I want to replace the existing flat, tar & gravel roof with a new one containing a 2" IKO rigid insulation and then build up the roof with asphalt membranes with tar & gravel. The existing roof has an air space between the roof wood deck and the interior ceiling with little or no insulation. There exists gooseneck vents to vent the air space. The existing roof is about 25 years old and to my knowledge has not leaked. My question is do I need to re-install the goose neck vents with the top of deck insulation? If not, what about possible moisture and condensation in the air space and how would the moisture get out?

Thank you.

Hi bill a couple of questions here. First off stone on a built up roof is there for only on reason. To take the heat off the roof. So why not use EPDM White rubber roof and do it in one applications?

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My question is do I need to re-install the goose neck vents with the top of deck insulation?

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Yes and that's more then likely undersized. The roof needs vented unless it would have been spray foamed from underneath so NO air cavities can pocket moisture in it. The majority of the moisture comes from the rooms below.

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If not, what about possible moisture and condensation in the air space and how would the moisture get out?

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With out venting it wouldn't get out. The rule of thumb on venting an attic/roof. It takes 10 square feet of venting per 1000 square feet of attic area minimum. 50% at the peak, 50% at the soffits (with no radiant barrier, use 8 square feet per 1000 square feet of attic area in hot sunny climates)

Thanks for the response. One additional question, if the air space is vented, would that not defeat the purpose of insulated the roof above the deck? Cold air would circulate in the air space.

Bill

What you need to wrap the head around is your trying to insulate the roof for the living space below.

If any insulation gets 5% of moisture in it then it losses 95% of its insulation properties.

How much room from the roof to the top of the ceiling between ceiling rafters?

If there is some room I would tear off the roof , lay some poly between ceiling rafters and spray foam there to get the highest (R) value. Then ply the roof and use EPDM White roof to stop the heat gain. Install roof vents and done.

The only reason there is stone on the roof is the heat gain in summer.

Either or the roof needs vented no matter what. If you can approach it my way then the venting will Never effect Heat/AC loss