Battens (Furring strips) or not under metal roof

[Kiwi55]

I know this has been discussed before but I could not find it in a search.

I have completed my roof sheathing with 5/8 ply (actual dimension 19/32) and have installed plytanium synthetic felt over top. Next comes the steel sheet roofing.
My intention was to screw the steel directly to the ply (following the manufactures spacing instructions). It has been suggested I should put down battens or furring strips 24" on center across the roof and attach the steel to those. The reason seems to be that the screws will have better holding power into the furing strips than the ply.

My biggest concern is that the horizontal battens will prevent any moisture from running all the way to the edge, perhaps trapping it and rotting the battens. A secondary concern is that it is more difficut to walk on the roof with the battens (The roof is fully supported if it's attached directly to the deck)

I'm in central Mississippi, High humidity, plenty hot, and while the location is well shelted we do get the occasional tornado passing by (OK neither solution is probaly going to help if a tornado hits).

So what is the prefered method? With or without battens?

Thanks...Paul

[MushCreek]

I like to double-strap it. First, furring strips running vertically, attached through the decking to the rafters. Then, horizontal furring (purlins) to attach the tin to. This keeps things open to drain condensation away. The vertical furring allows the water to run down to the eave, rather than being dammed up.

[Alasdair]

I did as Mr. Creek describes for those very reasons and also if it is well vented under the roof the temperature should remain similar to the outside temperature decreasing the chance of condensation. It also made it very easy and safe to work on.

http://countryplans.com/smf/index.php?topic=6980.40



This is also the method required by code here for the board and batt siding I used.

[Don_P]

I prefer to screw to a solid deck, it looks better, is easier to walk on and if you use closure strips has less potential for condensation. Condensation occurs when moist air hits a below dew point surface... this prevents the moist air from getting in there. If you screw to 5/8 on 24" row spacing it'll be good for roughly double hurricane force uplift.