Do you recommend bio-based soy foam insulation?
We need insulation for the attic in our 1920s home, which currently has no insulation at all. I have heard about bio-based foam insulation, but the company I am considering says their R-rating is about 23, and I have heard that ideally it should be R-49. The person who came to give an estimate said that it actually performs about double the R number so I am confused if this is a more green and efficient insulation, compared to other forms such as blown-in fiberglass, which offers a rating of 49. Which kind would you recommend? Other issues are VOCs, which they say are low because it's based on soybean oil, but I don't have the number for that either.
Wow, where to start? By my count, you actually have 8 critical questions packed into that one small paragraph. Here’s how I break them out:
- How should we deal with an existing uninsulated attic?
- What’s the real deal with so-called “bio based” insulation?
- How can I verify the R-values claimed by an insulation salesman?
- What is the correct R-value for my area of the country?
- I am confused about green vs. efficient?
- How do the various types of insulation compare to each other?
- What concerns should I have about insulation VOCs in my home?
- Given all of those factors, what product(s) should I be considering?
These are all exactly the right questions to be asking before spending thousands of dollars to put lots of potentially helpful or harmful materials into your home. And the wildly exaggerated marketing claims made by manufacturers don’t help clear things up at all.
So let’s put “marketing science” aside for now and focus on some “building science 101.”
Building Science 101
At the base level, all insulation materials work the same way. They trap air in one form or another to create pockets which resist the flow of heat. The level of resistance they create is what we call an R-value. The higher the R-value, the higher the level of heat resistance.
Next, heat does NOT rise. The thermodynamics of heat are that it will always seek cold. The heat doesn’t care whether that is up, down, or sideways. Hot AIR will rise because it is lighter (less dense) than cold air. But don’t let someone tell you that heat itself rises because this is false.
The reason the directional flow of heat matters to you and your home has to do with how your home’s “envelope” will perform throughout the year. Here in the mid-Atlantic region, where you are, we have it tougher than many other areas of the country when it comes to how we insulate.
- In northern climates, they are predominately worried about winter heat escaping from their home to the outdoors.
- In southern climates, they are trying to prevent the outdoor heat from coming into their homes.
- Here in our mid-Atlantic area, we are referred to as a “mixed-humid climate.” This means -- for your home in Alexandria, Virginia -- you have to think about heat trying to both escape AND come in depending on the season.
The fact that in a mixed-humid climate we have to consider multiple directions of heat flows and building behaviors makes it fairly difficult, but not impossible, to develop the right balance of:
- trapped air (or heat resistance value) and
- air permeability (what helps our homes dry during the very humid summers).
If there are large volumes of uncontrolled air being freely exchanged between our homes and the outdoors (which is usually the case with homes built in 1926), it doesn’t make any difference what insulation strategy you choose because none of them will work very well. Again, for any form of insulation to be effective, it must trap the air into pockets. So if the air is moving too freely, then the insulation won’t be able to achieve its stated R-value.
So, now that you have a feel for how insulation works, how heat moves, and the effect that air movement has on those two factors, you probably know more about thermodynamics than half of the salespeople you’re likely to encounter.
Let’s look at your specific questions.
Our homes are complex systems. If we go changing them too drastically in any one direction, we risk unintended consequences. If we seal them up super tight without also providing a controlled, intentional source of make-up air, they can become aquariums with little or no drying potential -- and that never ends well. Often, insulation salespeople want to sell you on air-sealing everything in sight and they completely neglect the counterbalance strategy (make-up air). Be careful of this.
if you were to get your 1920s home pressure-tested by way of a blower door test, you would likely find that it leaks air heavily.
- This means you could likely seal and insulate the attic space tightly and still get plenty of make-up air from lots of other sources (leaky doors, windows, basements, foundation intersections, etc.).
- But if you have also recently replaced all your windows or taken other measures, you need to think about the effect of sealing the attic too. It’s always a good thing to do, but it needs to be a calculated move.
When you have an uninsulated attic, you have a blank slate to start with. The first thing you want to do is seal as many (if not all) of the penetrations which come from the climate-controlled space below, through the ceiling, and into the attic. This means:
- recessed lights,
- electrical wiring and ceiling boxes,
- plumbing pipes,
- anywhere the top section of one wall meets another, and
- anywhere you see horizontal framing intersect plaster or drywall ceiling.
The more of this air movement you can prevent, the more effective your new insulation will be. Now is the best chance you’ll have to do this before everything gets buried under new insulation. Some folks like foams for this, but we recommend using Tremco Spectrem 1 silicone sealant for this purpose. It is zero-VOC and is specifically designed for dissimilar materials which move often and at different speeds (i.e., a metal light fixture or a PVC pipe and your drywall or plaster). Foams have potent VOCs and can eventually shrink and lose their seal.
Once you have the air-sealing done between climate-controlled and non-climate-controlled spaces, you can select and install the insulation based on the rest of the questions.
This is basically a non-starter. It is complete marketing hype and of little relevance in the real world.
- The “bio” to which they are referring is soy-based oils vs. petrochemical oil.
- The problem is that none of them have more than single digit percentages of soy-based oils in their contents.
Compare that with the new FTC-recommended advertising guidelines, which say to claim that your product is “bio-based” it should be AT LEAST 51% of the ingredients. Unfortunately, those guidelines are voluntary, so manufacturers are still getting away with hyping bogus quantities.
Unless they can show you in writing that they meet the 51% soy threshold, I wouldn’t even take it into consideration.
All of the credible building science laboratories measure R-value PER INCH when evaluating an insulating product.
NO insulation product currently on the market is capable of exceeding more the R-7 per inch. Not one.
- So for any salesperson to claim anything above that, they are assuming the multiplication of certain thicknesses which may or may not even be possible in your application.
- When you are comparing possible products for your home, look ONLY at per-inch R-values and nothing else for a fair and realistic comparison of their R-value compared to another product.
Also, when looking at these values, ask to see them in writing from a THIRD PARTY verification lab. The FTC has strict rules (non-voluntary) about how the packages have to be marked and what they can claim. There are some outlandish statements on some product websites, such as radiant barrier materials, which claim that their 1/4”-thick membrane can achieve values of 11 or higher. That would mean that their product, on a per-inch basis, is reaching R-44 or more! There isn’t a lab in the country that can replicate or will certify numbers like that. You will also never actually see it on their package because they would risk a court action by the FTC for false advertising.
Bottom line: trust only what you can verify. And if a salesperson is in fact telling you that their product “actually performs about double that stated R-value,” that would be my immediate cue to thank them for their time and move on to someone who’s going to be honest about numbers they can actually prove.
Your state of Virginia utilizes a Uniform Statewide Building Code. This code is based on the International Residential Code (IRC) 2009 edition.
- This code defines Virginia as Climate Zone 4 and as such requires R-38 in ceiling or attic locations.
- When checked against the International Energy Conservation Code (IECC) 2009 edition -- which is often more stringent on energy matters -- it also recommends an R-38 value.
Granted, this is code minimum, and there is nothing to stop you from going higher. However, these codes are developed with consideration given to the area and its specific climate, and you can reach a point of diminishing returns for your dollar where our climate simply won’t make use of higher levels installed for the extra expense.
A really great tool to help you answer this same question is the "Zip Code Tool" offered by Oak Ridge National Labs (a division of the Department of Energy). Their tool will allow you to enter your zip code, your house type, materials used, types of heating and/or air conditioning, the part of your house you want to insulate, your local cost of energy from the utility and any existing insulation in that location. It will then generate a customized response on exactly what makes real-world sense for your home (i.e., NOT what some salesperson is trying to promote in any given month for their benefit and not yours).
Aren’t we all. Here’s how I try to explain it. A product can be theoretically green for the environment, but yet completely energy inefficient when compared to other products in its category. Bamboo flooring is a perfect example. It may be renewable and not involve clear-cutting, but it has to come on freighters from across the ocean and then be trucked or train-ed all the way to you on the East Coast. That’s a tremendous amount of embodied energy compared to reclaimed oak flooring that comes from an Amish barn right up the road in Pennsylvania.
Conversely, spray polyurethane foams (SPF) are shown to be super efficient insulators, but the isocyanate chemicals they use have some of the worst offgassing of global warming potential (GWP) VOCs of almost any chemical made.
So what you’re looking for is that happy middle ground. An insulation product that is acceptably friendly to the environment while still doing a verifiable job of reducing the energy required to maintain your interior temperature.
There are so many types, formulations and brands that it’s impossible to answer that here.
- Some versions make more sense for different regions of the country and different sections within the same house.
But for a really good summary of insulation types, check GreenHomeGuide's "Buyer's Guide to Green Insulation."
Ultimately, you should choose the one that meets your environmental goals, your energy goals, your climate zone, and your budget. I give my recommendation for you below in answer 8, but that’s just my recommendation and you may decide on something completely different.
VOCs are a real and legitimate indoor air quality (IAQ) issue. As we seal our buildings up tighter and tighter, we’re trapping more chemicals than at any time before.
- At the same time, we’re spending more hours indoors than ever before.
- Those two are not a good combination for us.
There are some VOC-free insulation products: natural wool, untreated cellulose, and mineral wool are a few. Of those three, mineral wool (such as Roxul) has the highest embodied energy due to how it’s made, but is also the safest to put into your walls for multiple reasons (fire, insects, and mold, to name a few).
There are also moderate-VOC level insulators: typically fiberglass and treated cellulose. Fiberglass can contain varying levels of formaldehyde. Formaldehyde is a known carcinogen in high enough quantities. Cellulose is typically treated with borates to keep it from becoming a food source for termites or a nesting ground for critters. A contact at the EPA tells me that they have concerns that borates may be endocrine or reproductive disruptors, but I have not seen the data yet to support that.
And finally, there are the extremely high-VOC compounds known generically as foams. These can be:
- board products made in a controlled factory environment (EPS and XPS are most common) or
- field-applied SPFs (either open-cell SPF or closed-cell SPF), which might be recommended for use in your attic.
As mentioned before, these products are all based on isocyanate formulations. A few open-cell versions are waterborne as opposed to using hydrofluorocarbon (HFC) blowing agents, which makes them better for global warming potential, but they still rely on the isocyanates for their base curing and expansion agent.
This isocyanate category of chemicals, when field mixed and applied in an occupied residential setting (vs. vacant commercial or new residential construction) is drawing the attention of EPA, NIOSH, OSHA, and CPSC. The deaths as these have grown in popularity in recent years is getting pretty scary for my taste.of illnesses and even
Based on personal experience with some of our clients, documented reports and in-person meetings with EPA scientists, we have stopped using foams in occupied homes with very limited exceptions.
For your climate zone, house type and section of your house (attic):
- I would vacuum and clean the existing attic floor to ensure good sealant adhesion.
- Then I would seal all penetrations as discussed in answer 1.
- Next, if you currently have vented soffits, I would install foam baffles to maintain proper air flow. However, if the only openings in your attic are at the gable ends, you won’t need these.
- Then I would blow in a loose fill material to a depth that will provide the R-38 recommended by the IECC for your zone.
This could be cellulose, fiberglass, or rock wool. I would avoid fiberglass due to environmental and IAQ concerns, even though it is the cheapest of the three and thus can be attractive based on price. Cellulose is a very popular option, and I’m okay with it in a well-ventilated attic, but it’s not my first choice. I’m also not a big fan of using it for walls or other closed cavities due to moisture concerns.
My first choice would be rock wool or mineral wool. These have very high recycled content, no VOCs, no pest or moisture issues and excellent fire resistive qualities (have you ever tried to set a rock on fire?).
- The actual depth you will need will be specific to the brand you choose, but will probably be in the 13” range. Be certain that the installers use depth gauges throughout the attic so that you can visually confirm they have consistent and complete coverage per your contract.
- Also ask to see the bags the product came out of so that you can confirm it is the correct product and you can read the FTC-required product label regarding true R-value. That means you should be there when the work starts and when it’s finishing.
- It can be a little dusty during installation, so you may not want to be home for that. If you are, make sure to wear a N95-rated dust mask, and same goes for anyone else who’s home. If you have little ones, say younger than 6 or 7, you may want to find an alternate place for them that day.
For more information:
Check our best attic insulation Q&A to see what other homeowners and contractors are saying about mineral wool, rock wool, foam insulation, etc.