Vegan cooling: Mirrors on the roof?

June 27, 2013 9:36 AM

I have lots of mirrors. Put them on the roof? Y/N, Why.

I have something like 30 large mirrors that I picked up in a storage unit deal a while ago. By large I mean minimum 2x3 feet, and a few are bigger.

My house has a high roof, and it's hard to keep the place cool. The attic roasts, of course. I intend to install a fan up there.

But. The mirrors. They call to me. Is this crazy? What if I built a framework of...uh...PVC to hold them, just on the broad East/South face of the roof and mirrored the whole thing. Would it keep my house cooler?

Would all the mirrors break? I can cover them with something like plexi, but then it costs more than just PVC. Maybe layers of sticky film like race drivers have on their helmets for periodic bird shit/tire debris removal.

Googling says mirrors are too expensive but it should work, and I already have them. It also mentions I could be a nuisance, but I don't think the way my house faces it would bother anyone. But it would be very visible, and face the street. I live in a nice neighborhood, with members of local government and police for neighbors, so it stays pretty quiet around here.

Has anybody here done something like this?

posted by SlyBevel to Grab Bag (28 answers total)

Best answer: I don't know anything about this, but my first thought was that you could reflect sunlight into the sky and dazzle pilots or birds.
posted by Ruthless Bunny at 9:39 AM on June 27, 2013 [6 favorites]

Best answer: Another potential drawback is that they would get dirty pretty fast and lose their effectiveness. And if you live in an area that has hailstorms...
posted by TedW at 9:43 AM on June 27, 2013 [3 favorites]

Could you not just paint your roof white?
posted by mdonley at 9:43 AM on June 27, 2013 [2 favorites]

Response by poster: I don't have white paint, I have a bunch of mirrors.
posted by SlyBevel at 9:48 AM on June 27, 2013 [14 favorites]

Best answer: Also, even white paint seems to have an albedo in the 0.5-0.9 range; mirrors would definitely be (at least at first) at or above the high end of that range. I don't see why mirrors wouldn't work for this.
posted by jeffjon at 9:50 AM on June 27, 2013

Best answer: A long time ago I worked at a converted factory -> office space. They had a lower, 1 story, flat roofed structure directly to the south of my 4th floor office. One summer they painted the roof of that structure white/grey/silver. Whatever it was, it was SUPER reflective for a few months, and I definitely had to close my blinds for a while. Mirrors would certainly be more reflective, and remember that the sun travels in a long arc.
posted by Phredward at 9:51 AM on June 27, 2013

I think this depends on the kind of mirror. If they are "regular" mirrors with a glass front and a reflective backing behind the glass, then I think you might actually make things worse. This is because the sun light actually passes through the glass twice. The glass will absorb some of the light and heat up. it depends a lot on the quality and thickness of the glass. If the mirrors are polished metal with no glass, then absorption by the glass clearly isnt an issue...

It's easy to test. Take a mirror and put it out in the sun - compare it's temperature to a piece of wood or other surface also exposed to the sun for the same period of time. If the mirror is really reflecting the energy it should be noticeably cooler than the other surface. I suspect if you compare with a light color painted surface you would find the mirror actually absorbs more energy...
posted by NoDef at 10:01 AM on June 27, 2013

Best answer: If they are "regular" mirrors with a glass front and a reflective backing behind the glass, then I think you might actually make things worse. This is because the sun light actually passes through the glass twice. The glass will absorb some of the light and heat up. it depends a lot on the quality and thickness of the glass. If the mirrors are polished metal with no glass, then absorption by the glass clearly isnt an issue...

It won't be an issue unless the mirrors are actually embedded within the roof. As described in the question, they'll be raised on frames above the roof surface, so any heat absorbed by the glass (which will be a fraction of the heat energy formerly hitting the roof) and re-radiated will just be going out into the air surrounding the mirrors. Greenhouses work because that heat is captured in the greenhouse structure. Even if the glass is directly conducting heat to the attic, it very likely that it will much less efficient at doing so than whatever roofing material is already up there.

As a heat blocking/cool roof technique, the mirrors would work well, but as others have indicated, durability and maintenance will be a problem. Additionally, you'd likely have to get the installation approved by the building department, which would probably not go for it at all. Heaven help you if you live someplace with an active HOA. I can't see this being anything but a horrible nuisance for your neighbors if the mirrors will ever be in their line of sight.
posted by LionIndex at 10:10 AM on June 27, 2013 [2 favorites]

Best answer: Can your roof support the weight? Having lived and worked in buildings with accessible roofs but which had stringent weight restrictions, this is the first thing that comes to mind. Especially if you live in an ordinary single family home with no roof access at all.
posted by Sara C. at 10:19 AM on June 27, 2013

Best answer: Didn't turn out so well for the neighbors of Disney Hall. Granted, your home is much smaller, but your neighbors probably live much closer and ~200 sq ft of mirrors is still quite a lot.
posted by acidic at 10:24 AM on June 27, 2013 [3 favorites]

Best answer: That's a good point. And Disney Hall isn't even mirrored, it's just bright silvery stainless steel.

If your roof has any pitch at all I think this is a bad idea just from a community perspective.
posted by Sara C. at 10:26 AM on June 27, 2013

Response by poster: Think you guys nailed it. The mirrors will have to find some other use, and the wife has declared the bedroom at saturation (for mirrors, that is), so that's a no-go.

Thanks for the great answers!
posted by SlyBevel at 10:32 AM on June 27, 2013

Best answer: Non-roof-usage: Attach them to standing frames and make a mirror maze the neighborhood kids can wander through for Halloween. Might want to give them a stick-on film of plastic, but it could be done. Add in a few pots of dry ice for smoke effects?
posted by easily confused at 10:37 AM on June 27, 2013

Response by poster: I'm open to other uses! Keep 'em coming and I'll throw out besties for good ones.
posted by SlyBevel at 10:40 AM on June 27, 2013

A few years ago, I saw this art installation where the artist built an enclosed room/box about 10/12 feet square --- walls, floor, ceiling --- that was solidly mirrored inside and out: you didn't see any framework or anything, just mirrored surface everywhere but the doorway opening. Very freaky effect, walking around inside there.
posted by easily confused at 10:57 AM on June 27, 2013

I don't have white paint, I have a bunch of mirrors.

Sell your mirrors on Craigslist, buy aluminized roof coating, enjoy reduced cooling loads.
posted by a halcyon day at 10:58 AM on June 27, 2013 [3 favorites]

Best answer: Buy a treadmill and a mat and open your own neighborhood gym :)?
posted by NoDef at 11:01 AM on June 27, 2013

A roasting hot attic might be an indication of inappropriate/ineffective venting, by the way. Also the ceilings just below the attic (not the roof itself) should be loaded with insulation.
posted by plinth at 11:09 AM on June 27, 2013

Response by poster: Yes, everything is as it should be, it's just a big house and it's hot up there.

And the most obvious answer is an attic fan, but I'm not paying $300 for a fan I can build, so it's waiting until I'm damned good and ready. :)

We had extra insulation added up there a few years back as well, and while that's helped moderately with heating and cooling, it's helped more with air traffic noise. We live close to a muni airport.
posted by SlyBevel at 11:15 AM on June 27, 2013

Best answer: Find the location you sit in most often in the house, or alternatively the room that gets the least amount of natural light. Then place one mirror at a time away from that spot so that you end up directing a really nice view/a lot of sunlight to that spot. Like a real-life version of one of those laser|mirror video games.
posted by davejay at 11:26 AM on June 27, 2013

Best answer: Well, with that many mirrors, I might:

1. Break a bunch and inlay the pieces mosaic style in cement bordering a walkway. Symmetrically placed Mirror pieces slightly angled towards the house (going one way) and another external source of light (headed the other) might make for a pleasant "dazzle" effect at night and more importantly better mark the edge of the path in low/no visibility.

2. Make a DIY solar water heater.

3. I would cover part of the front wall of my garage so I'd stop running into/over my toddler's toys that she leaves on the floor near this wall, and when backing in (coming from the grocery store) be able to more accurately judge how far I have left to the wall, while still leaving enough room to open the tailgate.
posted by Debaser626 at 11:36 AM on June 27, 2013

If these are large floor-to-ceiling type mirrors, then anyone opening a dance studio would probably drive to your house to get them. They are needed somewhere.
posted by amtho at 11:45 AM on June 27, 2013 [2 favorites]

Response by poster: Debaser, my garage gets real work done in it, with bits of wood and metal flying around. I fear the mirror wouldn't survive it unless I gave it a plexi shield or something. It's a good start though. :)
posted by SlyBevel at 11:55 AM on June 27, 2013

Nothing makes a long narrow room look wider than mirrors, or if you have a small room, you can use them to make the room appear larger.
posted by Lynsey at 11:56 AM on June 27, 2013 [1 favorite]

You must cut them into small squares and glue them into a parabolic satellite dish, like so.
posted by echo target at 12:14 PM on June 27, 2013 [2 favorites]

Best answer: Inset them to a long fence in your garden that doesn't get (much) direct sunlight, then plant shrubbery in front and grow climbing plants around and generally hide the edges with greenery.

Put them on the ceiling in your spare bedroom. Say nothing when your mother comes to stay.

Purchase a laser pointer. Mount the mirrors at strategic points in the garden so you can communicate by laser via an extraordinarily complex path from one end of the garden to the other. Challenge small children to navigate the garden without breaking the beam.
posted by emilyw at 12:36 PM on June 27, 2013

Best answer: Flat roof? What the heck, I'd try it, but I'd glue them to plastic, in case of breakage, and secure them against the wind. Angled roof - pretty hard to mount them safely, and the wind could catch them and that could be deadly.

Put up a sign in a ballet studio, dancers like to practice in front of mirrors. Use Pinterest to find awesome framing ideas, frame them, and sell on CL.

As for the attic, mount a fan in the attic floor, and open a vent or window in the attic. Or put a vent in the attic floor and put an fan in an attic window or vent. We did this in my old house to great effect - hot air wants to rise.
posted by theora55 at 3:11 PM on June 27, 2013

My house has a high roof, and it's hard to keep the place cool. The attic roasts, of course. I intend to install a fan up there.

According to Fine Homebuilding in a recent issue, attic fans are mostly unnecessary and have a tendency to draw cool air in from the house. The attic, assuming it is vented properly, is separate from your living space and should have a proper thermal barrier. This is where you should focus your efforts.

* Add insulation to the attic (helps in winter, too). Talk to an expert about the R-value you have and what you should add.
* Seal all electrical connections. Use electrical foam inserts for the boxes and foam spray (do them all at once!) for the gaps around the boxes. Foam inserts for exterior wall receptacles as well.
* Seal all plumbing connections. Spray foam, again, and close all the gaps. Be a house detective and find them.
* There's a whole checklist, but some of them only apply if you're renovating or building new, as you can't reach these areas in a normal home.

Really, in all but the most modern, superinsulated house, the heat movement is upward -- the chimney effect. It's taken a generation for US home builders to adjust to this knowledge, known as the thermal bypass. There is now a thriving retrofit industry that will thoroughly comb over your house and find the thermal bypass zones, which are ripe for closing off and relatively inexpensive to fix in many cases, leading to a good ROI ratio.
posted by dhartung at 3:25 AM on June 28, 2013 [1 favorite]