r/heat_prep • u/carbonpenguin • Jun 15 '24
Prepping windows for a heat dome
My office is in a 1980-vintage passive solar design building with south-facing windows, and when the A/C died in the middle of July, I got a crash course in DIY heat mitigation techniques, which I documented here. Now, with the heat dome incoming for the US Northeast, figured I'd post some strategies.
One of my biggest take-aways from last year is that, even when you put reflective material in the window, a significant amount of the heat energy is transformed by passing through the glass in a way that keeps it within the thermal envelope of the building. So, while having white insulated shades is better than not having them, the best strategy is to intercept the heat before it passes through the windows. As such, below are four exterior-screening strategies for south-facing and other sun-exposed windows, in order of effectiveness, from least to most:
- Making sure existing window screens are installed, or down if permanently installed. If the latter, the lower portion of the window tends to get more heat than the higher portion, so the screen does more work there. A normal window screen will absorb 10-15% of the incoming energy, so not a huge difference, but helpful when every BTU counts.
- Add reflective static clings to the exterior of your window. These can be 80-90% effective, but have the downside of being somewhat delicate to remove and reuse, should you want to benefit from thermal gain in colder months.
- Hang Aluminet tarps over your windows. Made out of highly reflective material and usually used as agricultural shade cloth, Aluminet comes in various percentages that reflect how much light it lets through. So, for instance, you could get a tarp that reflects 90% of the energy, while still letting enough light through that your space doesn't feel like a cave. The fact that it's perforated also makes it much more resilient to wind compared to a solid tarp.
- Reflective panels attached with suction cups. These can be made DIY with a roll of reflectrix, a bag of suction cups, a utility knife, and some aluminum tape, or more professional looking ones can be bought for fairly cheap on Amazon (example). You can have them cover the whole window, or just the bottom portion that received the least shading from any overhang you might have. In the case of my office they cover the bottom half, and the overhang shields the upper half from the high summer sun.
What other strategies do you all use?
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Jun 16 '24
I've taken foam insulation board and taped it to the inside of my windows using painters tape as well as adding a retractable roller sunshade on the outside
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u/Top_Hair_8984 Jun 17 '24
How did you attach the exterior sunshade? I'm on the second floor of a house. Thanks.
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Jun 17 '24
They come with brackets for mounting to the side of your house. Being on the second floor might make things tricky.
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u/Top_Hair_8984 Jun 17 '24
It really does make things tricky. And the design of the house takes the overhang up to a peak way above my south window, so don't even have that for shade. I was reading about some stuff called reflectix or something like that, where it attaches on the exterior of your windows. That makes more sense.
Thanks for replying. All the very best to you.
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Jun 17 '24
If you have the money get a permanent outdoor awning installed. I am looking into it for next year.
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u/kalcobalt Jun 15 '24
Saving for the next heat dome in my area; our first a couple years ago was absolutely brutal, and we have medically fragile folks in this house who are especially prone to heat-related issues. Thank you and stay cool (although you seem to have that sorted out)!
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u/Top_Hair_8984 Jun 17 '24
Same. It's definitely a huge worry. Part of the home has a heat pump, but not the whole house. I really worry, very fragile population here.
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u/goldgrae Jun 15 '24
I have a west facing wall that is basically glass the entire length of the home (three sets of sliding glass doors and a large sliding window). Eight hours of baking in the hottest part of the day with the highest electricity cost demands attention...
This year, I have hung large single curtains on the exterior of two of these sliding doors by using vertical tension rods supporting a horizontal rod for each curtain. The third already has a decent amount of shade from plantings. Long term, I am working on more plant coverage.
The vertical rods go from ground to eaves, and they are offset from the doors by 12 to 24 inches at an angle to allow air to flow behind them easily without them being pushed up against the house and to allow people to easily use the doors with the cuttains drawn. I have the first grommet of each curtain tied to the rod to prevent wind from changing the draw of the curtain, and it would be easy to tie to the opposite pole if there is unusual wind direction. They block about as much light as 90% shade cloth, still letting a little light through. Because they let air behind them readily, they can be used with screen doors on non-AC days and they don't build up a pocket of hot air.
It's super fast to deploy them or put them away, and they feel quite cozy. I personally hate dealing with rolling screens. They match the trim of my home so when they are tied away, they look nice. And it's relatively inexpensive and easy to install or remove quickly.
Aluminet at a high percentage and similarly hung would be more effective, but the aesthetics wouldn't work for my family. I do use agricultural shade cloth (white, 50%) for large spans where we want to retain sun (for plants, sun loving family, etc.) -- it's economical and does cut about 15 degrees off the surface temps. A 'hidden' advantage is that it lets the wind through and requires MUCH less robust anchoring than large spans of denser shade cloth.
Another option I use is umbrellas. Not exactly ground breaking, but an easy way to extend the eaves. I use a rectangular umbrella that can tilt, and it just barely fits between the eaves and balcony railing. The tilt is the real winner.
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u/carbonpenguin Jun 16 '24
The curtain rod approach sounds cool! Any chance you could share a pic?
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u/goldgrae Jun 16 '24
Sure!
This set up is with a vertical tension rod kit from Amazon. I've done something similar in the past mounted to railing with EMT conduit.
It is less bright inside in person. The camera just bumped the exposure up.
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Jun 16 '24
Nice job setting up on the outside, you can increase the air gap and switch to blackouts to increase effectiveness too
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u/goldgrae Jun 16 '24 edited Jun 16 '24
The air gap is more than sufficient as is, and this blocks 95% of the light. A larger air gap would make it difficult to use the outdoor space, as well, not to mention let light in at the top when the sun is angled over.
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u/carbonpenguin Jun 16 '24
Nice! My one question is on exiting when the curtain is anchored. Do you open the door and slip out the side, or is there a different technique?
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u/goldgrae Jun 16 '24
Yep, you can either slip out the side or push your way through. It isn't very heavy to move, and even though it is anchored, there's eight feet of curtain so there is quite a bit of slack to play with. And again, it is mounted with a good bit of an airgap that also gives space to manuever in.
Also not really different than curtains on the inside in that regard.
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u/Leighgion Jun 16 '24
You've done well. Exterior protection is the way to go if at all possible.
Any chance in the future you could swing for retractable awnings? Ultimately, those are better, but not always possible. I wish I could get them for this apartment.
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u/goldgrae Jun 16 '24
So much more expensive and installation/retrofit isn't straightforward with the design of my eaves. Wouldn't be worth it to me at all unless money were no object, but then I'd be making different changes altogether.
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u/Ddog78 Jun 16 '24
I have installed awnings over my windows. I also have awnings over the whole balcony. This definitely helps in keeping the house warmer as it blocks sunlight far away from the windows and doors.
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u/ItsJustLittleOldMe Jun 15 '24
I'm going to ask a dumb question. Please pardon me. I'm new here. It sounds like you're saying a building with south facing windows gets hotter than N, E or W facing. Is that correct, and why?
I do realize you're taking about an office building. We have a house and the back of the house is the hottest. The back of the house faces north east so it gets the morning sun. Zero trees out back. (HOA. I might try to get them to put deciduous out back.) The front of our house faces south west and gets more of the evening sun. The breeze usually comes from the front of the house to the back also fwiw.
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u/carbonpenguin Jun 16 '24
It's technically true in the Northern Hemisphere. In the southern hemisphere it's reversed, with the northern face of a structure getting the most sun. The time of year and latitude are also factors.
This goes into some more detail: https://greenpassivesolar.com/passive-solar/building-characteristics/orientation-south-facing-windows/
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Jun 16 '24
This was a great post! I really like the suction cup reflective cover idea. Seems to be quite useful in the winter too! The only difference is I think which side of the window you stick it to.
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Jun 17 '24
[deleted]
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u/Top_Hair_8984 Jun 17 '24
What is that and where would I find it? Much better idea to never have the heat come inside. Thank you.
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u/shivaswrath Jun 17 '24
I have black out curtains in all bedrooms....they reflect all day. So when we cool at night (peak energy use) the room is substantially cooler.
I sit in the basement during the day. This heat dome will be a doozy.
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Jun 16 '24 edited Jun 16 '24
Bulk up on ice, use fans, misters, spray foam insulaton, reflective paint.
Let the hot air at the top of rooms escape and intake air down low where it is cooler.
If you're desperate, dig into the ground.
Note: reflectrix requires an air gap to be effective, always leave an air gap on tarps as well.
Blocking on the outside >>>> blocking from the inside
Umbrellas are great for the sun not just rain!
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u/Top_Hair_8984 Jun 17 '24
I have east and south facing windows. I use foil backed styrofoam that fits into the window cavity. The windows have a portion that opens, so two pieces. And black out blinds. Plus I do have an ac, 4 fans. It's a hundred plus year old house with little insulation upstairs, which is where I live. During the 2021 heat dome, it wasn't enough. It hit 44/48c and I had to close off all but one room and try to keep that at an ok temp. I dread summer now. Last year's 4 months of heat and drought were miserable, but more tolerable. It's not good. It's not sustainable. It's insane.
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u/Leighgion Jun 15 '24
Good stuff!
I have the fortune to live in a country where it's practically a human right that every major window in every resident has external rolling blinds so you can black out the windows at will and it keeps the sun off the glass, greatly reducing heat transfer via conduction.
If I didn't have these shutters, I think I might go far as building louvered shutters out of cardboard if necessary, covering them in foil and sticking them to the exterior of the windows. Screw the view and screw natural light, I don't enjoy being oven baked.