Triple glazing worth it?
jwyman
| Posted in Green Products and Materials on
New double wall house, western Massachusetts – climate zone 5.
I am ordering Marvin Ultimate Clad windows; a combination of casement, double hung and sliders. The south side of the house are specified as double glazed and glass doors are not available triple glazed. This leaves 7 out of 23 openings double versus triple glazed.
Is it worth the extra $4,800 (12% of total window and exterior door costs) for triple glazed on the balance of windows?
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Replies
Jon,
Your house; your choice.
Triple-glazed windows will lower your fuel cost; provide a more comfortable interior; and transmit less noise.
Perhaps what you are really asking is, How much fuel will I save annually? You'll need to use energy modeling software to answer that question. It would be necessary to model your home with the two options, and compare the energy use data.
Jon,
If your total window budget is $40,000, and you have 23 openings, that means you are paying $1,739 each for Marvin windows. That seems high to me.
Triple glazed Windows and Noise
From CBD-240 Sound Transmission Through Windows
http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-240.html
" Despite the widespread belief that adding another layer of glass must be beneficial, triple glazing provides essentially the same noise reduction as double glazing, unless the interlayer separation is very large. "
Stephen Thwaites
Thermotech Fiberglass Fenestration.
Martin,
The typical double-hung triple glazed windows are $963 each, while specialty windows and doors make up the difference. There are several doors costing well over the $1,739.
Thanks for the advice.
If you're looking at triple-glazing because of energy performance you might want to reconsider your choice of double-hungs. Depending on local wind conditions casements can offer significantly better air-sealing performance, also they can be substantially smaller than double-hungs and still meet code egress requirements.
This is not an uncommon question, but like Martin implies, it's impossible to for most of the people who chime in on this site to answer, since the answer is never straight forward. Really only an energy model will tell you what you want to know. But I understand what you're after, you want our gut feelings on the matter. but even that is hard without knowing how your windows are configured relative to the space, and how the space is going to use them (for heat gain vs. heat loss vs. daylighting).
Then there's the matter of how you feel about the investment. Lets shoot from the hip and say an upgrade in windows to triple pane saves you $240 a year. (using today's fuel costs) is it worth it to you? They are higher quality. They will feel different, even look a little different. I'm afraid there's too many variables to tell you for sure what you'd save or not save.
Let me know if you need someone to run energy models for you. (architect/HERS rater)
A bit more information would help, the R or U value for the double glazed vs triple glazed. The hdd for your area and the additional cost per square foot for the triple glazed over double glazing. With this information a simple payback can be estimated.
Jon,
Here's my gut reaction:
1. A 12% upcharge for triple glazing is less than the percentages I have heard from some other builders. That's not bad.
2. In 20 years, what will you regret about your specification decisions? Homeowners NEVER regret putting in too much insulation or buying high-performance windows. However, some homeowners get tired of the bathroom fixtures or kitchen cabinets. You might want to scrimp elsewhere, and invest in the good windows.
3. I echo James Morgan's point about double-hungs. I'm also guessing that Marvin doesn't offer full-thickness (1 3/8-inch) triple glazing -- but rather some type of compromise glazing that is only 7/8 inch or 1 inch thick. For the same price, you might be able to get (perhaps somewhat smaller) Canadian casements that perform much better.
Jon:
Briefly, triple glazing has both qualitative and quantitative benefits
Qualitative
1. Comfort
As glass areas get larger, having the inner glass warmer makes a big big difference in comfort. Think of a large cold window as a 'negative' campfire and/or draft generator.
2. Condensation Resitance
Condensation is admittedly a bigger concern in renovation, where ventilation is often haphazard or in any house where a setback thermostat is used aggressively. In short, any triple beats any double, although obviously a warm edge triple will have the least condensation.
Quantitative
Most window companies are delusional when it comes to their claims for energy savings.
As several others have suggested, modelling is your best bet to determine your savings. Keep in mind that modelling needs to take into account both solar gains as well U-factor losses. Air leakage losses for a new window are normally pretty small.
.
Delusions aside, as walls gets thicker, the relative savings of really good windows can be substantial. For example, one double wall house we simulated saved 35% with orientationally glazed triples, as compared to typical E-Star doubles. This is likely pretty close to an upper limit for any savings claims.
Good luck w/ your house
Stephen Thwaites
Thermotech Fiberglass Fenestration
Windows do not last forever, seals fail and gas fills degrade over tme. When considering payback, window life expectancy is a factor, same with mechanical equipment. The upgrade cost must be recovered sooner than building envelope enhancements. Windows that allow for easy glazing replacement down the road would be a plus.
Window Openings that allow for easy Window replacement down the road would be a plus.
I think Energy Modeling is a good Idea.
I would also consider reducing the number of operable windows and doors.
How many doors do you need?
Of course,
Safety Egress must be considered as well as strategically located ventilation ports (which could be small casements or awning windows.)
Fixed windows are superior to Operating windows in U-value , Air Tightness and durability.
Fixed windows usually cost less.
I remember visiting a house in LA
mostly fixed windows, a few people-doors and some well placed, custom size ventilation "door-ports"
I know that a window gives three in one package(light,view &ventilation)
Sometimes dividing the functions works too.
Jon:
As someone who has both Thermotech triple glazed casements and Marvin double glazed(Low-E) double hungs (renovation followed a few years later by and addition hence the mix of windows) I can offer a view of someone who has lived with both. My house is a little north of Ottawa, Canada, so it's cold in winter (though winters are getting warmer, it's as likely to rain then snow).
I do get quite a bit of condensation with with the double glazed Marvin's. I have an HRV and the relative humidity is at a safe (low) level in winter. For all intents and purposes I don't get condensation on the Thermotech triple glazed windows.
As for comfort, I'd much rather sit near my triple glazed windows on a cold night than my double glazed windows. You can feel the convective draft looping around when sitting next to the double glazed windows on a cold night.
Economically, what you pay for the double glazed you were quoted is a sunken cost. You can't upgrade to Triple glazed later, though you could look at storm windows (but they have cons: egress and maintenance).
We all need to start considering a very well insulated house, with a well sealed building envelope, and exceptional windows as an asset that spins off money in the form of yearly savings on energy.
To be honest from my experience double glazed windows don't make sense.
Cheers,
Andrew
I agree that the comfort aspect is important.
As to the window condensation advantage/disadvantage.
Has anyone ever considered that occasional window condensation might not be such a bad thing if materials were tolerant and drainage /collection were provided?
A truth window/dehumidifier?
John,
A window can't work as a dehumidifier unless:
1. Enough liquid water collects to drip off the window into a gutter, and
2. Each window gutter is connected to a drain that conveys the moisture to the home's waste piping system.
Since each window would need to be connected to a plumbing drain and a trap, it's unimaginable to me that the amount of water collected and sent down the drain would be more than evaporation from the trap.
If the water doesn't get past the trap -- if it just re-evaporates -- you haven't built a dehumidifier.
Thanks, everyone for the responses.
The house sits on a 70 acre lot, so sound is not a primary issue.
The house originally had casements and awnings, but were changed to double hung at the owners request, and is not an option at this point. We looked at other manufacturers (Pella has an assembly shop 10 miles from here) such as Serious Windows and the owners we not pleased with their appearance.
Chris Briley - thanks for the info. I listened to your Green Architects Lounge Episode 3 - Windows which was very helpful.
The Marvin double glazed U value is 0.33/SHGC of 0.31 at 1" thick - 12.3 SF for $583
The Marvin tri-pane U value is 0.24/SHGC of .31 at 1" thick - 12.3 SF for $963
West facing windows SHGC of .22
Colrain MA HDD = 7928 http://www.weatherreports.com/United_States/MA/Colrain/averages.html
Would casements versus double-hungs have any easier glazing replacement?
There are several fixed windows for daylighting and passive solar as well as operating ones for egress and ventilation. There are also substantial views and openings to exterior gardens. This is a middle age summer retirement house.
Energy modeling is a great idea.
Andrew - you pretty much answered my question. It had to do with mixing windows rather than being able to provide all triple glazed due to availability at glazed doors. Currently, south facing windows are double glazed. West windows (not doors) are triple glazed with SHGC of 0.22. North and east windows are triple glazed.
Given this great conversation, I am planning on the triple glazed. Thanks again.
I guess to get back to my question - is not the value of double versus triple glazing, but only doing one
Sorry -- a little quick with the trigger. Disregard that final sentence.
Martin,
you make sense(as usual)
Reminds me of a comment in the Bill Rose (Water in Buildings)book
the comment was about air conditioner condensate pans
the water has not been removed until it leaves the building.
Jon, If you decide to use some triple glazed I would research all offerings, U values in the mid-teens are available. You are in a climate zone (7928 hdd) that will take advantage of very efficient windows.
If you are trying to maximize solar gain insist on high SHGC windows, this really matters for the net solar energy gain.
A discussion of window performance and window economics is posted on our Equinox House blog site located at: http://www.newellinstruments.com/equinoxblog.html
A number of the items discussed above are covered regarding the net energy balance and cost of windows. Windows are among the most complex elements in a house and need very careful consideration in order to gain the views, daylighting and energy performance desired.
Ty
@ Ty Newell,
I spent a good deal of time at home yesterday evening check out the site progress diary for your construction project. Thanks a million for going to such trouble to create your website. I didn't post any comment at your website, but I did download the papers you published on the various aspects of your building design. Keep up the good work, and I will get back to you on this subject or others, if I can think of any comments I would like to make.
Regards, from Ireland.
I decided to post up a new query on the use of units, so that people such as myself more familiar with the European system, can better understand these debates.
https://www.greenbuildingadvisor.com/community/forum/building-code-questions/17820/metric-and-imperial