How can we build an eco friendly home in a climate of hot summers and mild winters?


How can we build an eco friendly home in a climate of hot summers and mild winters?

Asked by Robert Ventry

Sustainability is important. The site is heavily wooded, and the area has small tornados. Low to moderate budget.

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Elizabeth DiSalvo's picture

Hello Robert,

This is a good question because a lot of people associate energy efficiency and sustainability with cold climates.

A lot can be done in the south to reduce the cooling energy bills and live more sustainably. Here are some excellent ways to get started:

1. Insulate your walls well. Most houses in Florida have about an R3 or R4 insulation value inside the walls, and while it has been shown that upping the R value of the insulation inside the walls does not do a lot for the overall efficiency of the structure, it has also been proven that insulating on the outside of the walls helps quite a bit.

  • A 1 1/2 " layer of rigid board insulation (like polyisosanurate) on the outside of the walls can reduce energy consumption greatly by keeping the house cooler longer and later into the day.
  • It will help the house not depend on air conditioning in the morning when peak electric load occurs because - like a thermos -- it will keep the cool air form the night inside the house longer.
  • Go for an R10 wrapping the outside of the house and about an R5 inside the wall cavities.

2. Big overhangs. It used to be the norm for houses in the south to have large overhangs of 3 or 4 feet or more. There was a very good reason for this. If you can keep the actual sun off of the exterior walls, it makes the walls have to do less work to keep cool.

In the last 30 years, builders have reduced the size of overhangs to about a foot in order to cut their own costs. Don't do this on your house!

  • Give your house at least 3 foot overhangs if it is a one story house.
  • If it is a two story house, consider plantation style wrap around porches at the second floor level.

3. Tall windows and exterior shutters. Installing tall French Windows or doors on all sides of the house that open can allow you to create cross breezes.

Exterior shutters aid in the cooling even further. (Although if you have large overhangs you may not need the shutters depending on coverage- or vice versa).

4. Get double paned glass windows with low-e film and argon gas. Usually reserved for cooler climates, it is rare to install such windows in Florida where most are single pane. Tinting windows to keep out the sun is useful but also cuts down on views and natural light which really does make the house dark and unpleasant to be in.

There is glass available that lets in a lot of light while also cutting UV. One example is the PPG Sungate 1000 Solar-control glass. With a Solar Heat Gain of only .38 but a visible light transmittance of 73% and a U value of .24 this is a great glass for your climate. It keeps heat out, keeps cool in and lets in lots of natural light.

5. Fans. Fan motors do not use a lot of energy. On cooler days you can open all of the windows and turn on the fans. The cheapest air conditioners are the ones you don't turn on!

6. Keep the envelope continuous. Make sure that you are insulating your attic or the underside of the roof well. In your climate I would rather see the attic floor insulated and the roof given a lot of breathing room.

Think of your roof as a giant parasol. Keeps the rain and sun out but really just sits above the house like a shield. (Roof shingles on insulated roof rafters do not do well in hot humid climates. We might get away with it in the north, but no in the south.) So insulate the ceiling of the main house (or the attic floor) REALLY well. Keep that heat out and the cool in.

  • Provide a lot of louvered vents to the attic well so the heat does not build up.
  • Go for an R30 at the attic floor. Preferably a blown in product that covers and fills better than batt.

7. Install a reflective roof. Roofs that are light colored and highly reflective can reduce the heat gain on a roof easily by 20%. Use white metal or light colored tiles or if you are using asphalt, try a shingle like Solaris from CertainTeed.

8. Keep your ducts and HVAC equipment inside the envelope fully. This means all ducts are within the envelope of the house. Find a closet inside of your house for the equipment. Make sure your ducts do not pass through the hot attic space (thus losing a great deal of their cool to the attic!)

You can make your ceilings taller and build a dropped ceiling (out of sheetrock or anything) so that your ducts can all run through that plenum between the super insulated attic floor and the main house. You can also - of course- make soffits for the ductwork.

9. Make sure to seal all of your ducts well to keep the cool air travelling efficiently to its destination and make it easier for your equipment to do its job balancing the house temperatures and air flow. You can also oversize your ducts a bit to allow for less friction within the ducts and thus less hard work for the equipment.

10.Don't let your can lights poke holes in the ceiling envelope. Another great use of that dropped ceiling plenum is that is allows you to run electric and put up can lights in the ceiling without reducing the continuous R value of your attic floor insulation. Things like can lights cause a ton of air leakage through your roof! You can also get insulated can lights. Just make sure you have a good layer of insulation between your lights and the roof.

11.Get an ERV. An Energy Recovery Ventilator will re-capture cool air that is being circulated out of your house and allow your HVAC equipment to work less to cool the house.

12.Try a minisplit air cooling system. Air to Air heat pumps are probably the most efficient way to cool your house. Look into models like Mitsubishi or Fujitsu.

You can get these as 'ducted' or 'ductless'. Ductless are more efficient and more cost effective and you don't have to worry about sealing your ducts or where they travel (because there are none!)

  • BUT some people find them unsightly as they are units that simply hang on your wall in your living space and you have to have open flow between rooms to keep temperatures even.
  • Either option will work really well for you and they also can provide a bit of heat if you ever need it.

13. Think about finishes. Use a lot of tile flooring to keep things cooler. Use recycled or long life natural products that require little maintenance or upkeep.

14. Get low flow fixtures and low energy appliances.

15. Get some Photo Voltaic (PV) solar panels if you have any sunlight in your wooded lot. Face them South or West. In your climate west works great.

If you take all of these measures and get a good PV array- wow! I bet you could be a net zero house and spend nothing to operate your new home.

Good luck.