FLAT Roof - Ice and Water Shield (I&WS)

[bjferri]

I always lean towards overkill unfortuanately - is it a good idea to I&WS the entire roof before installing the TPO / Duro-Last membrane?

Thanks is advance...

[Dana]

I'm not sure what the advantage of adding I &WS is- they're both vapor-impermeable. There may better materials for providing a slip-surface to minimize strains on the membrane too.

There's a huge advantage to putting down a few inches of rigid foam insulation though- it blocks the thermal bridging of rafters leading to more even temps and less freeze/thaw stresses when there's a snow load, and keeps the roof deck & rafter tops warmer for far less winter moisture accumulation. In summer it blocks the thermal transfer of the short-circuiting rafters to the interior from the hot roof too.