One of the largest issues in a house is indoor air quality. Up until recently most people usually don’t pay any attention to it and subsequently the amount of headaches, foggy headedness, breathing problems and body aches are much higher than need be.

Not coincidentally the above body symptoms are also what happens to you when you are exposed to too much Carbon Dioxide. Basically your typical house has too much carbon dioxide, which is what humans exhale. Along with many other semi toxic gases and vapors.

With a badly built house this issue of indoor air polution is not crucial because the house has leaks that allow it to breathe. But now with high efficiency houses it becomes imperative that indoor air quality be addressed.

When we do a green renovation of a Brooklyn brownstone we seal up every single crack in the building envelope. We caulk, insulate, vapor wrap and tape the entire envelope so that not one iota of air can get in or out. That is great for energy efficiency.

Yet it can be deadly for indoor air quality because now the Brownstone does not breathe like it used to. Because we use natural materials there is no concern of toxins building up in the house from things like paints or wood, but normal living creates more than enough toxins – cooking, breathing, sweating, showering – all these things are a problem if not vented and replaced with healthy air.

So as green contractors specializing in energy efficient Brooklyn brownstones we need to pay extra attention to helping the building breathe. We usually do this with mechanical systems like an Energy Recovery Ventilator. We also design for good cross ventilation, a good stack effect, and for intelligent placement of rooms so they ventilate well.

But we need to remember that removing toxins is a job that has been, since the beginning of the planet, the job of green plants and the earth they root in! As we exhale CO2, the plants are concurrently breathing those gases in and exhaling the essential, pure oxygen that we need.

Therefore, it makes perfect sense to have plants in the house to help filter the air for us. The key is to not let humidity from the plants cause problems. The best options are actually the plants that are traditional in the home: English ivy, rhododendron. and spider plants. These plants seem to be especially effective at filtering out the bad air, and bring pure “green” air into our buildings.

I did some digging on the subject to find out how effective plants are at filtering household air. Its still actually being debated how many plants per person are needed, but I’m told about 40 spider plants could balance out a small studio apartment with one person….that is a lot of plants!

Bill Wolverton did one of the original studies and concluded 100 spider plants would filter a 1200 sq. ft. house. There is a formula per cm2 of leaf area.  Obviously at that level humidity would be an issue amoung other things.

Some interesting work was done with living walls (hydroponic growing walls). One was in a commercial office in Toronto. The studies indicated that even tuolene was removed from the air.

Living Walls allow air to pass through a wall on which there is moving water and various flora and fauna to clean and condition ventilation air. Do a Google and you should find built examples. (Canada Life Building in Toronto is one, designed by a “Wolf Amelung” , it was probably 15 years or more ago) St. Mary’s Univ in Halifax is the site of another).

There was a school of thought in the previous millennium that one could utilize a plant-filled attached sunspace to function as the “lungs” for a house to provide fresh ventilation air to the house without having to utilize mechanical equipment.

It was a nice idea but unfortunately more mythical than factual according to a study that CMHC did back then. According to them plants do *help* to clean air but it’s actually the soil that’s doing the “purifying”. I would guess the roots of the plants also play a large role in air filtration.

NASA did a study of this recently (presumably for space stations) analyzing the best plants for filtering and Oxygen conversion. According to the Wikipedia description,  the recommendation of NASA is to use 16 good-sized houseplants in 7-inch diameter containers for a 1,800-square-foot house.

For a Brooklyn brownstone that typically means about six good sized plants per floor.

The bottom line: plants do filter air effectively. The above recommendations are probably more plants than most people want to live with but it is a good idea to have plants in healthy soil around the house. They are measurably beneficial to our health.