R-Value of window screens
 

Cathy started fall house cleaning late this year. She's a bit concerned that having the screens off for a few days while she's washing the windows (she has a 30hrs/wk day job also) will cool the house enough to cause the heat pump to cycle. Any numbers I can throw to re-assure her it won't make a big difference?
Jim

Just mesh screens she has off? I don't think it would make any difference... They aren't retaining any air or heat...

The screen in place would have some micro effect of blocking direct sunlight and warming the window that would be measured only by a Physics professor. Having the screen off a window that receives direct sunlight will actually raise the temperature of the glass by some absurd fraction of a degree. You'll affect the house temp more when you open the door to go out and pickup the newspaper.

You have data to support that? CA Title 24, our state wide energy code has a provision for screening to reduce inside temps. This can be factored in a energy audit or to pass building plans.

Cathy has no reason to worry, it is true that she may get a little heat gain during the day, but no loss because of missing screens at night.

--Milt, your local window contractor.

I'd venture to guess that screens have an R value of about .01

I don't think that missing the screens will have any noticeable cooling effect on the house. The only reason that "solar screens" keep a house cooler in the summer is because they block the sunlight from getting to the windows. If anything, assuming that it's sunny, then having the screens off should warm the house, not cool it.

The only way that you'd have to worry about the R value of screens is if you had a 1" think bundle of overlapping layers of screen. Then they may offer some insulative value.

If your screens were made of aerogel...

The answer is zero.

Siht, I learn something new everyday around you guys. I will remember that even though its the architect's problem. Learning some things like this, I can pretend like I know what the heck I am talking about.

Thanks for sharing that Milt.

Jeff

If that.

If she (or you) is really concerned about loss through the windows you can probably do something similar to what I've done for the winter months with my old basement windows - get a sheet of rigid insulation and cut it down to fit the dimensions of the inside pane (outside the glass, just before where the screen typically sits), then plug the opening with that. Ugly and you lose the window but gets rid of the draftiness. As a temporary thing it might be fine. I don't care since they're being used on basement windows only for a couple of months (the rest of the house has been upgraded to double pane, more modern window assemblies - one of these days I'll get around to figuring out what I want to do with the basement). If you're concerned about the appearance, get a piece of thin plywood cut to the same size to go on the outside so you only see wood from the exterior rather than foil.

From a practical standpoint, removing the screens will have a negligible effect on overall building envelope thermal performance. Not even worth worrying about.

eeeh, it's winter right?
Sun = good this time of year.

In the basement who cares?

I'm more concerned about thermal efficiency (heating costs) than about being able to look out my basement windows for the six minutes a day I'm down there.

Thanks guys, I think I'll go with the .01 figure and tell her there is no rush to get them back on.
btw, is spring and fall housecleaning a mid-west affliction or does it occur in other areas also?
Jim

You wouldn't believe the cleaning that is going on at our house right now.


My wife is from the mid-west.

Psshhhh, tell her that taking the screens off will let in more sunlight which will actually heat the house. All screens do is keep solar radiation (heat) out, they don't insulate at all.

Years ago I had a plan that called for more windows than typical and it tipped the scale. The solution to maintaining the average R value throughout the construction is to surcharge another portion of the building. It should be pertinent to the immediate area in violation.

This was back when the plan checkers would do the calcs, you didn't have to take the plans to an energy engineer. Well, the plan checker noted my overhangs above the windows (overhangs are included in the overall calcs). He told me to hang a plastic patio blind off the facia in front of the windows and it would pass.

We did, the inspector came out for the final, sighed a bit and signed off. The blind came down that afternoon.

This sort of hi-jinks won't fly today. But it would if the blind was a permanent architectural element.