Any structural engineers or carpenters in the hous

02/17/2012 12:38:17 PM · #1

I'm looking to build a structure to provide cover for a hot tub and found some plans for a "wooden umbrella" which is four posts and a light roof supported by crossbeams going diagonally across the posts and joined with a lap joint. I would like to scale the plans up from 6'6" on a side to about 10' on a side. I'm searching for a site that will help me figure out what would be good to use for the crossbeams. The original plans call for 2x4s and I think that's too small to span 14 feet and support the roof.

Any thoughts? I'm thinking either double 2x6s or 2x8s. I could also go with 4x4 posts.

Nikon AF-S Zoom-Nikkor 28-70mm f/2.8D IF-ED

02/17/2012 12:43:50 PM · #2

Message edited by author 2012-07-24 16:47:09.

hihosilver

Nikon D200

02/17/2012 12:45:18 PM · #3

Ummmmm...isn't this a PHOTO site...I have no idea as to the answer to your question, but I'd be happy to come over and take pictures of you building it...;-P

02/17/2012 12:46:26 PM · #4

ok, hold on!

Canon EF 28-135mm f/3.5-5.6 IS USM

02/17/2012 12:51:34 PM · #5

Here you go.

Don't worry deeby, if the roof falls down it's my own damn fault. I do have experience (in case you worried). I put myself through undergrad framing houses and my dad is a general contractor. Of course, when I asked my dad he sent me back a completely different set of plans. But that's not what I want to do dad! Typical... ;)

I'm probably going to beef the vertical posts up to 6x6 mainly for aesthetics.

Message edited by author 2012-02-17 12:53:06.

Kelli

Canon EOS-D60

02/17/2012 12:52:26 PM · #6

~~Round, pointed roof~~? I could ask my husband later and get back to you. He's a carpenter.

You posted the same time I did. I'll have him look at it later.

Message edited by author 2012-02-17 12:53:52.

02/17/2012 12:55:14 PM · #7

I would go with the 2 by 8s, I only work in meters but I believe your span is just over 4 meters, that is quite long, here no matter what depth of wood we use we never go beyond 4.5 meters, you should be fine. I recently did a roof and I used cross beams of about 4 by 8, for a span of 12 feet, the 4 was only for aesthetic purposes because i was covering the top with wood so as to have a apparent ceiling, the wood was oak so a bit stronger I suppose.

02/17/2012 12:58:03 PM · #8

Ya, the span will be about that. I may squish it down to 9 feet from post to post (since the roof has some overhang) and that would make the span 12.7 feet or 3.9 meters.

02/17/2012 12:59:52 PM · #9

Originally posted by DrAchoo:

Ya, the span will be about that. I may squish it down to 9 feet from post to post (since the roof has some overhang) and that would make the span 12.7 feet or 3.9 meters.

you will be fine with 8inches then, no problem.

02/17/2012 01:08:27 PM · #10

Originally posted by jagar:

Originally posted by DrAchoo:
Ya, the span will be about that. I may squish it down to 9 feet from post to post (since the roof has some overhang) and that would make the span 12.7 feet or 3.9 meters.

you will be fine with 8inches then, no problem.

doubled up or just a single 2x8 across each span?

02/17/2012 01:17:16 PM · #11

Originally posted by DrAchoo:

Originally posted by jagar:

Originally posted by DrAchoo:
Ya, the span will be about that. I may squish it down to 9 feet from post to post (since the roof has some overhang) and that would make the span 12.7 feet or 3.9 meters.

you will be fine with 8inches then, no problem.

doubled up or just a single 2x8 across each span?

You could just use a single one no problem but if you are not sure about the quality of the wood (how its been dried etc) you might want to use two, you would have no twisting problem then. This is difficult to explain but i'll try, when you lay the beams down try and see which way the wood naturally goes, it probably, if only slightly will have a tendency to bow one way, depth wise that is, when you put them up do it the opposite way so its bowing towards the top, sometimes you can hardly tell but with practice you can.

cowboy221977

Canon EF-S 10-22mm f/3.5-4.5 USM

02/17/2012 01:28:14 PM · #12

For looks ( I would use 6x6 on the columns) They should be buried and set in concrete about 3'. If doing it on an existing slab they sell brackets that fasten to the concrete. For the beams double 2x6 would work fine but 2x8 would look much better. The rafters I would use 2x6.

Message edited by author 2012-02-17 13:28:56.

02/17/2012 01:34:50 PM · #13

Originally posted by cowboy221977:

Ya, I have straps. I'm actually leaning away from 2x6 on the rafters because there is so little to the roof and it would just wind up adding weight to support. You also don't need to notch the rafters for the eave so that makes 2x4s more doable. I used 2x6 rafters on a tool shed with a gable roof I built and I think it was a bit of overkill (but, hey, that roof ain't going nowhere).

Olympus 17mm f/1.8 M.Zuiko

02/17/2012 01:35:54 PM · #14

Originally posted by jagar:

Originally posted by DrAchoo:

Originally posted by jagar:

Originally posted by DrAchoo:
Ya, the span will be about that. I may squish it down to 9 feet from post to post (since the roof has some overhang) and that would make the span 12.7 feet or 3.9 meters.

you will be fine with 8inches then, no problem.

doubled up or just a single 2x8 across each span?

You could just use a single one no problem but if you are not sure about the quality of the wood (how its been dried etc) you might want to use two, you would have no twisting problem then. This is difficult to explain but i'll try, when you lay the beams down try and see which way the wood naturally goes, it probably, if only slightly will have a tendency to bow one way, depth wise that is, when you put them up do it the opposite way so its bowing towards the top, sometimes you can hardly tell but with practice you can.

Crown up. Got it.

PennyStreet

Olympus OM-D E-M1

02/17/2012 01:41:19 PM · #15

I work for structural engineers. I posed the question and the answer is..

Posts 4x4. Beams 2x8 and the wood should be White Oak, Doug Fir or Southern Pine. Exterior rated or pressure treated.
Hope that helps.

02/17/2012 01:45:47 PM · #16

Message edited by author 2012-07-24 16:47:24.

cowboy221977

Canon EF-S 10-22mm f/3.5-4.5 USM

02/17/2012 01:47:18 PM · #17

Originally posted by DrAchoo:

Originally posted by cowboy221977:
For looks ( I would use 6x6 on the columns) They should be buried and set in concrete about 3'. If doing it on an existing slab they sell brackets that fasten to the concrete. For the beams double 2x6 would work fine but 2x8 would look much better. The rafters I would use 2x6.

Ya, I have straps. I'm actually leaning away from 2x6 on the rafters because there is so little to the roof and it would just wind up adding weight to support. You also don't need to notch the rafters for the eave so that makes 2x4s more doable. I used 2x6 rafters on a tool shed with a gable roof I built and I think it was a bit of overkill (but, hey, that roof ain't going nowhere).

I am a civil designer...so overkill is my middle name

02/17/2012 01:48:05 PM · #18

Originally posted by PennyStreet:

white oak is a hardwood. Fir and Pine are softwood (typical lumber is s-p-f...spruce or pine or fir). I don't know why they would equate oak with spf

02/17/2012 01:54:49 PM · #19

If not oak, douglas would be best, doesn't look as good but structurally it's nearly as good.

02/17/2012 02:11:13 PM · #20

Originally posted by deeby:

Originally posted by PennyStreet:
I work for structural engineers. I posed the question and the answer is..

Posts 4x4. Beams 2x8 and the wood should be White Oak, Doug Fir or Southern Pine. Exterior rated or pressure treated.
Hope that helps.

white oak is a hardwood. Fir and Pine are softwood (typical lumber is s-p-f...spruce or pine or fir). I don't know why they would equate oak with spf

And some of those are eastern woods anyway. We're typically going to have hemlock or doug fir.

02/17/2012 02:14:01 PM · #21

Originally posted by deeby:

for the lap joint, you might consider using glue and bolts. You want that joint to be stiff because it, with the vertical and the roof, form a truss. If you use nails at a joint, consider it a pinned joint (not stiff). If the lap joint is not stiff, there will be no transfer of load from the vertical because they are at right angles.

Good idea. If I use a single 2x8, will the bolt actually weaken the board since the hole will be a significant portion of the width? (I assume you mean bolting down through the cross lap.)

02/17/2012 02:54:01 PM · #22

BTW, Thanks for all the help! If I get it done this weekend I'll post some pictures. I'm also redoing my deck in a hardwood called cumaru. The great thing is we got an answer before yanko could show up and complain that I'm doing yet another DIY project. :)

02/17/2012 02:59:44 PM · #23

Message edited by author 2012-07-24 16:47:32.