Anybody here mess with pre-cast deck blocks?

[Jackson Landers]

I'm putting up a little 120 square foot workshop of my own design. I'm looking at this as a warm-up for building the addition to my house using the 2 story universal plans.  I've got 6 of those pre-cast deck blocks to use as part of my foundation. These are the ones that have a slot for a 4x4 on the top and grooves for 2xwhatever in case one wants to just put the beams directly on the blocks. In my case, I'm putting 4x4 posts on top of the blocks.  Is there some sort of connector that I'm supposed to be using between the 4x4 post and the block? The post is hardly snug in it's pocket. I must be missing something.

This is such a small building and in a mild climate (VA) so I'm not worrying about frost heaving or anything like that. The deck blocks are just laid directly on little gravel pads 4" or so deep.

Any advice?

[glenn kangiser]

In this case I don't think a connector would do much but hold a 40 lb block to the bottom of the post as you are mostly relying on gravity for stability rather than tying into a footing.

Seems to me the important thing would be connecting the post to the beam above and possibly diagonal bracing from the bottom of the post to the beam and the floor joists so you have stability in both directions.

Others may have other ideas.

[Jackson Landers]

Glenn,

Thanks for the quick response. What I'm doing is essentially the same thing you see in the top photo here http://www.countryplans.com/nyikos.html except that the posts are about 18" tall. They do seem to wiggle around a lot. You think that once the weight of the beams is on them, they'll become more stable? It feels pretty 'mickey mouse' right now and I'd hate to get the beams and joists all built and then find out that I screwed up the foundation.

[youngins]

Check out PA Kettle's Little House:

http://cabin.foxlore.net/

[John Raabe]

As most folks already know, this is the foundation that was invented for and is used in the Little House plans. Lots of these structures have been built all over the country where the soil is stable and unlikely to move when frozen.

The plans are helpful if you haven't built this way before and have a number of tricks for stabilizing and strengthening the structure. Secondarily, a plan order helps fund this free forum and keep it open to all.

At a minimum read this free article from the main CountryPlans.com website: http://countryplans.com/foundation/index.html

Jackson: Don't use the open deck blocks you are describing if you can help it. Those provide zero uplift protection. Get the ones shown in the plans (with a steel bracket cast in) or build them yourself. There's an easy to build version in the plans for folks who can't get them locally.

[Jackson Landers]

John,

Thank you for the advice. The plans I ordered from you for the 2 story house didn't get into that particular type of deck block in the foundation options and I guess I know why now (plus it seems a little less than adequate for a house that size).  I already have these particular blocks in my possession so I'm going to use them since this is such a very small, inconsequential structure.  Half the reason I'm building this little thing right now is to practice framing and learn how to build a gabled roof on a very small scale before doing it 'for real.'  After the addition, when I get around to some more outbuildings, I'll order your 'little house' plans and use the type of blocks that you are recommending.

[glenn kangiser]

Jackson, for the little project you are talking about I think the bracing such as Pa Kettle did should work for you.  Looking forward to seeing how the little project goes before you are off on the big one.  

[youngins]

I asked him (PA Kettle) how he did it and this is what he replied with:

Hello,

From everything I have read on the posts and your site, I gather the following:

1. Mark location of foundation blocks
2. Dig 16" x 16" x 12" holes
3. Apply/tamper 8" layer of gravel for drainage
4. Set pier blocks into hole
5. Erected a plumb/level line to square/line up the piers
6. Cemented piers
7. Bolt Simpson ABA to each pier
8. Attach PT posts to Simpson ABA
9. Build beams and attach to posts with Simpson AC4

Chris,

Yes, this is about what we did.  We didn't use concrete on/around the deck blocks.  We just surrounded them with more crushed and compacted gravel.  Don't forget you will have to dig deeper and backfill with more gravel if your frost line is deeper than ours.  We assumed a 14" frost line and we dug at least 14" down.

We cut our first (shortest) post and then carefully placed and leveled the beam on it (by suppporting the other end) and then cut and fitted the rest of the posts to size.  It might be easier to use a tight line to simulate the beam, but we wanted to use the beam directly.

Were your floor joists PT?

No, the floor joists are not PT.  I would have to measure the distance to be sure, but with the post height and beam height, the bottoms of the joists are over 20" off the ground.  That seemed high enough to stay dry and probably be out of the reach of termites.

What kind of masonry bolt did you use to connect the ABA to the pier?

We used a 5/8" sleeve anchor with a 1/2" bolt from Home Depot.  http://www.concretefasteners.com/anchors-fasteners/sleeve/index.htm  Our concrete blocks had approx. 5/8" holes in them already and the ABAs have 1/2" holes through them.  Now that I think of it, I might not use them again.  They worked loose with all the banging we had to do to nail the ABA to the post.  Perhaps a long 1/2" carriage bolt would have been better.  Just make sure your bolt end doesn't stick up or the post will hit it when you place the post onto the ABA.

Also, what did you use to fasten the ABA to the post and the AC4 to the post/beam?

We used the nails specified by Simpson which (I think) are 16d for the AC4 and 10d for the ABA.  Double check that at the strongtie website. http://www.strongtie.com/  They will need to be hot dipped galvanized nails.

[John Raabe]

Jackson:

Yes, you are right that a deck block foundation would not be what you would want to do for the 2-story house.

The main disadvantage of using the open deck blocks (where things just sit in preformed grooves) is that there is no uplift protection and little sidewards resistance either. Now, that said, most of the weight of the project is above the block and will tend to stabilize as materials build up. You can still brace the posts and beams with diagonal 2x4's.

Even with brackets you are only adding the weight of the deck block to the building if it is sitting on a gravel footing. (You are "lacing up the boots" much tighter, however.) For hurricane or earthquake areas it is better to have a concrete or PT wood post deep into the ground for a tighter connection when these unusual forces show up.

Let us know how it works out.

PS - Good help Guys!