DIY stand for 3 Powerwalls raised off the garage floor

[wwhitney]

PS: I just picked up the lumber from Home Depot an hour ago, and ready to put this thing together!

A few point to consider:

Untreated wood should not bear directly on concrete. Use treated lumber on the concrete, or a barrier like galvanized sheet metal.

Green wood will shrink significantly perpendicular to the grain as it dries. Treated wood is typically sold very wet and will shrink even more than green wood.

The wallward-most Powerwall will be mounted to the wall, while the other two will be resting on the platform, and just attached to the previous Powerwall for lateral support. So if your platform shrinks in height, the front two will drop, and the connection between the middle one and the rearmost one will be stressed.

If you are going to use solid-sawn wood, ensuring that the height of your platform depends on members with the grain running vertically will reduce these effects significantly. Wood does shrink longitudinally as it dries, but the shrinkage is at least an order of magnitude less.

Cheers,
Wayne

 

[heytae]

Even with all of the specs available, it's hard to know how much the hanging bracket and spacers add to the total depth of 3 PWs. So, does anyone have that measurement? From the wall to the outer most front of the PWs. If someone has 2 units stacked, I can calculate out what it'd be with 3, since I know what 1 is with the wall bracket.

I appreciate all of the input here and I'm planning to add vertical "pillars" using 2x4s, placed directly underneath where the PW "feet" are, all for additional direct vertical load support. Because the 4 sides of the box are with 2x12s only a few inches away, that should be an overkill, even for ~900 lbs of weight in earthquake country. I'll add some pictures of what I've got done so far, in the next hour.

 

[Uncle Paul]

Think I'm with John on this one.
For a garage application I would consider using Concrete blocks, Masonary blocks or pour a pad.
Wood could degrade and not as structurally stable for this application.

Concrete blocks or pads would also provide the ventilation desired, be low cost and quickly available.

 

[MorrisonHiker]

I believe the switch location is an ADA requirement perhaps. Which makes Erik and David’s install (see YouTube) probably at the maximum height and no room for another set below them.!

Someone posted the powerwall installation manual here in this section recently, and I downloaded it. I dont think you will be able to mount powerwalls above other powerwalls on the wall.

We're planning for 4 PowerWalls - 2 on the floor, and if possible two mounted above - to provide more space around the S we park on that side of the garage.

As @boaterva and @jjrandorin point out, you can't stack them vertically. Our Powerwalls are mounted as high as allowed which is less than 41 inches off the ground. Since the Powerwalls themselves are over 45 inches tall, you wouldn't be able to fit another Powerwall underneath the wall mounted Powerwalls.

 

[wwhitney]

I appreciate all of the input here and I'm planning to add vertical "pillars" using 2x4s, placed directly underneath where the PW "feet" are, all for additional direct vertical load support. Because the 4 sides of the box are with 2x12s only a few inches away, that should be an overkill, even for ~900 lbs of weight in earthquake country.

Since you got your 2x12s at Home Depot, they are green, and they are going to shrink on the order of 1/4" across their width as they dry. So those vertical 2x4s will be carrying all the gravity load, the 2x12s will be gapped at the top or bottom.

If you haven't gotten the 2x4s yet, and you plan on getting them at Home Depot, they do sell a dry 2x4x8', it's the only dry lumber they sell (should be stamped KD or S-DRY). The dry 2x4x8' is advertised as "Whitewood" but at least locally if you look you can find some or all will be stamped D-FIR. Use those.

How are you going to keep the untreated Douglas Fir from contacting concrete?

Cheers, Wayne

 

[heytae]

All good points. I want to use wood so that the stand can be attached to the wall also along with the PWs. With wood pieces only 12" long, how much shrinkage should I expect? Was hoping for only a negligible amount but I suppose I can let the pieces all dry in 75 degree sun this week before putting it all together. I'm in the bay area of CA.

Here's a short video of where I'm at so far. Do I still need to worry about wood shrinkage for such small pieces?

 

[heytae]

If I paint the bottom sides too with PW color matching semi gloss paint, that should protect the wood and not require any flashing right? Guessing the question was due to concern about termites or dry rot.

 

[wwhitney]

All good points. I want to use wood so that the stand can be attached to the wall also along with the PWs.

Non-wood materials can also be attached to the wall.

With wood pieces only 12" long, how much shrinkage should I expect?

As I mentioned, it is entirely common to see a 1/4" of shrinkage across the width of a 2x12 between green and dry. E.g. 11-1/2" green and 11-1/4" dry, or maybe it's more like 11-3/8" green and 11-1/8" dry.

Was hoping for only a negligible amount but I suppose I can let the pieces all dry in 75 degree sun this week before putting it all together. I'm in the bay area of CA.

Yeah, one week outdoors is not going to dry it. Inside it might take a year to dry, outside would be a bit faster, but not 50 times faster.

Cheers, Wayne

 

[wwhitney]

If I paint the bottom sides too with PW color matching semi gloss paint, that should protect the wood and not require any flashing right? Guessing the question was due to concern about termites or dry rot.

A coat of paint is a better barrier than nothing, but not good enough. The concern is moisture migration through the slab and into the wood.

Cheers, Wayne

 

[heytae]

Wow that's a lot of shrinkage for a 12" cross sectional piece. I'm already committed so I guess I'll take a vertical measurement in 6-12 months and raise it back to original height then if needed (to reduce any possible vertical strain). At least I don't need to go through the trouble of sun drying it this week. =) I'll consider adding flashing to the bottom too.

Thanks Wayne.

Once I get the final depth dimensions from someone who has 2 or 3 PWs stacked, I'll finish this up. I'll post the finished pictures here if anyone's interested.

 

[wwhitney]

Here's a short video of where I'm at so far.

OK, I took a look at your video.

If it were me, I'd be using the lumber you have to make a form for a small concrete pad that would be sized just to the footprint of the powerwall stack, and of height equal to your concrete stem wall. It'd be under 2 cubic feet, so you'd just need a few bags of concrete mix. The new concrete should be mechanically fastened to the old; that could just be a pattern of 3" tapcons driven half way into the slab and the stem wall.

If you insist on using green wood, I would suggest:

- Make the bottom piece of plywood PT, and keep the stand from contacting the concrete anywhere else. Or set your regular plywood on a piece of galvanized sheet metal a bit larger than the plywood. Plan to fasten the bottom plywood to the concrete, e.g. with tapcons.
- Have the grain run vertically on the 4 sides of the box. I would suggest the left and right sides could be a U-shape in plan, composed of fastening together three members, a solid side, a front piece and a back piece. That would leave an opening at the front and back sides of the box for your ventilation. If necessary to stiffen the top plywood, you could add some dry 2x4 "joists" between the two U-shaped sides.
- Make the primary box an actual cuboid keeping it 5" off the wood framed wall. Then fill in between the primary box and the wood framed wall with a 5" x 5" x 30" filler made from 4 dry 2x4 pieces. Fasten the filler to the wall and the box to the filler. Keep the tops flush so your top plywood can run over both.

Cheers, Wayne

 

[heytae]

There are 2 "feet". 28" apart from each other.

Approx: 0.5" height x 1.0" wide x 4.25" long.

Note that they are flushed from the back side.

Goodluck with the project.
View attachment 467833 View attachment 467836 View attachment 467837

By 28" apart from each other, does that mean they're only 1"away from the sides? Since the PW is 30" wide basically.
If so, the vast majority of the load bearing part will be resting on the side 2x12s since they're 1.5" thick and maybe adding additional 2x4 bracing pillars won't do anything. Please see my video above if this doesn't make sense.

 

[RoBoRaT]

By 28" apart from each other, does that mean they're only 1"away from the sides? Since the PW is 30" wide basically.
If so, the vast majority of the load bearing part will be resting on the side 2x12s since they're 1.5" thick and maybe adding additional 2x4 bracing pillars won't do anything. Please see my video above if this doesn't make sense.

My bad, 26.5" apart.
1.75" from each end.
See view from bottom...

 

[wwhitney]

Wow that's a lot of shrinkage for a 12" cross sectional piece. 'm already committed so I guess I'll take a vertical measurement in 6-12 months and raise it back to original height then if needed (to reduce any possible vertical strain).

I don't think the mechanical part of the electrical connection between adjacent Powerwalls (the chase nipple) is going to like the 1/4" drop that occurs as the wood shrinks. Better to redesign to avoid the wood shrinkage problem.

Cheers, Wayne

 

[wwhitney]

P.S. Sorry if my posts come across as overly commanding. You did a good job with the design based on the information you had, and your video shows a nice execution. But now you have more information, and it is time to revise your design in light of the new information. You can reuse your existing materials in a different arrangement, as suggested.

Good luck,
Wayne

 

[heytae]

My bad, 26.5" apart.
1.75" from each end.
See view from bottom...View attachment 468232

Ok good to know, thanks for remeasuring. So I think I will add additional bracing right underneath the feet then using dry wood.

 

[heytae]

I appreciate your thoughts Wayne but I'm going to stick with the design. The solar company designers are the ones who said they use wood and i think that's good enough for this application. If the shrinkage turns out to be that much and a problem I'll address it then. I'll monitor it closely. Again, I appreciate your opinion.

 

[wwhitney]

No problem, it's your project.

If you put a full height dry 2x4 directly under each of the 4 feet of the outbound Powerwalls, that will address any shrinkage issues. The 2x12s will shrink, but they are no longer in the gravity load path, they just laterally brace the 2x4s. I wouldn't even bother to shim the 2x12s after they shrink.

Cheers, Wayne

 

[heytae]

No problem, it's your project.

If you put a full height dry 2x4 directly under each of the 4 feet of the outbound Powerwalls, that will address any shrinkage issues. The 2x12s will shrink, but they are no longer in the gravity load path, they just laterally brace the 2x4s. I wouldn't even bother to shim the 2x12s after they shrink.

Cheers, Wayne

Makes sense so I'll use 2x4s that are dry.

 

[heytae]

The entire stack is right up against my garage wall, which is double sheet rock, followed by double plywood as it's a shared wall in a townhouse complex. They some used serious long lag bolts to all the bracket through all the sheetrock and plywood. It sits nearly flush against the garage wall. There may be a small gap in order to hang it on the wall brackets, but for all intents it's right up against the garage wall and also sitting right against the garage floor on it's two legs (someone showed an imaged of that up above).

I'll get you an close up image in an hour once I'm home.

Hope the above helps before I get you the image.

Upon closer look at one of your pictures Zanary, I see now that the black spacers between PWs 2 and 3 actually add something like 1 to 1.5" to the total depth! Yeeks. Would you please tell me what your total depth measurement is? From the drywall to the front edge of your red PW.