seasons means you'll get at-best a COP of 2.5 out of it. If you let the thing modulate with the load rather than playing catch-up running at full speed a better-class mini-split will average a COP of 4 or better whenever the average daily temp is in the mid- 40s F or higher. From an operating cost point of view that's usually going to be cheaper than condensing gas.
I am planning to use a 24" overhang on my trusses, to provide shading in the summertime. Used http://susdesign.com/tools.php to help calculate sun/shading for different times of the year. As for roofing, I am using a light tan colored standing seam metal roof with vented soffits and ridgecap, so hopefully that will help keep the attic space a bit cooler. Anyone have advice regarding solar heat gain values I should look for in my windows? And does it make good sense to spec different values for north vs south facing windows?
Adam,
Q. "Anyone have advice regarding solar heat gain values I should look for in my windows?"
A. Yes. See this article for guidance: All About Glazing Options.
Q. "And does it make good sense to spec different values for north vs south facing windows?"
A. Yes.
Direct connection between potable systems and heating tubing is very dangerous Adam . I know at first glance it sounds like a good idea but I assure you it's not . Legionella is no joke and 80% of the cases of it are mis diagnosed as Pneumonia every year . It is everywhere and even in 50% of public water supplies . Not one mention of this on their site or others for that matter . Running cold water through the floors to preheat it before it hits the water heater is another bad idea . Can anyone tell Adam what will happen when that fluid is not above dewpoint ? Another simple fact Adam is that they run one pass of tubing down a joist space , even though that tubing is 3/4 as opposed to 1/2 the heat transfer surface in contact with the floor is 1/2 the size therefore cannot transfer as many BTUh . These are quite possibly the very systems that Martin warns of in his writing . Everything from Vermont is not Ben and Jerry's !
Be wary of online design outfits that do not offer their own errors and omissions insurance policies for when and if there is an issue . I have not been involved with nor have I heard of a single instance where these type of folks stood behind their design when it failed , believe me , I have been called upon to address many .
Richard, I have done my research and I understand the possibility of condensation occuring on the slab in the summertime with ~50 degree water flowing through the PEX. I had no problems with that happening last summer. It just takes a little bit of dehumidification in the living space. As for the PEX runs under the upper floor, I am going to have two runs of 1/2" PEX in each truss space and am shooting for at least 1/2 total coverage with aluminum diffusion plates. As for Legionella, I have also done my research and under the conditions that I will be operating the system, I don't consider it a problem.
I am also with Richard on using heating system water as domestic. Unless you are for sure you know the exact conditions in which it can occur it is a possibility. It is also against most health codes to do this. In fact some, maybe all, health codes won't allow a non-lined (HLW) stamped boiler for use in domestic water heating systems.
If you're out of the house for 48 hrs and the heat is on, could legionaires grow? Are there specific times or temperatures? I don't know, I'm not a bacteria specialist, but if it were me and my families health I would opt for a heat exchanger or some means to separate them.
http://www.radiantec.com/installation-manual/do_it_yourself.php
http://www.radiantec.com/pdf/Direct_Radiant_Heating_System.pdf
Adam ,
You are in fact this companies intended consumer . i'll give you a few facts after I state that you must pay close attention to the disclaimer at the end of the install manual . If this is code compliant with your model code (UPC2009) , ICC 2012 Mechanical code . I was only speaking to you from a place of experiance with this particular companies systems . Please hear me with an open mind .
If you have in fact researched Legionellosis you are aware that the perfect breeding temp for this are between 90* and 120* , this would happen to be the most common temperature range for a properly designed radiant heating system
When you have a domestic hot water demand the pump switch will open and cold water will rush through the entire tubing system actually robbing heat already stored in the mass . When the domestic call is over all that heat will need to be replaced before any usable energy is transferred to the space to be heated , this contradicts everything radiant is about .
Potable water entering the system in this way contains much entrained air which will eat away all ferrous components of the system (Circulators ) and with no air elimination devices ( I see none) all that air will in fact gather at the impeller of the circulator causing it to cavitate and rot away .
There are ways to actually do this but not this properly while still protecting your family and the cities water supply since I also see no means of backflow prevention .
I am researching what tubing they specify as it would have to be non barrier tubing since barrier tubing cannot be used in a potable system . This will allow osmosis further exacerbating the air problem you WILL encounter .
See Adam , once they have your money they will not give it back because it was for you to find out if the system was compliant to begin with . You should delve into your 2009 UPC to verify that this will be allowed .
This system is not allowed by our code and that is why I urge you to perform your due dilligence . many here have not and installed this very system and when it did not work and they got no real assistance from radiantec they called me or my peers and we must by law report such things that put the public water system at risk . I don't think I need to tell you where these cases went . Radiantec was not once held accountable either since they do have that little disclaimer . One such customer is actually a pretty smart guy also who happened to be employed by CSG .
These are just a couple of the pitfalls , there are more but I really don't have that much time .
Heatinghelp.com could really be of use to you .
I tried . Martin , see sometimes we can agree .
Richard, few things. I didn't purchase the "system" from Radiantec. I purchased my Polaris WH from them and two manifolds. The rest I have installed myself. I do have an air separator in my system, and it's works perfectly to remove air from the system. I also am on well water, so there is no concern with public water supply. Three, I wasn't aware that barrier PEX cannot be used in potable water systems. Mine is stamped NSF, so why can't I use it for potable water? I didn't purchase any PEX from Radiantec.
Well then Adam I guess you are all good . NSF is a testing agency only testing products for their intended use . Quite possible that you have no barrier tubing since air is not a problem . You are aware that entrained air cannot be removed until it becomes soluble , usually at around design conditions ? I would invest in a stainless steel or bronze pump for when you need that replaced , it will last longer than the cast iron .
Legionella is a naturally occurring bacteria and if you are willing to bet that it won't happen to your family , OK . At least you're not so cavalier about the public at large .
I do hope you are current on your ASSE mixing valve designations also , I would hate to see you get scalded as a result of a non pressure balanced mixer .
So how efficient is it to remove heat from the mass that you have built up every time someone uses hot water ? I'll have to go back in my books and see where that was the goal .
Please make sure you size that expansion tank for the full volume , pressure and temperature of the system , the result of that being wrong is very unpleasant .
Water quality and Ph can really wreak havoc on systems too , but you probably knew that . Please tell me you are at least neutralizing that condensate before it entering the sewer or septic system . All that acidic waste , terrible.
All things considered , not very green nor efficient . But you saved a load or did you ?
Enjoy your system and good luck Adam
Well, I hope to buy the land for my home in the next couple weeks, so when that happens I can jump into the fire and start making these types of decisions.