Durham commercial roof repair: what owners and managers should know

Durham's commercial buildings, and why their roofs are different

Commercial roof repair in Durham covers an unusually varied set of buildings. There are the brick storefronts on Ninth Street, Main Street and Geer Street, the strip retail along Roxboro Road and Hillsborough Road, churches and fellowship halls across East Durham, one-story medical and professional offices, and small apartment buildings with flat roofs. Then there is the part of the city that makes Durham different: the old tobacco warehouses and textile mill buildings that have been turned into offices, apartments, shops and restaurants. Places like Brightleaf Square, West Village, the American Tobacco Campus and Golden Belt are the best-known examples, and many smaller warehouses around downtown have followed the same path.

Nearly all of these buildings have low-slope roofs, which hold water briefly instead of shedding it. The roof is a continuous membrane, and everything depends on the seams, the flashings and the drains.

This is a free guide for owners and property managers, not a roofing company. Estimate requests go to an independent local roofing contractor partner. For membrane work, ask before anyone comes out whether they repair low-slope roofs regularly, and for a large or historic building, ask for references on similar buildings.

Heat: the roof cooks from both sides

Durham summers are long, hot and humid. A dark membrane in full sun gets far hotter than the air, and the building below is air-conditioned, so the roof sits between two very different temperatures for months at a time.

• Blisters. Modified bitumen and built-up roofs trap small pockets of air or moisture between layers. Heat makes those pockets expand, and they grow each summer. A blister that has not cracked is often left alone and watched; one that has split needs repair.
• Thermal movement. The membrane, the metal edge and the brick parapet expand and shrink at different rates every day. Sealant joints at coping and counterflashing fail quickly, and repairs done with caulk alone rarely last more than a season or two.
• Surface aging. Exposed asphalt, roof cement and older black rubber dry out and craze under constant sun. A reflective white membrane such as TPO runs much cooler on the surface, which is one reason it is common on newer re-roofs here.

Humidity and the moisture inside the building

Humidity is the problem owners overlook. Warm, wet air in the building moves up toward the roof. In a converted warehouse with apartments, kitchens and showers below, that moisture can reach the underside of the roof deck and condense when the deck is cool, especially overnight in the shoulder seasons. The result looks like a leak, with drips on a dry day, rusty fasteners and stained wood, but the membrane may be fine.

Outside, humidity and shade feed algae and mildew in any place where water sits. Ponding water still there 48 hours after a storm turns green, holds dirt against the membrane and ages it faster. Pine needles and oak leaves from the city's big street trees pack into drains and scuppers and hold moisture against the roof edge. If a building has drips with no rain, ask the roofer to check for condensation and ventilation problems before anyone starts patching the membrane.

Summer storms and drainage

July and August thunderstorms in the Triangle can drop a lot of rain in a short time, often with strong straight-line wind, and the remnants of tropical storms can bring a day or two of steady heavy rain in late summer and fall. On a flat roof, the question is whether the water can leave fast enough.

• Drains and scuppers sized for an older building may not keep up with a cloudburst, especially when strainers are clogged with pine needles.
• Water backs up behind parapets and rises above the top of the base flashing, then runs into the wall.
• Gutters and conductor heads on older brick buildings overflow and soak the masonry.
• Wind lifts loose edge metal and peels membrane back from corners, and limbs from nearby trees can puncture the sheet.

After a big storm, look for water stains inside along the exterior walls, debris and branches on the roof, and loose edge metal from the ground. The storm damage page covers what to photograph and how the claim side works; in North Carolina only a public adjuster licensed by the NC Department of Insurance can negotiate a claim for you, and commercial policies differ from homeowner policies, so read yours and ask your agent.

Old mill and warehouse buildings: what to watch for

Converted industrial buildings have their own roof problems:

• Old wood decks. Many have heavy timber framing and plank decking. Wood that has been wet for years can be soft in spots, and fasteners may not hold. A roofer should check the deck from inside where it is exposed and from above with test cuts.
• Tall brick parapets. Mortar joints weather, coping stones or metal caps loosen, and water gets into the wall behind the roof flashing. Some leaks blamed on the roof are actually coming through the masonry.
• Raised roof sections. Some older industrial buildings have raised monitor roofs, clerestories or skylight rows. Every vertical wall on the roof is another flashing line to maintain.
• Many generations of patches. Layers of old roofing, abandoned vents and equipment curbs left from earlier uses all create places for water to get in.
• New equipment on an old roof. Apartment and restaurant conversions add rooftop units, exhaust fans and grease ducts. Each one is a penetration, and grease from kitchen exhaust damages many membranes, so ask whether the membrane near a hood is grease-resistant or protected.
• Historic review. If the building is in a local historic district or a rehab used historic tax credits, visible changes to the roof may need review. Ask the city's planning office and the project's preservation consultant before changing anything you can see from the street.

The membranes you may have, and how each is repaired

TPO. A white or gray single-ply sheet with hot-air welded seams. Repairs are welded patches on a cleaned surface. Very old TPO can be hard to weld to, which is a sign the roof is near the end.

EPDM. Black synthetic rubber with glued or taped seams. Repairs use primer and seam tape or a patch. It runs hot in a Durham summer, and older sheets shrink and pull at the corners.

Modified bitumen. Asphalt-based rolls, torched, cold-applied or self-adhered, often with a granule cap sheet. Blisters, open laps and granule loss are common in the heat. Ask how torch work will be handled next to wood framing and occupied spaces.

Built-up roofing. Felt and hot asphalt under a gravel surface, still found on older buildings. It can be repaired in spots, but the gravel hides problems.

Metal. Some warehouse roofs and additions have low-slope metal. Fasteners back out, washers dry up, laps open, and rust starts at cut edges and around old penetrations.

What owners can check

1. Inside after rain: stained ceiling tiles, water at the tops of exterior walls, wet spots under skylights and around equipment.
2. Inside on dry days: drips, rusty fasteners or damp wood at the underside of the deck point toward condensation, not a hole.
3. At the downspouts: water should flow during rain; a dry downspout during a storm usually means a clogged drain above.
4. From the ground or the hatch: standing water, branches, loose edge metal, and blisters or wrinkles you can see.
5. After HVAC or kitchen service: ask what was opened or set on the roof, and ask for photos.
6. Your records: the roof system, its age if known, warranty papers, and every repair with photos and dates.

If you go on the roof, use a proper hatch or ladder, stay away from edges and skylights, and do not go up wet. A roof in July sun is hot enough to burn hands and soften the surface, so early morning is safer for everyone.

A maintenance schedule that fits Durham

A spring check in March or April clears winter leaves and the pine pollen that coats everything, confirms the drains are open before storm season, and catches anything the winter freezes opened. A fall check in October or November clears leaves and needles before they pack into drains, and looks again at flashings and blisters after the summer heat. Add a look after any severe thunderstorm or tropical-storm remnant. The roof inspection page explains what a written inspection report should contain.

Commercial roof repair step by step

1. Start inside. Water moves along the deck, so the drip may be well away from the source.
2. Rule condensation in or out. Especially in converted buildings with apartments or kitchens below.
3. Trace the source on the roof: drains, curbs, parapets, penetrations and seams uphill of the stain, with a water test if needed.
4. Test for wet insulation. Core cuts or a moisture survey show whether the insulation is wet. Wet insulation does not dry in this climate under a membrane, so repairs over it keep failing.
5. Repair the detail and the drainage, not just the hole.
6. Photograph before and after, and get a written description of what was done.

When to stop repairing

If the insulation is wet across large areas, blisters and splits are showing up all over, or each repair is followed by a new leak somewhere else, it is time to price a re-cover or replacement. A coating may extend a dry, sound membrane, but it is not a fix for wet insulation or failed seams. Whether a new roof can go over the old one depends on what is there and on code; check with the City of Durham or Durham County (or your town's permit office) and ask each bidder how they handled it.

Comparing commercial repair bids

Ask each bidder to put these in writing:

• The cause, and where it is on the roof.
• The repair method and the named materials.
• Whether they tested for wet insulation and condensation, what they found, and a unit price for more repairs if needed.
• Drainage work included or excluded.
• Protection for tenants, customers, cars and the sidewalk.
• Who handles any permit, and whether it is in the price.
• The workmanship warranty on the repair, in years.

For larger projects, also compare edge metal and coping, tapered insulation to stop ponding, how rooftop units are handled, and whether the price includes masonry work at the parapets or leaves it to a mason. Commercial roofs are priced per square foot, and the cost page is written for houses, so ask for a separate written quote.

Warranties

• Workmanship warranty: the contractor covers their own labor for a set term.
• Material warranty: the manufacturer covers defects in the membrane, usually not the labor.
• System warranty: a manufacturer warranty on a new roof installed by an approved contractor, sometimes after a manufacturer inspection. These often require documented maintenance and approval before others cut into the roof.

On a roof still under warranty, call the warranty holder before anyone else works on it.

Questions to ask a commercial roofer

• What low-slope roofs like mine have you repaired recently, and can I see photos or speak with an owner?
• Have you worked on older brick or timber buildings, and do you handle parapet flashing and coping?
• How will you check for wet insulation and for condensation?
• How will you protect tenants and the space below during the work?
• Can I see your certificate of insurance before work starts?

Licensing rules depend on the size and type of the job, so check a contractor's license with the NC Licensing Board for General Contractors and your city's permit office before you sign. If you lease the building, read the roof clause first and ask an attorney if the landlord and tenant split is unclear.

Getting a written estimate

If water is coming in now, protect electrical equipment and anything valuable, put down buckets, and photograph the damage with the date. Then call or request an estimate. If part of the building has a pitched shingle roof, the roof repair page covers that side, and the metal roofing page explains metal options for additions and outbuildings.