Looking for Affordable Strategies for Building Green
Hi all,
Long time reader of these forums. We finally bought some land to build on, at 8800 ft. in the CO mountains (Zone 7) and starting the process of coming up with a house plan. First thing I have learned is that building is over the top expensive in our area (most full service GC’s are ballparking $350 per sq ft for run of the mill 2×6 construction with minimal advanced thought about being green or efficient) and without finding an economical way to build a family house we simply won’t be able to do this project.
I’ve done boatload of reading and youTube watching (think GBA and BSC vids) to attempt to come up with a simple, DIY possible method of building that is also smart, efficient, and green. So many options; I have to admit I’m still a bit confused and it’s always frustrating to see these ultra green projects with their new, designer, Euro products that end up costing millions to build.
I need a poor man’s green plan. I’m fine with functional (think rectangle and single gable) over fancy. In fact; despite what most here have already condemned as inferior building science, I’ve recently talked to a post frame builder (Morton) about a plan with a single monolithic (frost protected) slab, tall, open span, rectangular building that would house living area and shop/garage (Is one slab/building versus two that much more economical?). They are fine building a shell and letting us finish the interior. Everything about their construction method seems pretty simple; but, looks leaky as can be and I’m skeptical despite their R-value claims how the building might perform. So, I’m wondering if there is a better way to build this type of building to get similar livability along with low cost. We’d like to have 1800-2000 sq ft of living area and 1000-1200 sq ft of garage space.
At this point I’m really just looking for ideas on cheapest way to construct a decent house with “pretty good” green and efficiency metrics. Wall assembly? Roof assembly? House shape? One story preference; but, is it appreciably cheaper to do two? Should I run from the post frame/pole barn concept? Heating system (we don’t need AC here!), mini-splits with passive solar and wood stove..the norm here is in floor radiant these days? Any thoughts or ideas you’d like to share would be greatly appreciated.
Thanks,
Chris in CO
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Replies
Pole construction is a cheap way to frame a building. But framing might only be 10% of the cost of a finished house. What tends to happen with pole buildings is that every other step to finish the building is more expensive.
I'm going to suggest that the most cost-effective construction is not going to involve unusual materials or techniques. In fact, what is most common where you live is probably least expensive. I'm going to go out on a limb and say that drywall is going to be the cheapest interior. Other things vary a lot regionally, but I'm going to bet that 2x6 framing on 24" centers is your best bet.
Green construction is more of a mindset than anything. The two most important things are air sealing, and having enough room for thick enough insulation. You want a design that's easy to air seal, which means simple surfaces without complicated junctures. You also have to put the work in during construction to seal every assembly as you go. The other design consideration is building in space in walls and ceilings so you can use cheap fluffy insulation like cellulose and fiberglass. The actual materials are pretty nominal in cost.
Windows and doors are a major expense, on a custom house they might cost more than the framing. And they have a major impact on energy efficiency. Good windows are expensive. From an energy perspective the most cost-effective thing is to have as few as possible, and you're better off with a small number of expensive windows than spending the same amount on a larger number of cheap windows. This is where you really have to balance what's important to you because a windowless house may not be enjoyable to live in.
If you really want to nerd out, create two budgets for your house: a financial budget, and an energy budget. Create a spreadsheet and get some energy modeling software, and start building your house on paper. Try different designs and materials and see how they affect both budgets.
You are already on the right track building a rectangular shape with a simple game roof. That minimizes the heat loss form factor.
A poor man would realize that many green ideas have a cost that cannot be recouped, even if green building is supposed to be about saving energy/money.
I respectfully disagree that windows are a major expense. Inexpensive windows are usually cheaper than the wall they displace and if you face them south you get free winter heat.
A poor man would have movable insulation to go over his windows when the house stops gaining heat in the evening. And two inches of xps movable insulation is better than the best window you can buy so you win two ways.
The color of your house is free so a poor man in a hot climate may go with a white roof and light walls and In a cool climate you meet go with a dark roof and dark exterior walls.
A poor man might sun dry his clothes instead of purchasing a heat pump clothes dryer.
Etc etc
"Inexpensive windows are usually cheaper than the wall they displace and if you face them south you get free winter heat."
I have to respectfully disagree. We've gone over this many times here, and I've run the numbers. There is no climate in the United States where a window provides a net energy benefit compared to an equivalent area of well-insulated wall. What is true is that if you're going to have windows anyway, there are things that you can do with the siting that impact the energy cost of that window.
Interesting debate on the windows. The house we live in now has great southern exposure and a wall of older, double pane, clear glass windows. Further, the house is not well insulated by today's standards; nor is any appreciable thermal mass employed strategically; but, the sun coming through the windows gives us an incredible amount of heat. Heck, we're opening doors and windows on a sunny day at 25-30 degrees F. My plan was to employ high SHGC windows on the south wall (Low e 180?), lower SHGC/low e windows east and west, and no windows at all on the north side of the house. And, where practical thermal window coverings to help with night time heat loss. At 8800 ft we live in a pretty harsh winter climate; but, it is Colorado and we do get 300 days of sunshine.
I understand the trade-offs in regard to the cost of windows and their inherent heat loss; but, in a cold climate with short winter days who wants to sit in a dark box. That said, for a budget build are triple pane windows worth considering or would they be considered a luxury better suited to higher end builds?
High quality triple pane windows are fabulously expensive. They do not belong on a poor man's build(I call my poor man's house a peasant house)
Inexpensive windows with the insulation will outperform them if you are up to the work involved.
We put 364 sf of clear double pane glass on our ongoing build. Shgc .65, u value .62
The house is not insulated yet and on clear days we were hitting 75 degrees in january.
It's going to be amazing in winter and after 5pm I plan to have r14 panels that will go over the windows. These windows 3x8 were less than $250 each. This is the way of the peasant :D
Deleted
We're concerned that you would put out there that there is an issue with the quality of our window. What specifically was the problem? Were we made aware of it? What is your issue with the frames? We're curious.
I didn't say there was a meet energy benefit. In response to your statement that windows are very expensive, i said windows can be cheaper than the wall it displaces so no need to build a windowless house just to save money.
Furthermore, I believe that high shgc south facing solar windows with affordable movable insulation would outperform ANY triple glazed window. It would also likely outperform a typical windowless wall. This is the poor man's solution.
I'm not going to try to convince you of anything, since you're already committed to your plan. But for the sake of others, I have to point out some fallacies.
"I believe that high shgc south facing solar windows with affordable movable insulation would outperform ANY triple glazed window.."
This is dubious at best. A u-factor of 0.62 is abysmal compared to a good, triple glazed unit that will be around 0.12. Going with your R-14 figure for the insulated panel, you've got a window/panel with a u-factor around 0.064 when the panel in place (assumes good air sealing), and 0.62 when it's not. Don't forget that even when sun is shining though the window, it's still bleeding heat at over five times the rate the triple glazed is. When it's overcast, you're gaining hardly anything. (Are you putting the panel in under those conditions?)
"It would also likely outperform a typical windowless wall."
This is a flat no, unless you're building a time machine first and then building your house 40 years ago. Your R15.6 window/panel combination doesn't even beat a code minimum wall in most places, without even considering the significant portion of the time that it's a regular window with an R value of 1.6.
On the subject of placing and removing the insulated panels as needed, who is doing that? Unless you have an indentured servant, or you never leave your house, I don't see how it's happening consistently. Even when you are home, it's going to get old very fast. And even at night, having windows is very nice and serves a purpose. You can still see out the vast majority of the time at night. What you're proposing is essentially an "only at night" windowless home.
"The house is not insulated yet and on clear days we were hitting 75 degrees in january."
This may sound impressive at first blush, but it's not. A single pane, completely glass greenhouse will achieve the same thing.
You're also likely to run into condensation issues on the surface of the glass when the panels are in place.
An idea that might actually make some sense in very cold climates is insulated covers on the outside of windows. You could have them cover up the windows after you go to bed. This would need to be automated, which obviously throws it out of the "poor man's" model. It still wouldn't validate the use of cheap, high u-factor windows.
This is exactly what I was trying to get at Trevor. We've run the numbers in greater detail in other threads, but there is no heating-dominated place in the United States where the energy you get in from the sun from a hole in the wall is greater than the energy that goes out through that hole. In non-heating-dominated climates the heat that comes in through that hole in the winter is overwhelmed by the heat that comes in during the summer that then needs to be removed.
Colorado has the most favorable climate, with mild summers and 300+ days of sunshine a year, but even there windows don't come close to breaking even. The most you can get out of a window is to say, if you're going to have windows anyway, do a few things to get the most out of that window: get the lowest U-value you can justify, and site it and select the SHGC based upon your climate.
Im enjoying the debate. I believe healthy debates leads to overall knowledge. So,
lets discuss: you said
"This is dubious at best. A u-factor of 0.62 is abysmal compared to a good, triple glazed unit that will be around 0.12. Going with your R-14 figure for the insulated panel, you've got a window/panel with a u-factor around 0.064 when the panel in place (assumes good air sealing), and 0.62 when it's not. Don't forget that even when sun is shining though the window, it's still bleeding heat at over five times the rate the triple glazed is. When it's overcast, you're gaining hardly anything. (Are you putting the panel in under those conditions?)"
this is simple. When the sun is shining, at least in my area, a window is a huge NET heat gainer. 1 square foot at .62 u factor , over 24 hours with average temp of say 40 degrees, target internal temp of 70 degrees, would have lost 432 btu over a day(with no movable insulation). the same sf of window over that 24 hour period, would have gained 1,119.33 btu
compare to a code minimum r13 wall with no windows, which would have lost 55 btu over 24 hours but gained virtually nothing from the sun
compared to a u.12 , .30 shgc window, which would have lost 86 btu and gained 533 btu
so , you can see that in all three cases, the high shgc, high u value window, had the best net gain. this is without any movable insulation. add movable insulation (which a poor man would do) and there is no contest.
you said::
"On the subject of placing and removing the insulated panels as needed, who is doing that?"
the people who really care about green living.
which is greener? sun drying clothes, or getting a heat pump clothes dryer
which is greener? adding an extra blanket when its cold, or using the keeping the COP 3.0 heat pump running at a higher temp?
true green living is not about automating things or relying on electricity. it does involve some effort on our part.
I look forward to your response
I'd like to see some of the math behind your final numbers. How many hours of sunlight are you assuming, and does it account for the correct insolation angle for the season and time of day? Are you using an average day, or a best case scenario day?
Why did you choose a SHGC of 0.3 for the triple pane window? Triple pane windows with SHGC of 0.6 are available. I think that right there sinks your entire case, regardless of any other issues.
If you care about being green, I suspect that the use of 2" thick XPS on the window might just negate any energy savings you achieve. The stuff is probably the worst building material currently available in terms of environmental impact.
I'm sorry, but the idea of manually moving the panels in and out of the windows tens of thousands of times is laughable. I'm sure you could find something more practical to apply that effort towards. How about dispensing with a heating system and using a stationary bicycle instead?
"which is greener? sun drying clothes, or getting a heat pump clothes dryer"
I have a clothes line. Sometimes it rains. Sometimes it's -10 outside. Sometimes the sun doesn't shine for two weeks. You can't dry clothes in any of those conditions.
"which is greener? adding an extra blanket when its cold, or using the keeping the COP 3.0 heat pump running at a higher temp?" The blanket is obviously greener, but how far are we going to go with this line of thinking? If greenness is literally the only concern, then what rationale is there for stopping at a blanket? What could be greener than not even having a house? Just wear a coat and mitts and build a lean-to from fallen branches and foliage.
i thought I had posted a long reply but for some reason its not showing up.
in my area the high shgc, high u value window is the clear winner. if you use an average temperature of 40 degrees, with 70 degrees internal, the "bad window" gains about 700btu NET over 24 hours
the good window gains about 450 btu
and the r13 code minimum wall loses about 55 btu
this will not be the same for all climates obviously(im in zone 3a)
The analysis we did looked at heating degree-days and average monthly insolation. Basically in the shoulder months -- October, November, March and April -- windows are a net benefit. But you get crushed in December, January and February when the days are short, the sun is low in the sky and the nights are cold. Since the shoulder months contribute relatively little to the annual heating bill the net effect is negative.
And in Zone 3A, you have to think about the impact of that high SHGC window in summer, when it means you have to run your cooling system longer and have a bigger cooling system.
It's too bad that Manual J doesn't include this kind of analysis, it would be helpful in selecting windows. Manual J doesn't care about annual loads or average loads, all it cares about is sizing for worst case loads.
in response to trevor I showed that in January , a bad window facing south was more efficient than either a wall or a triple pane window.
care to show your analysis?
Max,
You didn't really show it as much as claimed it. You listed a bunch of numbers without listing any underlying premises or assumptions. Without those, we cannot determine if your numbers are plausible representations of real world circumstances.
Even if your math is correct, it only applies on the days the sun shines. And only for the few hours it shines completely on that window (on the days it shines). In my neck of the woods, those hours are usually few and far between during the winter months.
And for days when it's 40F outside during the winter we'd be outside sitting in lawn chairs in the snow bank with the neighbors celebrating with beer, lol.
Here's a chart I've made showing the cost-effectiveness of various types of insulation:
Cost/board foot R-Value/inch Cost/Rvalue
Wool batt $0.41 3.6 $0.11
Polyiso $0.58 6.5 $0.09
Rockwool batt $0.23 4.1 $0.06
Fiberglass batt $0.11 3.5 $0.03
Rockwool board $0.81 4 $0.20
Cork $2.10 4 $0.53
XPS $0.47 5 $0.09
EPS $0.39 3.9 $0.10
HFC Closed cell Spray Foam $1.00 6 $0.17
HFO Closed Cell Spray Foam $1.50 6.3 $0.24
Open cell spray foam $0.50 3.6 $0.14
Dense pack cellulose $0.10 3.8 $0.03
Blown wool $0.50 4.3 $0.12
(Sorry for the formatting. the columns are material name, cost per board foot, R-value per inch, and dollars per unit of R-value per square foot.)
The last column is the key one, cost per R-value. Fiberglass batt and blown cellulose lead at three cents per square foot of R-value. Rockwool is about twice as much, and board foams are 3-4 times as much. Spray foams are expensive, even more than sheep's wool.
So you should try to get as much of your insulation from the fluffy stuff. Avoid board foams except if you need their moisture resistance or air barrier properties. Avoid spray foam unless there is no other alternative.
I'll add that I threw cork in there but it's a bit of an unfair comparison because it can be used both for continuous exterior insulation and as exterior cladding.
Interesting. Is there a mfg that sells a cork cladding?
Doesn't cork break down when subject to UV rays?
How do you keep bugs from nesting in it, and animals from chewing on it?
See http://www.thermacork.com/
This is helpful. Thank you.
Presuming this is all for walls. Are you able to add wet sprayed cellulose for walls?
In my area, they don't know how to do the dense pack correctly, but they do well on the wet spray cellulose. It is affordable and seems a better option than fiberglass, which seems unhealthy.
The chart is really for illustration, because prices on these things vary regionally. Prices are what I pay here in DC. If you could get local pricing for wet-sprayed cellulose I could calculate the other numbers.
As has been stated here many times, the best poor man's trick is air sealing.
It can take awhile to be thorough, but the materials are minimal(caulk and tapes).
Also pays to plan, and that's free
No one seems to have mentioned using reclaimed materials yet. This is super win-win here, both greener (reusing stuff!), and cheaper! Rigid foam is commonly reclaimed and readily available. After reclaimed comes the manufacturer's second (B stock) stuff, which is almost always perfectly useable for most projects. You can easily save a big chunk of money on your insualtion at least by going this route.
There are companies that specialize in salvaging electrical (and mechanical) equipment too. I work with many of these customers since I offer refurbished equipment to my commerical customers as a way to cut costs (not too many green commerical guys around, BTW). You can get electric panels, circuit breakers, and sometimes even wire this way. I wouldn't use reclaimed electrical outlets though, those tend to get loose with age. If you go with salvaged circuit breakers, stay away from the FPE (Federal Pacific) breakers, those were notoriously unreliable and didn't always trip when they needed to.
You can get reclaimed steel, but I'm not sure that would help you much on a residential project. Many other things like hardware, and even doors and windows can be had this way. If you want the "distressed" look, this is a way to get it without paying a premium for "new" stuff that looks old (kinda like paying extra for someone to rip up your jeans before you buy them).
After that, try to keep your layout simple. Complex roof lines tend to add cost, as do other fancy architectural details.
Bill
Reclaimed foam is a good tip. The other stuff, you really need to know what you're looking for.
Both Goodwill and Habitat for Humanity recycle building materials - things like cabinetry, doors and windows, and leftovers. If you're not picky and/or you can be a bit artistic in your designs you can save loads of money on a one-off build. There are also architectural salvage companies that deal in items "salvaged" from old houses, but also leftovers and mis-ordered parts. We once designed a kitchen addition around a set of windows that were $10k off of their original price, still new in their packaging. That particular salvage company provided brand new 6-panel solid wood doors, several unique windows, new French doors and several other items for projects over the years. All for 50% or less than retail. You just have to be flexible and willing to adjust your designs.
Building cheap this year will be hard. The lumber prices are through the roof and keep increasing so postponing your project to next year may be an option.
Otherwise, the best way in my opinion, is to hire someone to frame the house conventionally. This way you won't get charged extra because you are asking them to build something they never have. Once the house is framed, you can add some kind of larsen trusses/double wall/... on top of the existing frame, fill that with cellulose and weather proof the house. Cellulose is pretty cheap and you can build the structure yourself. From there, you can finish the exterior and the interior the way you want. Hire someone or DIY gradually.
The best way to save money is to do some work yourself but that will cost you a lot of time in exchange.
Doing as much of the work yourself as possible will make a huge difference. I did about half of my house myself, and the cost was around $120 a square foot. This included everything but the land purchase (e.g. site prep, utility hook-up, etc).
*note: this was mostly done pre-pandemic, so material costs were much lower than now
Windows: What has not been mentioned is how airtight your windows are will have a huge impact on both performance and comfort; more I think than the window R/U value. Airtightness varies widely even among different types of windows of the same brand and same model (ie Pella 400 double hung vs. Pella 400 casement). Look for airtight windows. There is a third party site that tests them and you can look up the airtightness.
Other: Airtightness matters in both performance and comfort. NOBODY cares as much about your house as you do. If you have the time and some reliable and trainable help, consider doing the airsealing yourself. I don't think there is any other way to get it right.
Consider EVERY detail before you start and have a plan. Details worked out in the field rarely end up being what you want.
The challenge with what you want to do is there is just very little market for it, and many GC's and subs willing to do it, don't do it well and charge ridiculously. It's more of a marketing gimmick for them. They don't have to live with the house. If you do hire a GC, figure out a way to get objective performance criteria into your contract, such as ACH/50, R values, etc.
Framing - Agree on the 6" wall, but I would not do 24" oc. Instead, use 2x6 top & bottom plates, and do 2x4's at 12" oc staggered. This eliminates some thermal bridging which may be significant at night in your climate.
I wanted to do exterior insulation on an addition to my house and got blank stares from the contractors who looked at it for me. I ended up having a contractor build it just the way he normally would, except that sheathing aligned with the foundation below. I added the WRB/air barrier myself, along with window bucks, insulation, strapping and siding. Ended up costing $100/sf and included a full custom kitchen. I'm now doing the renovations to the house using the same system. Look at the REMOTE insulation system http://cchrc.org/remote-walls/
Thanks everyone for posting in here. I am also in the planning phase of my build so I feel your pain on most of these issues.
I’m actually a general contractor and have extensive building experience. However the building envelope can be very tricky and making an error in calculations or not going with a proven system can really ruin your day. I’ve personally taken apart many homes with moisture issues and it’s not pretty.
I’m not as experienced in building heavily insulated homes and this is the part where I begin to have pause. I’m doing as much research as possible and all these threads are extremely helpful so thank you to everyone chiming in.
As far as windows go I live in Wisconsin and I’d have to agree that buy the best windows and doors you can afford it’s always the weakest part of any envelope in my humble opinion. That alone can really help your house out most drafty houses it boils down to windows.
The thing I like about exterior insulation is that it is simple to build foolproof. The air/water barrier can be in one place (on the surface of the sheathing), and the exterior insulation can be in a thickness that leaves no doubt that there will be no condensation on the wall. You can even continue the exterior insulation down to top of footing to insulate your basement/crawlspace. The installation and materials are low-tech and your walls can stay open while you finish the interior of the house.
If you want to keep your costs to a minimum:
1.) Minimize square footage. If you think you "need" 2,000 sq. ft., design your spaces to fit into 1,500. Biggest savings of all. Period.
2.) Make it a rectangle, no extra corners, simple gable, no fancy Architectural roof planes. Single story with basement. You'll need footings down 5' deep anyway, so you may as well go another 2' down (and 2' up) and pour a full basement. Cheapest "2nd floor" possible.
3.) Average interior finishes. The fancier the cabinets, countertops, floors, and trim work, the more you'll (over)pay.
4.) Build the house yourself (or as much of it as you can yourself). You can go from $250 down to $150/sq.ft.
5.) Stick build with pretty good insulation (~R25-30), very good windows and doors (but not stupid expensive), vented attic, and shingled roof.
6.) Put the windows where you want them, and sizes you want them. But of course less windows and less window area, the lower the cost usually.
7.) Air source heat pump(s) with electric backup heat (e.g. cost effective electric baseboards). Minimal interior room separations so heat distribution is good without HVAC ducting.
8.) You will need some sort of ERV ventilation system. You don't need a Zehnder, although they are nice.
9.) Forget about radiant in-floor heating and passive solar (except for proper design of eave overhangs). Forget about a fireplace. If you want a fireplace, install an electric one.
If you build this carefully, it will be very efficient and comfortable. Much more so than most of your neighbors. If you follow at least some of these points, you should be able to afford a nice house. Splurge where you want, usually on some of the interior finishes.
Good points, except that I think building a two story on a slab is generally cheaper than single story on a basement. It depends somewhat on local conditions. Having said that, my biggest regret is having any stairs at all. If I could do it again, single story on a slab is what I'd do.
Agreed, except in cold climate builds.
Other than the "no stairs" issue (that I can totally relate to), in my opinion the cost to design, form, and pour a successful cold climate engineered slab, along with the amount of concrete required for the usually over-specified club footing, ends up costing as much as a proper stem wall/footing/slab.
Response to Robert Maynes, #28: I deleted my comment because it was not worded well.
We will be using Mathews Brothers windows on a current project, where Robert is the marketing director. They make PVC windows about 30 miles from me and have a higher-performance, triple-glazed line. This is my first time using their high-performance line; they came in very affordably, at roughly $400 per 32" x 54" triple-glazed unit. They offer "regular" North American-style window operation: double-hungs, casements and awnings.
The frames and gasketing are not as beefy as what you see on European-style tilt/turns and I don't have experience with them yet, but my initial impressions are that their design and details are good--not as elegant as the higher-end European tilt/turns or higher-end North American windows such as Loewen, but much better than your typical commodity PVC window.
Their performance values are decent, along the lines of other triple-glazed windows using glass from Cardinal or Guardian: https://37x7nz2g1j14x8d03xtz981d-wpengine.netdna-ssl.com/wp-content/uploads/2020/02/Sanford-Hills-Performance-Matrix-2020.pdf.
PVC is never my first choice for a building material for many reasons, but I do like that these are fabricated close to home, and most of my clients are a hard sell when it comes to how the windows operate, preferring North American-style. I am hopeful that they prove to be durable and perform as advertised; if they do they could help a lot of budget-oriented projects achieve better performance.
Thanks for the clarification Michael. When we reopen for tours, and since you're so close, you should stop on by sometime and see how we do what we do.
"I'd like to see some of the math behind your final numbers. How many hours of sunlight are you assuming, and does it account for the correct insolation angle for the season and time of day? Are you using an average day, or a best case scenario day?"
I had made some assumptions(aveage 30 hdd), 100 percent clear sky
so this time lets use accurate data
from degreedays.net I pulled january 2021 for my location. Average hdd is 17.4
average sunshine 52% (https://www.currentresults.com/Weather/Texas/average-sunshine-january.php)
and I used sustainable by design for the heat gain
https://susdesign.com/windowheatgain/index.php
u.62, shgc .65 for the bad window
u.12 ,shgc .3 for the triple pane( shgc .3 lo -e 366 is virtually all you can get in my area)
u.077 , shgc 0 for the wall
you can run the numbers and see that the "bad" window is a net heat gainer at +386 btu /psf/day
the good window gains +252 btu/psf/day
and the wall is a net loser at -32 btu/psf/day
NOTE that this is without movable insulation - so lets put that to bed. the passive solar house is the most efficient in January BEFORE movable insulation
moving a few insulation panels is not laughable to me. whats laughable is suggesting someone have no fenestration in order to save on heating or cooling costs
I assume from the links you're in the Dallas area?
I'll go back to my earlier comment:
>There is no heating-dominated place in the United States where the energy you get in from the sun from a hole in the wall is greater than the energy that goes out through that hole. In non-heating-dominated climates the heat that comes in through that hole in the winter is overwhelmed by the heat that comes in during the summer that then needs to be removed.
The gold standard for data for this kind of work is the NREL Insolation Data Manual. It has temperature and solar data for 248 locations. It's at:
https://www.nrel.gov/docs/legosti/old/789.pdf
Dallas is on page 233 (labeled page 211 in the document).
Dallas is a cooling-dominated climate, with about 1800 heating degree-days per year and about 2750 cooling degree-days per year.
Here are average daily temperature highs, lows and averages for Dallas:
Max Min Avg
Jan 55.1 35.7 45.4
Feb 59.2 39.5 49.4
Mar 66.4 45.2 55.8
Apr 76.3 56.4 66.4
May 83.1 64.4 73.8
June 90.6 72.6 81.6
July 95.1 76.3 85.7
Aug 95.7 75.9 85.8
Sept 88 68.3 78.2
Oct 78.4 57.5 68
Nov 66.4 45.4 55.9
Dec 57.8 38.6 48.2
Ann 76 56.3 66.2
The average January temperature is 45.4F . I can buy that in January a window can provide that. But what happens to that same window in July and August, when your average high is 95F? And the solar intensity is almost three times as high?
Well, let's look. For each surface, let's figure out the heat conduction, and also the insolation. Here's heat conduction by month, for the wall, the "good" window, and the "bad" window.
Wall "Bad" "Good"
Jan 39.6 366.0 70.8
Feb 33.1 306.5 59.3
Mar 22.8 211.3 40.9
Apr
May
June 10.6 98.2 19.0
July 17.2 159.2 30.8
Aug 17.4 160.7 31.1
Sept 5.1 47.6 9.2
Oct
Nov 22.7 209.8 40.6
Dec 35.0 324.4 62.8
I didn't do April, May or October because those months are so mild. This is based on an interior temperature of 70F in the winter and 75F in the summer. The formula is BTU=area*temperature delta* U-value, times 24 to get from BTU/hr to BTU/day. Note that while I have them all as positive numbers the flow is in opposite directions in the winter and summer.
OK, now insolation. I took the radiation numbers from the book:
Radiation, BTU/SF
Jan 821.5
Feb 1071.1
Mar 1421.8
Apr 1626.8
May 1888.5
June 2134.9
July 2122.1
Aug 1950.2
Sept 1587.1
Oct 1276.1
Nov 936.4
Dec 780.1
I multiplied each number by the SHGC. I also had to adjust for the angle of the sun. I just used 70% for simplicity. Here are the numbers:
Wall "Bad Window" "Good WIndow"
Jan 0 373.8 172.5
Feb 0 487.4 224.9
Mar 0 646.9 298.6
Apr
May
June 0 971.4 448.3
July 0 965.6 445.6
Aug 0 887.4 409.5
Sept 0 722.2 333.3
Oct
Nov 0 426.1 196.6
Dec 0 354.9 163.8
So we add up the conducted heat and the solar gain and we get totals. The negative numbers are contributions.
Wall Bad Window Good Window
Jan 39.6 -7.7 -101.7
Feb 33.1 -180.8 -165.6
Mar 22.8 -435.6 -257.7
Apr
May
June 10.6 1069.6 467.3
July 17.2 1124.8 476.5
Aug 17.4 1048.0 440.6
Sept 5.1 769.7 342.5
Oct
Nov 22.7 -216.2 -156.0
Dec 35.0 -30.6 -101.0
Heating: 153.2 -871.0 -782.0
Cooling 50.3 4012.2 1726.9
Total 203.6 3141.2 944.9
Now, it's always tricky to compare heating BTU's to cooling BTU's because typically they use different technologies. But the "good" window needs about 4.5 times as much HVAC btu over the course of the year as the wall, and the "bad" window uses about 15 times as much. True, it is a net positive in January, but it gets clobbered in the summer.
And that's for an R13 wall. Put in a R26 wall and the wall numbers drop in half.
Sorry, I didn't get a notification for this post. I would have replied earlier.
Yes, a south facing window will allow in a lot more heat gain in summer than a code minimum wall. But, the difference between an affordable high sgch and an affordable triple pane window is negligible. U.62 vs u.3 or so.
Stepping up to a state of the art window would drastically reduce the heat gain but the upfront cost would likely never be recouped so it's a non starter.
You can't use. 70 to convert from horizontal insolation to vertical. A south facing window in my climate admits very little solar gain in June(as low as a north facing window, in fact) and a high amount of solar gain in December.
I know for a fact that a white Interior curtain or shade would reduce that heat gain by at least half if not a lot more, and exterior shades would be even more effective in cutting the insolation,up to 100% effective.
You can use beopt to model this. I have, and the extra cost of all the fenestration is less than $50 a year iirc(364 sf south facing in my case). And this was with no shading. Shading drops the cost significantly
at Trevor Lambert, you posted:
"Max,
You didn't really show it as much as claimed it. You listed a bunch of numbers without listing any underlying premises or assumptions. Without those, we cannot determine if your numbers are plausible representations of real world circumstances."
i gave you all the needed data for the calculations. pray tell, what additional data do you need so i can provide it?
I already said this in comment #21:
"How many hours of sunlight are you assuming, and does it account for the correct insolation angle for the season and time of day? Are you using an average day, or a best case scenario day?"
You also completed ignored the point that you can get triple glazed windows with essentially the same SHGC as your clear double pane. So let's see that comparison, 0.12 u-factor and 0.6 SHGC versus 0.62 u-factor and 0.65 SHGC.
And let's all bear in mind that these claims you're making are based on a house in zone 3A in a thread you joined talking about a house in zone 7. So no matter what, this is of zero relevance to the original question. Your suggestion to the original poster in comment #2 to go with cheap windows and moveable insulation was unequivocally bad advice, after which you've tried to defend it by massively moving the goal posts. I'm not sure whether this is a conscious effort, but in either case it's getting pretty tiresome.
"How many hours of sunlight are you assuming, and does it account for the correct insolation angle for the season and time of day? Are you using an average day, or a best case scenario day?"
I used 52% of the time the sun was shining it was clear( this was in my post and I posted the source)
susdesign DOES account for the correct angle and for the season and time of day( you can click the link I added)
this is not a best case scenario- this is an actual case scenario
you said:
"You also completed ignored the point that you can get triple glazed windows with essentially the same SHGC as your clear double pane. So let's see that comparison, 0.12 u-factor and 0.6 SHGC versus 0.62 u-factor and 0.65 SHGC."
I didnt ignore that fact. I cant get that window in my area unless I want to spend an extreme amount of money, . That cost will never be recoupable so if we are still talking about a poor man's house, the suggestion to buy uber-expensive triple glazed, high shgc windows is asinine
you said:
"And let's all bear in mind that these claims you're making are based on a house in zone 3A in a thread you joined talking about a house in zone 7. So no matter what, this is of zero relevance to the original question".
it is extremely relevant to the original question if its only to stop people from making blanket statements that are untrue. you conveniently forget that his location is also one of the highest insolation locations in the country and they have 300 days of sun
we can go back and forth if you want but Ive shown the numbers, Ive shown the sources, and the data is factual.
Please check out these two articles about an actual passive solar home in CO (where sunshine is abundant), built almost 40 years ago with "cheap" windows (that's all that was available back then) and moderate insulation (considering what we can do today):
https://www.greenbuildingadvisor.com/green-homes/a-passive-solar-home-from-the-1980s
Nowadays we have so many more products available for air-sealing, insulation, and window upgrades.
The second article provides details about solar gain and heat loss, for passive solar or solar tempered design. There is no question that south-facing windows in CO WILL provide more heat than they lose during mid-winter (assuming you have solar access). And you can use cellular shades to cut window heat losses substantially (its dark two-thirds of the day during wintertime). People normally close their window shades after dark, don't they?? Or movable insulation if you are motivated. That's what I used sometimes, its not difficult at all.
https://www.greenbuildingadvisor.com/article/a-quantitative-look-at-solar-heat-gain
Its a real shame that we don't heat our homes primarily or partially with free and zero emissions solar gain using the windows we need to have in our homes anyway. Assuming the climate provides sunny winter days (the articles addresses this issue). And design subdivisions to give south-facing wintertime solar access to building lots whenever practical.
Not to mention daylighting and the positive psychological effects of sunlight during winter (for most people). And that south-facing windows don't cause the higher overheating that west-facing and east-facing windows do in summertime.
>"Not to mention daylighting and the positive psychological effects of sunlight during winter (for most people)."
Sitting in a warm blast of sun coming in through a southerly facing window is very nice on a miserably cold winter day. No question!
Note that Colorado, at least around Denver, has "interesting" winter weather. I have been there in february before and it will be 70ish during the day. Their weather is weird, not like the more "cold ALL winter" style cold weather most of us are used to. I have family out there, so I travel there a lot. I suspect their weather variation from brutally cold to nice and warm the next day might help with the solar gain prospects. Their sun is more intense too, I suppose due to the higher altitude. It's very noticeable, and surprised me the first time I was out there.
Low SHGC windows tend to be on the dark side too. I'm not a big fan of the really aggresive coatings like LoE-340. At some point the people comfort you're giving up with the darker windows and the tint they give to everything isn't worth the minor gains the more aggressive coatings have over the slightly milder coatings. If you focus entirely on the raw data, you miss that fact.
Bill
Thanks for posting bob. I have always wished the second link included more hot climate data, like where I live with only 2500 hdd.
I agree with you about the benefits of daylighting. We are perfectly happy to spend a bit more on continuous ventilation based on the air quality benefits. We should be willing to spend a bit more on daylighting as well especially when it provides cost savings
Yes the (already too long) article covered USA coldest winter regions. For some data on other cities or locations (high/low/average temps in various seasons, cloudiness, rainfall, and more), check out
https://weatherspark.com
Enter your city, and they provide a host of very nice, informative charts for that area.
Other good sites for climate and solar data include:
Sustainable By Design by Christopher Gronbeck. Seattle, Washington.
https://susdesign.com/windowheatgain/index.php
Bizee Degree Days
https://www.degreedays.net
if you live in a hot climate, you might want to place more of the window glazing on the north side of the house, which gets almost no solar gain year-round. And minimize west and east-facing glazing, to avoid heat gain in the summer months. The sun rises in the east, and sets in the hot afternoon on the west side. Those summer solar heat gains are brutal if not shaded well. I put too much glazing on the west side for the views...and had to figure out ways to shade those windows during summer.
Thanks for the links. I'm familiar with susdesign and degree days but hadn't seen weatherspark. Good info.
We have an almost equal number of heating degree days and cooling degree days so we chose to still do passive solar.
No West facing windows. Few north facing windows. Quite a bit of east facing but the worst part of the morning is shaded by trees and gonna of south facing.
The south facing windows are clear .65 shgc and the others are lo-e .3 shgc
We will use bright white shades which will reject back the majority of the heat that hits them.
What type of shading do you use for your West facing windows?
If I were building in CO today, I'd again use 2x6@24" stud walls with outboard polyiso (but thicker). But would use Roxul ComfortBatts instead of commodity fiberglass batts. Or especially for the north-facing wall, might try double 2x4 walls (offset studs). In dry CO, I don't think moisture accumulation without exterior continuous insulation would be a problem if using a smart vapor barrier. R60-R90 attic insulation DIY can be pretty cheap and effective.
Its important to calculate the heat losses and solar heat gains for each space in the building (room or open area) as well as the total building. (Tedious but not difficult to do, its just arithmetic, or use online tools.) You need good solar access (low winter sun track to the south) for passive solar or solar tempered designs to work well. Note that in a true passive solar building, or even solar tempered, you don't need any central heating system, so you are saving significant $$ compared to the cost of insulating and air-sealing if you DIY. A mini split for an open floor plan works well. Resistance or radiant heating units in bedrooms or other closed off areas cost little to install and won't be needed all that much if the building shell is tight and very well insulated. In small bathrooms I used heat lamps which throw off radiant heat very quickly. Again the installation cost is low and not used all that much. The cost of installing a central heating system is substantial, so deleting that item and putting that money into super-insulation and air-sealing is very sensible and saves money in the long run, if not from Day 1. A well insulated and airtight house is more comfortable, and will perform better when the power goes out, which will happen.
We're in a similar situation (Colo, 7,3000' CZ 6 and not rich) and I think I've heard:
- radiant floors in a very well insulated house are likely not worth it. Lots of info on GBA about this. We're planning to use ASHP for heating, and these are now good to at least -20. I expect we'll "backup" with a few resistance heaters in e.g. bathrooms and guest BR for various reasons.
- Gunnison Co has adopted IRC 2015 and IECC 2015, which requires 3ACH50. I understand many county inspectors have ignored this requirement in the past, but that's changing. If you're concerned (as I think you should be) about air leakage, put it in the contract and do the testing. We're building in Eagle Co and there are energy conservation programs that subsidize the cost of blower door testing and other energy conservation efforts.
- windows (much discussed above ...) are an economical decision, but perhaps even more importantly a comfort issue. My impression is that when it's really cold (like now) one wants a very good window, U= 0.25 or less, to comfortably sit near it. Who wants to build a $500,000 house and not be able to comfortably sit by the windows? See the GBA article about high-elevation windows (only Alpen will do argon/krypton fill at your elevation). Maybe go big on windows near the dining table, and less so in the bedroom.
Good luck with your planning. I'd be happy to visit with you about this as I suspect we're attempting to evaluate many similar issues, materials, suppliers, etc. We've also had some go-rounds about frost-protected slabs, excavation costs w/ rocky soils, etc. There are a bunch of issues common to mountain construction that are apparently not important elsewhere. We're well into design and hope to break ground later this year.
johng