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kgeorge's picture

Ok, I know this it probably NOT considered "Fine" woodworking, but my wife has asked me to build a cover for our patio. She wants it to span 12' out from the house, and measure 24' wide. My concern is that I make furniture - not homes.

With this in mind, she wants part of the roof for the cover to be a gabled roof (12' x 12'), while the other part will be just extending our current roof. I am concerned that to support that much weight, I would need something really strong to hold the cover up.

So, I am asking: Which is better, 2 2x4's glued/screwed together to form a post, or simply buying a 4x4 post?

JohnWW's picture

(post #114099, reply #1 of 10)

A single 4x4 will work just as well, and be just as strong as the paired 2x4's.

John White

John White Shop Manager for FWW Magazine, 1998 to 2007

kgeorge's picture

(post #114099, reply #2 of 10)

Thank you very much for your response. I was concerned that the tensile strength of a single 4x4 would not be as strong as 2 2x4's.

USANigel's picture

(post #114099, reply #3 of 10)

Only problem is a 4x4 made from PT lumber may twist as it drys.


A built up section is less prone to this.

bd's picture

(post #114099, reply #4 of 10)

If you are planning on using pressure treated stock, you may have to go with the 4x4s. Most 2x PT stock is not suitable for ground contact. Besides that, if you're planning on using the Simpson post anchors, or something similar, you may find that they are made only for 4x4 stock.

RalphBarker's picture

(post #114099, reply #5 of 10)

You may also want to check local building codes. My impression is that vertical supports are usually larger than 4x4, but I might easily be wrong on that count.

MikeHennessy's picture

(post #114099, reply #6 of 10)

It's not only the size that counts -- it's the number used, the spacing, live and dead loads, racking, how they are attached, etc. Is there any chance of snow load? Have you considered wind loads and lift? LOTS of variables. You may wanna talk to your BI or get an engineer or architect involved. Cheap insurance. Also, you'll need to consider all these things for the roof framing -- 12" is a pretty long span.


Did I mention you should get a professional consult? ;-)


FWIW, I generally use 6"X6" for this type of application. Sure, you could do it with 4"X4"s, but they look like carp, IMHO -- too "spindly".


Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

roqqytop's picture

(post #114099, reply #7 of 10)

I AM an engineer.
Give me the spacing, spans, and your LOCATION & I will tell you what you NEED.

8 foot 4 x 4 properly attached (top & bottom) are nearly impossible to BUCKLE.

Maybe if a train hits them!

KiddervilleAcres's picture

(post #114099, reply #8 of 10)

roqqy,


Give me the spacing, spans, and your LOCATION & I will tell you what you NEED.


You're on man!


I want to build a 12' x 20' pergola - one side will be attached to the house.  The other end will be the long side <20'> which I plan on spacing 8'-10' columns either 4' or 5' OC and a 2x cross beam on top (maybe mortise the beam into the columns) running ~ 20' with some overhang.


2x beams will then be added running from the house out to the cross beam with ~ 2' overhang, probably 16" OC.


I want a roof over part of it but I want to minimize how much it shows.  Fortunately the house sits up from the road which should aid in keeping the roof from showing.  I'm thinking of corrugated fibreglas panels.


What I'm thinking of doing is install the roofing material between the beams runnning out from the house to the cross beam.  Starting from near the top of the beams and pitching it down as it traverses the beam out to about 8' - 10'.  Haven't picked what material I'll use yet and may need to put in cross supports as well.


Yeah, clear as mud right!?  Oh, and I live in northern New Hampshire - read lots of snow!  If I have to I will fashion together a roof rake..........


Regards,


Regards,



Bob @ Kidderville Acres


A Woodworkers mind should be the sharpest tool in the shop!


Edited 11/6/2008 8:42 pm ET by KiddervilleAcres

Bob @ Kidderville Acres

A Woodworkers mind should be the sharpest tool in the shop!

FastEddie's picture

(post #114099, reply #10 of 10)

If you're only going 20', use a column on each end and one in the middle, use an LVL for the beam.  All the roof weight is on the side walls anyway.  Or can you set the columns is a little from each end, say 2' and then omit the center column since the span is only 16'.  You will need to spec the LVL correctly.

"Put your creed in your deed."   Emerson


"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it."  T. Roosevelt

"Put your creed in your deed."   Emerson

"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it."  T. Roosevelt

kgeorge's picture

(post #114099, reply #9 of 10)

Cool!

As I mentioned earlier, I want to build a patio cover over my existing 12-0 x 12-0 slab, and extend the length of it 12-0 to make it a 12-0 x 24-0 patio (12' deep x 24' wide).

The 12-0 x 12-0 needs to be a gabled roof, while the other 12' can just be a sloped roof (if this makes any sense).

I plan on screening the whole thing in later making it a screened-in patio.

I live in Houston, TX and I was figuring a 4x4 post every 12' making the span for each portion of the gable 6' from center to the end.

I also planned on using 2 x 6 for the rafters and the joists (and headers if I need them).

Does this sound structurally safe, or do I need bigger posts, joists, rafters?