Take the 2-minute tour ×
Home Improvement Stack Exchange is a question and answer site for contractors and serious DIYers. It's 100% free, no registration required.

We would like to install a 6' privacy fence with 6x6 cedar posts, between our house and driveway, that would involve 3 posts on top of our cement driveway and 1 in the ground. My intention was to hire someone with a core drill to dig 3' holes for footings, and pour cement into 10" tubes, but I am now wondering if it is "ok" to just install the footings directly on top of the driveway.

I have not checked the depth of the cement yet, so is there a recommended driveway depth for this sort of thing, if I can install directly into the existing cement? Or should I go ahead and get 12" holes taken out with a core drill and create 3" deep footings?

Also, is this a proper post anchor to use? It is the only type they had at our store.

[self-removed image]

share|improve this question

3 Answers 3

up vote 7 down vote accepted

A fence post has very little vertical force...mainly just the weight of the post and panels it holds. Your driveway slab would work fine as a footing for that. HOWEVER, the primary force on a fence is typically lateral--especially a 6' fence. The reason posts are put into the ground is to counter lateral forces on the fence (typically the wind).

I imagine there are types of brackets that could be used on the concrete to accomodate the lateral forces, but the type you have in your post is not that type...that's typically used to attach structural posts to concrete (it handles the vertical force, but not lateral).

The type of brackets you'd need would be something akin to a shelf bracket where there's a diagonal brace between the two plates.

So, one option is to cut holes in your slab and dig proper holes there. Alternatively, you could find plates designed for this (or have someone weld some up for you).

A third option would be to not build a straight fence, but rather stagger the posts in a zig-zag pattern.

share|improve this answer
1  
Thanks for the design suggestions. I really would prefer not to mount the posts into the cement in the event the fence needs to be moved or replaced (like gets hit by car). We may need to add more posts and get a better bracket as you suggest. –  Dave Apr 11 '12 at 19:20

I think your first inclination was correct. You should cut holes in the driveway and install the posts at least 36" deep in a concrete footing. Trying to mount to the surface of the driveway will not give the support you need for a 6ft fence. Wind, snow etc are powerful lateral forces against a large section of fence and could easily topple it.

The post support you pictured is designed for posts under a deck or structure. The weight of the structure bearing down on the post provides stability. These supports hold the posts from slipping horizontally where there is no chance of the post tipping over because it is secured to other framing members. I think your fence would fall over in the first stiff breeze if you used these instead of sinking the posts into the ground.

share|improve this answer
    
I'll definitely NOT use those brackets. Ideally I'd like to form the footing in such a way that the post can slide out. The fence might get hit by a car where it's located. –  Dave Apr 11 '12 at 19:27
    
If you make a sleeve that the post sets in, be sure to make it drain at the bottom, or your post will be setting in a vessel of water after a rain. –  shirlock homes Apr 12 '12 at 10:10

I did exactly this same thing last year. I rented a machine from Home Depot and "drilled" my own holes. The cores I cut were only slightly larger that the 4x4 posts that I used (6 inches I think). The hardest part was digging down the additional distance once the cores were cut. I have to admit that I only went down 24 inches, since I figure that the posts are laterally immovable where they exit the slab.

share|improve this answer
    
We probably could get away with 4x4. Maybe I'll reconsider whether I need 6x6's or not. Thanks. –  Dave Apr 11 '12 at 19:45
    
@Dave, I think they rent a larger cutter, but I wasn't sure I could handle it. –  uncle brad Apr 12 '12 at 16:01
    
A guy at work also said not to try using one of those big cutters. I guess we'll need to hire someone with a cutter. I didn't mention this fence may later become an arbor, by adding on to it, so we will need 6x6's for that I think. –  Dave Apr 12 '12 at 16:15

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.