metal roof design

[sandcruiser]

hi all
I'm building a roof over a patio.
15'5" x 14'3" is the patio size... planning to use 5meter zinc roofing, which is 16.4 feet long.

It'll be a simple shed roof design that slopes downward across the 15'5" dimension and is attached to the house along the same 15'5" dimension.

I plan to build concrete columns to support the other edge.

I'm trying to figure out the support structure. I plan to use .120wall Cee Purlin that is 2"x4" as the frame. Mostly for aesthetics, I'll "twin" two purlins so that the have an enclosed look. That will form a square that is approx 15'5" by 14'3"...

I want at least one center support from which to hang a fan.

My question: How many additional supports do I need?
The roofing is 26ga structural metal roofing and will not have any seams perpendicular to the slope, but will have 4 seams parallel to the slope of the roof (also parallel to the wall)

Any comments welcome. Hiring an engineer to get this figured out is a no-go.... it would cost as much as the roof!

local construction "experts" aren't usually very "expert"

 

[titanpat57]

Your local metal roof supplier shoud have spans based on the load requirements (which I would assume is only rain by your location) and wind loads. I probably wouldn't exceed more than a 4' span. Are you planning on doubling everyone? I would be tempted to screw them together more like an "I" beam then a box beam. How many columns would have holding up the front girder?..just 2?

For a 4" high C channel ..1/8" thick.. seems a bit undersized for the span. I would think a minimum 6" high. Have you determined a pitch? Sorry for the 50 questions but the more info the better..

Pat

 

[RavenTai]

Not sure what 5 meter roofing means, width? here metal roofing comes 3' wide and as long as you like, but 26 gauge steel roofing will not span much more than 3 feet or so, I prefer 22 gauge feels more solid under foot, especially if you are building in a high wind area.

You should have rafters running parallel to the slope purlins running perpindicular to the slope, spacing and span depends on the dimensions of each, for minimum purlin, rafter and beam sizes look at the local building code and see what they require, if you cannot get any guidance there I would use FL building code as it is also a hurricane area. if you are using metal structure you need to see the documentation from the manufacturer on spans

Florida Building Code 2007 DRAFT

 

[LandCruiserPhil]

I built mine a few years ago and it still standing

I went a little bigger 20'x30'

I went with 4 - 4x4 metal post
twin 2x8 purlins for beams on the 30' side
single 2x8 purlins on 5' centers - FWIR I could have gone 8' on center

Plenty strong it is undisturbed by high winds or rain and my RTT hangs from it.

HTH

 

[haystax]

Do you have any other materials available locally? A larger size of "C" iron would make me a little more comfortable.

If not, the double 2x4" above the columns supporting two end rafters and single center rafter and purlins at about 3' would be what I would do. The corrugated profile of the roofing will add a little rigidity but I wouldn't trust it to span 14' without purlins at least 4' oc

 

[sandcruiser]

That looks great.
Thanks!

After discussing some more with some folks who are pretty savvy (local building code.... doesn't really exist- they say "go hire an architect/engineer") I think I've re-vamped my design to the following:

A 4x4 column at each corner
A 4x4 .150 wall framework boxing the columns and extending slightly along the front (about 30cm cantilever)
Then 2x3" either .120 or .150 wall box tubing as nailers running perpendicular to the slope of the metal roofing, which will be 5m x 1.07m sheets

I'll put the 6 nailers in on about .86m centers (between 2 and 3 feet).

We do have wind loading, and rain. Both can be heavy. We don't have hurricanes, thank goodness.

I'm planning a slope of 1 meter across the 5 meter span- which is 20% (more than 2/12 but less than 3/12).

I'll see if it makes sense to go w/ 3x6" or even 2x6" instead of 4x4" for the framework. Depends a little on availability and pricing.

I may also do a single extra 4x4 (or 2x6" or 3x6") running parallel to the slope of the roof, from the front of the frame to the rear, and supporting the nailers as I'm a little nervous about a 2x3" spanning the 4.3meter width (14'3")

More thoughts are very welcome!!

As I said before-- getting a "pro" to design this isn't necessarily any insurance that it would be done better. To wit: I specifically asked the hardware store guy if we could get 4x4 tube in galvanized, he said "no". Which is incorrect.

I feel that the galv will hold up much better in the long-run, mostly from the inside.

I built mine a few years ago and it still standing

I went a little bigger 20'x30'

I went with 4 - 4x4 metal post
twin 2x8 purlins for beams on the 30' side
single 2x8 purlins on 5' centers - FWIR I could have gone 8' on center

Plenty strong it is undisturbed by high winds or rain and my RTT hangs from it.

HTH

 

[sandcruiser]

phil
did you you Cee or Rectangular steel for the cross-bars?
-Steve

I built mine a few years ago and it still standing

I went a little bigger 20'x30'

I went with 4 - 4x4 metal post
twin 2x8 purlins for beams on the 30' side
single 2x8 purlins on 5' centers - FWIR I could have gone 8' on center

Plenty strong it is undisturbed by high winds or rain and my RTT hangs from it.

HTH

 

[LandCruiserPhil]

I was able to find sites to get load info on the purlins. I did go a little oversize to keep in scale with the rest of the structure. Also on my main beams needed to be a little larger because they cantilever about 8' past the post on one end. My slope is a minimum 1/12 FWIR without any issues. Everything except where the main beams attach to the post is attached with self-tapping screws. It like a big boys erector set...fun to build.