Many roofers specialized in residential roofing services while others may specialize in building commercial roofing services. Many will specialize in the commercial end of the business because they do not have to deal with individual homeowners.
Another reason is that a lot of industrial or commercial roofing done is a form of laying down a sheeting material like corrugated metal or forty foot long sheets of flat metal shingles. You can also look for the best metal covering in London.
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Often the buildings will have a metal structure and they don't require special rafters or decking. This is not true of all commercial or industrial structures but of a lot of them.
A residential roofing service that specializes in roofing houses is who you would call to come and re-roof your home. You may also call on them to repair your homes roof if it is damaged or leaks.
There are a lot of home roofing materials to choose from. If you have a residential roofing service come and give you a quote they will suggest what roofing material you can use on your home. Generally most home owners will replace like with like materials.
You may upgrade the shingles to a better quality or one with a longer warranty. Or you may choose to put on asphalt shingles that cost a bit more and perhaps look more like a shake roof. But generally you will stay with the asphalt shingles.
One reason to stay with a like roof is that if you were going to change to a concrete tile roof, your existing roof structure may not support the weight of these tiles.
So to get concrete tiles put on the roof you would have to have that roofing specialist build up the underlying structure so it can support that additional weight and this costs some money.