Flat roofing on Long Island, done so the water has somewhere to go.

Most residential flat roof replacements on Long Island run $8 to $16 per square foot installed, which puts a typical 800 sq ft rear addition or garage roof somewhere between $6,500 and $13,000. EPDM sits at the lower end, TPO and modified bitumen in the middle, and built-up roofing at the top. Tapered insulation, new drains or scuppers, and rotted deck replacement are the items that move the number, which is why we price them line by line after we have been on the roof — never over the phone.

Sometimes. If the deck is sound, the existing roof is a single layer, and a core cut shows the insulation is dry, a re-cover is a legitimate way to save money and disposal cost. If the insulation is saturated, you already have two layers, or the pitch has to be rebuilt to fix ponding, a tear-off is the only honest answer — laying a new membrane over wet insulation traps the water and the new roof fails early. We take core cuts and show you what came out before we recommend either one.

No, but it is a warning. Water that drains within 48 hours of rain is normal on a low-slope roof. Water still standing after 48 hours means the pitch or the drainage is not doing its job, and standing water accelerates everything that kills a flat roof: seam creep, UV breakdown, freeze-thaw splitting in January, and algae that hides the leak until it reaches your ceiling. Ponding is a symptom of a drainage problem, and the fix is tapered insulation, a relocated drain or a new scupper, not more sealant.

Both work here. EPDM rubber is the more forgiving of the two: it stays flexible through freeze-thaw cycles, handles nor'easter debris well, and its seams are repaired with tape rather than heat, which makes future service simple. TPO is white, so it reflects summer UV and keeps the room below noticeably cooler, and its heat-welded seams are extremely strong. If you have living space directly under the flat roof and want the cooling benefit, we usually recommend TPO. If the roof is a garage, porch or low-traffic addition and you want maximum durability for the dollar, EPDM is hard to beat.

A typical residential flat roof — a rear addition, dormer, porch or garage — is a two to three day job: one day for tear-off and deck repair, one for insulation and membrane, and part of a third for flashings, terminations and the water test. Larger roofs, full tapered systems and commercial buildings run three to five days. We only open what we can dry in the same day, and we watch the forecast so your deck is never exposed to a surprise coastal storm.

The membrane manufacturer warrants the material itself — typically 15 to 30 years depending on the product and thickness you choose. The exact term varies by membrane, so we go through your specific coverage with you before you sign.