Solid polycarbonate sheeting roof muntin detail ?

[Sam Maguire]

Building a lean to on side of house as a continuation of car port. 3000mm long x 4000 wide.
Going with 6mm solid polycarbonate on timber rafters at 600mm ctrs at 8 degrees approx.
Not keen on multiwall and want a cheap alternative to glass.
To minimise waste I'm placing the 2 no. 3m x 2m sheets as shown so need a water tight joint across the centre as shown (ie at right angles to rafters). Also needs to be as flat as possible to prevent water build up. Don't think standard glazing bar will work as water will build up and not run across at 8 degrees capping.
Just looking for a bit of direction please.
Options are:
(a) h section shown
(b) what about an overlap detail similar to one shown but for flat sheet ? Joint will be on noggings below so support not an issue. Use glazing tape to seal with mastic on outside.
Just think overlap would be all round better detail. Thoughts ?

 

[conny]

If you have a router you may be able to rebate a 3mm deep lip on the underside of the top piece and a matching 3mm deep lip on the top side of the lower piece. The top one could then overlap the bottom one allowing the rainwater to flow across the joint to the gutter edge. Make the width of the rebate about 20mm to ensure a good overlap and you could even smear a thin layer of clear adhesive along the joint to help prevent seepage through capillary action.

 

[catlad]

Or don't be foolish and do it in the traditional method!