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Stacked lumber

D

Durant

Bronze Member
Joined
Aug 6, 2012
Messages
86
Location
Oklahoma
I haven't been called to inspect it yet; but, have you seen stacked 2X6s to build a joist?

It is two 2X6s stacked on top of each other to build a joist; and the HVAC unit is on top of them in the attic. There are intermittitent 2bys nailing them together about every 4 feet.

Wouldn't this be engineering?
 
what you mean "stacked" tonto ?, like a flat stack, or "built up" as in side by side, please clarify. a 2x6 doubled up is permissiable as a joist/girder so long as the spans do not exceed those allowed in tables 2308.9.5 and .6 of the ibc 2006 for headers and girders
 
ARE THEY JUST BUILDING IT UP TO GET PITCH ON THE CONDENSATE OR TO CLEAR INSULATION? Or is it some funky structural stuff going on?...... Sorry bout the caps.....
 
It could be calculated out, would I do it? No. If they provided calculations that matched provisions in the code I would review them.
 
Stacked; as in one on top of the other and secured together by nailing 2bys vertically to them to hold them together making a 2" X 11" (5 1/2 plus 5 1/2 inches high) single joist.
 
Residential or Commercial, and what codes are you using?

Also, I believe that the fastening tables are referring to wood framing

members being attached together in the "face-to-face" style, and not

"end-on-end".

One reference for nailing "built up" girders and beams is from the

American Wood Council, Details For Conventional Wood Construction,

Page 25.

http://www.awc.org/pdf/wcd1-300.pdf



.
 
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This is not end to end this is edge to edge one 2x6 in an existing ceiling joist situation. Then someone realizing that to use the space and load these to support the furnace they needed more structurally or to get the required depth beneath the floor the furnace will sit on for insulation purposes they needed height so they stacked an additional height of 2x6 directly above the existing ceiling joists creating a 2x12 (actually measures 11" as Durant stated). I am interested in one of the engineers on here will comment about this. I know there is some value in this and I am curious if this is still calculated as repetitive, what connections they would recommend, how this application compares to whole pieces of lumber of comparable size, etc..

ZIG
 
zigmark,

You are correct sir! I should have stated "edge-to-edge" attachment.

I believe that this type of built up wood construction would fall

outside the prescriptive codes and require an engineered design.

.
 
what is the span, wil the 2x6's be gussetted with plywood or truss plates, wha.....wha.....wha....why not use a 2 x12
 
Zigmark,

You got it right; it is to increase the height for insulation. They didn't want to go get 2X12s so they stacked the 2X6s to get the height.

It's crazy, I've never seen this attempted before.
 
I see a 2x added to the bottom cord of trusses all the time. This furring allows for insulation as stated. No big deal IMO.
 
As long as the original 2x6 is the correct member for that location then there shouldn't be any problem doing this because extra support is not required.
 
Durant said:
Zigmark,You got it right; it is to increase the height for insulation. They didn't want to go get 2X12s so they stacked the 2X6s to get the height.

It's crazy, I've never seen this attempted before.
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it sounds as if they are building a platform for the HVAC unit to sit on. That should not impair the integrity of ceiling joist and would amount to the same as building a soffit.
 
If a 2"x12" were required for structural concern and you found a 2"x12" that's split down the middle for it's entire length.....would there really be a sound?
 
If a single 2x6 will do the job then they are fine. One 2x6 above another 2x6 does not make a 2x12 structurally unless the joint between members is designed to handle the shear. where maximum bending moment occurs at midspan, maximum shear is at the ends of a simple beam.
 
Question: usually the furnace and water heaters are place near or over interior bearing walls; otherwise do you require to calculate the weight distributed over the effected ceiling joist or is it accounted for with attic limited storage span table?

Francis
 
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If it is the bottom cord of a truss then no it is wrong unless the bottom cords are designed for the additional wight. The unit needs to be suspended from the top cords.

If it is a ceiling joist then yes it will be fine.
 
Francis Vineyard said:
Question: usually the furnace and water heaters are place near or over interior bearing walls; otherwise do you require to calculate the weight distributed over the effected ceiling joist or is it accounted for with attic limited storage span table?Francis
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Or how about the HVAC being hung from the roof rafters. There are a lot of retrofit units installed in attics without consideration for the additional load, proper access and service platform.
 
Thanks for all the input,

According to the 2009 IRC, R501.1 the joists under the HVAC are floor joists. I see nothing in the codes that allow framers to manufacture joists. The stacked joists, secured together by nailing vertical 2bys to the two joists is not anything I can find in the IRC. If you inspected floor joists of a two story home and saw stacked 2X6s installed in this manner instead of 2X10s would you pass it?

I believe that this is manufacturing joists (on site) and it should require engineering by a qualified engineer.
 
Definitely need to have it engineered. We had a project like this and when the joists were tied together the engineer calc'ed them in bending as one deep joist if I remember correctly; I'm not sure if he did a reduced value but it's very likely.
 
Durant said:
Thanks for all the input,According to the 2009 IRC, R501.1 the joists under the HVAC are floor joists. I see nothing in the codes that allow framers to manufacture joists. The stacked joists, secured together by nailing vertical 2bys to the two joists is not anything I can find in the IRC. If you inspected floor joists of a two story home and saw stacked 2X6s installed in this manner instead of 2X10s would you pass it?

I believe that this is manufacturing joists (on site) and it should require engineering by a qualified engineer.
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It would depend on span and load. If a single 2x6 will handle the load then the second one stacked over it is blocking, it would pass. If the single member cannot take the span and load then they are counting on some contribution from the built up member and have designed a beam. The second issue, depending on the location and weight of the HVAC unit it is a point load, the span tables are for uniformly distributed loads. In bending formulas a beam can take half the load if it is a point load at midspan compared to a uniformly distributed load. However the unit can weigh less than the design load for the area it occupies. I would want to verify those before requiring an engineer. I suspect you are right in this case, but, I can add non structural wood onto structural wood as spacing or blocking without having designed a beam or having incurred the need to get an engineer.
 
DPR,

I wish I could post pictures but I have some computer problems that prevent it. I don't think some are seeing what is going on here. Picture a normal install of a 1 1/2 inch wide by 5 1/2 inch high floor Joist and then add on top of it another floor joist of the same diminsions "stacked" on top of it 1 1/2 inch width on top of 1 1/2 inch width that is the same height and held together by nailing a nailing few vertical 2bys to both to make a 1 1/2 inch by 11 inch floor joist. This was done on site by a couple of framers; not by an engineer's design with some type of specifications for securing these two boards to each other. You don't see a problem with that?
 
I understand the situation. I strongly suspect you are making the right call, but for the wrong reason. That is what I'm working on. "They stacked lumber thus they need an engineer" is incorrect. They overloaded an inadequate 2x6 joist, or, they tried to create a structural 2x12 out of two 2x6's is the correct reason to fail it.

Look at the span tables first, is a single 2x6 capable of spanning this distance? If not engineer.

If a single 2x6 is within allowable span then look at the load, assess its' magnitude and its' location in relation to the support below. If the HVAC's load is out in the span and greater than design load, engineer it.

If the HVAC weighs less than design load for the single joist, or, if the unit is over a support that upper 2x6 is just blocking. Make sense?

In a post above I mentioined that if they have attempted to build up a beam the joint between members needs to be designed to handle the shear. Take a phone book and hold the binding in your left hand thumb under, fingers on top. Grab the right edge the same way and hold it out in front of you flat like a beam comprised of many horizontal fibers. Bend it and notice what happened on the right edge. The fibers slid past one another, horizontal shear failure. Note the shape of the beam. Now set up again but pinch hard on the ends, don't let the pages slide, and bend again. You should feel more resistance to bending and see a slightly different shape. By controlling shear at the ends we have designed a beam that is stronger than one fiber sagging into the bending fiber below.

Historically when framers needed a heavy timber beam of greater depth than available material they would key the members together with horizontal pieces of dense wood or iron spaced along the joint between the two timbers... more towards the ends, fewer towards the middle to eliminate the slip betwnne layers, or, they would sheath the verttical faces with diagonal boards in opposing directions on either face, again eliminating slip. Plywood at both ends of this assembly on both faces with enough nails into each member to safel handle the shearing stress between members with a few blocks across the center to maintain alignment would accomplish the same thing. These are design efforts. Don't forget, I'm a framer, RDP's feel free to correct if I'm mistaken in any of that.
 
Durant,

A picture would be nice, HVAC unit is staked on top? Do they meet M1305.1.3? Floor requirements for appliances in attics and access to the appliance?

pc1
 
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