Rigid Board Insulation: The Ultimate Guide - Rise

13 Jan.,2025

 

Rigid Board Insulation: The Ultimate Guide - Rise

Rigid Board Insulation: The Ultimate Guide

Properly insulating your home is one of the most important things that homeowners can do to improve the overall energy efficiency of their homes. The United States Department of Energy estimates that the energy that homeowners use for artificially heating and cooling their homes accounts for almost half of total energy use. Investing in more efficient heating and cooling technologies such as a heat pump or high-efficiency furnace is one way to but back on your heating and cooling bills. However, an unsealed building envelope or insufficient insulation in your walls, roof, or foundation will increase your energy use, regardless of your type of heating and cooling.

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Rigid board insulation is a relatively new product. It is long-lasting, easy to install, and can improve the energy efficiency and thermal performance of even the oldest and leakiest homes. If you find that your energy bills are always high, even after adjusting the thermostat and upgrading to Energy Star appliances, a retrofit that focuses on improving your insulation might be in store. In the best of cases, this type of insulation can help homeowners save up to 40 BTUs of energy for each BTU of energy consumed by the home heating and cooling systems. For older homes, improving your home's thermal envelope with rigid board insulation could increase your home's energy efficiency by up to 70 percent. Below, Rise offers a complete guide to the pros, cons, and rigid board insulation installation process.

What Is Rigid Board Insulation?

The vast majority of houses across the country continue to use batts or mats of soft insulation. Fiberglass, cellulose, and even natural sheep wool insulation continue to be the most popular insulation alternatives for homeowners. Rigid board insulation is made from rugged, dense sheets of certain types of foam. The most commonly used foam products for rigid board insulation include polyurethane, polystyrene, or polyiso. Due to the chemical structure, these types of foams are considered to be "closed-cell." In contrast, the majority of insulation products are open cells. 

Closed-cell insulation products like the rigid board are generally stronger, more durable, and resistant to natural elements. In addition, they have a higher R-value than open-cell insulation products. R-values measure the level of insulation capacity of different products. The higher the R-value, the more insulated your home will be.

Rigid foam insulation products are generally sold as 4 foot by 8-foot sheets (the same size as plywood). They come in several different thicknesses ranging from ½ inch to 2 inches.

How to Use Rigid Foam Board Insulation?

Because rigid foam board is sold as solid sheets, many handy homeowners might be able to self-install these products in strategic areas around your home. For example, it is possible to enhance the insulation in an unfinished basement by installing sheets of rigid foam board between the exposed studs or along the basement's concrete wall. After attaching the foam boards to the wall, you can place furring strips over the board. These strips will give a secure base for finishing your basement with drywall, bamboo plywood, or other wall material. For homes with concrete walls in the basement, rigid foam board will be much more durable, especially when compared to the loose rolls of fiberglass or cellulose insulation. Concrete tends to seep moisture. So, most open-cell insulation products (like fiberglass) will absorb moisture and could lead to molds and mildew that compromise your indoor air quality.

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Rigid board insulation is an excellent option for every other home area, including foundation walls, regular walls, roofs, and attics. Because they are naturally moisture resistant, however, this insulation alternative is usually recommended for external insulation or below-grade applications (such as basements).

Where Can Rigid Foam Board Insulation Be Used?

Foam insulation board is applicable virtually anywhere that insulation is used in the home. You can use it on foundations, basements, regular walls, roofs, and attics. When used in above-grade applications, such as walls, ceilings, or attics, foam board insulation can reduce thermal bridging and improve the entire home's energy efficiency. When used for the interior or exterior of foundation walls or below-grade basements, this type of insulation can improve insulation while avoiding moisture buildup or leaks.

Foam board made from polyisocyanurate (polyiso) generally offers the best insulation capacity and 6.5 per inch. Water is the primary "blowing agent," making it one of the most environmentally-friendly foams used. Of course, it is still sourced from petrochemical materials, thus increasing the embodied energy footprint of the product. Fortunately, almost all rigid board insulation made from polyiso does not contain any brominated flame-retardant chemicals. Great news, since these chemicals can be hazardous when inhaled. This type of foam, however, will absorb water and is thus not suitable for below-grade applications.

According to the National Institute of Environmental Health Sciences, some chemical flame retardants are known to cause adverse health effects, including:

  • Immune system impacts
  • Disruption of endocrine and thyroid
  • Reproductive toxicity
  • Cancer
  • Changes to neurologic functioning, and
  • Adverse effects on child and fetal development. 

When searching for the best rigid foam board insulation products, it is always good to prioritize products that use low-toxicity flame retardants like TCPP. You should certainly avoid any product that relies on polybrominated diphenyl ethers or PBDEs.

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Quick Comparison of the Best Rigid Foam Board Insulation Products 

Expanded Polystyrene Board (EPS) Insulation

  • Pros: Cheapest option and doesn't deplete the ozone layer, water resistance at higher densities
  • Cons: Lower density products will not offer complete water resistance, lower R-Value than other types of foam
  • R-Value: 3.6 to 4.2 per inch
  • Cost: $0.31 per square foot for one-inch thickness

Extruded Polystyrene Board (XPS) Insulation

  • Pros: Stronger and more water-resistant than EPS, better for below-grade applications
  • Cons: Most products include strong chemical flame retardants. The blowing agents used will deplete the ozone layer
  • R-Value: 5 per inch
  • Cost: $0.47 per square foot for one-inch thickness

Fiberglass Rigid Board Insulation

  • Pros: Higher R-value per inch than traditional fiberglass batt insulation, easier to install
  • Cons: Not water-resistant and will require a vapor barrier installation
  • R-Value: R-11 for 3.5-inch board
  • Cost: $1.25 per square foot

Graphite Polystyrene Board (GPS) Insulation

  • Pros: Inclusion of graphite particles increase the thermal performance compared to EPS, increased vapor permeance to reduce the likelihood of trapped moisture
  • Cons: Costlier option
  • R-Value: 4.5-5 per inch
  • Cost: $14 to $16 per board

Mineral Wool Rigid Board Insulation

  • Pros: Natural option, fireproof, no off-gassing
  • Cons: Dangers when installing. If not correctly installed, tiny slivers can become airborne and be inhaled
  • R-Value: 4.2 per inch
  • Cost: $0.50 per square foot

Polyiso Rigid Board (ISO) Insulation

  • Pros: Highest R-value among foam products, environmentally benign blowing agent, no brominated flame retardant chemicals
  • Cons: Cannot be used for below-grade applications due to a lack of water resistance
  • R-Value: 6.5 per inch of thickness
  • Cost: $0.60 per square foot at a one-inch thickness
Disclaimer: This article does not constitute a product endorsement however Rise does reserve the right to recommend relevant products based on the articles content to provide a more comprehensive experience for the reader.Last Modified: -07-22T17:34:11+

Shop/garage insulation plan?

This most likely a rehash but I'd like to see if this sounds feasible.

My shop/garage is a 40' X 48' x 11' pole type building with metal siding and roof. Side wall post and trusses are 8' centers.
What my plans for insulating the walls is to place 1 1/2" foam board type insulation with the slick side towards the metal cut to fit between the wall purlins with either fan fold or 1/2" insulation board on the interior face of the purlins covered with 7/16" OSB. Don't really want to stud the walls out flush between the post.
For the ceiling, I plan on building a 2' on center grid between the bottom cord of the trusses with 2"x4" and 2"x6" material to attach either corrugated ceiling metal or the flame proof poly corrugated ceiling material then add blown or roll insulation above that. Where the 2"x6" grid is I plan on decking this for storing light weight items.
The overhead doors I plan on either gluing in the foam board type insulation or using the roll type bubble/foam insulation.
I'm not looking to run around in my shop in a tank top and shorts in the middle of winter just to be comfy.
I heat with a wood stove but may purchase a heater burning fuel oil or diesel possibly electric to get it warmed up while the stove is catching up.

Thanks for any help.
Jeff Might want to think about a vapor barrier in there somewhere, and I would not put the rigid insulation flush against the exterior wall tin, for you might have a condensation problem, and long term rusting. Id at least fir it out 1/4" or more.

If you're using OSB on the walls, you might want to hold it up off the floor at least a 1/2" and trim it out with non-flammable base, so if your welding or cutting, and a hot ember makes it to the edge of the wall.....(no fire) if you search the site (google usually works better than the GJ search tool), you will find allot of warnings about OSB in garages, not usually a good idea...I know I wont be using it. They do make a thin interior tin for ceilings and walls too, not everyone knows that.

I'm getting ready to do the same as you, Ive got an 50 x 100 that is wide open and I need to close in. Ive been trolling the site looking for ideas too...
Might want to think about a vapor barrier in there somewhere, and I would not put the rigid insulation flush against the exterior wall tin, for you might have a condensation problem, and long term rusting. Id at least fir it out 1/4" or more.

If you're using OSB on the walls, you might want to hold it up off the floor at least a 1/2" and trim it out with non-flammable base, so if your welding or cutting, and a hot ember makes it to the edge of the wall.....(no fire) if you search the site (google usually works better than the GJ search tool), you will find allot of warnings about OSB in garages, not usually a good idea...I know I wont be using it. They do make a thin interior tin for ceilings and walls too, not everyone knows that.

I'm getting ready to do the same as you, Ive got an 50 x 100 that is wide open and I need to close in. Ive been trolling the site looking for ideas too...

I'm using OSB on my garage walls, and I'm going to lay a treated 2x4 on the floor to keep the OSB off the floor, and have a little room to spray the floor off if needed for cleaning purposes. This is where the foam producers try and confuse people.

They slander fibreglass by saying things similiar to what Toyotadriver, when, in fact you also have to take into account the vapour barrier/kraft backing that is used in with fibreglass insulation in any thermal senario - The only time you do not use a vapour barrier/retarder with fibreglass is in an acoustic situation. You should ALWAYS be using some form of vapour retarder/barrier when using fibreglass, cellulose or mineral wool for thermal application.

Up here we don't use kraft back batts, we use straight fibreglass and we caulk all joints, cracks and seal with a rubber, flexible sealant called acoustical sealant and lay a full 6 mill vapour barrier and tape polypans around electrical and caulk or foam around all wires or pipes coming through the 'warm' side out to the 'cold' side. The local spray foam company's ad on the radio claims "Foam stops airflow unlike typical pink (fibreglass) insulation." - They are right, fibreglass doesn't stop airflow, but the sealed vapour barrier(building standard in our region) does. You have to be careful on what you take as fact.

"R-value" is a essentially a numeric scale of thermal resistance. If the product says R-5, wether it's foam, fibreglass, cellulose, etc, if it's installed correctly, it's R-5. Actually, R values are a very inaccurate method of measuring the value of an insulation. Think of it this way. If it's cold outside but very still air, you can wear a fleece jacket and feel nice and warm. Now, raise the temp but add wind to it, and you're gonna feel cold.

But, the fleece jacket is the exact same level of insulation why do you feel cold even though the temp is warmer? Well, because the wind is blowing right through the fleece and you are losing heat quicker than when there was no wind.

Now, while wearing that fleece jacket, cover it with a light windbreaker. Now you're back to feeling warm again.

Try wearing a windbreaker covered with the fleece. Will you be warm? Well, probably warmer than wearing just the fleece but not much. Why? Well that fleece isn't holding in heat...the wind is blowing right through it. But, the windbreaker is stopping the wind reaching your body so you still are loosing heat...just not as quickly.

Fiberglass doesn't do a good job of stopping the flow of air just like that fleece jacket without a windbreaker. Putting the vapor barrier on the inside (while certainly needed for other reasons in your cold climate), is like wearing your windbreaker covered with a fleece.

Foam insulates the same regardless of whether it's wet or dry, windy or still. Fiberglass changes depending on the weather conditions. Under ideal conditions, fiberglass works fine. However, since things are rarely ideal, there are far better insulation choices than fiberglass...especially in extreme environments. In more mild climates, the increased costs of foam may not pay for itself. In extreme climates, the increased costs of foam may well pay for itself in a very short time.

R5 is R5...assuming that the environmental conditions are perfect. Change the conditions and R5 of one type of insulation will NOT be the same as R5 of a different type of insulation.
Actually, R values are a very inaccurate method of measuring the value of an insulation. Think of it this way. If it's cold outside but very still air, you can wear a fleece jacket and feel nice and warm. Now, raise the temp but add wind to it, and you're gonna feel cold.

But, the fleece jacket is the exact same level of insulation why do you feel cold even though the temp is warmer? Well, because the wind is blowing right through the fleece and you are losing heat quicker than when there was no wind.

Now, while wearing that fleece jacket, cover it with a light windbreaker. Now you're back to feeling warm again.

Try wearing a windbreaker covered with the fleece. Will you be warm? Well, probably warmer than wearing just the fleece but not much. Why? Well that fleece isn't holding in heat...the wind is blowing right through it. But, the windbreaker is stopping the wind reaching your body so you still are loosing heat...just not as quickly.

Fiberglass doesn't do a good job of stopping the flow of air just like that fleece jacket without a windbreaker. Putting the vapor barrier on the inside (while certainly needed for other reasons in your cold climate), is like wearing your windbreaker covered with a fleece.

Foam insulates the same regardless of whether it's wet or dry, windy or still. Fiberglass changes depending on the weather conditions. Under ideal conditions, fiberglass works fine. However, since things are rarely ideal, there are far better insulation choices than fiberglass...especially in extreme environments. In more mild climates, the increased costs of foam may not pay for itself. In extreme climates, the increased costs of foam may well pay for itself in a very short time.

R5 is R5...assuming that the environmental conditions are perfect. Change the conditions and R5 of one type of insulation will NOT be the same as R5 of a different type of insulation.

Interesting view. If we left Insulation exposed on the exterior of houses your logic might proove something.

Put your windbreaker on, then your fleece(You'll need to pick the fleece that meet's the R-Value recommendations set out by your regions minimum code requirements). Now go back and seal your windbreaker with acoustical caulking and tape and seal any penetrations or cracks(Zippers, pockets, draw strings). Now sheet over your fleece with 3/8's plywood and your choice of siding or stucco.

If you seal your building envelope properly, it doesn't matter how windy it is outside. Regarldess of your insulation material, you loose your heat out your roof primarily and air can and will infiltrate through even the most effecient windows and doors.

Fibreglass actually insulates by have thousands of layers per batt which creates millions of air pockets to allow a temperature differential or a thermal break much the same way foam has millions of tiny bubbles which do the same job. No, fibreglass doesn't stop wind, but the siding on the exterior of your home does.

If foam was as great as everyone believes, by the "foam logic"(I'll call it), you wouldn't need a furnace anymore, the residual heat from the people, furniture and appliances would be enough to heat your home.