Problem in Florida - Wood Purlins for Metal Roof

Help! I am building a Dock on Lake Jessup here in Central Florida, all under permit and with plans. Plans call for decking and shingle over a Gazebo on the dock, but local inspectors will allow options on materials for roof. I wanted to reduce weight so I am opting for a metal roof. My first problem was to find a “product approval” for constructing a metal roof over an open frame with 2x4 purlins WITHOUT plywood decking. For the non FL residents out there, we have enacted an insane process for satisfying the Florida Building Code that requires preapproval for products used in construction. That’s a whole forum on it’s own, so quickly to the bottom line: I have found one supplier that has the approval for their panel, a pretty standard ribbed 29 gauge metal panel for roofing, and they give all the details of attaching the panel to 2x4 purlins but no information on required fastening of the purlins to the trusses, or 2x6 rafters in my case. So, I’m interested in any attachment details anyone may have seen in a similar situation that would satisfy or overkill wind loading. I guess a couple of 3" screws at each crossing would do the necessary, but I would like to hear any experiences or just quote from a spec somewhere. I am not in the High Velocity Wind Area and not subject to the Miami-Dade code.

Thanks for ANY help


Every local municipality usually have their own requirements. You could try to ask your local inspector if he would be okay with your 3" fasteners. (Never hurts to ask) As far as the number of fasteners 2 every rafter should be fine, it would just be the length that could be challenged.

If I were you. I’d go 3-3/4 inch screws for my fastening just to be on the safe side.
Sometimes it is just better to meet or exceed Miami codes just to avoid any hassles. Miami-dade wants you to be into your truss/rafter by a minimum of 2" or at least they did last year when I did some work down there.
Also the longer screws would definitely make it so your system never blows away.
just my 2 cents

3 inch screws will work just fine.
you can put a small truss strap on every one too.


I would think the first thing might have an issue with is a 29 guage panel with the screws being secondary.

To me, that’s a pretty thin piece & is going to be prone to damage a bit too easily, thereby providing the potential to get torn OFF the screws.

Let me also suggest that it is a lot easier to add the extra screws you are in need of @ the time of the panel installation vs. having to go back & add them later. When the panels are going up, you (on a ladder or working from the frame system) can see right where the purlins or stringers are located vs. having to measure a lot for a later project with all panels up.