# Boardwalk design



## leeboh (Aug 5, 2011)

Looking for some building standards with pt lumber, length and span. Usually we use 2x8 , 8-12 ft long for stringers and 5/4 decking 2-3 ' wide. For ground support we often use 4x6 pt lumber to raise, level and keep the other wood off the ground. These boardwalks are for foot and bike traffic only. I was on a project last year that used far bigger lumber. 16' 4x8 pt stringers and 2x8 pt decking. Seems like overkill for foot and bike traffic only. Any advantage to using really big lumber like durability and or service length ? We use 3 stringers under the width of our decking.


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## TFitz (Jun 21, 2008)

I'd say you're using the right approach for that kind of traffic over that kind of span, although I would use 2X6 or 2X8 decking. Dog walkers tell me their pets feel more secure when the tread boards are spaced no more than half an inch apart. For more durability, maybe put a strip of building paper (tar paper) over the top of each stringer, and use concrete pier blocks to support the structure off the ground.

The 4X8 (or two 2X8's nailed together) stringers are appropriate for the longer span when that's required.


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## leeboh (Aug 5, 2011)

OK. We do put a small gap, maybe 1/4inch on the decking for water and mud to go through.


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## hado_pv (May 26, 2006)

Wider gaps between treads will increase the life of the stringers, allowing water and dirt that gets between the treads to dry out faster. I would never gap less than 1 inch. No real dog's paw is smaller than that.


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## leeboh (Aug 5, 2011)

Does PV have a set spec for boardwalk?


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## TFitz (Jun 21, 2008)

Pv ?


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## Dave_schuldt (May 10, 2004)

Also Google punchon for more info.


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## ghglenn (Jan 26, 2012)

We just use a 5/4 on edge as a gap gauge. Everyone seems happy with the results.


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## hado_pv (May 26, 2006)

PV - being Pioneer Valley - uses a bunch of different boardwalk technologies depending on class of trail. At the trail schools, and for structures built with RTP grant moneys, we use stringers and deck sized per http://www.midsouthtrails.com/docs/trailbridgedetails.pdf.

For other projects, We've had good luck with 4x4 stringers 8' length or felled in place and stripped of bark hemlock, decked with 5/4 up to 24" wide.

We've also done several projects using "T" beam construction. A pair of 2x8 or 2x10 glued and screwed to a perpendicular 2x4 or 2x6 and blocked on 4x4 or 4x6 sleepers. Looks like a typical AMC horizontal plank bridge, but it doesn't sag!


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## redd4573 (Apr 15, 2012)

Can I ask what you are trying to traverse? I have seen everything used for supports from RR ties, PT 6x6's, to concrete parking curbs. the first two rot quickly and the second seems to sink into the wet ground exposing the deck material to the dampness which results in rot. I recently started looking into using rock in a causeway in a local project with easy accessibilty. I beleive it will reduce liability, and actually reduce maintence! The cost between the two seems to be about double for stone and a little more labor, but would never need replaceing in ten years and agin in twenty years! If this is not possible for you then I would try and use large rocks to raise and support the joints of the decking anything to reduce the contact between water and wood!


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## leeboh (Aug 5, 2011)

In New England it is usually streams, wet/ muddy areas or some spots with seasonal drainage. Our PT lumber works best for ground contact.


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## Dirt Engineer (Sep 12, 2012)

I like those drawings and all but don't see any specs for stringer OC distances. I think doing more than a 24" OC span with 2X is pushing it a bit. And 12" of over lap for 5' wide decking is a bit much IMHO, too.

I've used 4x4 for stringers in the past but support them every 4-5 feet. I've done 8-10 foot bridges with 2 4x4 stringers and 5/4 decking and can tell you from experience that it has a lot of flex. I don't use 5/4 decking anymore. Bare minimum is 2X dimensional. 7" or bigger utility poles or 6x6 lumber for stringers. Or 2 2x8' sistered together.

I over build everything as the liability isn't worth the minimal cost savings and it just plane feels sturdier.

And Woody Keen still thinks I should use true 2x lumber.


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## snug dug (Jul 7, 2012)

Sure, use 2x lumber! Just choose the appropriate dimensions for your span, then double, triple, or quadruple them using construction adhesive and spiral nails. These are 2x12x20's.








Don't forget to armor the banks!








Use the beefiest decking you can, those are rough cut 4x8's








Most importantly








Don't forget to anchor that sucker down! Four foot long 3/4" rebar doesn't always work!








But, we're talking about boardwalks! The structure is pretty much the same as bridges, they're just elevated...somehow. Before I ever bury another post in the ground and anchor it in concrete, I'd have a long, hard look at something like this: Pin Foundations Diamond Pier


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## ghglenn (Jan 26, 2012)

Wow, that bridge is burly! I assume you are accommodating horse traffic/ATV's? Lots of the boardwalks we build are for foot traffic and bikes only, much less material and weight to consider. Frost line is minimum 36" so concrete piles are impractical (heaving is a problem). We auger 4', add 8" of gravel at the bottom, pack with home-made hand tamp in hole, and set 6X6 posts. In super soft material, we build A-Frames (to spread the load) with sacrificial bases (2x12 on the flat) that will have to eventually be replaced (8-10 years) by removing A-frame and putting another in it's place. 

For heavy traffic bridges, the power company donates new "green" 40' poles that we use as trusses. Makes them look good, and gives us free material that would cost us a fortune. 4x6 for the treads.


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## deezler (Jun 21, 2011)

ghglenn, I know you've got some pictures of this handy-work! Share the love.

Snug dug, that must have been quite the flood. Do you think building up the armored banks to elevate the bridge another foot or two would have prevented the dislodging? By the pics, if that bridge had enough hydro-force against it to push it downstream, that whole area must have been deeply flooded!

I am trying to plan a bridge for my own property, so I like these type of threads! I need (want) one that is big and strong enough for my tractor (3500 lbs) and maybe even pickup (5500 lbs) to cross safely every now and then. It only has to span 12-15 feet or so. Problem is, I'm also a cheapskate, so I am considering using logs that I chainsaw mill myself. Will probably need to buy some rough cut decking. And what to use for the supports? I have some piles of big thick concrete slabs to work with.... Fun to dream about.


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## snug dug (Jul 7, 2012)

It was a 500 year flood event, Tropical Storm Lee. It wasn't so much the force pushing against the side of the bridge, rather the rising water pushed it up, then it floated away, 300 yards downstream. But, yeah, it was a whole lotta water! Months later, we took it apart and hauled it back, piece by piece.

Deezler, that bridge will support 10,000 pounds.

When we rebuilt it, we built it higher and ended up driving these big, spear like rods in the ground to anchor the bridge to the spear using wire rope.

Now, here's a bike boardwalk I'm working on.


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## deezler (Jun 21, 2011)

Awesome, looks like a roller coaster track. Mo' pics!


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## thumpduster (Nov 19, 2008)

Time for a thread hijack: Snug Dug, please post more pictures of that curved bike boardwalk you're working on!


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