wood roof over ice and water shield

[wfpa]

i'm having a barn(unheated)built and the roofer wants to put down ice and water shield over the entire roof(1x8 T&G)then cedar breather and 3/4 handsplit heavies on top any suggestions

[jmorgan1]

Where are you? Heavy snow conditions? What's the slope of the roof? I don't loke using Cedar Breather on steep slopes, with heavy snowpack. The ice can freeze onto the shakes and "pull" the shake downward, bending the nail and making a small tear in the Ice & Water Shield. Out West we are dry enough to install shakes directly over the IWS. In more humid areas, underside venting of cedar is needed. Sounds to me like your contractor is trying to put together a good roof.
Jim

[wfpa]

i'm in ct the pitch is an 8 should i be consured with interior humidity with the iws acting as a vapor barrier would gable vents be advisible

[jmorgan1]

Yes. There must be an air space below the roof deck for ventillation. Min. ratio of ceiling to roof is 1:300. If you have an attic, gable end vents will work fine. Making sure that the vapor retarder behind the drywall (over the batts) is installed correctly. Raw batts covered with Visqueen is better than foil or paper faced batts.
Jim

[wfpa]

the ceiling area is uninsulated at this time just the 1x8 then iws matrix then shakes is that ok

[homebild]

Since this will be an unheated barn...vapor, condensation and ventilation will be of little concern.

There will be no temperature and humidity variances between inside and outside for the most part.

It is only when there is a temperature/humidity differential with a heated structure that these issues become more serious problems.

The 'attic' area should be ventilated, but your contractor is providing you with a proper structure as already mentioned.