Barn Post Question

[rswyan]

I have a Menards Pole Barn. It was built in an area that seems to have a high water table. The poles are pressure treated 4x6. There is a concrete pad at the bottem of each hole and then the holes were backfilled with dirt. I think the dirt in several of the holes is constantly wet and now I have what looks like black mold on the poles near ground level.

Any ideas if this is going to be a long term issue and what I can do about it?

You didn't say what causes you to believe there is a high water table ...... or whether the barn has a poured concrete floor or not ..... but ....

First thing I'd do is determine whether or not you actually do have a high water table - dig a couple of holes 3' or 4' deep around the perimeter of the barn and have a look at what's actually down there - see if they fill up.

If you find sub-surface water, then consider installing a french drain system around the perimeter of the barn. If you don't have concrete you could even install some lines inside the barn itself.

If you do not have enough elevation to get the water to flow away from the barn and drain out somewhere you may have to build a sump and then use a pump to empty the sump ...... well away from the barn.

 

[Believer]

Thanks guys. For the gravel crowd, I have creek rock I can put in the hole. How much depth of rock should I put at the bottom of the hole?

 

[wedge40]

Based on what most people are saying, those 100+ year old barns I see still standing are all figments of my imagination.

Its all smoke and mirrors.

But then again thats the same question I ask myself every time this question comes up. I agree that you shouldn't have the "Pressure Treated" post sitting in water so something on the bottom of the hole is good idea, but other than that I'd fill the hole with dirt and call it good.

Wedge

 

[spc]

You didn't say what causes you to believe there is a high water table ...... or whether the barn has a poured concrete floor or not ..... but ....

First thing I'd do is determine whether or not you actually do have a high water table - dig a couple of holes 3' or 4' deep around the perimeter of the barn and have a look at what's actually down there - see if they fill up.

If you find sub-surface water, then consider installing a french drain system around the perimeter of the barn. If you don't have concrete you could even install some lines inside the barn itself.

If you do not have enough elevation to get the water to flow away from the barn and drain out somewhere you may have to build a sump and then use a pump to empty the sump ...... well away from the barn.

When I built the barn several of the post holes filled with water within the 12 hours between digging the hole and setting the post. The barn is located at the bottom of a gentle slope on my property. I didnt have much choice of where to locate it. I do have the drainage down the slope working pretty well. Any water coming down the slope is redirected around the barn. I have a gravel floor and its never wet in the barn.

Arent there different "grades" of pressure treated wood? I had heard that posts used for barn building had a higher level of the preservative chemical. Hope that is true. They use PT post for building docks.... and those posts are submerged 100% in water....

 

[rswyan]

When I built the barn several of the post holes filled with water within the 12 hours between digging the hole and setting the post. The barn is located at the bottom of a gentle slope on my property.

Yeah .... that's a pretty good indication

I do have the drainage down the slope working pretty well. Any water coming down the slope is redirected around the barn. I have a gravel floor and its never wet in the barn.

Good !

Arent there different "grades" of pressure treated

Yup - some are rated for "ground contact" ... I think point 0.60 is the minimum rating for ground contact wood.

I had heard that posts used for barn building had a higher level of the preservative chemical. Hope that is true.

Probably depends on who built the barn ....

Based on the above, I stand with my original recommendation - install a french drain system around the perimeter (not right next to but out a ways to pull the water away from the poles - and inspite of the interior being dry, you may wish to run one or more drain lines in there. Run it to a sump and use a pump with an on/off float switch to drain it out of the sump.

 

[nebraskasparks]

Had the same thing years ago...dig around each post. All the aerobic/bacteria/anything living is going after your wood from the surface down to about 8 or 9 inches depending on your soil. Dig down around all sides of the post (pain in the keyster and very time consuming) and use your spade against the wood and find out how much it has rotted away.
I had to cut one post free by digging down a couple of feet, cut the rotten section out, inserted a new section of treated post, used lag bolts and metal brackets on three sides of the post to attach to old post...cemented around new section. I did this to every single post on the old pole barn and it has paid off. Beats tearing it down and building a new one (like I'm doing now). Most people pay attention to the frost line but they don't pay attention to the rot zone. Most gardeners know that most of the activity in their soil occurs in the first foot.

 

[MarkV]

To the OP, as you can see there isn't a universal "right" answer. There are opinions, regional differences, codes and theories mostly. In my area it is code to use a 16" hole with a 6" concrete donut at the bottom. So for those that think that is wrong don't try and build here. The question of concrete or no concrete is debated often. Many feel concrete will trap moisture against the wood causing rot, others feel it is the only way to ensure longevity. If using gravel as a backfill you have to ask what size gravel. The friction of the compacted fill against the post has a great deal to do with the buildings ability to resist wind loads. Not all gravel compacts well. The engineers that design pole buildings for pole barn companies seem to go with a 4' hole and a 6" concrete donut at the bottom. They have to warranty their buildings and meet national codes.

Regardless of how you set your posts the way to avoid rot is to have your barn on a higher grade than the surroundings and have overhangs on the building. If the water can't get to the posts then they can't rot.

MarkV

 

[77transam]

Wood that is submerged in water will not rot. In order for rot(fungus) to develop it needs oxygen, which is why logs submerged in rivers are preserved for 100+ years.
When the moisture content of air-exposed wood exceeds 20%, that's when rot begins to develop. Once the wood dries out the fungus(rot)spores' growth stops.

 

[buckeyefarmer]

A lot of old 100yr+ barns sitting like a box on the ground, with the posts rotted at ground level, slowly sinking as they rot. Others are sitting on rock foundations and are still solid.

 

[MacLawn]

All I can add is: keep 'er high and dry!