Construction question (deck)

[pat32rf]

Building a beam out of shorter pieces doesn't bother me, as long as the joints are well staggered (evenly, with 6' between) so you have the required number of two by's at any given point. Using 2x10 when the plan calls for 2x12 does bother me however.
I don't know if you will be haveing snow coming off your roof and landing on this deck, but if so I would be worried, especially about conditions 10yrs down the road. Is it pressure treated lumber? Cedar?
The blue prints (plans) should have some info in the bottom right hand corner stating who drew them up. I would get in touch with them first and explain my worries.
If I bought your house and found this problem I would probably add a 18' 2x12 to each side of the beam, or two pressure treated 2x6's laid flat (with staggered joints) to the bottom.
Many homemade laminated wood beams will start to deteriorate as soon as the rain gets to it and it can't dry out. We find that after 10-15 years many home made decks are starting to get shakey due to this.

 

[capi75rs]

We've got a guy who's building a deck and adding a small area to the house.

Attached is a picture (sorry for the BLUE, seems I had camera on "indoor lighting")

Anyways...

I've tried to draw in the item of my question.

Today, they added another post (the skeleton in yellow). In addition to this post and per the blueprints, they added "two 2x12 dropped girder" and this section is the left/right yellow (pardon the great draw job I did!)

This girder is two 2x12's that on the house side, go into a slot that they cut into the block wall so it's got great support. On the post side, it's currently nailed to the post and they'll probably add the hanger later on. At least, that's how they did the other joists.

Here's the crux of my question...

They took a SINGLE 2x12x18 (this span is right at 18') and in essence, took another 2x12x15 and a 2x12x3 and married the 15' and the 3' boards onto the single 18' board to give them "two" 18 footers.

I don't know but my logic says that this is NOT two 18 footers since there is a break in one of them...I'm ONLY going to have the full strength of a single 18 footer and maybe some additional strength by the added parts but I will NOT have the strength of TWO 18 footers.

Is my logic correct or am I being too ****?

I'm ready to call the builder and have him yank those down but don't want to put my foot in my mouth as I'm so wanton to do.

Any thoughts would be appreciated.

BTW, I'm looking at the blueprints and they call for "2 2x12 dropped girder"

??

If the contractor glued (liquid nails) the boards and then nailed them about every 4-5 inches in a diagnel pattern (think of a heart rate monitor) and put a plate across the joint, the two boards will be fine. When I constructed my hayloft, both my sister-in-law who is an architect and my local contractor suggested doing this for the strength. I made a 18'x16' hayloft and keep over 200 square bales of hay (@80lb each). The main thing is that if you use 4 boards instead of 2 is to keep the joints away from each other. My joints are 10' apart and I've never had any saging or bowing. In short if they were glued, nailed, and have a joint plate I would not be worried.

 

[Sherweld]

Building a beam out of shorter pieces doesn't bother me, as long as the joints are well staggered (evenly, with 6' between) so you have the required number of two by's at any given point. Using 2x10 when the plan calls for 2x12 does bother me however.
I don't know if you will be haveing snow coming off your roof and landing on this deck, but if so I would be worried, especially about conditions 10yrs down the road. Is it pressure treated lumber? Cedar?
The blue prints (plans) should have some info in the bottom right hand corner stating who drew them up. I would get in touch with them first and explain my worries.
If I bought your house and found this problem I would probably add a 18' 2x12 to each side of the beam, or two pressure treated 2x6's laid flat (with staggered joints) to the bottom.
Many homemade laminated wood beams will start to deteriorate as soon as the rain gets to it and it can't dry out. We find that after 10-15 years many home made decks are starting to get shakey due to this.

I'm an old guy who has replaced and rebuilt many decks. I try my best to never sandwich boards together when water has a path to the joint. And absolutely never if they are not pressure treated. I've experienced far too many structural "beams" in an advanced state of decay as a result of moisture standing between surfaces for long periods then eventually partially drying out in the summer and so forth.

I even go so far as to "flash" the top of such a beam with strips of a product such as Nervastral, so that water falling through the deck doesn't wick in to the joint.

But before a face to face sandwich, I will try to somehow leave at least a 1/2" space between faces. This usually means using full length boards between supports.

Bottom line, I have nothing against composite sandwiched beams, just not unprotected in the weather.

Best wishes
Sherweld

 

[kenmac]

Richard, I would do as some others have suggested. Have local inspector check this out.I don't know about your area. But, here you have to get a permit for almost any project. The project has to be inspected in steps. Footings, electrical, etc,.

 

[2manyrocks]

Sherweld is describing the best construction practice. Lots of decks don't have the maximum life expectancy because the builders don't go the extra step to make them shed water. I don't know whether a built up beam in an exterior deck is a code violation or not since the code is a "minimum acceptable standard." But a beam that traps water is not the best practice.

 

[shane]

Along with all the other great info you've been given I'd bet a nickle that if your beam is made of pressure treated wood that when it "drys" out you will be able to see light between the layers. Not a good thing when they are relying on the strength of each other.

 

[Tractor Factor]

I've been a general contractor for nearly 30 years, and I can tell you that when it comes to girders, the depth of one is the critical factor. Reducing the depth of any load bearing joist or beam weakens it exponentially, more so than by increasing the span. My ex-partner is an engineer these days, and we used to talk about this stuff all the time.

How long are the joist spans in this area? Is the girder below only stiffening full-span joists at or near the mid-point, or are the joists two separate members that butt over the girder? This is important because if the joists are not full span the girder is carrying fully half the floor weight.

But either way it's a moot point, because you simply cannot decide to alter the plan specs for your own expediency. Years ago inspectors routinely allowed us to substitute, say a triple 2 x 8 for a double 2 x 10 for short spans like headers over windows and doors; today we don't even do that...just follow the prints exactly.

You can have joints in a girder, yes, but typically you need to have a post within a certain distance of the joint. Granted a deck load isn't calcuated anywhere near, say, the first floor living space of your house, but the principle is the same.

As you can see, you need to put numbers on a lot of variables when you build, and this is why it's just not adequate to by-guess and by-gosh your way through things when you begin to stray from the plans.

Without more specific info it's impossible to tell you what to do, but if it's my house I would without question put one or two posts under that girder, spaced evenly. If you don't want these posts in your way (and who would?) I would rip out that girder and do it right.

 

[mjncad]

...by-guess and by-gosh your way through things when you begin to stray from the plans.

My term for this kind of winging it is, "Rectal Engineering." Tractor Factor just put it more politely than I do.

 

[jimmysisson]

In Mass, a deck load is calculated at 40 psf, just like living space. I agree with getting your builder to put this together as spec'd. And splices are not best practice unless done properly. And sandwiching exterior beams can be done but with spacers and bolts, no plywood. I'd ask him to change the beam from something he mis-ordered to the correct size.
Jim

 

[Whitey]

I don't like what I see........to many people think they know how to build decks. You should never test the span limits of wood especially when it is out of doors. Also, I never depend on common nail connections for building. I do things the old fashioned way.........I notch materials together. Outside band boards or stringers are always notched into 4x6 wood replacing wood directly transferring bearing into column into spread footing. If I have a long span or want to support a cantalever.....I use a galvanized fitch plate between dimensional lumber. Last but not least......I use galvanized all thread, nuts and washers for all major connections and 20d nails for common connections.