The basic ethos of a passive house is to ensure that heat is not lost and to do that it needs to be airtight. This requires quality insulation but what is the most eco friendly insulation material to use? There are lots of natural insulation materials for homes, here are five options that we are looking at:
People have used straw for centuries as a natural insulation material. Wattle and daub huts in Africa use straw in the mix to bind the mud and provide insulation. This kind of cob construction has been used around the world.
Straw bale homes in the US date back to the mid 1800s. Early settlers in Nebraska had no sod to build with and instead used straw baled by the first horse powered bale presses. Straw bale homes are built all over the world by self builders and construction experts for those who want a home built with natural insulation material.
Straw bale construction is surprisingly fire resistant when constructed correctly. The University of California Richmond ran an ASTM E-119 fire test on a straw bale wall in 1996 that showed that straw bale walls can be ‘one hour walls’ (ResearchGate).
It is possible to retrofit an existing home with straw bales according to strawbale.com but, as with new builds, the major concern is ensuring that the straw bales are kept dry during construction. A simpler solution might be a structured insulation panel that is prebuilt.
Prefabricated straw insulation panels are made off site. A form is laid horizontally and plaster added, the straw bales are then inserted into the plaster. The exposed straw bales are plastered like a screed as the form is still horizontal. Once dried, the panels are transported to site.
In 2017, the Endeavour Centre built a straw insulated house called the Zero House. They used prefabricated straw insulation panels which they had developed themselves in 2000. If you are unable to source prefab straw SIPs locally in the United States, contact the Endeavour Centre. They’re based in Peterborough, ON.
In the UK, Modcell makes a prefabricated straw insulation panel. A Modcell insulated straw panel is made up of an FSC/PEFC timber frame, straw insulation, a split timber sole plate with insulation in between the plates and a window or door opening, if one is required.
The estimated R value of straw bale walls is between R-1.3 and R-1.5 per inch (American Council for an Energy-Efficient Economy or ACEEE). This is much lower than the previously reported range of R-17 to R-54.
We know that a wooly jumper or cardigan can keep us warm but how many of us think about using that warmth to insulate our homes? Wool is a natural, sustainable byproduct of sheep rearing. This makes it ideal for use as wall insulation.
The estimated R value of wool insulation is between R-3.5 and R-3.8 per inch, making it significantly higher than straw.
Did you know that wool is used for firefighter’s clothing? It has high flame retardancy and doesn’t melt when exposed to high temperatures (HD Wool).
As a natural product wool does not emit toxic odors, nor is it a skin irritant, so installers do not need to wear any specialist equipment. This means that rolls of wool can easily be installed by the homeowner in the loft to increase insulation.
Don’t be confused with Rockwool (brand name) or mineral wool batts. Rockwool is made of basalt rock and recycled slag from the steel and copper industry. The minerals are melted and spun into fibers.
Where to buy natural wool insulation
Thermafleece in the UK makes wool and hemp insulation products. CosyWool is available in rolls or slabs. Wool.life in Dalton, Georgia sells New Zealand wool as insulation for both residential and commercial projects.
Hempitecture are American grown and American made producers of hemp home insulation. HempWool thermal insulation is plant based and bio-based, with no VOCs. It is 92% hemp and 8% textile polyester binder. The estimated R-value of HempWool is R-3.69 per inch and it has class E fire resistance.
Cellulose is a natural component of plant and bacteria cell walls. In its natural state, it is not fire resistant so it has to be treated before it can meet fire retardancy regulations (American University Washington DC).
One of the reasons to use cellulose insulation is the high insulation properties. Loose cellulose insulation has an R-value of between R-3.2 and R-3.8 per square inch. That’s higher than fiberglass which is another common insulation material, but cellulose is more sustainable.
The R value of cotton is between R-3 and R-4 per inch, making it comparable with cellulose insulation. We recently wrote about how sustainable cotton is.
Frost King makes foil backed ‘no itch’ natural cotton insulation for pipes and ductwork. It is available in all the major retailers including Walmart and The Home Depot.
Why should I buy eco friendly insulation materials?
The building industry uses a lot of petroleum and oil-based materials for insulation. Polyurethane, phenolic foam and polystyrene insulation have outstanding thermal resistance and outperform natural insulation materials by almost double (Local Surveyors).
In order to get the same insulation levels, you need to use more of the natural materials, making it more expensive to install. So why buy eco friendly insulation materials?
The answer lies in the other benefits of using natural materials. They are eco friendly. They are non-toxic. They are renewable. They can be fire resistant. As with many other environmentally friendly materials the added expense can be worth it for peace of mind about the planet.