U Value....important in San Diego coastal?

last year

We're building a house near the coast with a fairly large amount of glass (almost none facing north). Our weather is almost always between 55F and 70F. Almost never need a/c. We're more concerned about the house feeling cold, since that seems to be the common problem around us.

The windows/doors we've been looking at range from U values of .49 to .30. While that's a big % difference, we're still only talking about R values of 2 vs 3. Does it matter in our climate?

Thanks for any insight.

Featured Answer

millworkman

last year

Title 24 requires windows and doors with a U-Factor of 0.32 and a SHGC (Solar Heat Gain Coefficient) of 0.25 in most climate zones of Cailfornia.

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Comments (6)

David Cary
last year
last modified: last year
The difference between 2 and 3 is 50%. The difference between 10 and 11 is only 10% but there is a huge difference between 2 and 3.

That being said, if you are always having windows open then it may not matter.

Might depend what temp you are comfortable at which may depend on humidity. If you like the house at 68 or 72, that is roughly the difference between 2 and 3 assuming outside temp is 60.

Most heat loss occurs at night and then it matters zero if a window is North or South facing. South facing windows give you heat gain during the day which is only helpful if you can tolerate it. If you open the windows to get back down to 68, then it hasn't helped. Probably fairly obvious stuff just wanted to point it out. Again it comes down to temperature toleration.

Most CA cold is in the morning and whether it matters is person dependent. If your house is 50% glass, then the difference in windows is roughly a 25% difference in heat loss.

Last I looked at CA codes, I am surprised they would allow .49 windows. They are strict with not a lot of flexibility even when the temp doesn't require it. But perhaps you are using whole-house methods which basically get away from specific numbers?

There are not too many situations/places I might be jealous of but building on the coast in San Diego would probably be one of them. Sounds fantastic. I would be thinking about how to flush the heat in the evening. When you say rare a/c, is that on a glass house? You surely can flush it most of the time but you may need some airflow to get it down quickly. And there maybe times due to outdoor air quality that don't want to do that. Pretty rare on the coast but probably not unheard of.
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tparillo18
Original Author
last year
I just looked up the T-24 stuff and yes, we have to use .30. The SHGC is actually a bummer, because we want lots of solar gain. Winter is sunny, summer is generally not.

David -- Don't be jealous. It's crazy expensive!
chispa
last year
What is that comment, something about the coldest winter I spent was a summer in San Francisco! That was also my experience the 3 times we visited La Jolla. We would leave LA and it would be really sunny/hot and then turn foggy/cold as we drove into San Diego.
PRO
Charles Ross Homes
last year
Comparing the energy performance of two different U-values for windows is a function of the total area of glazing and the temperature difference.

A HERS rater's evaluation of your home design will help you make a more informed choice or you can use a free online evaluation tool like REScheck https://www.energycodes.gov/rescheck.
PRO
Windows on Washington Ltd
last year
To make a completely informed decision, you somewhat need to look at the overhangs, shading, and orientation of the home. That said, Cardinal makes several types of glass that will preserve the higher SGHC range and allow for that passive solar heating. Whether the home is designed to take advantage of it, orientation, interior finishes, solar mass, overhangs, draperies, etc....is another story.

U Value....important in San Diego coastal?

millworkman

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David Cary

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U Value....important in San Diego coastal?

millworkman

Comments (6)

David Cary

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tparillo18Original Author

chispa

Charles Ross Homes

Windows on Washington Ltd

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tparillo18
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