Insulation with best life expectancy and low embodied energy?
I’m researching insulation options. I want to keep embodied energy down, but also want to have something with a life expectancy of centuries, not decades. Although I’ve mostly nixed SIPs (PU) because of it’s high embodied energy, if it lasts centuries while other insulation materials last decades, then should it be considered? I’ve also been finding different opinions on the life expectancy of SIPs. Some people say 300 years, others say 50-100.
Cellulose: At first cellulose seemed like a good choice, but then I read a claim of a life expectancy of 20-30 years due to the paper breaking down over time, but they didn’t provide a source. And then I read in another Q&A thread that Martin’s opinion is it should last indefinitely, but he didn’t provide a source either. So which is true? Does anyone have a real source that they can share? If the cellulose does indeed only last 20-30 years before it needs to be maintained, than that’s an issue, and the embodied energy of service should be included.
How’s mineral wood fair?
Any other materials stand out as good options.
Ultimately, I want my structure to last generations with little to no maintenance.
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Replies
Mike,
Cellulose has been installed in attics for over 40 years, and I've never heard of cellulose wearing out. Old cellulose is still there.
I've seen a lot of old fiberglass, and it looks terrible -- especially compared to cellulose. It is far more likely to be stained with rodent urine and riddled with mouse tunnels.
I imagine that most types of foam insulation will last a very long time, as long as the ants don't tunnel through it and chew holes in it.
Many building components wear out, but I wouldn't worry too much about insulation longevity. Most insulation problems are due to installation errors or water leaks.
Mike, you want your structure "to last generations with little to no maintenance", which means that your selection of insulation material is not nearly as important as the design and execution of your structure. Those SIPs you looked at are notoriously vulnerable to moisture and therefore risky, and so the structure must be designed with multiple redundant safety margins in order to keep them intact. Cellulose is great, and properly installed will indeed last generations, but it too is just one part in a system that can fail if some other part doesn't do its job. I mean, a bad roof can quickly cause damage to even the most resilient house. You could consider cork, blue jeans, and even mushrooms (https://www.thisoldhouse.com/ideas/insulation-made-mushrooms)
Embodied energy is a good factor to consider when selecting insulation, but then so is recyclability, and toxicity, and fire resistance, and ease of installation, and that perennial bugaboo: upfront cost. Controlling for all the individual circumstances, cellulose probably wins this race every time.
Mike,
As you probably know, when it comes to embodied energy, cellulose wins the contest. For more on embodied energy, see All About Embodied Energy.
Cellulose only wins the low embodied energy contest if discounting the manufacturing energy of the paper due to it's being made from recycled or surplus stock. The embodied energy of paper making is still pretty substantial, at about 700-1300 BTU/lb to process trees in the forest into finished sheet paper, which is comparable to (or even higher than) converting sand into glass fiber.
Converting scrap paper into cellulose insulation takes only modest energy input, but if trees were being harvested for the purpose of manufacturing cellulose insulation the embodied energy comparisons wouldn't necessarily be a slam-dunk.
Humidity-cycling cellulose can take a toll, but if kept reasonably dry it should be good for more than a century, maybe even two. But like books not kept in a humidity controlled vault, there will be degradation over the very long term. I've found pieces of 100+ year old newspaper in attics and walls that was still readable, but also pretty fragile.
Vermiculite, perlite, asbestos, and pumice all fill the bill for low embodied energy and centuries long durability. They all have their pluses & minuses. Asbestos and vermiculite would be illegal to install in new construction in the US due to health concerns.
On the organic material front, rice hulls do pretty well- nothing eats rice hulls, and it takes external energy to burn them. Rice hulls are a disposal problem, since they don't compost well, or burn well on their own, both of which are assets in an insulation application. Most estimates are that rice hulls run ~R3/inch in loose fill applications. The silica coating on the exterior is what makes them less-burnable & compostable, but the lignin-loaded cellulosic fiber that makes up most of their bulk makes them less crushable too- the stuff won't settle very much even when applied in VERY deep layers.
Dana, regarding time + humidity cycling of paper breaking it down over time, any thoughts as to how that would affect paper as an insulator in a dense-pack wall application? I mean, the structure of a newspaper seems to break down after 100 years in a wall cavity, but is the mass of the paper reduced or has it just become more brittle/fragile? Would this affect its ability to insulate or remain dense-packed?
Just curious, this is an interesting discussion.
Before going to college 20 years ago I worked for a building supply and delivered to several old farmhouse remodels where they had pulled newspaper from the walls. At one job the paper was from 1908 if I remember right, and though I didn't open a paper and look through it the printing on the outside was clearly legible, the pictures nice and clear. They had set a pile of it aside for someone from a local museum to look through for interesting stories. Neat stuff.
Mike,
I understand the impulse to build an enduring house, but I'm not sure that choosing materials that will last centuries is an effective way to ensure it will still be there in that time-frame for several reasons.
No houses last long without constant maintenance. Stone farmhouses in Europe, Scandinavian wood homes, concrete structures - all descent into ruins in a remarkably short time if uninhabited or neglected.
The factors that affect the lifespan of a house aren't primarily the materials used. They are demographic, changes in the local economy, taste and adaptability. No matter how robust the structure may be initially, if no one wants to live there, for whatever reasons, it won't be maintained and will soon be derelict.
I'm not advocating building with materials that won't endure for a reasonable period, but probably more important is designing a house that can easily be updated and adapted to the needs of future inhabitants.