In part one of this series, we discussed the basic principle of life without air conditioning:
Suck cool air into your house at night. Keep hot air out during the day.
We explained that even on the hottest days, a well insulated home will only see a thermal gain of about one degree (fahrenheit) per hour. But even though that’s still tolerable in most climates, it pays (both in dollars and in comfort) to do everything you can to minimize that thermal gain.
The main entry points for heat in your home are windows and your attic. These are the culprits that will lead to rising temperatures in your home, and they are fairly easily and inexpensively neutralized.
The attic
First, let’s discuss the attic. We all know attics get hot. Really hot. HELLISHLY hot on summer days. They are generally not climate controlled, have poor ventillation, and black asphalt shingles soak up the heat from the sun. What you may be surprised to learn, is how much longer it takes that attic to cool off in the evening than the rest of your home.
As you might imagine, people in Florida have a keen interest in keeping homes cool. The University of Florida did a study of new homes where they asked homeowners to cut the a/c for a few days to see what would happen.
Surprisingly, the results were that the most miserable time of day for those homeowners was in the early evening. Even though it was cooling off outside, the insides of these homes were staying REALLY hot, and temperatures were still climbing.
So the researchers investigated and found that the problem was attics. Specifically, heat got in and was trapped. It couldn’t escape through the heavy fiberglass insulation these homeowners thought they were doing themselves a favor by installing. So even though temperatures outside were falling, the attic held heat over the home and so the temperatures in the living areas continued rising.
The solution to the attic problem is to keep heat from entering in the first place, and to mitigate whatever heat does enter with good ventilation.
Take a trip up to your attic and see what the ventilation system looks like. Make sure any and all vents (called “soffits”) are unobstruted. Check any gable openings as well.
If there is a fan in your attic, either gable mounted or roof mounted, make sure it works. It’s probably not worth it to leave it on at all times, but they do sell attic fan thermostats that will automatically turn on when the temperature of your attic reaches a certain level.
If you don’t have a fan to ventilate your attic, you may not need one. Monitor the temperature in the space over the course of a few days, and see if existing passive ventilation is doing its job and clearing out hot air. If it is, I would skip the fan step. If it’s not, then by all means, get thyself an attic fan and use it!
So, ventilation is important and something that can be addressed quickly and easily. Quite often, homeowners find that they already have the appropriate systems in place, they just need to uncover vents and turn on ventilation fans.
But there are also practical ways to keep heat from entering the attic in the first place. If you’re constructing a new home, there are all kinds of roofing choices (light shingles, metal roofing, etc.) that can greatly decrease the amount of heat entering your attic. But for the purposes of this article, we’re assuming you’re retrofitting an existing home.
Hands down, the most effective thing you can do is install a radiant barrier in your attic. We’ll do an entire article on radiant barriers some day, but for now, what you need to know is that this stuff is pretty much space age tin foil that can reduce the cost of cooling your home by a solid 40% (according to studies at the University of Florida).
Radiant barriers work by reflecting heat from the sun’s rays. You can install them on your attic ceiling, on the walls, and on the attic floor. These babies are easy to install, inexpensive (about $100 shipped for 1000 square feet of material), and work REALLY well.
Today’s radiant barriers are perforated to allow moisture to escape (eliminating mold concerns in humid areas), are multi-layered (so you don’t have to replace them due to dust build up), and come in a wide variety of applications (some are affixed to bubble wrap, fiberglass insulation, or foam).
To install on the ceiling/walls of your attic, you can literally just staple gun the stuff to whatever surface you want it to be on. For floor installations, you can simply roll it out over your attic floor (no glue, staples, etc. necessary).
To keep heat from entering your attic, there is no better solution for existing homes than installing a radiant barrier.
Windows
Windows are the other place where thermal energy from the sun enters homes en masse. Luckily, we have solutions for you that don’t involve purchasing $10,000 worth of insanely expensive new windows for your home.
The best solution possible is to keep the sun from hitting your windows in the first place. Once the sun hits your windows, the heat has to be disipated (in this case, into your house). There’s no getting around that. Yes, shades, blinds, etc. can help lessen the blow, but the heat will simply be transfered into the walls instead of the living area. Your house will still get warmer.
So, shade the OUTSIDE of your windows. You accomplish this with existing vegetation (ie, trees) if it’s available. But if that’s not an option, consider UV filtering window screens, or window awnings to shade your windows.
Solar screens allow you to see out your window, but filter UV rays entering your home by as much as 95%. Generally, I recommend getting the filters that are in the ballpark of 75-85%. Once you cross that threshold, they soar in price and you don’t really get much bang for your buck. Solar screens also provide additional privacy (it makes it harder for people to see into your home).
People with solar screens installed estimate that they observe a 10-15 degree difference over windows in rooms without solar screens, and they reduce their energy expenditures by 30%. Obviously, solar screens can be a big help in reducing thermal gain inside your home, and your need for air conditioning.
Window awnings consist of frame that holds metal or canvas in order to shade an area. Those areas might include doors, patios, or windows. As a quick aside, be sure your door is either covered by a porch or an awning. They present the same problems as windows.
Metal installations are more expensive, but white metal is highly emissive, and will reflect a large amount of solar radiation back into the air. But as the ultimate purpose of the awning is to shade windows so that the sun doesn’t hit the window, canvas will work just fine.
There are a gazillion (it seems) different ways to install awnings, different styles to choose from, and different materials to use. We’ll have to cover awnings more fully in a special post at a later date.
If solar screens and awnings are out of your price range (both are reasonable diy projects), try this cheap, ingenious solution:
Purchase mylar shades (you know, the ones used for car windshields) at the dollar store. Duct tape them together to fit the size window you need. Purchase a white roller shade (or bamboo roll shades work fine as well) and afix your mylar sheet to it (this step is mostly for appearance sake, but does provide added durability). Then attach to the outside of your house.
These babies are cheap and effective!
Once you’ve taken care of the outside of the windows, implement all of the things you’ve probably heard already for the inside of your windows:
-Use white blinds and keep them drawn to keep heat out.
-Same deal on the curtains.
-Consider installing cellular blinds for added efficiency.
Other considerations
Even though windows and the attic contribute to thermal gain in the home more than any other culprit, keep in mind that once any sunlight hits your house, the heat has to go somewhere. So an important strategy is to overall limit the amount of sun that hits your roof and walls.
The most practical ways to do this (aside from installing a new roof and siding) are to use plants to shade the areas. Use trees to shade your home if possible. Grow vines up trellises to shade the walls of your home. The roof is a bit tricker to shade in the absence of trees, but with the proper support systems in place, I’ve seen REALLY neat homes where homeowners have grown gourds on ropes over the roof.
Even keeping the heat out, air circulation is very important in order to maintain the comfort of your environment. We’ll discuss circulating the air inside your living space in our next section.
Return to Cool Your Home Without Air Conditioning: The Plan
Continue to Part 3: Circulating Interior Air