Natural insulation for Corrugated Metal Roof

Hi everyone,

My family and I are thinking about our first serious build for a communal space on our land in the semi-arid area around the city of Fundão, Portugal. I'm very keen on water capture because we have a very limited water supply and when it rains, it rains for a year (and then not again for another 7 months); plus I'm a complete amateur, so I like the idea of smooth, simple corrugated surfaces as a roofing material.

The issue that immediately arises in my mind is that corrugated metal does not offer much in the way of protection from extreme heat and cold (both of which we are blessed with). Can anyone suggest some good insulators that can be used for roofs?

Thanks,
Freyja.

Within natural materials you have:

hay
ash
wool

you can make pillows and fill the structure beneath the roof with them...

Okay great. Thanks for your reply. Given the abundance of sheep and goats around here I think wool makes sense. My concern with this is that filling a compartment in the roof with wool is likely to create good habitat for mice, who may then make a nest there. Is this likely? If so, is it as problematic as I think it is? Is there a way of getting around this? In terms of not creating habitat for food-eating little friends, ash sounds like a better option....?

To be clear, when you say filling the structure beneath the roof with pillows (I love this idea btw), I guess you mean that we would need to build a sort of false roof that would be the ceiling of the room..

you can take some good ideas from this image search: https://www.google.pt/search?q=roof+insulation&safe=off&espv=2&biw=1025&bih=927&source=lnms&tbm=isch&sa=X&ved=0CAYQ_AUoAWoVChMI1Om2tNmPxwIVxQfbCh2RugCt

Rats could obviously an issue, but if people are using rock wool in roofs it seems, to me, feasible to admit the use of plain wool in it's place...

Hi Freyja,

Can you share any more details about this structure? Since you are talking insulation, this implies a fully enclosed, heated and/or cooled building? Don't want to assume anything. As with so many threads, the more information you provide the more people can help!

As far as mice/rats/pests in general, I have read more than one account of rodents gleefully tunneling into and inhabiting all sorts of artificial insulation; rigid foam boards, spray foam, etc. I would think that most types of insulation would be fair game to them, and thus you'd need to keep them out by making the insulation space rodent-proof.


Other insulating materials that might be considered natural:
cork
sawdust or wood shavings
You wouldn't want to use hay in most cases, but straw is a good option
other waste agricultural products of various sorts; rice hulls, corn husks, nut shells
combinations, including light-clay, cob; mostly a mix of some sort of earth and a better insulator

You could make a case for rock-wool being natural...depending on definitions. Ditto for other manufactured expanded mineral products like perlite/vermiculite.

There are also a variety of interesting modern manufactured green insulation options I've seen mentioned in excited press releases or new articles... but if any of them are actually readily available and affordable, it's news to me.

I would expect that most installation options would include a ceiling below the roof, creating a space between the ceiling and the roof for insulation. If you specifically want to avoid this, you're limited a bit; suspended pillows or draped fabric with lightweight insulation above it, or something which can be attached directly to the underside of the roof without detaching and falling on your communal heads... I'd go for a ceiling, myself! Just having this enclosed area above the inhabited portion of the building will help insulate.

Furthermore, if you have a peaked roof, building a ceiling/attic would save on insulation, as you can put the insulation on the flat floor of this space, covering less area than the sloped roof.

Hi Dillon, i mostly agree with you, just a small correction: earth is not insulation. it's thermal mass. So it should not be used as insulator.

I was particularly interested in your suggestion on corn husks. In your opinion is it a heavy or mild insulator? What about decay? Have you got any experience with it you would like to share?

Freyja, i hope you don't mind me sidetracking

Hi João,

As far as I understand it, dry earth does insulate to a slight degree as well as providing thermal mass, but it's *quite* slight. Maybe somewhere around R 0.125 per inch. And if wet not even that. Certainly it would not be practical to use straight soil as attic insulation.

I'd included earth in that list more because it plays a role in combination insulators like light clay and cob, but this morning that doesn't seem quite so logical! Removed it for clarity, thanks for pointing that out.


Unfortunately I have no direct experience using corn husks. I saw a reference to a modern insulation that used them as a base, and thought they might be usable in a similar fashion as other agricultural byproducts like straw. It seems like most possibilities of this sort were used somewhere at some time.

It would be interesting to see if they could be used in light clay in place of straw.

The modern insulation article is here, never heard of it since. https://www.newscientist.com/blogs/shortsharpscience/2009/05/insulation-made-from-corn-wins.html

The only other mention I turned up in a quick search was in the book 'The Pattern Under the Plough', which mentioned corn husks used to insulate the floor of the second story; apparently they rain fine dust in heavy winds, but the house in question was probably about 400 years old.
https://books.google.ca/books?id=NEZj1cwXzwcC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

Corrugated metal (galvanised iron or zincalume) is standard on housing here in New Zealand. People use a variety of commercial insulation under it, including wool batts. There are some issues with condensation, and so in a consented building there needs to be building paper or some other kind of barrier between the batts and the metal. That's even in a dry climate.

The thing about insulation is you want the best loft/air space within it, that's what creates the insulation. This is the dilemma for DIY insulation. Commercial insulation designs for gravity over time to stop compaction of whatever material. So commercial wool batts have a small % of synthetic in them to create a structure that doesn't slump. I think there is a lot of potential for DIY insulation but I don't see this issue being resolved very well in discussions. Either you have to build smaller cavities for the insulation, or you build something that can be removed and fluffed up every few years, or you accept a lower degree of insulation value over time (as well as loss of loft, the slumping can create gaps between insulation and thus heat leaks), or you find something that doesn't slump.

If I was working on an experimental building I'd use DIY insulation from local materials. If I wanted a low maintenance, worry free building I'd go for commercial wool batts because where I live it's the best option available in sustainability terms (actually the only option, all the others are either synthetic or use toxic chemicals).