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Question DetailsAsked on 1/6/2017

Enter your many square of architecture shingles will it take to cover a 1,000 sq. Ft.

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OK - is this a trick question ? A roofing "square" is 100 SF of roofing surface - so ignoring cutouts for vents or any open valleys (valleys where the roofing surface material does not continue across the valley), there would be 10 "squares" of finished roofing in 1000 SF of roof surface (measured on the slope - on the surface actually being covered).

Shingles are commonly sold as "covering" so much of a square - so say commonly 3 or 4 bundles per square (per 100SF) of coverage for simple 3 or 5 tab composition shingles depending on manufacturer (5 for a very few heavy-weight hurricane or hail resistant shingle brands), commonly 4-5 or rarely 6 bundles per square for architectural or "texture" shingles, and sometimes with designer or almost always with metric shingles and also with a few off/imported brands can be an odd number of bundles per square. Usually 4 bundles per square for wood shingles and 5 for shakes but can vary by manufacturer and thickness of shingle/shake.

But shingles technically come by square feet of coverage per bundle, not in "squares" - because a square is a roof area measure, not a measure of materials needed. Ditto with most water barriers - they are commonly labelled by total square feet of material and also by square feet of coverage using the manufacturer-recommended overlap, but that is a measure of the material amount - not necessarily what it actually "covers" on the roof, though of course with underlayments the difference is not so great as with shingles because you do not have starter courses and lots of throwaway due to cutoff and angle cuts at valleys and such. Provided you use the manufacturer recommended overlap of course - which is not always the case, especially with ice and water shield, and also with some which show 1 or 2 inch overlap when 4 inches is pretty much the accepted minimum - more like 6 or 8 in ice damming or heavy wind-blown rain country.

Now - how many bundles or square feet of of roofing material will it take to do the job - that is possibly what you are asking. With extremely simple single-gabled roofs (one ridge, no valleys) around 4-6% additional material is commonly needed for cutoffs and starter courses and ridge shingles - more like 10% (a common rule of thumb) to maybe 15% on most normal roofs, and up to 20% or so on complex multi-angled roofs with lots of valleys or dormers, or on very long, narrow houses or houses with long roofed-over walkways where the ridge and starter courses constitute an unusually large percentage of the roof surface area. I think the worst I have seen was 30% additional demand on a building which was all peaks and valleys and octagonal turret and dormer roofs.

And of course, the quality of the shingles themselves (i.e. how many defects you are likely to hit) makes a big difference - typically with a high-quality brandname manufacturer you might figure 1% defects on a job, while with some cheapo box store brands I have heard of as much as 10-15% defects in a typical shipment. Not counting the rare shipment from any manufacturer that is factory defective or more commonly storage-damaged by the pallet load or lot load and has to be returned en masse.

Also, the workers makes a bit of a difference either way - some slam-bang roofers will put anything on a roof (including factory-defect shingles totally without asphalt or granules that I have seen on roofs) and some are picky and throw out questionable ones. Also some are rough and tear a fair number of shingle strips or do sloppy cutoffs or throw away all cutoffs thereby increasing waste, others handle it carefully and reuse all but the unreasonably short cutoffs. This latter factor (reusing cutoffs) can make quite a difference - many roofers use the previous row cutoff to start the next row as long as it is at least one tab wide - others like me will not use less than two tabs for any piece. Ditto at the tail end of a row - cutting the second-from-end piece back to provide a long piece at the end of the row (to increase wind tearoff resistance by having at least 3 nails or staples in it) can increase cutoff wastage factor. This is something a roofer learns from experience - what his typical wastage factor is for various types of roofs.

And of course, whether you are shingling over the ridge vents or not, and if you are cutting bundle shingles to make ridge and starter row strips or buying ready-made ones, also affects the final material demand. I have heard of inexperienced contractors and DIY'ers going back to the store 2 or even 3 times for more shingles because they tried to estimate too closely or forgot the various forms of "wastage" or doubling up of shingles at certain locations like at edges/terminations and in woven valleys.

Also - how many shingles depends greatly on the tab exposure you are using - most manufacturers give a "coverage" assuming a certain exposure - but that exposure (usually the maximum at which they will warranty the roofing) can be reduced for high wind areas and also in some areas with icing or hail issues. In fact, "normal" coverage is generally such that you have just 2 layers of shingle at any given point on the roof (so the exposure is 1/2 shingle) - but in some severe climate areas the tab exposure (the amount sticking out under from the row above) will be reduced to give three layers at every point. Generally, this is NOT done with many brands of architectural shingles because it messes up the appearance - instead of giving a nice pattern or random appearance, it makes for banding or obvious alternating rows or tabs that stick up in the air that appear different on the roof than intended. And it wrecks havoc with the shingles that are designed to give a specific roof pattern.

How many shingles it takes to do a particular roof requires either detailed measurements and a line-item calculation of the demand (plus a safety margin), or else the more usual method of guessing a wastage and then overbuying by a certain amount, if unopened bundles are returnable for credit. And I always recommend keeping the last partial bundle plus one spare full bundle on-site for repairs - slitting the bundle wrapper and inserting waxed paper or even better a strip of waste flashing between the shingles at the adhesive strip to prevent the asphalt "tabbing" from sticking during storage - and of course always store flat and fully supported.

Answered 1 year ago by LCD

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