Thread: Is it possible to insulate galv iron sufficently?

Originally Posted by do-it-dog

We are building a small (40 sqm) cabin in the country with hopefully all the passive solar benefits.

My question is - is it possible to insulate a building sufficiently that's clad in galv iron (walls, roof)?

(We are building in a heritage zone that has a lot of galv iron architecture (sheds/barns). We'd prefer to build straw bale but suspect we in a potential flood zone - backs on to a river).

Any thoughts?

Hey Dog....let's face it, what's a space capsule but a small, round cabin made of metal. They insulate THAT!

I'd be looking into styrofoam panels, checking the R rating, and then go from there. These days, you can bond anything to anything, and if you can find a material that would address the obvious problem of the corrugations, you're home and hosed.

We've been thinking about a second story on our home, and there are manufacturers who make modular panels made of a sandwich of hardiflex, styrofoam and gyprock...virtually ready to paint on the inside, and fabulously well insulated.

I'd suggest talking with a foam supplier. Of course, if you are lining the inside with plasterboard, there's all manner of possibilities, such as blow-in stuff.

Some ideas for you....hope they get you going!

Michael

Like Cellist said - it's the whole walls insulation value that you have to work out.

The galv iron has a R value of approx zero, but it's only the outside layer. The interior lining and any insulation you stuff inside the wall has to be added to the walls total. So if you put a good insulator between the interior lining and the galv iron outside then the walls total R value will be good.

Same for a roof, plenty of insulation on top of the ceiling and you will be fine. The attic space wont be well insulated, but the rest of the house can be.

Ian

I wouldn't put any insulation hard up against the gal. Mind you, I've had no practical experience with the spray on expanding foam.

I'd remove the gal, line the walls with Solartex or a similar reflective foil insulation - shiny side out - then replace the gal sheets and add any further insulation from the inside: batts would be simplest. Perhaps add the batts & then the foil while the gal is off to minimise effort?

The foil lining provides an air-gap between the gal and the interior insulation which, as well as providing a modicum of insulation itself, more importantly adds a moisture barrier so that any condensation on the inside of the gal isn't trapped where mould can get a start...

The neighbour next to our block used rockwool to insulate his steel frame and Colourbond house.

Another option is a material known as Ritek http://www.ritek.net.au/. It is two sheets of corrugated iron with insulation in-between and can be used to span larger rafter gaps than normal.

Just a small note, before insulating the walls the most important thing with iron is proper eaves. Keep the sun off the walls as far as possible... hence the typical Aussie verandah right around the house. Obviously, the roof is the issue, but if it's a tin cabin and you aren't throwing a pile of money at it, I'd have nice wide eaves, a well insulated roof and plenty of windows....

If you want to line your walls with an eco product that has a hi R-value though (not as high as styrofoam it must be said), there is a sheet product called AMPAN http://www.geca.org.au/Ampan.htm made out of compressed rice straw. I've not used it myself but a friend who does a fair bit of eco building near Lismore uses something similar and loves it. I think it's made in NSW too.

Berlin

As Skew said a layer of foil in contact with the iron and then batts is the most practical
I'd use glass batts or rockwool batts, theres no chance of heat burning them.

Blue Scope of the other mob make a variety of gal iron sheeting which has aluminium foil bonded to the inside.
the physics is that a smooth shiny surface is a poor radiator of heat so when the gal iron heats up in the sun, the heat is preferentially re-radiated from away from the building – with normal gal iron approximate equal amounts of heat are radiated inwards and outwards.

I'd go for this material plus wide eaves and an air gap between the cladding and any insulation

if you want passive solar, you will need some form of heat mass
what do you have in mind?


ian

I going against the grain... get some Permastop
It goes hard up against the tin as the tin is screwed down over it, its a foil backed glass wool, just built a little shed using it.
At 41° its still hot but not unbearable, if you insulate the inner walls with say r2.5 batts and 100mm permastop under the tin it will give you r4.8 not including the r value of the inner walls and any air space.

Thanks!!! I get more good avice from you experienced and hands-on guys than from any other resourse.

We are currently thinking of using concertina double sided radient barrier foil - roof and walls - with an air gap - along with R2.5 rated batts. And taking advantage of all passive solar principles (north facing, big eaves, deciduous trees on the east and west sides etc).

Although now I'm investigating Permastop (your land is beautiful Harry) and AMPAN (I like the sound of that) and Ritek, which may change everything.

Originally Posted by do-it-dog

We are currently thinking of using concertina double sided radient barrier foil - roof and walls - with an air gap - along with R2.5 rated batts. And taking advantage of all passive solar principles (north facing, big eaves, deciduous trees on the east and west sides etc).

I think you'll find that probably gives the best R-bang for the buck.

Not because it's "better" but because it's a common, well-tested method of insulation and there are multiple mfrs vying for the same market share.

"do-it"

If I were you I'd still investigate foil backed "wriggley tin"

Gal iron has almost zero thermal mass which means that it heats up and cools down very rapidly
when hot approximately 50% of the radiated heat from the sun is transmitted into the building where you have to either extract it and/or use insulation to keep it at bay.
The foil backing to the gal iron greatly reduces the amount of heat radiated into the building.

a layer of thin sarking and then an insulation layer may achieve similar results.



ian

A double shell of gal is also a possibility - separated by 2x4's, make sure there is an air gap that runs top to bottom all round. The air between the layers becomes super-heated and makes its own breeze sucking air in at the bottom & shooting the hot stuff out the top.

As you are 'country', another possibility for the roof is to cover it with solar power panels - again, the air gap means the roof with generate its own breeze & move heated air out of the gap. Think of the Federal Govt. subsidies

Ianab - do you know if timber (weatherboard) has the same or similar R value as galv iron? I'm just considering my options. Will definitely investigate the foil backed wriggly tin.

In reply to the other Ian - the floor will be concrete either polished or with crushed limestone finish.

Otherwise true north facing, 3rd of the northern wall glass, sufficient windows on the other sides for light and air, decent eaves, deciduous trees on the east and west faces and probably deciduous vines covering the east and west walls as well (could quite happily cover the entire house/cabin with them which I guess would add another level of insulation).

Might upload my drawings on here.

worth a look

http://www.sydneycityroofing.com.au/...ing-paint.html