Modified bitumen, usually called mod-bit, is an asphalt roofing sheet reinforced with polyester or fiberglass and blended with rubber (SBS) or plastic (APP) modifiers. It goes down in two or three layers, torched, mopped, cold-glued or self-adhered, with a granule-surfaced cap sheet on top. It is tough, handles foot traffic well and is easy to repair. Common problems are open laps, cracked flashing, granule loss and blisters. We compare a mod-bit repair or replacement with built-up roofing, its older multi-ply cousin.
The estimate will say how many layers you have, what type of sheet it is and what we plan to keep.
We check the existing layers and surfacing before choosing a repair or replacement detail that will bond to them. Old mod-bit can be repaired with new mod-bit, but some coatings and patches get in the way of a good bond. The building's access rules and work hours are worked out with the owner or manager first, and our inspection results set the basis for the work.
Knowing what layers are there
Mod-bit roofs are often installed over an older roof, sometimes more than one. We look at any roof records you have and take a core cut to count the layers and see how they were attached. Patches made with incompatible products, like silicone sealant, are noted because new asphalt will not stick to them. We note any section we could not walk.
Unknown coatings get a bond test first, since aluminum and silicone coatings in particular can keep new sheets from sticking.
A commercial roof inspection shows us the surface, the laps and the flashing. The cores tell us whether the layers underneath are dry and bonded. If the deck looks damaged, or there are too many old roofs stacked on top of each other, a tear-off may be required and an engineer may need to look at the deck before we plan a recover.
Insulation and the base under the sheet
Mod-bit needs a firm, dry base. Wet insulation under the sheet causes blisters and soft spots that tear under foot traffic. Infrared and cores show where the blisters are coming from, and failed boards are replaced with new insulation and cover board. A cover board also protects foam insulation from the heat of torching or hot asphalt.
Untested spots stay listed as unknowns until we can cut a core there.
If more soaked board shows up during tear-off, you hear about it and the cost before we go on. Soft deck is replaced only after you approve it, and we keep the price for each sheet of deck on the estimate so there are no surprises. Each opening is closed the same day, and core holes are patched before we leave. That way the estimate reflects what is under the cap sheet, and the building stays dry while we work.
Laps, flashing and other roofs
Most mod-bit leaks start at laps where sheets overlap, at base flashing on walls and curbs, and at metal edges. New sheets have to overlap old ones by the right amount and be fully bonded, with granules removed from the lap area. Where mod-bit meets another roof, such as an EPDM roof, the materials do not bond directly, so the two are joined at a curb or with a transition both systems accept. Pitch pans and pipe boots get checked too.
Each repair ends at sound roofing with a fully sealed lap.
Walls and curbs get new two-ply base flashing with a cap sheet and metal counterflashing above. If a replacement raises the roof, we check drain, curb and door threshold heights before going ahead. Granule-surfaced cap sheets reflect some heat, and white or reflective cap sheets can help keep the building cooler in Ventura's sunny summers.
Related Roofing Work
Torch safety and other trades
Torch-applied mod-bit is common, but an open flame near wood, insulation or rooftop equipment needs care. We follow fire watch practices and keep extinguishers on the roof. Where torching is a poor fit, such as near wood blocking or air intakes, cold-applied or self-adhered sheets are an option. Our roof condition reports also flag zones where torching is off limits.
Each section is closed before the crew moves to the next.
Rooftop units, drains and electrical lines are handled by those trades, and we schedule around them. Lifting a unit for curb work is the HVAC contractor's job, and they reconnect it once the new flashing is done. Deliveries and debris removal are planned around tenants and customers, and odor from hot asphalt or adhesives is managed around air intakes and doors. The owner gets one clear schedule for every trade.
Closeout and future repairs
The closeout shows the new base and cap sheets, the laps and flashings, and any board or deck we replaced, with product names. We note where each repair starts and ends and what it ties into. Areas we could not reach and work still owed by other trades are listed separately, so nothing gets lost after the crew leaves.
For older roofs near Downtown Ventura, it also records how many old layers are still under the new sheets.
Later, a commercial roof repair crew can see right away which sheets are ours. Mid-job changes are marked on the roof plan. That helps the next roofer start in the right place, and it gives the owner a clear picture of the roof's condition when planning budgets, refinancing or a sale. We also suggest a simple inspection schedule, such as a check each fall before the rainy season and after any major storm.
Common Questions
What should come with the square footage of new sheet in a mod-bit estimate?
The flashing at walls, curbs and edges, any wet insulation or deck to replace, and the number of existing layers that stay or come off. Those items often cost as much as the field sheet, so they should be listed, not hidden in one number.
What if there is an old patch or coating we cannot identify?
We test it before deciding how to tie into it. Some products, like silicone sealant, prevent new asphalt sheets from bonding. If it cannot be bonded to, we remove it, and the estimate says so.
What changes if we find more bad insulation once the roof is open?
We stop and show you the area before going further. The estimate is updated for the extra insulation, cover board or deck repair, and the opening is closed the same day so the building stays dry.
What will a future repair crew get from this job?
A photo log, the sheet and flashing products, repair boundaries and any open items. That tells them which areas are new and which are older roofing that was kept.
Get your modified bitumen roof inspected
Send the address and tell us where the laps or flashing are giving trouble. We will core the roof, count the layers and price the repair or replacement line by line.