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DIYguy2000 04-22-2010 02:52 PM

Floating deck questions
I plan on building a deck in Ontario this summer (approx. 14' x 16', with 3 steps up to a 4'x8' deck in front of the patio door). I plan on using floating deck blocks instead of concrete footings/piers.

I have a few questions:

1) I'm going to excavate into the ground to place stone dust (compacted) then place my deck blocks. Is there any advantage of placing 2'x2' patio stones down on the stone dust, then the deck blocks for a larger footing area?

2) It is my understanding that pressure-treated wood should not come into contact with dirt/soil. Can the entire deck block be sunk below surface level, and backfilled/compacted with stone dust to the 4x4 post? Or will this still eventually lead to the 4x4 post rotting? If so, how far off the surface should the bottom of the 4x4 (resting on the deck block) be off the surrounding ground surface?

3) Is there a minimum 4x4 post length to rest on the deck block? For example, the 4x4 key on the deck block is counter sunk 1-3/4", can I cut a 4x4 post to a length of 2", then use a post-to-beam connector ontop of that? It seems like it would be 'too short' to me, but that's why I'm asking here.

4) What is the minimum slope I should grade underneath the deck for proper drainage?

That should be it for now.. I'm sure I'll have more questions as I move ahead!


troubleseeker 04-22-2010 09:07 PM

1. I'm from warm climate, but isn't there going to be a problem with frost heave in this set up? Since the patio stones are only a few $, it cannot hurt to spread the load over a larger footprint.

2. PT lumber can be treated to a retention level that is even rated for submersion in salt water. Although .40 retention (look at the little tags stapled to the ends of the lumber for this info) is rated for ground contact, I never bury anything less than .60. You usually have to order anything over the commonly stocked .40, but if you have a lumber yard in the area that deals with the marine trades, the may stock the higher rated material. I always like to use tamped drainage rock to backfill around wood posts.

3. I don't get your question here. Just set the ends of the 4 x 4's in the recess and leave them tall enough to go all the way to the deck beams, or better yet, tall enough to act as newel posts for the handrail.

4. 1/2" per foot will provide adequate drainage. You don't want to go overly steep and promote erosion under the deck.

DIYguy2000 04-23-2010 06:44 AM

1 Attachment(s)
Hi troubleseeker, as far as frost heave goes, yes, I am expecting some heave, but I'm on a tight budget and have had several friends in the area build similar decks with minimal heave. I'll run my design past the local building inspector to get his take on this as well.

As far as question 3 goes, sorry if it was unclear. I'm trying to get the deck as low to the ground as I can. I'll be using 5/4" decking ontop of a doubled up 2x8" beam resting on the 4x4 post resessed into the deck block. To make the deck as low as I can to the ground, I can sink the deck blocks into the ground (provided the 4x4 post is above finished grade), and cut the 4x4 post to 2" so that the beam resting on the post is just barely above the top of the deck block. Since I'm doubling up the beam, I can't lay the beam right across the deck block in the recessed areas for a single beam. I was just wondering if there is anything wrong with having the 4x4 post so short.

If the deck is low enough I shouldn't need a railing.

Thanks for the other tips.

mrgins 04-23-2010 08:53 AM

DIYguy, troubleseeker gave you good advice. The only thing I'd change is that the minimum drainage slope could be 1/4" per foot. As far as frost heaves, I live on sandy soil in a northern climate and have two decks whose footings sit on top of the ground. If your soil drains well, you should be ok, it's only a deck! Just remove any vegetation (grass etc) before you place the footing block on the ground. Vegetation will rot and caused uneven compression under the block. Lastly, the block you show accepts 2x stock as well as 4x4. Using a 2" 4x4 is ok but if you're unsure, you could use 2x stock and attach the metal connector to a the lenthways part of the grain. Hope that makes sense

DIYguy2000 04-23-2010 09:50 AM

Makes sense, thanks for the further info.

troubleseeker 04-23-2010 10:27 AM


Originally Posted by DIYguy2000 (Post 432355)

As far as question 3 goes, sorry if it was unclear. I'm trying to get the deck as low to the ground as I can.
If the deck is low enough I shouldn't need a railing.
Thanks for the other tips.

A case of not paying attention to what I was reading. As soon as I saw the part about the 3 steps, I jumped to the conclusion that the deck was 3 steps above the ground, and the given location at the pato door did not sink in.

I would still let the posts come up the top of the beam level, and mount one 2 by on each side of the post. This would not only eliminate having to fumble with beam connectors on a tiny 4 x 4 stub, but would help eliminate a future decay problem due due the two beam members being sandwiched together and staying wet between them. Seal the end grains of the 4 x 4's with a couple coats of any old paint you have around to help prevent moisture wicking. If you backfill with rock instead of moisture trapping dirt, the common .40 retention treatment should work ok.

But to the original question... any length 4 x 4 stub that you can apply your chosen style of beam connector to is ok.

Right, no need for a handrail on a deck this low, but the extended posts also work great for rear legs on built in bench if you are so inclined. I have always liked to define a larger deck at the outside corners with something like a pair of simple L shaped benches. Not only does it define the deck and make it feel more like a "space", it takes away that flat boat dock look.

DIYguy2000 04-23-2010 10:59 AM

thanks troubleseeker! I've seen the beams attached to either side of the post before, but I never clued in for this deck. I will likely do that, thanks for the advice.

As far as benches go, I'll keep that in consideration. My wife will be the decision maker for this aspect! :) I do like the idea of railings, even on a short deck, especially with a horizontal 2x6 on top to place drinks, or lean on while standing up. We'll come up with something.

As far as paint goes on the cut end of the post, does the end-cut preservative work just as well? I know my dad used to put two coats of the preservative on any cut end of pressure-treated lumber.

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