My opinion is cedar posts in MA are going to rot in about 2 years. Tell him to use PT. 42" is fine, but use well compacted gravel as backfill, not concrete.

 

wants to know how deep he should set fence posts. No cement, just cedar posts

fuggetaboutit

 

My bro used to be cabinet/furniture maker (REAL GOOD) up country, but now he's here in Mass doing general carpentry (I keep telling him, don't work out of trade :laughing.
Anywho, he called last night and wants to know how deep he should set fence posts. No cement, just cedar posts for a 48" stockade fence. Six feet between posts. Post will be 53" above ground. I immediately say 48" (standard here in Mass for below freeze).
I guess he would really like to use eight foot posts because he's wondering if 43" is enough. Any opinions I can pass on ?Thanks

If it's Eastern red cedar, it's probably good for 20 years with a gravel base.
Course they cost about the same as solid copper 4X4's.
Western red cedar, might last 10 years.
If he gets the new PT SYP, it barely looks treated at all,
and is supposed to take stain much better than the older stuff.
(Tags say "MicroPro")
Why would he want to take the chance of it heaving to save a couple of bucks?
That said, with established sod all around it rarely freezes to the "frost line".

 

POST SETTING--The difference between a post life of 8 years and 30 years.
http://prowellwoodworks.com/gate/postholes.htm

we took out a 40-year-old cypress fence in Jacksonville Beach last winter. Oceanfront. That's pretty rugged.

 

I'd have to disagree with the information on that link. I've torn down lots of decks where the cedar post (WRC) were installed like fence post & they were rotted bad after 15-20 years. We have alot of termites here that only make it worse as they come up the post from the ground. Even tho TP post will check, warp, ect. I think they are a better choice over cedar. The local cedar (actually juniper) here holds up much better than WRC as they are mostly heartwood. Those will last 30 plus years & still not be rotted. If you look at the end grain of the post & chose ones that come the center of the log they will be the best ones to use regardless of species.

Al

 

Thanks all,

I appreciate all the thoughts about retarding rot, but my brother's question was only about the depth the posts should go.

My parents (and his too - although neither of us will admit it :laughing: ) have always surrounded their homes with 8' high cedar stockade fences from "Walpole Woodworking" here in MA (can guess which town arty. They last a little longer than twenty years. When I bought this house, I made my own fence around the swimming pool and used 4x4 PT. In the 16 years it's been up, only one post has completely rotted. So basically whether cedar or PT, life expectancy is around twenty - unless you can get your hands on some creosote, but since that is illegal, none of us would even THINK of doing that . . . . RIGHT?

 

The "code" frost depth is meaningless for a fence.

For a structure, it is important since any cracks caused by heaving will destroy the servicablity and appearance of the structure. That is why there is a specified depth for building footings.

For a fence, a little heaving is not easy to notice and does not destroy the servicability of the fence. If it comes back in the spring, there is no problem. If it stays up, no one will notice and there is no problem because it usually moves with the soil.

The depth required structurally is determined by the soil's resistance to lateral loads and the area of the material in the ground. Obviously, a thin metal post needs more depth than a wood post because of the width. The wood post will need more depth than the same width post set in a wider concrete base.

The durability of wood varies widely depending on the LOCAL species available. There is also a range of effectiveness of pressure treated wood depending on the type of preservative and the concetration. The durability of the post also depends on the amount of wetting and drying cycles, as you would expect. A wood post (any type) will last longer in concrete that projects above ground that another wood post that is in the concrete that is 100% below grade because the first situation keeps the wood moisture content more constant (no wetting and drying). Piling for piers rots and deteriorates just above the low water line where the wood dries out and gets saturated on a regular basis.

As a comparison, a rough sided post or a hand dug post hole will heave more from frost than a smooth, waxed Sonotube that is frequently used for a good deck installation

There is no absolute right or wrong way for fences in all climates, since it depends on the post size, soil type and installation method.

 

Thanks Dick,

I wish I had your post to reference before I called him.

He definitely has some "old world" knowledge about keeping a fence post from rotting. Although I've always noticed it, I've never really thought about the fact that the posts rot first within the first 12 inches of grade (give or take). That's where all the "aerobic organisms" (I think that's the term he used) live (little beasties needing air that love to eat organic material). We all seen wood buried DEEP in the ground for decades that look pretty good when excavated, and we know about underwater wrecks that need stabilization when they are salvaged hundreds of years later because oxygen immediately rots/rusts them.

He's had luck even with spruce whose butt end and first 12 inches below grade are sheathed in copper. Little pricey though. And I guess he's scorched the wood that is below grade. And backfilling with any material that does not hold water is always good also - not only to prevent rot, but also to mitigate the freezing of the ground.

After listening to his dissertation on all this, I began to wonder WHY was I asked the question in the first place? He seems to have a pretty grasp on what needs to be done !!!!

 

I would hardly say "frost depth is meaningless for a fence". Granted soil conditions may determine different depths, but i live in the north east and if i ignored frost depth the fences would end up looking like roller coaster tracks. I would never use cedar post,there generally only good for a few years around here. Our min depth is 30" for wood or chainlink,regardless of pipe or wood size for a standard residential fence, however if its a large commercial fence/gate with a 4"-6" or 10" pipe the hole will be deeper ,36" or better at the min. I have seen the ground freeze to almost 20" before,and spent hours digging one hole(in the middle of what use to be a puddle) I have seen plenty of heaved fences before, its ussaully chain link , hole is dug about 24" ,12" of dirt thrown back in and then topped with a foot of cement. Here on long island there are a few different types of soil conditions,Basic soil ,sandy ,clay and lots of stone on the north side (an area i try to stay out of) The 30" min rule works for most fences here. 6' Stockade is around 64" to the top 2x3 , add 2" above the rail and you have 66", leaving 30" in ground, making a 4x4x8' the proper size post. Chain link pipes are different, putting up a 4' fence ,you buy 6' post.Terminal is 50" above ground, line is 46" above ground, leaving 22"-26" in ground. The mistake here is people think what ever is left over is all that has to be cemented in, wrong, hole still has to be at least 30" deep with concrete.

 

nywoodwizaed -

Glad you agree that the "code frost depth is meaningless".

There are more factors (soil, diameter, line or terminal, etc.) that people do not realize that can increase the depth.

 

post depth

Up here in WI I recomend going 4' deep (frost Line). It may not be needed foe support, but frost does terrible things to post. Someone said that a little heaving is not noticeable. I have to greatly disagree. If a post a 1" higher than it is supposed to be it looks bad. I also recomend gravel to set posts. You will have far less frost heave, and if it does heave you can easily fix it. If you set a post in concrete and it heaves, how do you fix that? You end up digging it out and resetting . This can be an hour job, compared to a few minutes with a sledge when set in gravel. If you are setting your post in concrete, the only right way to do iti s to use a sono-tube, and very few do this because of time and cost. I do not install fence, just sell material. Mostly contractors, and mostly vinyl fence. I still have a few that use concrete to set post, mostly dumping a dry bag into the bottom of the hole then filling with the spoil. These guys have more problems than those using gravel. 3/4" clear gravel works best.
Mark