Modified bitumen
Modified bitumen roofing for flat roofs in North Jersey
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Modified bitumen is the modern version of the built-up asphalt roof. It goes down in layers, stands up to foot traffic and is the most common roof on small residential flat roofs across North Jersey. We install and repair it on homes and commercial buildings.
What it is
What is modified bitumen?
“Mod bit” is asphalt that has been blended with polymers and reinforced with fiberglass or polyester. It comes in rolls about three feet wide. A typical system has a base sheet and a cap sheet, and the cap sheet is surfaced with ceramic granules like a shingle.
There are two families:
- SBS is modified with synthetic rubber. It stays flexible in cold weather and handles building movement well. It can be torch-applied, set in cold adhesive or self-adhered.
- APP is modified with plastic. It is normally torch-applied and holds up well to summer heat and sun.
Because it is installed in two or more plies, a mod-bit roof has built-in redundancy. It is thick, tough and forgiving of foot traffic, which is why it is popular on balconies, porch roofs and roofs with a lot of service visits.
Installation methods
Torch, cold-applied or self-adhered?
| Method | How it works | Where we use it |
|---|---|---|
| Torch-applied | The underside of the sheet is heated with a propane torch until it bonds. | Masonry and non-combustible decks, with fire-watch precautions. |
| Cold-applied | Sheets are set in a manufacturer’s adhesive. | Occupied buildings and anywhere an open flame is a poor idea. |
| Self-adhered | Peel-and-stick sheets rolled into place. | Wood-framed houses, porches and dormers. No flame and little odor. |
Open-flame work near wood framing is a real fire risk. On wood-framed homes we favor self-adhered and cold-applied systems.
On houses
Common on North Jersey homes
You will find modified bitumen on:
- Rear additions and low-slope sections of two- and three-family homes
- Porch and portico roofs
- Shed dormers and the flat tops of mansard and hip roofs
- Garages and small commercial buildings
- Balconies and walk-out roofs under pavers or decking
The critical detail is the tie-in where mod bit meets shingles or a wall. We run the membrane well up under the shingles and finish walls with metal counter-flashing.
Repairs
Modified bitumen repair
Most modified bitumen leaks start at the laps. As the asphalt dries out over the years the seams open a hair, the granules wash off the edge of each sheet and water finds the gap. That does not call for a new roof. We clean the laps, re-seal every seam with a compatible flashing cement, and check the drains, pipe boots and wall flashing while we are up there.
Blisters and worn spots are cut out and patched with new modified bitumen. When the base sheet and the deck are sound, the work carries our minimum 2-year workmanship warranty on the repaired area. If we find soft decking or water trapped under the membrane, we show you the photos and price a replacement instead.
Questions
Modified bitumen questions
How long does a modified bitumen roof last?
Typically 15 to 20 years or more for a two-ply system with good drainage. Granule loss, blisters and open laps are the signs of age to watch for.
Can you repair a mod-bit roof?
Yes. Open laps, blisters and failed flashing can be cut out and patched with compatible material. It is one of the easier flat roofs to repair well.
Is torch-down roofing safe?
In trained hands and on the right building, yes. The roofing industry runs a torch safety program called CERTA for this reason. On wood-framed houses we prefer systems that need no flame at all.
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