I would like to install a 30 x 60 inches wood panel (1 inch thick) in the ceiling. Not sure how much this wood panel alone would weight. Looking for suggestions of what kind of wood to use.

The idea is to leave a gap between the ceiling and this wood panel so wires can pass through, if necessary.

This will act as a second ceiling, so we can hang things and occasionally being able to replace the panel for a brand new installation (therefore not needing to drill new holes in the ceiling). The things we will hang will change - we will install some lights and plants, but one day it might be replaced by a projector, Christmas stuff, etc. If the wood panel gets too used, it would be replaced by a new panel (simply removing the existing panel, and putting the new one with no new holes in the ceiling). I'd say items to be hang will be around 30 pounds (lbs).

Is there a standard math/formula or expertise you can give me to know:

  • How many anchors I need? Two (one each side)? Four (one each corner)? Five (each corner plus center?)
  • What anchors are recommended taking into consideration that we want to be able to replace the panel occasionally (therefore removing and reinstalling the anchors with no new holes)?

I'm not concerned about estetics yet, it's easy to do later (thin painted wood to create a box).

Thanks for any help!

  • It's not easy to fasten anything under a concrete slab, failure can seriously hurt or kill someone. Please consult with an engineer/architect for your own safety.
    – r13
    Dec 1, 2021 at 0:31

2 Answers 2


Four anchors are adequate if:

  • They're substantial enough to secure the load to the ceiling, such as lag screws with expanding shields
  • The plywood is rigid enough to handle the span (you could place the anchors at the 25% points lengthwise to reduce span)

Otherwise, use six or eight screws. It's hard to say more without more detail about your situation, such as type of concrete. Some general advice:

  • If you're able to drill 5/8" holes, lag shields are a sure bet
  • If not, #12 or #14 screws in plastic anchors should do well if everything is sized properly
  • I'd use 3/4" plywood. It's less likely to warp and will be rigid enough. You could get away with 1/2" or 5/8" with six or more anchors.

Followup questions from comments:

  • I didn't use any math. Math isn't great here because it makes all kinds of assumptions, many of which depend on your carpentry prowess. For example, if you use the wrong size screws in plastic anchors you'll cut holding power by 80%, and if you run screws too deep in plywood you reduce its hold by about the same. If the integrity of the concrete isn't there it's all out the window anyway. I'm relying on more than three decades of professional and personal experience, but I don't have all the information I'd need to be specific.
  • I think four plastic anchors are barely adequate for a 30# load in tension (as opposed to in shear, such as with wall-mounted stuff), and I'd use at least six. Again, properly sized screws, to create the required internal friction, are critical. Test well before putting it to use. If it doesn't hold you up, it's not done well.
  • Screw head type doesn't much matter as long as they aren't small-head trim-type screws. Good plywood won't allow them to pull through if you barely counter-sink them flush or leave them above the surface.
  • To reiterate, just four corner anchors may leave you with substantial sag in the sheet. I'd move them inward somewhat to reduce span.
  • Thanks! Very informative! The four anchors are based in your experience or did you do some quick math? I have trouble knowing how many are needed. I believe 5/8" holes might be too much, and very hard to remove later if ever needed. For now it seems the plastic anchors. You think four plastic anchors (one each corner) would be able to hold: 3/4" plywood 30x60" + 30 pounds of stuff installed on the plywood (not counting the plywood weight)? Any specific recommendation about the screws, the head type? Do I need to use a washer? Thanks very much!
    – igorjrr
    Nov 4, 2020 at 21:21
  • Additional questions addressed above.
    – isherwood
    Nov 4, 2020 at 22:19

I would anchor some 1x2" strapping to the ceiling using concrete anchors, then attach the panel to the strapping with standard wood screws.

  • To be on the "safe side", if I were doing it, I would probably put 3 or 4 anchors per strap into the concrete.
    • My wife would tell me that this is overkill, but it's better than having it fall.
    • If you use concrete screws (like a Tapcon™) you can unscrew a piece of strapping and install a new one should it get too torn up. If you use concrete nails, that would be a much harder proposition.
  • Likewise, I would probably use at least 4 screws per strap to anchor the board to the ceiling strapping.

I would run four 30" strips spaced evenly along the 60" dimension. If you wanted, you could inset the outside ones an inch or two, and make the strips an equal length shorter (26" or 28") to make it look like the panel was floating.

This would allow you to run cabling between the top of the panel and the bottom of the ceiling. It would also allow you to change out the wood panel for something with a different "look" based on the season, or maybe even have a "Christmas panel" with lights and mistletoe preinstalled, etc.

Please bear in mind requirements for running electrical in a situation like this. That would be good fodder for a new question, just to make sure you're not causing yourself further issues in the future.

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