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Question DetailsAsked on 7/14/2015

how many bundles of shingles to repair a 665 square foot carport with 3 tab shingles

I am replacing a roof that is 665 SF on a carport. How many bundles or squares of shingles will I need?

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You can google a search phrase like this to get articles on estimating roofing materials needs -

what percentage excess shingles to order

Several of the main manufacturers also have estimators on their websites - some pretty simple, some pretty detailed.

First you have to measure the actual roof square footage - the on-the-slope square footage for the actual roof including all overhangs, NOT measured based on the footprint of the building itself, so the roof is typically 20-40% larger than the house itself - sometimes more, and of course with no overhangs not greratly more because the increase in square footage is only due to the slope of the roof.

Then figure excess needs for end-of-row throwaway cutoffs, ridge shingles (don't forget overlap), eave and gable starter row shingles, a bit for errors in cutting and the occasional bad shingle or one that tears pulling it off the bundle, adjusting for any dormers, etc. Plus adjustment if you are not using the same "show" or "exposure" (amount of shingle showing under the next row up, which is commonly 4 to 5-1/2 inches but can range from 3 to as much as 6 depending on desired overlap and brand of shingle) as the manufacturer assumes for its coverage numbers. Then compute a wastage percentage or square footage based on the above factors and number of angled wall intersection and valley cutoffs or overlaps/interweaving, which have substantial trimming throwaway or overlap. This added demand number may be as low as 3-5% or so for a large simple single-ridge gabled roof with no valleys or dormers, on up to as much as 20% or more for some of the current day architect's nightmares with multiple valleys, several ridges, dormers, multi-level roof, etc. Also, the smaller the roof the greater percentage needed for starter row and ridge shingles - so the extra shingle need for a small shed or playhouse for instance can run to 30-40% more than measured square footage, whereas for a very large and deep single-ridge ranch it can get as low as 3-5% or so.

Of course, if your carport is a simple single slope without many of the above, much simpler to figure your need - may be only starter rows and a bit of wastage.

I also recommend ending up with at least a full bundle plus any remaining part bundle of shingles at the end of the job, for repairs on a house reroof - perhaps half a bundle minimum for your carport. Having an extra bundle (or even 2 on a larger house) also gives you some backup in case you hit a bad set of shingles or ones with stray asphalt sprayed over them in the course of the work - nothing worse than running out of shingles in the middle of the job. Most distributors will take back unopened bundles for a refund.

If 665 SF was the actual square footage on-the-slope of your carport, that is 6.65 squares (there are 100 SF per square) without allowance for cutoffs and ridge shingles and starter shingles and such - which might be 2 bundles with some 5-tab shingles, 3 bundles per square with simple 3-tab shingles from most manufacturers, but could be 4 or 5 or even 6 bundles with architectural and multi-layer shingles - and there are a few manufacturers out there that ship in bundles that do not add up to an even number of bundles per square at all - like it might take 2.7 bundles/square for instance. In addition, metric shingles are showing up, so the bundles are sometimes sized not for so many bundles per 100SF but rather maybe 3 square meters per bundle or such.

And don't forget with water barrier and ice and water shield to allow for the overlaps - end and row to row, and also the end overlaps for flashing.

Answered 5 years ago by LCD

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