Cold Hot Cold Days: Upgrading Your Florida Home’s Insulation

Temperature swings. Otherwise known as Springtime (and Autumn) in Florida. Cold nights that require you to cover or bring inside your sensitive plants and wrap yourself in a sweater and blankets inside. Followed by soaring daytime temperatures which find you switching the thermostat from Heating to Cooling. Until sunset when the temperature drops again.

Did you know that a well-insulated house doesn’t have those temperature swings with the weather?

Most people understand that insulation keeps you warm in winter. But it helps you stay cool in summer (or a Florida winter), too. We can all picture the pink, fluffy insulation that comes in rolls and is installed in attics, but there are other types of insulation. And just because your house was built with some insulation, the science and therefore the newer Energy codes have increased those requirements since your house was built. So, your house is probably in need of more insulation.

Before building science research disproved it, many concrete block homes were insulated this way, and, unfortunately, some still are. Injected foam insulation is the best way to remedy this.

Up in the attic, take a look at what you have. If your insulation looks like a golf course, with high mounds and low spots, you are not alone. Years of wind coming through the attic, critters nestling inside, people storing boxes, and maintenance people crawling through the attic have disturbed the insulation. If your old insulation is wet or dirty (if it looks dirty, it may have gotten wet), remove those portions.

Most of you have fiberglass insulation. A few of you might have perlite, which is loose-fill lightweight pellets installed in homes before the 1950s. New fluffy blown-in fiberglass insulation can be added on top of both of these.

A rare few of you may have vermiculite, which looks like irregularly shaped and variegated colored pellets – this needs to be tested for asbestos. If it tests positive, it needs to be completely removed by a professional.

Looking up inside this home remodel, the ductwork is connected to the ceiling wood framing, while the white spray foam beyond is on the underside of the roof. To the right there is rigid insulation board glued to the concrete block wall with greenish wood furring strips over it. This house achieved 2 energy certifications. (Project #09-09)

Today’s building code (FBC v7) requires attic insulation with an R-value of 38 in most of Florida except Miami-Dade and the Keys, and the next code revision will increase that to an R-value of 49. The code applies to new houses only, so in old houses, the goal is to fit as much as we can. For fiberglass and perlite insulation, that means about 11 to 16 inches is the ideal total (old plus new insulation). So try to attain that where you can, although you will likely have much less near the attic edges where the roof comes down to meet the attic floor. Maintain at least 1-inch clearance between the insulation and the underside of the roof deck to allow airflow between your soffits and your ridge vents.

If you really want the most R-value, you can always add rigid insulation board, which comes in panels like plywood, on top of your roof, too. This is typical for cathedral ceilings, where there isn’t always enough space between the rafters for insulation. The “extra” insulation is glued to the top of the roof plywood, then covered with more plywood and the roofing underlayment, followed by the shingles, tiles, or metal roof covering. This type of roof still needs soffits and ridge vents for airflow.

What about adding insulation to walls? Well, start with the attic first. You will get the most savings on your energy bills from starting there first. Then consider the walls.

Many of us live in homes with concrete block walls. You might not have any wall insulation! But if you do, it’s a rigid insulation board, and is about 1/2 to 1 inch thick. The R-value is about 5 or 6, which is Code minimum for this type of wall. Originally, the insulation was attached to wood furring strips, and the insulation was cut to allow wiring and electrical outlets to be installed (insulation with holes in it!). There may be a plastic vapor barrier nailed under the drywall, too, which is required Up North, but can grow mold in Florida. Today, due to updated building science, the insulation is glued directly to the block before the electrical wiring is installed (no holes!), then covered with drywall (gypsum board, also called sheetrock) or plaster.

Concrete block walls properly and continuously insulated with rigid insulation board glued directly to the block. Wood furring strips on top of them allow drywall and electrical wiring to be attached. (Project #09-09)

The best way to update this wall is to use injected foam insulation. This is similar to sprayfoam, but lighter weight, and doesn’t harden as much. Since concrete blocks are empty (except the places with concrete and rebar), it makes sense to fill these with insulation. The insulation will fill all the cracks and holes, making the wall airtight, blocking humidity, drafts, and sound. It’s also treated with insecticide and termiticide. To install, the worker will drill 1-inch diameter holes on the outside of your house at about chest-level. Then they will use 2 hoses to combine 2 different liquids and spray the mixture into each hole. They use a pressure gauge to determine when each hole is filled. The liquid expands inside and dries. The resulting R-value is about 20, which is 3 times what the Code requires!

If you live in a house with wood frame walls (those Bungalows of the 1900s to 1920s, Ranch homes through the early 1950s, and the upstairs of many houses are wood frame), you might decide to update your insulation when you add or remodel the house, or if you need to replace the siding or stucco. Adding insulation to this type of wall is intrusive, and you may want to update the electrical wiring at the same time. Options include adding fiberglass batts in between the wood studs as well as adding rigid insulation boards to the outside of the wall. In both instances, you should cover the outside of the wall with a WRB (weather resistive barrier – the white, green, or black wrap material) especially if there wasn’t one before, and then re-side or stucco.

This 1950s home has new fiberglass batt insulation in its walls when extensive termite damage required replacing the wood siding, sheathing (plywood), and some of the wall framing. Note that hurricane straps were added and the windows were also replaced, but the plaster inside was not touched. (Project #21-03)

Wood frame houses often have crawl spaces, many of which have never been insulated. The easiest way to insulate is with fiberglass batt insulation between the floor joists, then cover with plywood to keep out critters. Make sure you keep the crawl space floor or dirt level with a slight slope towards the outside, so water doesn’t pond under the house. And keep crawl space vents clear of mulch and plantings so humidity isn’t allowed to build up under there. Or you will find your house floors will get wet, stay wet, then attract mold (and you won’t know it until it’s too late).

Remember to check the insulation between your garage and your house, whether your garage is separated by a wall, or your garage is under your house. Because the garage is not heated or cooled, you should have the same insulation as you do on an outside wall or floor/ceiling.

Insulating the garage ceiling for a second floor addition. (Project #16-09)

Although the Code doesn’t require insulation for a Garage or Porch, we usually recommend it anyways. It will help keep the heat of the sun out of either space.

Your other option for insulation in the above situations is to use spray-foam insulation, which is a different approach. Sprayfoam insulation comes in open-cell and closed-cell, which refers to the air bubbles in the foam. Open-cell is like a sponge, where the air bubbles are connected to each other, while in closed-cell, the air bubbles are separated. Closed-cell has a higher R-value per inch (about 7). We use it for walls and in crawl spaces, where it keeps out burrowing critters. Up North, it is also used for attics (* see note below). Open-cell has an R-value similar to fiberglass insulation, and is used in attics in Florida. Both types are very good at keeping the humidity outside and minimizing drafts.

A slightly blurry photo showing an attic with ductwork inside and sprayfoam insulation on the underside of the roof. (Project #14-12)

However, sprayfoam insulation can be tricky to install in an attic without removing the ceilings. It also requires a slightly different approach – instead of venting your attic with soffits and ridge vents, you will close those and the insulation will be applied to the underside of the roof. This gives you an attic area that is insulated but not necessarily heated or cooled (it will travel through the ceiling). And it’s much more efficient for your heat pump if the ductwork runs through an insulated attic.

* We use the research papers from the Florida Solar Energy Center to recommend only open-cell sprayfoam insulation for attics in Florida at this time to avoid a build-up of humidity at the attic peak and to allow the roof sheathing (plywood) to dry out.

Upgrading your insulation is a great way to pay yourself back! It is a small investment with a big return that you will notice with every energy bill. We have upgraded the insulation in our attic (fiberglass) and walls (injected foam insulation) and hope you will, too.

Published by designfreedominc

Your Forever Home Architect

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