Modified bitumen roof repair
Modified bitumen ("mod bit") is asphalt reinforced with polyester or fiberglass and modified with rubber (SBS) or plastic (APP), laid in rolls that are torched, mopped with hot asphalt, cold-applied with adhesive or self-adhered. Repairs typically cost $3 to $8 per sq ft; a new mod bit roof runs $4 to $8 per sq ft and lasts about 20 years.
Mod bit repair
$3 to $8 per sq ft
Replacement $4 to $8 per sq ft.
Common modified bitumen problems
- Open laps (seams) where the rolls overlap.
- Blisters from trapped moisture or air under the sheet.
- Lost granules, leaving the bitumen exposed to UV.
- Cracked or alligatored surfacing on older roofs.
- Failed flashings at walls and curbs.
What modified bitumen repairs typically cost
| Job | Typical price |
|---|---|
| Mod bit repair Per sq ft of repaired area | $3 to $8 per sq ft |
| Blister repair Cut, dry, re-adhere and cap | $250 to $1,500 |
| Crack repair Strip-in and seal | $200 to $1,500 |
| Flashing repair Curbs, walls, pipe boots and pitch pans | $200 to $750 |
| New mod bit roof Installed | $4 to $8 per sq ft |
Typical US prices from published national roofing cost guides, January 2026 editions, read November 2026. Installed, in US dollars, before any local tax. A guide, not a quote.
What a sound modified bitumen repair includes
A dry, clean, primed surface
Patches and seams only hold on clean, dry membrane. A roofer who patches over standing water or dirt is selling a callback.
The cause, not just the drip
Water travels under membrane and along deck flutes, so the wet ceiling tile is rarely under the hole. A good repair names where the water got in.
Fire safety with torches
Torch-applied repairs need a fire watch and care near combustible materials and wood decks; on some buildings a cold-applied or self-adhered repair is the safer choice.
Wet insulation found and dealt with
Wet board loses most of its insulating value and holds water against the deck. Cores or a moisture survey show how far it has spread; badly wet areas are cut out and replaced.
Photos before and after
Dated photos of every repair, and its location on a roof plan, protect your warranty and any insurance claim, and help the next roofer.
Safe access and fall protection
Work near an unprotected edge on a low-slope roof calls for fall protection under OSHA 1926.501: guardrails, safety nets, personal fall arrest or the combinations the rule allows. Ask how the crew will get up and stay safe.
Mod bit roof leaking? Send us the building ZIP and we will find a roofer working in that area.
Ask for a free quoteHow a modified bitumen repair usually goes
Find the entry point
The roofer walks the roof, checks the areas above the leak and upslope of it, and may use a moisture meter, infrared scan or cores.
Make it watertight
If water is coming in, a temporary repair first: a compatible patch, sealant or tarp held down so wind cannot lift it.
Permanent repair
The proper detail for the system: a heat-welded patch, taped seam, re-set flashing or a section of new membrane.
Report and photos
Before and after photos, what was found and what to budget for next, so you can decide between repair and replacement with facts.
Questions people ask
Can you repair a modified bitumen roof?
Yes. Laps are reheated and resealed or stripped in, blisters are cut and capped, and damaged areas get a new piece of cap sheet.
Should modified bitumen blisters be repaired?
Small, intact blisters are often left and monitored. Broken, growing or soft blisters should be repaired because they let water in.
How long does a modified bitumen roof last?
Typically about 20 years, longer with good maintenance and recoating of the surface.
What is the difference between SBS and APP?
SBS is rubber-modified, more flexible in cold and usually mopped, cold-applied or torched. APP is plastic-modified, more UV-resistant and normally torched.
What do mod bit repairs cost?
About $3 to $8 per sq ft of damaged area.
Where our information comes from
Get the mod bit roof repaired
The building ZIP, where to reach you, then a few taps about the roof. About a minute.
This is a free matching service, not a commercial roofer. We look for one who works in your area and tell you their name before anything is shared. Nobody contacts you until you say yes.
Thanks, your enquiry is in.
- We look for a commercial roofer who covers your building and does this kind of work, then email or call to tell you who it is.
- Your details reach that firm only if you say yes.
- They inspect the roof and give you a written price. No marketing from us, ever.