Insulation for a Hot Climate

By Scott Sidler July 31, 2017


insulation for a hot climateInsulation is a very regional discussion. The best advice for a home in Boston can be disastrous for home in Phoenix and vice versa. In order to insulate a home properly getting advice from a local contractor is essential. But since almost every bit of insulation advice I have ever seen on the interwebs is focused on cold climates I thought it was time to give a little focus to those of you who live in the sunbelt instead of the rustbelt.

After all, my work is based mostly in Florida and so insulation for a hot climate is comfortably in my wheelhouse. How do you know if you technically live in a hot climate? If you have more days that you use air conditioning than heat then you live in a hot climate. If you heat more days than you air condition then you live in a cold climate.

On a side note the Nest Thermostat has a cool reports feature than shows you how many hours you heated and cooled in each month. We recently got one and the information has been super helpful! I posted a tutorial on how to install one here as well.

Obviously this is a very black and white delineation so for those of you in the middle you’ll likely need a little bit of both types of insulation techniques.

Insulation For a Hot Climate

Insulation works much the same no matter where you are in that it slows down the transfer of heat. The difference is that in a southern climate the heat is outside trying to work its way in. There are three types of heat transfer: conductive, radiant, and convective and I written about the difference between them in an earlier post.

In hot climates think about the temperature delta. For example if you are living in Houston, Texas and it is 96°F outside and you want the indoor temperature to be 76°F indoors that is a 20° difference you have to overcome. Now let’s assume you live in Burlington, Vermont and the outside temperature is 14°F. To get to a comfortable temperature of say 68°F in the winter is a 54° difference. That’s huge!!

It may seem miserable in the summer in the deep south but the work to keep a building insulated properly is much easier than it is in the great white north. Despite what you may hear you don’t need to worry about insulation for a hot climate nearly as much much as you do in a cold climate.

For those of you in the southwest states where temps regularly exceed 110° the situation may be a bit different, but the ideas in this post still apply. You just need to take them further.

Where to Insulate

There are only two places you should be spending the bulk of your insulation dollars in a hot climate. Picking these two low hanging fruits first will yield big results with the least investment so let’s start there.

The Attic

The brutal sun in the southern states will cook your attic and turn it into an oven (literally). If you want to bring your energy bills down this is where you start. Focus a lot of energy (pun intended) on the underside of the roof to keep the heat out of the attic and not just the floor of the attic.

You can use products like radiant barrier on the underside of the roof, spray foam, or even good old fashioned batts of rock wool, denim or fiberglass. I discuss the different types of insulation you can choose and how to decide on the right one in a previous post.

Once you’ve insulated the underside of the roof to the max, then it’s time to focus on the floor of the attic if it is unfinished. If you have a finished attic then the focus should be solely on the roof, but for those of us with open and unfinished attic spaces every inch is fair game.

Use my tutorial on how to install blown-in insulation onto the floor of your attic. Blown-in insulation is dirt cheap, easy to install and does wonders to bring down energy bills. You can load up the attic floor with as much insulation as you can fit for very little money (think $600 for a 1300 SF house!).

There are a couple things to look out for when insulating an attic though:

  1. Knob & Tube Wiring – If you still have active knob & tube wiring do not disturb or cover it in insulation that’s how fires start. Call an electrician and have it removed immediately.
  2. Airflow – Make sure your insulation doesn’t block any airflow whether it’s is to soffit vents, gable vents, or ridge and off-ridge vents. You attic needs to breathe to keep your house healthy.

How to weatherstrip wood windowsWeatherstrip Doors & Windows

The next biggest offender of heat getting in and AC getting out are your windows and doors. No, it’s not about them being single-paned it’s about air sealing. The heat transfer that happens through doors and windows is because of the tiny gaps that allow air to seep through.

Learn to weatherstrip your doors and windows with my tutorials. It costs less than $20 a window to weatherstrip properly compared to replacement windows which can cost thousands of dollars and don’t really give the payback they promise.

Sealing these openings not only gets rid of hot drafts but will beat those energy bills into submission as well.

Don’t Waste Your Money Insulating Here

I have a 1920s bungalow in Orando, Florida. Our energy bills are under $175 a month in the summer consistently and that is with a family of four. I have insulated very sparingly and strategically to keep our bills low and i want to show you where you should absolutely NOT insulate because the payback is so minimal it’s not worth it.

The Crawlspace

The crawlspace is possibly the most comfortable place around your whole house year round. It is shaded from the sun and is cool in the summer and relatively warm in the winter. Why would you need to insulate an exterior area that is usually within 10° of the inside temperature? I’m not mad at you if you insulate the crawlspace, but usually it’s not worth the time, expense and considerable difficulty it requires.

Replacement Windows

Don’t waste your money replacing your windows. Replacement window companies have often been dragged into court by the FCC for lies and deceptive advertising. No window will cut your energy bills by 30-50%. Weatherstripping your original windows will let you keep your money and your windows.

Exterior Walls

Pulling down plaster or siding to stuff the walls full of insulation causes a lot of expensive work to put things back together and often causes problems. I’m not against insulating the walls of a house, but you must have proper water management in place before you pump a wall full of any kind of insulation.

Old houses often have no way to ensure water isn’t getting into the wall cavity and once you fill it with insulation (aka a sponge) you get mold, rot, and health issues. A deep energy retrofit is a possibility, but think about the payback. If you send $25,000 to completely revamp the shell of your house and get a monthly savings of $150 on your utility bill that is going to take you about 14 years to see a return on your investment. Always look at the return on your investment when it comes to insulation.

Final Thoughts

I hope this has given you some guidance on how work with insulation for a hot climate. It’s not as complicated as it may seem. Always, always start with the low hanging fruit and work your way up the tree as money and time permit. You’ll be better off in the end if you do it that way and so will your wallet.

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13 thoughts on “Insulation for a Hot Climate”

  1. Thanks for recommending not insulating the crawlspace. My husband and I decided to renovate the 1930s Craftsman home we bought last month, and we need to redo all of the wall insulation. I’ll let him know that we don’t need to do the crawlspace, and we’ll be able to use the money we would have spent on that area on a more important part of the house. //

  2. I spent a lot of time last year researching this topic and came to the exact same conclusions. The predominant amount of online information applies to cold-weather homes, so I really appreciate your post. It was particularly interesting to read that you too have determined that a priority for homes in hot climates requires addressing the underside of the roof. Cheers!

  3. I”m ready to do some work to get my 1916 four square up in Jacksonville as energy efficient as possible for the long term. I have an open attic- just lattice on front and back of house between the attic outside. A couple items I’d love your opinion on: it has blown in insulation now, but what if I wanted to put some plywood down for storage? Spray foam under plywood? Could you enclose it ie close up open lattice with some vent or would that make matters worse? Just want a bit of storage and max effiency

  4. Thanks for the info Scott. I am surprised you recommend against insulating crawlspaces. I thought it was a moisture issue? For hot and humid climates like New Orleans, what do you think about insulating directly under the floor in a crawlspace, either with rigid foam or batting?

    1. Joel insulation and moisture control are two different things. I would recommend installing 6 mil poly sheeting over the dirt to keep the moisture from entering the crawl space. That will make a big difference and is cheap.

  5. Hey Scott I purchased my house with cellulose blown in through the siding (small holes were drilled and plugged into the siding). Is there a concern with no vapor barrier or the “sponge” effect like your article states? If so, should I remove it?

    Thanks for your articles!

    1. If water is getting to the insulation then yes there is concern. It is a sponge and will hold water and cause rot, but it depends on whether things are getting wet or not.

  6. What is the solution for weather stripped two craftsman casement windows that meet in the middle? I have two sets and there is no frame in the middle, the one window has a brass latch into the frame and then they have a brass latch that locks them together in the middle. The prior owner bunched upholstery fabric and tacks in it to keep the draft out. hahaha. I want something that looks nice and preferably some what blends in or not really easy to notice. Last winter we had heavy rains that beat against that window and leaked water all over our mantle.

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