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Question DetailsAsked on 10/14/2012

Does copper sulfate help to reduce mold growth on new or old structural wood for future use. We live in humid Florida were mold thives.

We had a roof leak that caused some wood to rot on the existing rafters in the attic. We resolved all pending mold issues and problems. We since repaired and replaced the rafters with yellow wood pressure treated pine about a year ago Just want to know of a feaseable way to prevent this in the future.

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2 Answers


You could run a strip of copper or galvinized steel at the peak of the roof. This will prevent mildew and algae below it. You have already protected the attic beams by buying the pressure treated wood no more inside work is necessary. Remember to properly vent the attic and for ways to save big on your A/C bill see my blog on radiant barriers.


Answered 7 years ago by jccasper


NEVER use copper sulfate on structural timber with metal connections or fasteners - causes rapid corrosion as it creates sulferic acid when moist. It is designed for ground-contact and in-ground timber treatment of posts and wood walk borders and piers. There are copper napthalate and and other copper treatments that are less corrosive (though still corrode normal galvanized fasteners to some extent in damp/wet environments) - they come with designations like CCA, ACC, ACQ, ACA etc for the various treatments. Here is a brief article on the various treatments -

For interior use, copper napthenate and copper-borate treatments are used - your rafters presumably used one of these - I think you may mean YellaWood brand southern pine was used in your case - which is a micronized copper treatment suitable for interior structural use in houses.

Your rafters should need no further treatment, and except in extremely wet, humid climate like the tropics, are usually not treated and experience no problems.

The key is keeping the water out of the attic wood -
1) keep your roof clean of leaves and debris - usually an annual washing with a regular hose with jet nozzle will do fine
2) if you have moss buildup try to remove trees causing excessive organic material dropping onthe roof or heavily shading it.
3) if you have moss or lichen buildup despite annual cleaning, have a zinc anti-moss strip installed just below your ridge, or sprinkle every year or two as needed with a zinc powder like MossOff.
4) When cleaning the roof, inspect all flashing and caulk to see if repairs are needed to ensure you don't get leaks
5) repair any damaged shingles immediately
6) if your attic is readily accessible, do a visual inspection of the underside of the sheathing, rafters, and top of the insulation for evidence of water staining or drips every 1-3 years (more frequent interval with older roofs).
7) ensure your roof has adequate ventilation suitable to your roof type - usually screened eaves and ridge vent for peaked roofs.

Answered 6 years ago by LCD

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