About Aerogel - InterNACHI®

by Nick Gromicko, CMI®Aerogel is a class of porous, solid materials that exhibits an impressive array of extreme properties. Invented in and used for decades in scientific applications, aerogel is becoming increasingly feasible as a building insulation, largely due to a decrease in the price of the material.Aerogel is still prohibitively costly for most homeowners, and the few who can afford it probably don’t know what it is. At expensive properties with environmentally friendly features, however, inspectors should be prepared to encounter the material. Also, the prevalence of aerogel is likely to increase in the coming years as it becomes more affordable and widely known.Physical Properties and Identification Aerogel holds 15 world records for material properties, a few of which are listed below. Aerogel is:

• lightweight. It is, in fact, the lowest-density solid on the planet. Some types are composed of more than 99% air, yet they still function as solids;
• extremely high in surface area. It can have a surface area up to 3,000 square meters per gram, meaning that a cubic inch of aerogel, if flattened out, could cover an entire football field; and
• strong. It can support up to 4,000 times its own weight. In the picture at right, a 2-gram piece of the material is supporting a  5-pound brick.

The following qualities will also assist with identification. Aerogel:

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• appears blue due to Rayleigh scattering, the same phenomenon that colors the sky;
• feels like Styrofoam® to the touch. Although a slight touch will not leave a mark, pressing more firmly will leave a lasting depression or even produce a catastrophic breakdown in the structure, causing it to shatter like glass; and
• is rigid. Despite its name, it is hard and dry, little resembling the gel from which it was derived.

ProductionAerogel is derived from gels, which are substances in which solid particles span a liquid medium. The first aerogel was produced from silica gels, although later work involved alumina, chromia, carbon and tin oxide. Through a process called super-critical drying, the liquid  component of the gel is removed, leaving behind the hollow, solid framework. The resulting aerogel is a porous, ultra-lightweight lattice composed of more than 90% air. Ordinarily, drying of a gel results in its shrinkage and collapse (think of Jell-O left out for a few days), but super-critical drying is performed under intense heat and pressure that preserve the structure of the gel.  

Manufacturers offer the material in a variety of forms, such as the granules pictured at right, made by Cabot, which are sometimes used as insulation in skylights. Aspen Aerogel® offers 57-inch wide rolls of the material in 0.2- and 0.4-inch thicknesses, while Thermoblok® comes in 1.5-inch wide strips that are used to cover framing studs and help prevent thermal bridging at a cost of about $1.99 per foot. 

Safety

Aerogel safety is dependent on the safety of the gel from which it was made; it will be carcinogenic, for instance, if the gel from which it was derived had this quality. Fortunately, silica-based aerogel is not known to be dangerous, although it may irritate skin, mucous membranes, eyes, the respiratory tract, and the digestive system. Aerogel is hydroscopic and extremely dry to the touch, which can, in turn, cause it to dry out unprotected skin. Gloves and goggles are recommended for inspectors and contractors who must handle the material.

Aerogel does not seem to be an environmental threat. Aspen Aerogel’s® website states: “Aerogel blankets do not meet any of the characteristics of a U.S. EPA hazardous waste,” and further notes that scrap aerogel may be disposed of in landfills that are approved to accept industrial waste.In summary, aerogel is a safe, remarkably effective thermal insulator whose use should become more widespread as it becomes more affordable.

I want to do an efficiency and cost comparison of using aerogel sheets vs. fiberglass batting in residential homes. I have found a resource with different construction material R-Values that I will use to compare the thermal loss of traditional fiberglass batting vs aerogel with a price comparison at the end.

Any critics/improvements of the math involved would be appreciated.

Thermal Comparison

Using US standard wall construction: every wall is composed of 2"x4" studs (actually 1 3/4" x 3 3/4") separated by 16". This makes each wall 11% thermally bridged by studs and 89% fiberglass-insulated.

1 3/4" / 16" = 11%
(16" - 1 3/4") / 16" = 89%

Using the R-values from the link above, where 2x4 studded wall portions are rated at R-5 while fiberglass-insulated portions (without polyurethane, the yellow foam, and polystyrene) are rated at R-15. This leaves a standard wall with a rating of R-13.9

• (0.11 * 5) + (0.89 * 15) = 13.9

Since aerogel is applied in a sheet, there is no thermal bridging at the location of the studs. This makes 100% of the wall rated at the R-value of commercially available aerogel which is R2.8 W/K/m² (metric) or R-16 imperial

• 2.8 * 5.7 (hr ft2 oF/Btu) / (W/K/m²) = 16.0

This makes a single sheet of 5mm aerogel 15.1% more efficient than a fiberglass-insulated wall

• (16/13.9) - 1 = 15.1%

Cost Comparison

Commercially available aerogel is available at $4/sqft This is the cheapest I could find; if you find cheaper please let me know.
Bulk purchase fiberglass batting is available at $0.34/sqft

Conclusion

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Even though aerogel is more efficient than fiberglass, the price does not justify the ~15% home heating and cooling savings. A hybrid solution is to cover 89% of the wall in fiberglass while aerogel protects the other 11% from thermal bridging across the studs. This leads to an R-value 4" wall of R-15.1

• (0.11 * 16) + (0.89 * 15) = 15.1

With a 6" wall, this hybrid solution is entirely mute since 6" batting has an R-value of 23 which leaves a 6" wall R-value at 21.0

• (0.11 * 5) + (0.89 * 23) = 21.0

Any thoughts/solutions for improving thermal efficiency/cost? I did not include spray-in polyurethane foam in this comparison.

2" x 4" lumber is not 1 3/4" x 3 3/4", as the link you provide says, so you would need to readjust your math. That 1 1/2" thickness takes up space in the 16" spacing, so it is 14 1/2" between each stud.

As mentioned, some newer style construction uses 2" x 6" (1 1/2 x 5 1/2) studs 24" on center (22 1/2" between), but stupidly it isn’t as common as online articles would have you believe. Being in Florida with very hot temperatures and hurricanes, you would figure people would not make houses from under 1,200 sq. ft. to over 12,000 sq. ft. with 2" x 4" exterior walls because of the large energy savings and ability to use larger hurricane tie down hardware, but it’s pretty rare in my experience. The government mandates cars by efficiency, yet houses that use much more energy don’t have efficiency ratings. Construct as cheap as possible and pass the buck.

Another thing to note is the sheets of aerogel would have to be structurally capable of being used with an adhesive in order to get zero thermal bridging, as any nails or screws would be highly conductive. Maybe only a small percentage of the total area, but still a measurable number. It doesn’t look like it can be sandwiched without compression, and thus a drop in efficiency, but maybe other products have it sandwiched in structural panels.

Those links for aerogel available for purchase is great, thanks. If it had a slightly higher temperature threshold it would have even more uses. I wonder if it is the aerogel or the batting it is contained in that is the limitation.

Since you are looking at doing a tiny house, you might want to look into ones that have been Built With SIP’s. If they aren’t available locally, you could probably construct your own. That might not be feasible for a huge house, but with a tiny house you could make it exactly how you want it while laying on the ground and then just stand it up. I know I have seen a few on YouTube like that so a search should yield some results.

My understanding is that R13 insulation made for 4" walls is derated to R11 at 3 1/2". I think there are some fiberglass batts out there now which do slightly better. A big problem with fiberglass is installation. If it gets compressed and isn’t fluffed out again when installed it has a big drop in effectiveness. Having to cut and piece things together in some of the odd shaped bays can easily lead to gaps that allow thermal transfer from one side to the other. You can end up with an entire bay that effectively has about R1.

If this tiny house is fixed in place it might not be as bad, but one that gets dragged down the road will likely experience a lot of settling. The same goes for cellulose insulation. It fills better than fiberglass, but I would be afraid of it settling quite a bit if it is moved around regularly. This settling would lead to large gaps. I guess you could leave the tops of the bays open and stuff more cellulose fiber in as it settles. Spray foam and foam panels would not settle and would be a better choice for houses that see a lot of time on the road.

Unfortunately this ignores what most houses ignore, and that is the surroundings. If it is constantly changing then you may not have control over this, but the surroundings of a house have an Effect On The Microclimate which can lead to a significant loss of efficiency. I think there are calculators online which can show the energy savings of using trees to block the sun and reduce the need for cooling. Having shade to the South and West would be good in warm climates and bad in cold climates. Having a large masonry wall a short distance North could absorb sun all day and radiate that heat through the night. Keeping this in mind for a mobile house could help if you have choices of where to park.

Even something as simple as having a white or reflective roof in a warm climate or a black or charcoal gray roof in a cold climate can make a noticeable difference. I always see people so happy to get a great deal on cheap black roofing and wonder why their air conditioner is running all the time.

Permanent shutters that actually work and can be manipulated from the inside could also increase safety and efficiency. They could provide protection from road debris and prevent someone from breaking a window. When closed it could trap an air pocket to reduce heat transfer. Being able to open them from the inside would be mandatory in case of a fire or other emergency.

I’ve framed a lot of houses and been a fan of tiny houses for a long time. I personally like the idea of a small permanent house and large work spaces with plenty of space for gardens and trees and nature. If you have any other info about your build or take pictures along the way, then post them up! Good luck!

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