Exterior Mildew

Robert Jones asked 4 years ago

I live in a 100 year old house with stained shake cedar shingle siding. The roof rafter tails are exposed as is the roof material on the eave overhang. (3/4″ thick beaded fir like they used to put on porch roofs.)

Five years ago I used to heat gun to totally strip the exposed rafter tails, overhanging roof eaves, and window and door trim.

I then sanded all the wood with 80 grit sandpaper on an orbital sander.

I then brushed/vacuumed all the surfaces, applied two coats of national name brand oil base primer followed by two coats of oil base gloss white paint by the same manufacturer.

One year later there was noticeable mildew growth on all roof eaves on all four sides of the house as well as on the vertical window/door trim.

In two years, the mildew under the roof eaves had turned so black it looked like the wood had been burned.

Two summers ago I treated all the surfaces with Jomax House Cleaner Mildewcide mixed with bleach according to the directions. This did not remove all the stains, so I next scrubbed these surfaces with a green kitchen pad and the Jomax solution. Some stains still remained, so I scrubbed the areas again with comet and a green kitchen pad.

In one year’s time, the mildew started returning and in two years time the eaves are almost coal black again. The house is in the city and sits at the top of a hill and gets almost constant sun.

Where did I go wrong and how am I to fix this problem? I’m not looking forward to stripping all this down to bare wood again but am also scared to ignore the problem and enclose the soffits.

The cedar shingle siding has some isolated mildew in locations, but no where near the degree as the roof eaves, rafter tails, and door and window trim.

Thank you in advance for your help.

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