Wall Insulation Tips: What Kind & Installation

Our houses are becoming more energy efficient thanks to building codes focused on driving down US energy consumption. Similar to Energy Star appliances you see at the store, building materials like wall insulation must also meet more stringent building codes. In Florida, there are different codes based on the type of construction and where the insulation will be installed:

• Wall insulation R-values are confusing when you find different references giving different values …
  Insulation requirements are different for wood-frame versus concrete block and metal framing.
• Block walls where the insulation is installed inside (interior insulation) require wall insulation to meet or exceed R-7.8.
• Where insulation is installed outside block walls (exterior insulation), the code is slightly lower at R-6.
• Ceiling insulation must be R-30 or higher; raised floor insulation must be R-13.
• Thanks to MyEnergyMonster's article, A Brief Overview of Insulation Requirements in Florida. It's been challenging pouring through Florida's building code documents to find this information.

What's included in this article:

1. How to Identify Wall Insulation Requirements
2. How Wall Insulation Materials are Evolving
3. Installing Wall Insulation the Right Way! … because the right materials, installed the wrong way, won't deliver the results you want.

Sadly, when I went to my insulation go to resource, the information needed was missing. The table below provides insulation recommendations for attics and the floor.  The recommendations for walls (below the table) only addressed remodeling, and then only for wood-frame walls. There was no guidance for a block wall house in Florida.

That's when I discovered that there is a separate map for builders. There is an Energy Star Certified Homes Program that covers a lot more than insulation. It focuses on cooling equipment, heating equipment, ductwork and thermostat, the envelope (insulation, ventilation and radiant barriers), windows, doors, hot water heater, lighting and appliances. Certification is based on a reference design home (see features for Florida) but the features aren't mandatory.

How to Identify Wall Insulation Requirements

While researching house specifications for my new home in Florida, one concern I had was energy efficiency. I kept asking for the R-values for the attic and walls. While the builder told me attic insulation was R-38, they weren't able to give me an R-rating for the walls – they were about to change their wall insulation. Here are several ways I tried to uncover what Florida's wall insulation requirements are:

• Read multiple article online, like My Energy Monster's blog post quoted above.
• Crawled through Florida building codes multiple times. Finally discovered the information is located in the Florida Building Code for Energy Conservation … under the Building Thermal Envelope (Section R402). Most of Florida is in climate zone 2 and the insulation requirements for block walls falls under “Mass Wall R-value”. What was interesting is that placing insulation outside the home provide more benefit than interior insulation.

My concern with concrete block walls (cost-effective and structurally sound) is they provide very little insulating value (called thermal resistance). ArchToolbox.com gives 8 inch Concrete Masonry Unit (CMU) an R-value of 1.11. They also provide an R-value for “air space” which I needed to calculate the R-value for my new house … 1.0 for space that's at least a half-inch deep and no more than 4 inches.

When you live in the northeast, insulation is extremely important. The FiFoil insulation (I call it pretend insulation) my builder wanted to put in my home is nothing more than a radiant barrier. It has almost no insulating value so it works for Florida when it's warm (about eight months a year) but what happens when we have a cold winter.

FiFoil insulation approved for Florida … think brown paper bag + aluminum foil?

Remember global warming and extreme weather events around the world. Texas weather is a lot like Florida but that changed in 2021. Texas had a record low temperature at Dallas/Fort Worth International Airport of −2 °F (−19 °C) on February 16, the coldest in North Texas in 72 years. Unfortunately the electrical infrastructure in Texas failed causing death and billions of dollars in damage due to burst pipes and flooded houses (learn why you never want to deal with a flooded house).

So I calculated the R-value for the new insulation my builder planned to put in my house … not good. Fortunately I caught this before it was installed and was able to get foam board instead (details follow).

Fortunately it was possible to upgrade to a radiant barrier in the attic, which is the most important place for insulation in your home. There will also be insulation on the attic floor to reduce the amount of conditioned (heated or cooled) air that escapes from the house into the attic.

Researching home insulation for the first time? Here are some articles that will help you get started:

• Home Insulation for Comfort & Lower Energy Costs
• How Many Types of Insulation are There?
• Cost of Performance of Home Insulation Options
• Insulation Doesn't Work by Itself … as too often my handyman clients called assuming insulation was the answer to their problem. This led to a discussion about HVAC, where V=Ventilation and it's just as important.

How Wall Insulation Materials are Evolving

The wall insulation is changing in the community where I'm building my Florida house. It's still not clear what the new standard will be although the good news the wall insulation will now include a radiant barrier. This is a great improvement over the original styrofoam shown here (below).

Styrofoam insulation used as wall insulation is a new experience for me, along with block walls. Neither material is used very often in the northeast where I've lived most of my life. Here are some interesting facts collected while researching this type of insulation:

• Styrofoam is a trademarked name of closed cell, extruded polystyrene foam. The trademark is owned by the Dow Chemical Company and the product is light blue in color. It is used to insulate walls, roofs and foundations.
• The insulating R-value of rigid foam panels increases as the thickness of the boards increases. What's funny is while taking photos of the R-values documented on the insulation boards, I didn't realize I needed to measure the thickness of the board to identify it's R-value.

• Rigid foam insulation panels can be glued to block walls (use only glue recommended for rigid foam and masonry). This video on How to Attach Rigid Foam Insulation to Concrete, also shows the use of plastic anchors to secure the panels to the block walls.
• Once installed, the foam wall panels should also be taped to block air and thermal transfer. Foam wall insulation panels should also be sealed with spray foam insulation where they meet the floor, the ceiling and corners which have almost invisible gaps.
• Floor to ceiling furring strips need to be installed over the insulation panels to serve as nailers for the drywall that will cover the insulation.
• Other rigid insulation characteristics to consider are how the material responds to moisture and compressive strength to withstand job site abuse. Here is a video that goes into these choices in more depth, Which Foam Board? Polyiso vs XPS Insulation.

Installing Wall Insulation the Right Way!

This article started because I noticed that two other houses being built had radiant barriers on the walls. I upgraded to radiant barrier panels under the roof but there had been no mention of an option for the walls. As I started thinking through who I could talk to about my wall insulation, I realized that I had a much BIGGER problem.

Insulation should be continuous meaning no gaps between the panels. As identified above, seams between panels and gaps where the insulation panels abut the floor, ceiling and corners should all be sealed to reduce air infiltration (leaks). Unfortunately the framers didn't install the insulation before they framed my house.

So I sent an email to the building supervisor identifying the problem. My goal is to discuss the alternatives to fixing the problem. His first response via email wasn't acceptable to me, so I'm waiting for a phone call. The truth is you only learn how to build a house shadowing those with years of  experience and making your own mistakes. Fixing mistakes are unfortunately, are one of the best ways to learn what works and what doesn't work.

In this case, the supervisor appeared to be passing on the face saving solution offered by the subcontractor … except it doesn't make sense, except for the subcontractor. Here are the solutions I've identified, along with my best guess at how the problem will ultimately be dealt with. Wish me luck as negotiating with a production builder is like dealing with any large corporation.

1. Best and unaffordable solution would be to remove all the framing, install the wall insulation and re-frame the house. Of course that isn't going to happen for time and cost reasons.
2. Risky but worth mentioning, would be to cut out the wall studs next to the block wall. This would provide space to slide the insulation behind the interior wall framing. That would deliver the continuous layer of insulation that is supposed to be there, and the wall studs could be reinstalled over the insulation. For a custom home builder or remodeler this wouldn't be a problem. Unfortunately the skill level of framers on a production build is much lower, so it might be too risky.
3. Remove the furring strips and install the insulation panels between the wall studs, reinstalling the furring strips which are needed to nail the drywall to the walls.
4. Install the rigid foam insulation on the exterior side of the block walls but the builder doesn't have the processes or subcontractors to then finish the house exterior correctly.
5. Switch to using foam spray insulation which is actually the best solution because it not only insulates the house, it does the best job sealing all gaps that will allow air movement between the conditioned space inside the house and outdoors. Of course this solution is more expensive and while I would be happy to pay extra, the builder only wants to follow their documented business processes.

If you understand the options I've outlined here, you should understand why my response to “… the furring strips on the block is so that the insulation can be stapled to it when it is installed” is pure bullshit. This would leave a gap between the insulation and the block walls. It would take more living space away from the interior of the house. More furring strips would have to be installed for the drywall to attach to.

You're more likely to finish your basement than build a house, so here's a video from This Old House, showing how they recommend attaching rigid foam insulation to the walls, followed by two layers of furring strips to support hanging drywall and running electrical wiring.