Keeping Masonry Homes Cool in the Summer

​Hi, I want to build a two story building with concrete block filled with concrete and rebar. As you know, Florida is hot and the UV rays heat up a concrete wall big time. Do you folks have any experts on staff who have experience applying materials and paints to exterior concrete blocks to create 'cool' walls?

The most common way to insulate your home in Florida is to use a foil type insulation spread between the furring strips on the inside face. Using a 1 5/8" furring strip rather then a 3/4" furring strip allows you to slightly increase your interior insulation value of the available foil products.

The maximum recommended insulation for Florida homes is a 3/4" polyiso board with a reflective side. The board is glued or nailed to the inside face of the masonry wall with the foil face pointing inward. 3/4" furring strips are then attached over the board and the drywall attached to the furring strips. This gives you a through wall insulation value for a typical block wall of R10 or an added insulation value of R7.8 (insulation value of the 3/4" board plus the insulation value of a 3/4" reflective air space).

Normally block walls are either painted, sealed or stucco'd on the outside and none of these adds any appreciable energy efficiency to the home.

The truth is that masonry homes require very little insulation in the Florida climate. We proved this with extensive research done at the Pacific NW Labs, one of the top energy research labs in the Country. Results from that testing are attached to this blog and clearly show that your typical foil interior insulation is the best value for money. The actual energy $ savings between the minimum R4 foil interior insulation and R20 super insulation is only about $100 per year (not per month - per year). This is for a 2000 sf one story home in Miami. The $ difference in Central and Northern portions of the State is even less because of the cooler evenings which makes the masonry thermal mass work better.

You can super insulate all you want but you will never recoup your investment with energy saving. That is because the opaque exterior walls just don't contribute that extensively to the overall energy use of the home. Things like efficient hot water heaters and air conditioners, extra attic insulation and better infiltration packages make a HUGE difference your energy bill. The opaque portions of exterior walls just don't contribute that much to your energy use. Thus, there is only a minor gain in heaping insulation on these walls and your return on investment drops off to almost nothing after a modest amount of insulation is added.

​Additional Information: 

Residential Wall Type Impact Analysis 

PNNL Energy Research Report