Johns Manville Commercial Roofing in Yonkers, NY

Johns Manville is one of the older names in commercial roofing, so a JM label on a Yonkers building can mean several things. The company has made built-up roofing, modified bitumen sheets, single-ply membranes in TPO, PVC and EPDM, and polyisocyanurate insulation boards. An owner who says the roof is a JM roof has narrowed the question without answering it. The first task is to learn which layers are on the deck.

Names change, too. Roofing brands are bought, merged and renamed, and a product label from decades ago may belong to a line that no longer exists under that name. We rely on what the roof shows, on the product data we can read and on any records the owner holds, and we note the gaps.

Our work on these assemblies follows the written product requirements. The visit report holds photographs, a layer-by-layer note where we can confirm it and a repair boundary for the owner to approve.

Count the Layers

Older commercial roofs often carry several generations of material. A built-up roof may sit under a modified bitumen cap, under a coating, with a recover above. Each layer has its own age and behavior. Cores and test cuts, taken where the evidence points and patched the same day, show what is there. We log each location on the sketch, with a photograph of the cut face showing the layers in order, so the owner and any later contractor start from the same cross-section.

That matters because the repair and the weight both change with the layers. Adding a membrane over wet insulation traps the moisture. Adding weight to a deck that already carries several layers can exceed what it was planned for, and an engineer's review may be needed before a recover is priced. We record what we find and flag any limit on adding layers for the engineer or the city to confirm. The note goes into the file whether or not a recover is planned, since it answers the first question any later buyer or lender will ask.

Built-Up Roofing and Its Failure Signs

A built-up roof is made of alternating plies of reinforcing felt and asphalt, topped with gravel or a cap sheet. The layered construction gives redundancy, but it also hides damage. Blisters, alligatoring of the surface, exposed felts, and splits at expansion joints are the usual signs of aging.

On a built-up roof, we probe blisters, check flashing at walls and curbs and look at the gravel for bare spots. A small blister may be left and monitored, with its size noted on the sketch so the next visit can measure any growth. A broken one is opened, dried and patched with compatible plies. Where the surface is worn but the plies are dry, a coating or cap can extend life.

Gravel needs its own attention. Loose gravel scours the surface and clogs drains, and bare patches expose the asphalt to sun. We rake displaced stone back, clear drain strainers and note where the surfacing has thinned, since those areas age faster than the rest.

Modified Bitumen and Its Laps

Modified bitumen sheets add polymer to asphalt for flexibility. They are installed in layers, with laps that must be sealed. Aging shows up as open laps, granule loss, splits along the sheet edges and wrinkled or ridged areas.

We inspect the laps first, clean and re-seal those that have opened and patch splits with matching sheet. Torch-applied repairs raise fire-safety questions on some buildings, so we describe alternatives such as cold-applied adhesives before scheduling. Our modified bitumen roofing work follows the chosen method, and the closeout file records which was used and why.

Edges and terminations deserve a second look on these roofs, and the check costs little. The sheet is only as secure as its attachment at the wall, so we check the termination bar, the sealant above it and the counterflashing. A gap there lets water run behind the sheet, where it is invisible until the interior shows it.

Polyiso Insulation and Moisture

Polyisocyanurate boards sit below many membranes. They give thermal value, but they lose it when wet and can swell or deteriorate at the facers. Boards can also crush under repeated foot traffic, leaving low spots that hold water.Wet boards show up under a probe, a meter or, on a big roof, an infrared moisture survey, and a small core confirms the finding.

Wet insulation is cut out and replaced before the membrane is repaired. The cut is squared and sealed, and the new boards go down fastened or adhered to the pattern the system calls for. A cover board over the insulation resists foot traffic and impact. The proposal lists boards, cover board, fasteners or adhesive, flashing and labor as separate lines, so the owner sees how the cost adds up. When insulation boards are replaced in part, the new boards are tapered or shimmed to match the old surface, and the transition is detailed so water does not pool at the seam between old and new.

Cold, Thaw and Heat in Westchester

Weather context for asphalt roofs comes from the Westchester County Airport normals, recorded northeast of Yonkers. Over 1991 to 2020 they show 47.75 inches of precipitation, about 105 days with a freezing low and about ten days at or above 90 degrees. They frame the seasonal swing.

Asphalt-based roofs stiffen in the cold and soften in the heat. Repairs in freezing weather may be temporary, with the permanent detail scheduled for a warmer window. For roofs in the Nepperhan and Saw Mill valley or near Getty Square, we plan the season into the schedule. Work that needs warm, dry surfaces waits for them, and urgent protection goes on in the meantime. Snow and ice come into it as well: a roof that holds ice at the edge or in a drain needs a different first visit than one that is simply wet, as our snow and ice damage repair notes show.

Warranty, Code and Records

A warranty on a built-up or modified bitumen roof can set rules for repairs, such as who may do them and what notice is due. We ask for the paperwork before any repair, and the scope flags any step that could touch coverage. Code questions follow the same split: the state's 2025 Uniform Code is fully in effect, and permit details belong to local authorities, so we check Yonkers before work is scheduled.

The closeout file records the layers confirmed, the products installed, photographs and open items. A roof that also carries a Holcim Elevate section or a GAF section gets its own entry for each section, and an annual maintenance visit keeps the file current.

Commercial Roofing Questions

How do you know how many layers are on my roof?

We take small cores or test cuts where the evidence points, then patch them the same day. Records and edge views also help.

Can a built-up roof with blisters be saved?

Often. Small blisters can be monitored. Broken ones are opened, dried and patched. If the plies are wet over a large area, replacement is the sounder choice.

Is torch work allowed on my building?

Rules and insurer requirements vary. We describe cold-applied and other alternatives and confirm requirements before scheduling.

What does wet insulation do to a new membrane?

It traps moisture, shortens the membrane's life and can cause blisters. Wet boards come out before new material goes.

Can I add another layer over the old roof?

Only if the existing layers are dry and the deck and code allow it. We test first and confirm the limits with the city.

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