preventing wood rot in shed timber

We have a tractor shed at our new house, with a side roof for wood storage. It's fine, does its job, etc., but the side storage columns are sunk way into the dirt.



We're waiting on a friend to help us dig out a bit more space there, and will add gutters for rain collection. As we do that, we're wondering about what might be better than dirt up against the wood posts, to slow down decay. There's concrete at the base of the posts. Do we backfill with gravel? And is there something we should put on the posts (which I believe are already "treated").


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Well since it is just holding up that awning, I'd cut them short and set them on pier blocks. Seems to be the quickest, cheapest and easiest thing to do.

I suppose if it gets windy enough that might be a no-go. But even then, just pour your own little piers with some anchoring. Concrete isn't permaculture but I don't like to mess around with my "real" structures.

Dan Fish wrote:Well since it is just holding up that awning, I'd cut them short and set them on pier blocks. Seems to be the quickest, cheapest and easiest thing to do.

LOL, I hadn't even thought of that! Of course! And doing it that way, it actually isn't an emergent project. I could put it lower on the long list, since at least for now there's no rot in sight!?

Oh I totally hear that. It could buy you a few years to catch up! I only bought my place 3 years ago so according to my neighbor just 2 years to go til I can rest!

I think the concrete base must be tiny, and needs its footprint enlarged.
Adding those stirrups as suggested would be smart, but widen the base first.
This link may help you
Rainfall collection

Usually the rot happens at the soil/air edge, the less dirt-to-wood contact within the first 3-4 inches the better and at the bottom where it's anaerobic that might last the longest. Have any leftover/recycled plastic sheet you could wrap around the wood, then backfill with gravel?

If the posts are treated they should last 10 years in the dirt. And if the dirt at the base stays mostly dry (the drier the better) maybe longer.

My Blacksmith shop has natural Pine log posts that are sunk in the bare dirt, but I have a large overhang so they don't get wet and I haven't noticed any rot in these last 4-5 years.

Hello,

These are some options that I know are in use here in the UK, particularly within the "Natural Building" community who generally eschew the use of cement. I was taught about these by Adrian Leaman on a roundwood framing course that he ran earlier this year. I've added some images, hastily thrown together, to illustrate my descriptions.


Post-in-Hole:
This is where the post sits inside a hole dug in the ground. The depth of the hole should be "as deep as you can easily reach". Place a flat stone in the bottom of the hole as a solid base (unless you've hit bedrock - lucky you), seat the post on the stone and add gravel to fill the rest of the hole. Use a tamper as you fill, tamping each layer 3x to ensure it's well seated. The diameter of the hole should be width of post + (2 x width of tamper).

Gravel is used as infill because it drains freely and keeps moisture away from the wood.

Pros:

Quick and easy

Rigid, no need for wind braces

Cons:

Will rot at ground level, eventually

Uses larger posts to resist rot

Sleeved Post-in-Hole
This is a variant of the above that uses a commercially available sleeve made of a bitumen-soaked material. The sleeve is placed over the timber at ground level (which is almost always the rot point) and prolongs the life of the timber.

It may be possible to DIY a sleeve using old cloth and tar but I have no experience of this.

Pros:

Greater rot resistance

Cons:

Reliance on [another] commercial product

Bitumen is quite nasty stuff

Above Ground
This is the best solution in many cases, although there are drawbacks regarding stability when building (it needs propping up!) and the need for extra wind-bracing. The post sits on top of a stone plinth/cap which spreads the downward load across the pit foundation. The slate on top of the stone prevents water from wicking up into the endgrain of the post (as slate is impermeable to water - you could also use EPDM/rubber/pondliner or even create an air gap using metal fixings).

The hole should be about the same size as for Post-in-Hole. The infill is 0 - 75mm3 road base rather than gravel. This is because it compresses better when tamped and forms a better foundation - the gravel was desirable more as a means of improving drainage.

Pros:

More durable than other options

Cons:

More aggregate required

Needs wind bracing

Thanks for all the great responses. I'm leaning toward Dan's pier block solution, improved by the addition of a gravel infill underneath. There is actually a good wide cement base right now under the posts - just hard to see with all that dirt! So I can easily choose any of the solution you describe, Luke. Those illustrations are very helpful!

Luke Mitchell wrote:Hello,

Above Ground
This is the best solution in many cases, although there are drawbacks regarding stability when building (it needs propping up!) and the need for extra wind-bracing. The post sits on top of a stone plinth/cap which spreads the downward load across the pit foundation. The slate on top of the stone prevents water from wicking up into the endgrain of the post (as slate is impermeable to water - you could also use EPDM/rubber/pondliner or even create an air gap using metal fixings).

The hole should be about the same size as for Post-in-Hole. The infill is 0 - 75mm3 road base rather than gravel. This is because it compresses better when tamped and forms a better foundation - the gravel was desirable more as a means of improving drainage.

Pros:

More durable than other options

Cons:

More aggregate required

Needs wind bracing

Treated 4x4s are typically rated for ground contact, and may last 20-30 years or more depending on conditions. If there is currently no sign of rot at ground level, I would just backfill (preferably with gravel) and let it be.

Does it need posts connected to the ground? Pivot the posts 45 degrees and attach the to the side of the shed as a triangle. Do it right and it should outlast you!

James Alun wrote:Does it need posts connected to the ground? Pivot the posts 45 degrees and attach the to the side of the shed as a triangle. Do it right and it should outlast you!

That's a cool idea. With the height of that side roof, and the height of my head, I believe one of us would be hurting at some point, though!

Don't forget about scalene triangles. Take the supports and attach them above the roof attachment. The only difference is that now the roof is in compression and the supports in tension. Ideally, attach the supports as high as possible, this decreases the load on the joints and increases the stability of the triangle (wind, snow loads).

But first, if it ain't broke, don't fix it. If the posts which are bearing on solid concrete footings are not beginning to fail, I see no reason to think about alternate construction methods for this shed roof support. Brainstorming methods in general is fine for other situations.