Construction Advice Needed

[Keith Starosta]

Howdy folks. I was hoping to get some good advice as to the best way to assemble some faux beams I'm going to use in my basement. I will be using four of these "beams" spread evenly across the ceiling, and each will have three 3" can lights installed in them. I'm committed to using 3/4" MDF to construct the beams (already purchased material), as we will eventually be painting them, and want a smooth surface.

My question is, what would be the best way to assemble the beams? I was originally thing about using biscuits and glue along the lengths of the 45 degree miters. Would the biscuits and glue be strong enough, or should I consider some other way?

I already know how I will affix the "U" shaped beams to the ceiling, so that shouldn't be an issue. I've attached a Sketch'ed Up drawing of one of the beams. As you can see, they will be almost 12' long when completed, but each whole beam will be made up of two equal lengths of "U" beams.

Thanks very much for any help you can give me!!

Keith

[Tom Hamilton]

Hi Keith:

My experience with MDF and biscuits is that once glued it will not come apart. In your application there will be very little force once hung, so I suspect that you will have them on the ceiling for years.

The FWW article on using MDF a couple of years ago, pointed out that for a really smooth finish prime with oil base paint and then you can put latex on for a final coat. I use KILZ because it is only $10 a gallon. Latex as a primer soaks into the MDF and causes a bumpy, fuzzy surface.

At 12 feet the beams will be plenty heavy. Gear up for the install.

Merry Christmas, Tom

[Jamie Buxton]

Yes, glue on the miter faces will hold these U-channels together. After all, they're not holding anything up. Biscuits will help align the pieces for the glue-up.

Heck, as long as you're painting the channels, you might consider simple butt joints instead of the miters. They're easier to make.

[Vaughn McMillan]

Keith. consider my amateur status with a grain of salt, but if you're painting the beams, why bother with the mitered corners? I'd think biscuited butt joints would be plenty strong, and easier to get nice and square cuts and assembly. The mitered joints exhibit (and require) more skill, but if they're covered with paint I don't think they're worth the extra effort.

Like I said, I'm somewhat of a rookie, so maybe one of the cabinet pros around here will have a better reason for the mitered joints...I just can't see it.

- Vaughn

[Walt Pater]

Keith, I wouldn't bother with the mitered corners. When I run box beams I like to dado the sides 1/2" or so to accept the soffit piece- I usually leave about a 3/16-" reveal below the dado. This gives you plenty of fudge room if whatever you are boxing is warped/ buldging, allows for wood movement, and gives a nice look. I have also seen the sides just rabbetted, which allows for a different reveal, but haven't tried it. Just make sure all your electrical stuff will fit in the beam before you throw 'em up.
Good luck.

[Andy Hoyt]

Keith - don't cut anything until you have your lights selected. And be sure that there's enough clearance between the fixture and anything comustible, including the mdf. Be very very careful with this. Building and electrical codes are quite clear on the point.

Clearance will be determined by the light fixture - not the salesman.

I know this because I once got hired to rip out an entire floor system to repair and replace something very close to what you're describing. My work ocurred after the fire.

[Steve Stube]

Well Andy beat me to it, but it was my first calculation when I clicked on the sketch. 3/8" is too close for combustionable material (at least on any cans I've worked with). Be safe.

PS. Yes the screw base flor. lights will run cooler but I would not use them because down the road (long after the proper clearance has been forgotten) someone is likely to re-bulb with incandecient. It might be like setting a trap. Good UL listed cans will state the proper spacing necessary for safe operation.

[Keith Starosta]

Thanks for the great feedback, guys!!

First I will address my potential use of mitered corners on the MDF. I only wanted to maintain a nice, clean look all the way around the beam. Using the mitered edge would eliminate the cut line of the butt joint....in my eyes. This will be my first actual use of MDF, so I could be wrong here. With sanding and spackle, can I be sure of being able to make that joint line almost invisible? LOML is pretty particular about these things, so I want to make sure I get it right.

Andy and Steve, thank you very much for your comments about heat build-up. They helped me realize that I didn't really explain the complete installation properly. While I am going to drywall my ceiling, the beams are going to be installed such that they run parallel to the ceiling joists above. I've attached a quick rough stetch of how I hope it looks when complete. I've laid out these beams such that, after installing some 2x4 blocking between joists for hanging purposes, the area above the beams will be left open. The beams aren't going to be mounted to an enclosed space.

I've already purchased the lights I am going to use, and while I couldn't actually find a picture of them on the internet, I did go through the installation instructions and pulled out a few items that I thought would help understand the lights:

- Thermally Protected
- UL Listed for damp locations
- Approved for through branch wiring

The diagrams indicate that I need a minimum of 3" clearance from insulation around the fixture, which will work because I'm not insulating the beams and will be sure to keep the R-19 in the ceiling at a proper distance.

I know this was a bit long-winded, but I wanted to make sure I provided enough information this time. Does this information give you a better idea of what I'm trying to accomplish? If absolutely necessary, I guess I could install some sort of venting mechanism at each end of each vent, but that's only if absolutely necessary. I don't want to muck them up.

- Keith

[Vaughn McMillan]

I think the butt joint, sanded (and spackled if necessary) and painted will be impossible to see, unless the joint is loose. Good glue and clamps should handle that.

Regarding the light can clearances, I'll let others chime in, since I don't have any comparative experience.

- Vaughn

[Keith Starosta]

Thanks, Vaughn! Easier is better in this case, so I'll just go the butt joint route.

- Keith

[Keith Starosta]

OK, I took a few pictures of the light I am going to use. These are 3" can lights, for use in new or remodeled construction. The white cannister is 3 1/8" in diameter, and the overall height of the unit is 6". Based on the fact that almost all of the unit will be housed in the beam, with a completely open joist space above it, my uneducated opinion is that heat shouldn't really be an issue.

Is this a correct assumption?

- Keith

[Kent Parker]

Keith,

If your going for butt joints consider dadoing the sides or bottom. I use to dado the fore and aft staves of hollow box sectioned masts I made and it really aids in alingment during glue up. You don't need much...3/16" to 1/4" is fine.

Maybe I missed it in your post but how are you going to attach the beams to the overhead??

Cheers,

Kent

[Mark Rios]

Keith, as has been mentioned, there are codes for minimum spacing AROUND the lights. Kind of like the spacing around a heating vent of some kind. Some lights have a zero clearance rating and some have as much as a 3" clearance rating (maybe more). The installation instructions that came with the cans should provide you with that info. It's not a question of heat build-up but more of a radiated heat thing. Non-insulated (zero clearance) cans get VERY hot. Please check the rating.

BTW, the sketch you provided looks great. Looking forward to seeing pics of the finished room. Nice going.

P.S. After looking closer at your pics (silly me, not looking before) the clearance info looks like it might be right there on the can. I saw some conductor rating info but couldn't read all of the printing on all of the can.

[Keith Starosta]

Mark, this is what it says on the side of the can:

"WARNING - Risk of fire: Do not install insulation within 76mm (3 inches) of any part of the luminaire."

The "insulation" part is obvious, but does this also mean that the sides of the "beam" also need to be at least 3" away from the can once installed? That's going to make for a pretty wide beam...wider than I thought, anyway.

If it has to be this way for safety purposes, so be it. But, a narrower beam would be more preferred.

Thanks!!

- Keith

[Mark Rios]

I'm a little fuzzy but....if I remember correctly non-IC (insulation contact) rated can fixtures need to have a minimum of 3" of clearance from insulation and a minimum of 1/2" clearance to any other combustibles, i.e. the sides of the soffit box. Different areas have different code requirements that vary from the NEC. I would strongly suggest that you give a call to your local building department and just ask them what is allowed for your locale. You might also ask them about the heat build up inside the enclosed soffit. After looking at your drawing again you might get quite a build up of heat with a non-IC rated can with no ventilation inside those soffits. Better safe than sorry, eh? lol

Just my two cents.

P.S. I just reread your posts again and saw that you mentioned that there is "a completely open joist space above it". If you mean attic or crawlspace then you are right, there shouldn't be an issue with heat build up.

But another thought just hit me (sory, lol), I count 12 lights total and two fans in your drawing. Are there any other fixtures or outlets on the circuit supplying the lights? You might want to check the amp ratings of the lights and fans and be sure that you aren't maxing out that circuit. For example, if there was an outlet in the room on the same circuit and you plugged in a heater you probably would blow a 15 amp circuit, maybe even a 20 amp circuit, depending on the draw of the lights. You might want a separate circuit for your lighting requirements. Again, just my two cents. Well....thats four cents now. sorry lol