What to do for fungus on ashpalt shingles?

It depends on a variety of factors, including cost, longevity, style, and local climate. Metal is the most durable roofing material, but it can be quite expensive and is not suitable for certain architectural styles. Asphalt shingles are much more economical and typically last 20-30 years, depending on the climate and other external factors. In some climates, asphalt is still the preferred choice because it is better at resisting damage caused by extreme cold or snow. Ultimately, the best option will depend on personal preference and budget.

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If it's a mobile home he probably has it 2-12 pitch roof I would use roll roofing instead of shingles hope this helps

Ash fault? I think you mean "asphalt" but that's OK. You haven't given enough information to solve the problem, but here's what you need to do.

You know the area of the roof is 300 square feet (sq ft). You should know the area of each asphalt shingle, although that's the information you didn't give. When you know that figure, the calculation is very simple:

number of shingles needed = area of roof / area of one shingle

I don't know if this is a class problem, or if you really have a roofing job. Don't forget that on a real roof, the shingles overlap. If you do the calculation, the number you get is right only if you lay the shingles edge-to-edge. A real-world roof would need probably twice that number. Shingles come packed in bundles, and they usually tell you the area they cover. (By the way, 100 square feet is termed a "square".)

the boot slips over the vent pipe. The plastic rectangular part of the boot slips under the shingles that are toward the ridge. The rectangle part forms a shingle.

Picture where the water will go when flowing down the roof

there should be a minimum of 50mm verge overhang on the gables,more if the roof is open to exposure, and the same 50mm into the gutter