Do I need to seal the underside of flat roof decking?

[loofer2]

I'm replacing a flat roof with new ply and EPDM rubber, I know years ago it was best practice to seal the edges of the ply with gloss and varnish the underside, is this still recommended?

 

[Notch7]

I dont know anybody that does that, but I guess it would protect the board if it rains before the epdm goes on and help if there should ever be a leak.

I cant see how it serves any function for the duration of the epdm doing its job correctly....

 

[loofer2]

I guess it's partially to stop a leak from doing too much damage as you say and partially to keep atmospheric moisture out, the top would be sealed with adhesive and the sides and bottom sealed with paint/varnish.

 

[catlad]

OSB 3 is recommended not ply wood for EDPM

 

[big-all]

i would personally not seal the bottom
if you have a leak and it stops and holds the water then you may not know about the leak until the painted surface lets water through because the sheet has lost its strength
where as a leak will not damage the board if fixed when the damp patches first appear

 

[loofer2]

OSB 3 is recommended not ply wood for EDPM

I thought that was just a minimum recommendation but that ply was better?

 

[loofer2]

i would personally not seal the bottom
if you have a leak and it stops and holds the water then you may not know about the leak until the painted surface lets water through because the sheet has lost its strength
where as a leak will not damage the board if fixed when the damp patches first appear

That's maybe a good point.