My information is commercial, not residential.
Commercial code no longer allows true flat roofs, they require a
minimum of 1/4 per foot fall. The parapet/gutter decision may be
influenced by your exterior material. Parapets require attention
to detail so they are structurally sound. The exterior wall will
be subjected to very different weather conditions above the roof
line. The inside of parapets are typically roofed with the same
material as the roof with a metal wall cap and fascia. The
dimension of the fascia is determined by what needs to be covered
up to overlap the finish exterior surface. Parapets would
typically have roof drains with overflow scuppers, sufficient
pitch to shed elsewhere, or through-the-parapet piping usually to
a conductor head and downspout.
I would think your biggest concern would be compatibility with
what is there now as you describe a 3 wall addition. Are you
tying into an exterior face or are you picking up an existing roof
line? If you are tying into an existing face, you need to pay
great attention to flashing at the tie. Any waterproofing at the
parapet should continue at the same height across the tie.
Parapet walls will eliminate eave overhang and sun shading and
will require good attention to water exclusion from the building
envelope. If you have an existing pitched roof you should make
every effort to continue the roofing system and pitches in my
opinion. Many commercial buildings use parapet walls, are you
sure that is the look, or did you mean a mansard-similar, but more
Keep the whole world singing . . . .
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