this might sound dumb, but can someone let me know if I am able to use any ceiling fan rated box on engineered joists (wooden I-joists) or does it need to be a special one? I want to replace the light fixtures with ceiling fans, and the current electrical box is not rated for a fan, and is side mounted to the flange of the joist. If it has to be one rated for engineered joists, do you have any recommendations for a side mounted one?


This is what is currently used for my light fixtures in the house, from the builder...


Pictures of what I am trying to change and how it is set up in the unfinished basement

  • by "engineered joist" you mean an engineered wooden I-joist, correct? Commented Dec 3, 2023 at 0:33
  • Yes, sorry that is what I meant. Commented Dec 3, 2023 at 0:41
  • What is the make and model of the ceiling fan(s) you want to install? How heavy are they? Do you want light kits with them? Commented Dec 3, 2023 at 22:57
  • Are you able to use the type of box that has a crossbar/brace?
    – Huesmann
    Commented Dec 4, 2023 at 14:04

2 Answers 2


The answer with engineered I-joists is always "ask the manufacturer." I know that LP I-joists don't make a big deal of this sort of thing. Personally I would use 10d box nails to attach a vertical chunk of 2x4 at the top and bottom flanges, two nails for each flange. Now that 2x4 provides a nice connection point for a fan rated box.

If you're desperate to avoid drywall patches, then you could probably sneak an OSB chunk into the ceiling to provide a flat surface across the bottom flange and the web. Making the attempt sounds foolish to me. It would be structurally inferior to the 2x4 chunk.

If you know your manufacturer or can figure it out, then look up their installation instructions. You can borrow inspiration from their point load details at bearing points if they don't explicitly address your use case.

  • 1
    I took your advice and actually emailed the manufacturer and they informed me that a light fixtures and ceiling fans are a light enough load to be supported by the bottom flange. Thank you so much. I have NI-40X joists by nordic structures in case anyone was wondering. Commented Dec 4, 2023 at 21:25
  • The bottom flange can support a fan, but I don't think a fan should be attached to the existing metal box by the threaded holes in the corners. The threaded holes in the tabs are not rated for a fan or chandelier. If you wanted to provide support for the existing box I think you should detach it from the side of I-joist and pull it down for access. Then work a 23-1/2" length of 2x4 blocking up into the space and bridge between the joist by the hole and the neighboring joist with wide side down. Fix this by a 2-1/2" screw on each end thru the drywall, thru the flange and into the 2x4. Commented Dec 6, 2023 at 21:30
  • If you wanted to use the original box, you would have to attach the fan support bracket by screws going through the top of the box and close to 1-1/2" into the 2x4 blocking. The fan would therefore not be hung from this box. Instead of reusing the original box you could use a fan rated box (1-1/2" deep) attached properly to the bottom of the 2x4 blocking and the fan could be hung from that box. Commented Dec 6, 2023 at 21:39
  • Or you could insert the blocking edge down with or without notches in the ends depending on whether you wanted the face to be right at the drywall or 1-1/2" above the drywall. If you would have the edge just at the inside of the drywall you would use a special fan rated box called a saddle fan box or a special fan rated pancake box. Commented Dec 6, 2023 at 22:07
  • Would I be able to just swap the current box with a side mounted ceiling fan rated box like this? Or even then I need to provide more support? Commented Dec 7, 2023 at 0:28

It makes a difference what kind of fans you want to mount and what kind of controls you want for it. Hunter makes fairly light weight ceiling fans that are designed to use an existing light weight ceiling box mounted to the side of a standard ceiling joist. These can be installed without having to change to a fan rated box.

This is possible because the fan is not supported by the box and is not directly under the box but rather is directly under and secured to the joist by a pair of special rated screws provided in the fan parts. The shroud for the fan is larger than it would have to be if the fan were hung directly under the box and large enough to cover the boxes side mounted on sawn lumber joists.

The base of your I-joists appears to be side (2-1/2" or 3-1/2") down rather than edge (1-1/2") down. So in your case it could be that the shroud would not fully cover the box if the fan were mounted under the center of the joist.

The alternative would be to remove the existing box which is not rated for hanging a fan and insert a special fan rated box which has a horizontal support rod that stretches from one I-joist to the next one. These are designed to be fitted through the original hole in the ceiling. These can fit through the original hole because the rod is inserted and secured by expansion and then the box is fastened to the rod with special bolts.

In looking at boxes with brackets some are "new work" and cannot be used with drywall in place and others are old work but designed for standard sawn lumber joists with drywall in place. It could very well be that they can be used with I-beams by cutting off 1-1/2" of the positioning arms because I would think you would want to place the rod on top of the 2x3 or 2x4 bottom element of the I-joist. We have two new Hunter fans hanging from these fan rated box/brackets secured to the sides of the 2x4 bottom cords of our roof trusses which are 24" on centers.

We also have three heavy old Hunter fans which I installed decades ago (with attic access). These are hung from extra 2x4 blocking (22-1/2" long) inserted between two 2x4 joists/bottom cords.

If you want to mount a fairly heavy fan or one which requires a fan rated box, then you will I believe have to remove the existing box and use a fan rated bracket box designed for installation with drywall in place.

Possibly the positioning arms don't have to be cut but simply flipped over for I-joists. Maybe manufacturers have built in this capability for hanging fans from I-joists. Maybe a bracket box like this* would work if the box itself were attached to the side of the bottom element by a screw or two through the side. *https://a.co/d/1UrDPnu but I really have in mind the Raco Hubbell 936 which I think tightens by rotating the rod https://www.amazon.com/Hubbell-Raco-936-Ceiling-Fan-Support/dp/B000HEIYHA/ref=asc_df_B000HEIYHA/?tag=hyprod-20&linkCode=df0&hvadid=194952682001&hvpos=&hvnetw=g&hvrand=11314824144809144662&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9026950&hvtargid=pla-313976743614&psc=1&mcid=a7abc6c5c7433353b0c37688fe9e1a32&gclid=Cj0KCQiA67CrBhC1ARIsACKAa8R_u1rph5HSoY9ucbM_qqaJcNrQiYp2vZeo66ZkgtfNlL2TGVfqitAaAqhpEALw_wcB

The specs of the Hubbell Raco 936 says it will expand to 24" max which it would have to do to fit between the webbing of two I-joists 24" on center. For sawn lumber on 24" cnters it would only have to expand to 22-1/2". If the mfgr is too loose in description, then some improvising might be required.



The Hunter fans allow separate control of fan and optional light kit by wireless controller. The usual single switch is kept ummodified and there is a wireless battery powered remote controller which switches an electronic receiver/switch under the shroud at the top of the fan. This allows separate control of the fan and the lights. There is a small bracket which fits over the single switch on which the remote controller can be hung. The original switch stays and can be operated by lifting the remote off of the bracket.

The wireless controller can also be placed anywhere (e.g., bedside table) to control the light or fan.

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