HomeRoof Decking and Underlayment in Sioux Falls
Roof decking and underlayment in Sioux Falls
Under the shingles sit the wood deck, a sheet of underlayment, an ice barrier at the eaves and drip edge along the edges. Here is what each one has to be, when rotted decking gets replaced, and how it is priced.
What does roof decking have to be?
Solid wood the nails can bite into. The decking, or sheathing, is the plywood, OSB or old boards the whole roof is nailed to.
Shingle makers set the minimums in their install instructions. One maker calls for at least 3/8 inch plywood or 7/16 inch OSB, with gaps of 1/8 to 1/4 inch between sheets. Another allows no more than 1/8 inch between boards, and wants nails at least 3/4 inch into a board deck or just through plywood.
The two disagree on gaps. The shingle line on your quote decides which rule your deck has to meet.
Some older houses have board decks instead of panels. Ask the contractor whether your boards and gaps pass that maker’s limits, or whether new sheathing goes over them.
Panel choice moves the price. A national home services site, on 2025 data, puts OSB at about half the cost of plywood.
When does rotted decking get replaced, and what does it cost?
When the tear-off shows soft or rotted wood. We found no code section, in any source we could read, that spells out when decking must be replaced on a reroof, so the shingle maker’s deck rules and the contractor’s judgment decide.
Spot repairs during a reroof are priced by the sheet. A 2026 national planning guide puts them at about $75 to $150 a sheet, covering labor, tear-off, disposal and the new panel, and $2 to $6 a square foot for larger areas.
Replacing every sheet is a bigger job. A national home services site gives $2,600 to $9,000 for full sheathing replacement, averaging $6,400, on 2025 data.
All three are national figures. We found no Sioux Falls price for decking, and what a replacement costs here shows how the rest of the quote adds up.
What should the contract say about decking?
Ask that the contract state the price per sheet of replaced decking.
Felt or synthetic: which underlayment goes under the shingles?
Underlayment is the sheet rolled over the deck before the shingles. Model code wording quoted in city handouts lists four standards it can meet: ASTM D226, D1970, D4869 and D6757.
Felt is the old standby. No. 15 felt is ASTM D226 Type I and No. 30 is Type II. The numbers are nominal: a 2006 paper from a roofing consultants’ institute gives minimums of 11.5 pounds a square for No. 15 and 26 pounds for No. 30.
Synthetic sheets are tested to a separate standard, ASTM D8257, and accepted through evaluation reports, according to a roofing exam study guide.
We found no independent price comparison or durability study of felt against synthetic. Ask that the quote name the product, then check it against the shingle maker’s instructions.
Laps matter too. On a roof of 4:12 pitch or steeper, the same handouts lap underlayment 2 inches at the sides and 4 inches at the ends. Slopes from 2:12 up to 4:12 need a double layer.
Does Sioux Falls require an ice barrier?
Yes. The city’s code table marks ice barrier underlayment as required. For what it is, how far up the roof it runs and what it cannot stop, read how the ice barrier works against ice dams.
Does a roof need drip edge?
Under the model code, yes, at the eaves and rakes of a shingle roof. Drip edge is the bent strip that wraps the edge of the deck.
Wording from the 2018 and 2021 codes, as quoted in city handouts: pieces overlap at least 2 inches, the strip reaches below the sheathing and back onto the deck, and nails go no more than 12 inches apart. At the eaves the underlayment laps over the drip edge. At the gable ends it tucks under.
One Oklahoma city amended the rule so drip edge need not be metal. We could not confirm the 2024 wording, so check it with Sioux Falls Building Services at 605-367-8670.
Does every layer have to be the same brand?
For the top warranties, yes. One shingle maker’s system warranty needs its shingles plus at least three of its own accessories from this list: ridge cap, starter strip, leak barrier, its underlayment and attic ventilation. A contractor it has certified must install them.
In return, that warranty covers the leak barrier and underlayment for defects as long as it covers the shingles. The same maker’s higher wind warranty needs at least four of its accessories. Another maker’s lifetime warranty requires a ventilated deck, explained in how venting affects a shingle warranty.
Mixing brands can cost you the system warranty. Ask which warranty the quote is for, and whether every layer it names qualifies. Then compare what each shingle warranty covers.
Questions about roof decking and underlayment in Sioux Falls
How much does it cost to replace roof decking?
Nationally, spot repairs during a reroof run about $75 to $150 a sheet installed, and full sheathing replacement $2,600 to $9,000. We found no Sioux Falls figure.
What thickness should roof sheathing be?
One shingle maker’s instructions call for at least 3/8 inch plywood or 7/16 inch OSB. Check the instructions for the shingle on your quote.
What is the difference between 15 and 30 lb felt?
No. 15 felt is ASTM D226 Type I and No. 30 is Type II. A 2006 industry paper gives minimum weights of 11.5 and 26 pounds per square.
Is synthetic underlayment better than felt?
We found no independent study or price comparison. Ask for the product name and check it against the shingle maker’s instructions.
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