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missin44
Help - Question on deck rebuild?

The previous owner did something I nor anyone else I know had ever seen. He pored a concrete elevated deck. Anyway I'm tearing it out because I'm getting some wood rotting due to the concrete. I will need to replace the header/beam/girder (lots of rot), the long beam that spans the from pillar to pillar. The span is 14 feet. That beam was a left over log from the house, 6"x7" (it's a log house). See picture below.

Anyway I have calculated I can double up 2 2x10x16's and make the span work. My question is this I have a bunch of 2x8x16's. Plus the 2x8's would look better for a number of reasons, additionally I have no idea how I'm going to get the 2 2x10x16's to the house. I friend picked up the other decking, but now he's out of town for the next 3 weeks. My question is this, can I triple up 3 2x8x16's? If I can't, I would be curious as to why I can't.

canuk

The span of 16 feet is too much for the depth of a 2x8 unless it is supported midspan.... even tripled up.

The 2x10 at 16 feet is pretty much at it's maximum unsupported span.... but there is the issue of side loading the longer the span.

The issue is with dimensional lumber is the grain of the lumber is running the same for all members when doubled or tripled. This is unlike engineered lumber of equivalent size ... the grain is staggered or random placed which is one reason they can be stronger than dimensional lumber.

missin44
canuk wrote:

The span of 16 feet is too much for the depth of a 2x8 unless it is supported midspan.... even tripled up.

The 2x10 at 16 feet is pretty much at it's maximum unsupported span.... but there is the issue of side loading the longer the span.

The issue is with dimensional lumber is the grain of the lumber is running the same for all members when doubled or tripled. This is unlike engineered lumber of equivalent size ... the grain is staggered or random placed which is one reason they can be stronger than dimensional lumber.

The span between pillars is 14 feet. Would this work?
Thanks

canuk
missin44 wrote:

The span between pillars is 14 feet. Would this work?
Thanks

Nope ... too far of a span.

Depending on your local /state code this may follow the Internation Residential Code of an exterior balconey which is spec'ed at 60 pounds of live loading.

Sounds like you're set on using the 2x8's ... the suggestion by jkirk is a very good option.

missin44

nope, not set on using 2x8's just an idea so I asked the question. Never hurts to know why.

ma2804

Something you could think about doing if you're set on using the 2x8's is to cut a piece of exterior/half inch plywood and put that in between the two 2x8's. I think it's called a fitch plate and is used commonly in headers above windows in houses. The span is still a long one. If you use the plywood, nail the bejeezus out of it with 16d nails to make it a solid unit. You might get by but if it were my deck and I'd be standing on it, I'd go with larger dimensioned wood and even then, maybe use the plywood plate.

canuk

ma2804 ... i would have to disagree with your suggestion .... it's still too far of a span of 14 feet for the 2x8 .... even with the plywood.

One of the benefits of adding the plywood came from using 2x4 framing , With the thickness of the 2x4's being 1 1/2 inches when doubled only gives 3 inches .... the 1/2 inch plywood also gives the extra 1/2 inch to bring the thickness equal to the 3 1/2 inches for the 2x4 width. This allows headers to be flush with the framing and the finish wall surface.