floor and ceiling insulation

This question is directed to Jim and Bob, but please anyone with experience respond

In your experience, what are best practices for ceiling and floor insulation in a cold/wet climate (Northern Michigan). For example is it common to use bales in the ceiling and floor?  Seems like many times some kind of sprayable cellulose is used instead.

Thanks for you commentary - book looks great!

Hi Bri,

Many have experimented with straw bales as both ceiling and floor insulation, and both are now widely discouraged.  Buildings lose most of their heat through ceilings because warm air rises, so it's no surprise that building code minimum R-values for ceilings are often twice or more than what's required for floors.  Here in S. Oregon the minimum wall insulation is R-21, and ceilings are R-49. In colder places more insulation in both places is a good idea, and may be required.  

We know that straw bales are rated at R-1.55 or R-1.85 per inch, which is based on their density--a minimum of 6.5 lbs./cubic foot.  If your required ceiling insulation is R-49 (it may be higher where you live), divide 49 b 1.85 or 1. 55, and you’ll see how many inches of densely compressed straw bales you'll need above the ceiling--between 26" and 31."  Not only do bales not come in those dimensions, but that's a lot of weight!  So you'll need to use extra lumber in the ceiling framing to support the weight.  While we know straw bales burn about as well as phone books, unless you plaster the tops of the bales in the attic they would potentially pose a fire risk as they are otherwise untreated, and that adds even more weight.

Straw bales under the floor, if in contact with the ground, also fare poorly--they decompose.  If stuffed between floor joists in a crawl space there may be ways to keep them dry and less likely to be a fire hazard, but that's where other types of insulation work better.  

There are just some places where more natural materials like straw don't do well, and we need to substitute things like blown-in cellulose for ceiling insulation, or foam insulations that aren't damaged by moisture for below grade applications, or use recycled cotton batt, fiberglass, or rockwool for crawlspace insulation.  

It's a trade-off.  It’s very difficult to build a high-performance building to code with entirely natural materials.  I try to make reasonable compromises, with the goal of building with “mostly” natural materials.

I’ll second the OP’s question. I’m not going to advocate any manmade insulation ceilings. Looking for natural alternatives if anyone knows of any that have high insulation value?? This seems like a major weak area in construction.

For the last few weeks I’ve been insulating my self built home attic with sheep’s wool from https://havelockwool.com

It’s been awesome. Would recommend.

Hi Jeremy, Scott beat me to the suggestion to use wool--an excellent and light-weight alternative!  I have seen it used for ceiling insulation on two projects and know the homeowners are very satisfied with it.  I imagine it would perform well as floor insulation so long as it was under a floor above a well-ventilated crawl space.  On the horizon (I hope) in N. America is blown-in straw, with a weight and R-value similar to blown-in cellulose...which is also plant based, although processed in that it is recycled paper waste that has been treated with borate or some similar substance that is both a fire retardant and has repels insects.  This is already available in Europe (https://www.iso-stroh.ch/en/) and in my view, the technology couldn't arrive in North America soon enough!  Apparently there have been pandemic related supply chain disruptions for cellulose, which may also be related to the significant decline in newspaper publications.  My local paper, the Medford Mail Tribune just ceased print publication and is now available only on-line.  I understand that newspaper is a huge part of the waste stream that goes into blown-in cellulose as we have known it.  And although drought in grain-growing regions of N. America can influence crop yield and thus straw (a "waste product" of grain production) availability, it doesn't seem that grain production will suffer the same fate as newspapers.  

Still, new materials and sources come along, and may prove useful.  For example, every autumn I shred dried cornstalks and the flowering spikes of kniphofias, commonly known as Torch Lilies or Red-Hot Pokers.  Both produce a light-weight mulch almost like foam peanuts.  As I mulch trees with this material I sometimes wonder how it might perform as a wall or ceiling insulation?  Who knows what some enterprising individual might one day stumble upon?

Jim
Many Hands Builders