exterior staircase footers - pylex screw vs traditional piling vs cement footers

[nereo]

Cold-weather climate with frost depth of 42".  Compacted clay with some rocks.

I have to replace a badly weathered and poorly constructed exterior staircase (10 steps or so).  Thinking we'll use the opportunity to build it a bit better (and to code!), with slightly wider treads and a bit wider on the exterior landing.  Regardless the structure will need two 4x4 support posts.  My question is the easiest way of supporting them.

Option 1:  Posts set on pre-cast concrete footings.  around here lots of decks use those cement block on the ground, set on gravel with (i'm told) rigid foam underneath.  Most seem to work, but I've seen a lot of failures (upheavals).  Guessing its poor insulation but perhaps it's inherent.  Plus:  cheap, fast.  This is what is there now. 

Option 2: Traditional posts dug into the ground, set in concrete.  Tried-and-true, but I'm going to need to dig 4' down and mix up several bags of concrete  Would likely need to rent a mechanical post-hole digger to get that deep.

Option 3: Pylex-type screw footer.  From what I've seen these are pretty fast to dig in and require no concrete.  They're $40 a pop but I'd only need 2, so cost isn't a great issue.  Also allows for some vertical adjustment (+/- 3"). 

I'm leaning towards #3 (Pylex screw) but have never used them.  My biggest concern is whether I'll be able to get the screw 4' into the ground without hitting a rock or tree root.  Honestly either are possible in this location.  But that's a problem for Option #2 as well.  Perhaps this is why so many people choose Option 1 around here?

[Sanitary Stache]

Option 1 isn't a long term solution.

I am on sand with an occaisional layer of urban fill, some silt lenses, and very few rocks.  Option 2 is what I would do, but I would try with a shovel and post hole digger.  Dig down the first foot or two with the shovel in a 1x1 square to make going to full depth with the post hole digger easier.  If it took longer than 1 hour to get the first hole to 4 feet I might give up (In my ideal soil for digging it takes about 10 minutes to get to 4 feet).  If the digging was particularly hard with rocks in the way of the post hole digger, I would immediately move to digging the hole with a shovel.  4 feet isn't that deep and its easier to dig around rocks with a larger hole, but the hole becomes much larger. I go 1:1 slopes, but your clay might have better structure and you might be able to have more vertical excavation walls. I like to lay out a tarp to control the pile of dug material and make clean up easier, but I would want to backfill most of your hole with new clean sand or stone...  This is getting pretty expensive.

I convinced myself to try to pylex. I have always wanted to anyway. 

[nereo]

I convinced myself to try to pylex. I have always wanted to anyway.

ha!  Yeah, that's basically the way my thinking has gone.  I don't like the pre-cast footers set on the ground, so figured I would "do it right" and put posts down 4' in concrete (#2).  But then thought of all the work and mess that would make, so I started thinking "hey, a $40 Pylex screw sounds way easier".

FWIW I've known a few people who built their decks this way in Canada.  For some reason it doesn't seem to be as common here in the US... maybe because msot of the states have lower frost-lines...?  In the Canada home Depot they;'d sell 66" Pylex screws (here they are 50", unless you special order).

[lthenderson]

I'm not sure why option 1 isn't a long term solution. In my opinion, that is the best tried and true solution. Getting concrete on firm clay below frost depth assures that you won't get any heave. By attaching a post to the top of the concrete footer above ground level using stainless brackets, you assure that moisture rot from rain won't be an issue though air moisture still will but you can easily replace it when that time comes.

Option two is the worst. Most posts you buy are green meaning they will shrink as they dry. That means that one set in concrete essentially becomes one set in a giant cup filled with water. Once it rots out, they are a bear to replace because you have to lift dig out that mass of concrete.

I don't have any experience on the ground anchors you mentioned. In theory it looks like it should work but my concern would be two fold. One, all the weight is resting on a very tiny amount of surface area. I would think you would need very specific soil conditions four feet down to ensure it wouldn't sink more under load. Concrete footers are sized by load and soil conditions as well and I've never seen one that small. But a stairway would have very little load so it might be alright. My second concern would be them being made out of steel. Any nick or scratch would be a conduit for rust. But I have dug up some very rusty and heavy pieces of steel out of the ground before and it would probably last a lifetime for most people. Not sure it would outlast a concrete footer but if the price is right, I might consider this option for your application.

[nereo]

I'm not sure why option 1 isn't a long term solution. In my opinion, that is the best tried and true solution. Getting concrete on firm clay below frost depth assures that you won't get any heave. By attaching a post to the top of the concrete footer above ground level using stainless brackets, you assure that moisture rot from rain won't be an issue though air moisture still will but you can easily replace it when that time comes.

Option two is the worst. Most posts you buy are green meaning they will shrink as they dry. That means that one set in concrete essentially becomes one set in a giant cup filled with water. Once it rots out, they are a bear to replace because you have to lift dig out that mass of concrete.

I don't have any experience on the ground anchors you mentioned. In theory it looks like it should work but my concern would be two fold. One, all the weight is resting on a very tiny amount of surface area. I would think you would need very specific soil conditions four feet down to ensure it wouldn't sink more under load. Concrete footers are sized by load and soil conditions as well and I've never seen one that small. But a stairway would have very little load so it might be alright. My second concern would be them being made out of steel. Any nick or scratch would be a conduit for rust. But I have dug up some very rusty and heavy pieces of steel out of the ground before and itwould probably last a lifetime for most people. Not sure it would outlast a concrete footer but if the price is right, I might consider this option for your application.

To be clear, option one doesn’t involve any digging... below frost line or otherwise. The concrete footers are placed on the ground over a layer of gravel which is insulated with foam. Extremely common, but also seems to fail frequently, though I’m uncertain if that is due to the method or execution (I suspect both are at fault)

Option two is what most builders use around here for larger decks when pulling permits. Definitely the most work. Typically sonotubes are used for the form, and 3” of gravel to keep the post above water. The old-timers swear this method will last 25 years when done right

Pyrex screws seem much more common in Canada. Not sure why there is such a difference in building practices given a similar climate to us

[lthenderson]

I totally misread that. My preferred method is the sonatube form set below frost line and ending up four to six inches above ground level with a bolt for an anchor bracket embedded into the concrete. I like to have them elevated above the surface so that water never gets near your post and after you add rock to prevent weeds from growing, they end up flush to the surface of the rock and hardly noticeable. 

I don't understand the physics of how number one is supposed to work. With the insulation between the concrete block and gravel set in the ground, which way is it preventing thermal transfer? I definitely wouldn't go that route as I now understand it. I've never seen it used around here either.