Deep litter pig housing, part 2

I've been thinking about the pig shelter.  The parameters I'm after: 

1) No exotic parts.  Everything comes from a local hardware store.
2) Cheap, but durable enough to survive pigs and time. 
3) Easy to repair -- stuff gets broken. 
4) Allows equipment to drive through

I think version 1 of the pig shelter will be a variation on a hoop house.  Metal tubing bent into arches with a tarp or fabric roof, and eventually I'll anchor it to ecology blocks.  

I've looked at a variety of metal tubing sources; most small hoop houses are made of toprail pipe -- this is the pipe that is used as the top of a chain link fence.  It comes in 10' lengths, and is swaged on one end, so that you can fit the pipes together by sliding one into the other.   Here's a picture of the big greenhouse that I put up a few years ago

This is a commercial greenhouse that I bought used, and then assembled on my property.  What the manufacturer did was have every other hoop in this design have a truss.  You can see them in the picture.  A truss makes the arch much stiffer and stronger.  I mention this because this hoophouse has been through three snowy winters here, and 15 snowy winters in eastern washington.  So this is one version of a hoop that will survive the local weather conditions. 

Another way to strengthen the hoop is to use either a bigger diameter pipe, or a thicker walled pipe, or both.   Toprail is 1 3/8" in diameter, and the walls are 17 gauge.   Electrical conduit comes in three different strengths - electrical metal tubing (EMT), Intermediate Metallic conduit (IMC) and Galvanized rigid conduit (GRC).  I'm looking at  IMC or GRC as potential material for the hoops.

As far as cost goes, toprail is about $1/foot, and GRC is about $2/foot, retail price. 

Why would I go with a bigger pipe?  See that truss?  the tractor has to fit underneath it.  If the truss wasn't there I'd be able to use a shorter sidewall and still be able to get the tractor inside.   

Here's the tractor inside this greenhouse after completion.  After working with it for a few years now, I've found that the 30' wide greenhouse is a nice size.   The weather here is cold and damp most of the year, and I've found the greenhouse to be really nice to work inside.  It's light, and usually 20 degrees warmer than the outside.  The plastic seems to be pretty durable, too; 4 year rated plastic is still going strong after 6 years on my first greenhouse. 

The more I think of it, the more I think that i'll go for a 30' wide pig barn. 

As far as coverings go, the greenhouse has a big drawback in the late spring through early fall:  It gets too hot for pigs.  On a partly sunny day it can hit 100 degrees, and on a sunny day it tops out at 135 degrees.   pigs don't do well at that sort of temperature.   But plants seem to do fine...  and that brings me to the 4 season plan:  Fall and winter, pig shelter.  Spring and summer:  Greenhouse. 

Now for the ecology blocks.   I don't know if my tractors front loader can lift an ecology block.  Ideally I'd be using materials that I could move around without having to have additional material.  The blocks themselves are pretty cheap - $15 - and a row of blocks on either side allows for easier cleaning with the tractor.  Just lower the front loader and scrape it out.  Two ecology blocks stacked means that the pigs can't reach the plastic or tubing, which is a good thing.