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post #1 of 27 Old 08-08-2013, 01:56 PM Thread Starter
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building a long valance

Hello, new guy here ... I have just built an addition to my house, a study, with the help of a friend who is a carpenter. Just got certificate of occupancy yesterday (!!) but there is some interior stuff left to do.

Main thing I want to do is to built a valance along each of two opposite walls of the room. These would run the entire length of the wall and be attached to the neighboring walls at each end. Each would be T-shaped. A vertical piece, maybe 8-9" tall, would run across the room; there'd be a horizontal piece between the wall and the vertical piece. So the cross-section would be a "T" lying on its side. Basically each valance would be a long shelf, with a band at the outer edge of the shelf that extends several inches above and below the shelf. The band serves to hide what's on the shelf and to support the outer edge of the shelf. One valance would be 15+ft long and about 1ft wide, the other about 13ft long and about 2ft wide. I'd have rope lights for diffuse room illumination on top of the shelf, and attach task downlighting to the bottom of the shelf.

Hoping I've explained the basic design in a comprehensible way, here's my question. What should I build the vertical member from ? It not only needs to support itself across the entire 13/15ft width of the room, but it needs to support one edge (so half the weight) of the horizontal piece. The horizontal piece is less critical and would probably just be 3/8" plywood, and wouldn't carrying a lot of weight, mainly just the lights I mentioned.

At first I thought I would use 2x10 clear fir, but the local lumber yard that can get the fir says 2x10 would be hard or impossible to get. Carpenter recommended radiata pine, but again, as a wood primarily used for trim, it does not seem to be available in 2x10. Current plan is to use plywood. Of course plywood doesn't come in the length I need, so I'd glue & screw a sandwich of two pieces of 1/2" or 3/4" plywood (with the joints staggered), with a 1-by band along the top and bottom edges. Plywood also means I'd have to probably give up my plan to have a wood finish, and paint it instead - but I think I'm ok with that.

Anyhow, does plywood seem like the best bet ? If so, what kind of plywood ? Thanks much !

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post #2 of 27 Old 08-09-2013, 10:38 PM
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Plywood is absolutely the best choice IMHO. Thinking of it as a beam, the plywood piece in the vertical orientation is exceptionally strong since it will be about 8-9" - practically no deflection for your intended purposes as a decorative niche.

I would consider how to hide the joints - if it was me, I would space them so that it makes it look as if it was part of the design. Perhaps use a piece of molding, like a quarter round where the joint is to be hidden or something similar to your tastes.

For a piece that is that large you would want to consider it being trim color or wall color to be a backdrop and not so much a focal piece as the intended items on display should do that part.

Plan on having a recess on the underside for your wiring that can be concealed, keeps it looking clean underneath and if you should need drapery in certain areas, it will prevent a snag.

The t shape you mention - if the space between the front of the T is adequate, its a popular place for crown to be installed. If your room already has it or you are planning on adding it, you might want to skip it as it can be overkill.

Last edited by chopnhack; 08-09-2013 at 10:43 PM.
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post #3 of 27 Old 08-10-2013, 02:49 AM Thread Starter
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Thanks for responding !

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Originally Posted by chopnhack View Post
Plywood is absolutely the best choice IMHO. Thinking of it as a beam, the plywood piece in the vertical orientation ...
Great, plywood is really what seems right to me.
Quote:
I would consider how to hide the joints - if it was me, I would space them so that it makes it look as if it was part of the design. Perhaps use a piece of molding, like a quarter round where the joint is to be hidden or something similar to your tastes.

For a piece that is that large you would want to consider it being trim color or wall color to be a backdrop and not so much a focal piece as the intended items on display should do that part.
Yeah, actually I was thinking to paint the plywood "beam" the same off-white color as my drywall, with a 1-by band along the top and bottom in the same clear-finished clear fir as my window and baseboard molding. Or maybe that'd be too "busy" and the whole thing should be wall color.

Quote:
Plan on having a recess on the underside for your wiring that can be concealed, keeps it looking clean underneath ...
I figure all the wiring can be on top of the horizontal "shelf", where it won't be visible at all (since this thing will be above the windows and below the top of the wall where the sloped sides of the vaulted ceiling start). So the rope lights for general room lighting will just be tacked up there, and the wiring for any underside task lighting we be up there and come through the shelf where it needs to. Make sense ?
Quote:
The t shape you mention - if the space between the front of the T is adequate, its a popular place for crown to be installed. If your room already has it or you are planning on adding it, you might want to skip it as it can be overkill.
I'm not following you at all. The T shape is: the beam we've been discussing is the top of the T and the horizontal shelf is the stalk of the T. Not sure what you mean about "between the front of the T". Anyhow, my house doesn't have crown molding.
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post #4 of 27 Old 08-10-2013, 06:15 AM
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I agree with chopnhack...ĺ" plywood would be what I would use. If you wanted a woodgrain finish, you could use a hardwood plywood of your choice, or if painted, you could use Birch, Maple, or Poplar.

His recommendation of joining the ply in three equal lengths is a good one. IMO, the best method would be with a half lap, and you could make the overlap a bit long, like 6" or more. Once glued and clamped, the total length would be as structurally sound for your application as if it was one piece.

I would also run a small wall cleat along the wall above the shelf to attach the shelf. That would be a big help in stabilizing it's overall length.







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post #5 of 27 Old 08-10-2013, 09:31 PM
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Quote:
Originally Posted by cabinetman View Post



His recommendation of joining the ply in three equal lengths is a good one. IMO, the best method would be with a half lap, and you could make the overlap a bit long, like 6" or more. Once glued and clamped, the total length would be as structurally sound for your application as if it was one piece.


.
An excellent idea on the half lap. You could probably then get away with routing a small v groove as an architectural detail instead of using an applied molding.

Let me illustrate the T with crown concept:
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post #6 of 27 Old 08-11-2013, 12:56 AM Thread Starter
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I think I've done a poor job of explaining the design. Here's a drawing. Maybe "valance" is the wrong term. It'll probably extend as far, or farther, above the shelf than below. I hope I used "cleat" correctly. I'm imagining it's just a 1x1" or so strip of wood running the entire length of the valance, to which attach the shelf from below.
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post #7 of 27 Old 08-11-2013, 01:14 AM Thread Starter
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Quote:
Originally Posted by cabinetman View Post
Thanks for the nice welcome !
Quote:
...ĺ" plywood would be what I would use. If you wanted a woodgrain finish, you could use a hardwood plywood of your choice, or if painted, you could use Birch, Maple, or Poplar.
Any thoughts about aesthetic of woodgrain versus painted versus painted plywood with woodgrain strip at top and bottom edge of plywood ? FWIW, the room is sheetrock walls and vaulted ceiling with woodgrain window interiors and trim and woodgrain baseboard/shoe molding.

If I paint the plywood, why not just use A-C pine, why birch, maple, or poplar ?
Quote:
His recommendation of joining the ply in three equal lengths is a good one. IMO, the best method would be with a half lap, and you could make the overlap a bit long, like 6" or more.
I'm not a real woodworker, so some of this lingo is lost on me - please be gentle. I didn't get the part about three equal lengths. Are you saying the plywood pieces would be like the drawing below ? If the longer valance is 15ft, I imagine one ply would be two 7.5ft pieces and the other three 5ft pieces, lapped as shown. Why not make the center piece the full 8ft and the other two 3.5ft ? This would also allow the thing to be made from four strips ripped from one sheet of plywood; otherwise, five strips would be required, which might not allow the thing to be made from one sheet of plywood, unless the height is only about 9" (allowing for kerfs).

Should I just glue and clamp, or also screw, or also use a finish nailgun ?
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post #8 of 27 Old 11-03-2015, 03:10 PM Thread Starter
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Bumping. because I'm getting back to this project (after two years, yikes !!) ...

To summarize, I want to build a beam that spans 15ft across a room. I'm going to use two thicknesses of 3/4" plywood, glued and screwed. Something was said earlier, that confused me, about how to lap the layers. I was planning to rip a sheet of plywood lengthwise into 10" wide strips. I'm thinking one layer should be two 7-1/2ft strips, and the other is one 8ft strip in the middle and two 3-1/2ft strips at each end (see thumbnail). But someone seemed to be saying one layer should be three equal length (5ft) strips; is there some reason this makes more sense that what I intend ?

I'd face the beam so that the exposed face is the two 7-1/2ft strips, so there is only one joint to conceal. I figure I'd bevel the edges at those ends of the strips slightly, and then I could spackle with wood putty and then paint the whole thing. With a strip of polyurethaned 1x2 clear fir at the top and bottom.

I also wanted to confirm that people believe this beam won't sag in the middle.

Thanks !
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post #9 of 27 Old 11-03-2015, 06:28 PM
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Hi Rusty,

I looked at the responses from two years ago.

The suggestion was to "half-lap" a single layer of 3/4" thick plywood strips together. Basically, you would have three strips each six feet long or so, then cut away half of the thickness for six inches on each end, so that the last six inches of the plywood strip is 3/8" inches thick. This is the half part. Then you glue the halves together and it is 3/4" thick where they overlap. This is the lap part.

However, looking at your picture, there is nothing to keep this whole thing from sagging down away from the wall. Something will have to be done to support the load of this shelf. As drawn, it will not stay up.

Think of what you're proposing as a shelf with a heavy front edge, because that's really what it is.

Shelf supports, or corbels, or something is needed to transfer the load of the shelf to the wall studs. Even a single cleat attached to each stud, and then a length of plywood attached to the cleat and then the shelf will help.
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post #10 of 27 Old 11-03-2015, 06:38 PM
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Actually, falling off the wall is what I meant to say. I just couldn't edit
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post #11 of 27 Old 11-03-2015, 07:40 PM Thread Starter
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However, looking at your picture, there is nothing to keep this whole thing from sagging down away from the wall. Something will have to be done to support the load of this shelf. As drawn, it will not stay up.
Sorry, I should have said, the beam I show will be in a vertical orientation. The only horizontal element will be a piece of 3/8" or so plywood between the wall and the beam. All it'll be supporting is some rope lights. (See post #6 above).

Thanks for explaining what the half-lap means. I'm thinking I don't really need to get that fancy though.

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post #12 of 27 Old 11-03-2015, 09:31 PM
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I have an incredibly ugly valence above my kitchen sinks. It was meant(?) to hide the double-tube fluorescent light fixture. Just bandsaw 3/4" plywood with some curves and corners.

1. Out comes the fluoro fixture.
2. In goes a bank of 4 x 8W warm white LED lights
3. I have 24" western red cedar split into 3/4" thick x 6" panels which will be carved to represent the 4 seasons.
4. That gets screwed into the crappy plywood.

With 7,000 - 8,000' mountain ranges both east and west within 5 miles, my winter days are cut short by 2 hrs when compared with the "theoretical rise/set."
I want good light and something nice to look at.

Before this winter is over.
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post #13 of 27 Old 11-03-2015, 10:56 PM
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Quote:
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Sorry, I should have said, the beam I show will be in a vertical orientation. The only horizontal element will be a piece of 3/8" or so plywood between the wall and the beam. All it'll be supporting is some rope lights. (See post #6 above).
Hi Rusty,
I was referring to the picture below that you posted.

That looks like a pretty wide horizontal piece. When i look at it, i think that piece plus the 3/4" plywood "beam" will be too heavy for just a cleat above and below. All that's holding that is some screws close to the end of the horizontal "shelf" that are going into the cleat.

Anyway, if all you are doing is rope lights above, why not just use crown molding? Google "crown moulding with rope lights"
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post #14 of 27 Old 11-04-2015, 12:52 AM Thread Starter
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Hi Rusty,
That looks like a pretty wide horizontal piece. When i look at it, i think that piece plus the 3/4" plywood "beam" will be too heavy for just a cleat above and below. All that's holding that is some screws close to the end of the horizontal "shelf" that are going into the cleat.
The plywood beam is the support, not the thing being supported; it is securely fastened to the wall at either end of it (the walls that are perpendicular to the beam and to "wall" in the drawing). So the horizontal shelf is supported for its entire 15ft length by cleats along both sides: one cleat is attached to the wall studs, the other to the beam (maybe I am using the word "cleat" incorrectly). Does that make sense ?

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post #15 of 27 Old 11-04-2015, 07:57 AM
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If it were me ....

I would construct the "bean" using 1/2" plywood and have 3 layers rather than 2. A span of 15 ft is considerable, so you need a beam with a good section. A hollow beam made of thinner material may also work. The deeper or wider it is, the stronger it will be.

If you could support it from the ceiling in the center with a strap or a wire that would help. A French cleat, or several on the back of the shelf would also help support it, and make it easier to install.

You are only supporting the beam with very little "load" from the lighting. The beam will want to twist because of the span, but your shelf prevents that. It's doable!

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #16 of 27 Old 11-04-2015, 08:29 AM
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Quote:
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The plywood beam is the support, not the thing being supported; it is securely fastened to the wall at either end of it (the walls that are perpendicular to the beam and to "wall" in the drawing).
I see. That does help somewhat. I assume you will be attaching it to studs on the end walls? As Bill said above, 15 ft is a considerable span, so you may want to add an additional support in the middle.
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post #17 of 27 Old 11-04-2015, 03:47 PM
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I meant to say beam....

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I would construct the "bean" ...... beam .....using 1/2" plywood and have 3 layers rather than 2. A span of 15 ft is considerable, so you need a beam with a good section. A hollow beam made of thinner material may also work. The deeper or wider it is, the stronger it will be.

If you could support it from the ceiling in the center with a strap or a wire that would help. A French cleat, or several on the back of the shelf would also help support it, and make it easier to install.

You are only supporting the beam with very little "load" from the lighting. The beam will want to twist because of the span, but your shelf prevents that. It's doable!
edited to spell beam

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #18 of 27 Old 11-04-2015, 04:08 PM
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Could use an lvl beam. No seams. Save trouble of gluing up plywood.
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post #19 of 27 Old 11-04-2015, 09:29 PM Thread Starter
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Thanks for the suggestions, guys.

LVL is interesting. Looks like it might be as low as $60, *if* one of the local suppliers is as cheap as an online price I saw. A bit more than the plywood route ($42), but I wonder if the finish is as nice as the plywood I'll likely use (looked at it today, has very nice primed surface): http://www.lowes.com/pd_520360-53547...=50121139&pl=1

How much strength improvement does three 1/2" layers provide (over two 3/4" layers) ? A bit more work too: with the 3/4", only the two joints between the three long sections are critical (I'm guessing the two 3-1/2ft pieces at the end don't do much structurally).

Yes, the ends will be very firmly attached - stronger than studs. To a big header at one end; to a piece of 2x10 I put into the wall when I built the room, at the other end. Use big angle brackets, carriage bolts on the beam side, lag screws on the wall side. And I just can't really see it failing catastrophically. Likely won't twist, because of shelf bracing it, as @woodnthings says. But I imagine sagging could happen. I can't brace the center to the floor; I could brace it to the ceiling, but I'd rather not, so much so that I don't think I'll do it at all if it seems that's a likely outcome.

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post #20 of 27 Old 11-05-2015, 01:24 AM Thread Starter
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How much strength improvement does three 1/2" layers provide (over two 3/4" layers) ? A bit more work too: with the 3/4", only the two joints between the three long sections are critical (I'm guessing the two 3-1/2ft pieces at the end don't do much structurally).
Looking at post #4 above, someone seems to be suggesting a single 3/4" thickness; I don't want to try the half-lap, but it makes me wonder if I should consider two layers of 1/2".
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