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abraham 04-23-2010 10:24 AM

Brick mailbox in MI
Looking for advice/suggestions on how deep to dig my foundation. The frost line is 42" and thats how deep I was going to go but dont want to do the extra work and spend the extra money if this is overkill. I keep reading online to just pour a 8" slab, but what state are they in. Should I go 42" or just do 8"?

DangerMouse 04-23-2010 11:29 AM

Hi and welcome.

Is this to be attached to your home?
If it's just an "up by the road" mailbox, I'd go 8". That should be more than sufficient for many years.


abraham 04-23-2010 12:52 PM

It is an up by the road mailbox but I want it to be straight in 35 or 40 years. I plan on being here for at least another 20 and dont wan to have to build it twice.

DangerMouse 04-23-2010 12:55 PM

How wide of a foundation? ?X?


abraham 04-23-2010 01:15 PM

2'x2'x? I was thinking of using block if I go 42". Just need some opinions.

DangerMouse 04-23-2010 01:37 PM

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I'd be more inclined to worry about block movement than solid concrete. If you want to overkill a bit, go with 2' deep X 2' X 2" wide. If worried about frost heaving it, perhaps put a 1" foam square form around the four sides? (not the bottom though, pack some gravel there first.) That should cover you very nicely.
I've never done what you're doing before, it's merely my opinion.
Other opinions here may vary by location, and/or mental stability.

My mailbox post is concreted to the ground, as is an upside-down welding tank with a sparkly green bowling ball PL Adhesived to the top.
It keeps the random drive-by baseball batters at bay nicely where it's positioned and it's solid as !@#!
I pity the dumb@$$ that tries to whack it thinking it's a glass globe or something.....


abraham 04-23-2010 02:38 PM

appreciate the opinion. Looking forward to more. Just as a side note. I was going to use 4" hollows for block then fill with concrete. Frost heave is my main concern. I just don't understand why code for footings is 42" but yet a mailbox wont heave? I would just think as tall and skinny as it is it would not take much movement to make it crooked. Just seems to me that if the frost line is 42" and one only goes 41" or less it is bound to move. But I don't have much experience in this area hence why I am posting the question. Again, thanks for your reply and looking forward to any other conversation/opinion/suggestion I can get.

DangerMouse 04-23-2010 03:02 PM

No problem, I'm in W. Mi. and have never really had any problems with heavy freezes, but we're a ways away from the lake too. We get pretty nice weather here.
I don't think a 2' solid concrete square would move


abraham 04-23-2010 04:17 PM

Well if it can move a whole house I'm sure it can move a small mailbox and 2' slab. Otherwise why would the 42" rule be in effect. Not trying to argue or anything, just trying to get to the bottom of this issue. I dont understand why a house needs a 42" footing or a fence, etc... but a sidewalk or paver patio does not, and does not seem to heave. I dont know, I just want to make sure I dont have a crooked mailbox in a few decades or less. I have seen them and always figured it was because they did not go past the frost line? I'm in E Michigan by the way and just trying to find out whats proper/overkill/inbetween. I just got my builders license and they state 42" so as not to get frost heave. Then again they are talking about buildings. I would assume if a building would heave then a light weight mailbox would surely? I dont know. Hope to get more folks to chime in. Thanks.

NJ Brickie 04-23-2010 06:43 PM

You can't go wrong by going down to the frost line. It would be your best bet. I would pour the footing and if you want a 2X2, I would lay two 12" block next to each other with a 8" block on the end to make up the 2X2 pier.To just below grade. Just alternate the end with the 8 every course. I think that way would be easier for you to keep it plumb and level and would be faster.

You could do it on a concrete pad just below grade, but you will be risking movement. You never know it may last it may not? What you said about a sidewalk or paver patio is not true. They do heave all the time. Pavers are a flexible system designed for movement. Sidewalks heave all the time.

kwikfishron 04-23-2010 06:55 PM

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It's just a mail box. A wider footprint is better than deeper.

NJ Brickie 04-23-2010 07:12 PM


Originally Posted by kwikfishron (Post 432683)
It's just a mail box. A wider footprint is better than deeper.

You are right it is just a mail box. But the right way to do it is to go to the frostline. Wider is not better than deeper:no:.

concretemasonry 04-23-2010 08:31 PM

abraham -

If it for a mailbox it also may be on the state , country or right-of-way. When you are dealing with supporting things along roads or where there at buried utilities, so you may not have virgin soil. - Just another concern for determining the depth. Do you own the land the mail box is going to be built on?

Are there any requirements by the post office or local government agencies regarding set-backs or construction requirements? In some northern areas, there are requirements for swing-away mail box supports to save them and prevent damage to the plows.


abraham 04-23-2010 08:44 PM

I do own the land and will check for gas lines as I know they run somewhere around there. And yes there are height and setback requirements but I have that taken care of.

jomama45 04-24-2010 08:38 AM

I've done a few projects like this, & deal with frost concerns on every project. I'd tend to agree with NJ Brickie: get below the frost line.

What I would personally do is drill in a 28-30" sono tube, 48" deep, & fill with cocnrete to grade. Much less involved in this approach when it comes to excavating, etc..

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