Expert: Daniel Humphrey - 12/6/2008

Question
QUESTION: I know this isn't house related, but it is construction and design.I am trying to design a dock. It is to be built on 5 existing boulders/rocks. The tops of 4 boulders are all well above the high tide mark, and 3 have preexisting 4x4 timbers anchored with wedge bolts as brackets. I plan to bolt 2x6 planks on both sides of the 4x4s to create a level top surface for the deck boxes to be bolted to. The question I have, is the 5th boulder only has about 30"wide showing during a full moon tide, how do I anchor a timber bracket on the uneven surface of the boulder? I can do another 4x4 with sleeve anchors for more grip, but I also have to build up about 12" to meet the level of the rest of the dock, and am concerned about wave, and ice pressure during storms. What would you recommend? Thanks, Brian

ANSWER: Brian,

Have you considered drilling into the rock and putting in 6x6 post saddles with epoxy? (or 4x4 if that is strong enough.)

You could then build all the deck, supported by those 6x6 posts, approximately 12 inches tall. I'm sure if you secured everything with good joinery and metal brackets, it would be as resilient as any other method, the advantage of building on posts is that you can begin with a level supporting structure that ties into your other framework.

Hope that helps.

Daniel

---------- FOLLOW-UP ----------

QUESTION: Daniel,  Thanks, but I've never heard of post saddles. What are they, and do you mean that the top of the saddle would give me a level surface? Is there a special epoxy to use? Haven't found many resources for this project, so I really appreciate your help!

Answer
Brian,

Yes, post saddles provide a socket for securing the end of a post. They normally epoxy into a 3/4" hole drilled in the rock with a rock bit, and the post is secured with some through bolts.

Here is one kind I was thinking of. Check out the rest of the Simpson site for ideas.

http://www.strongtie.com/products/connectors/EPB44T.asp

Daniel