How to Repair a Flat Roof

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How to Repair a Flat Roof

In the past, flat roofs garnered a reputation for instability. Water tends to pool on flat roofs, leading to leaks that ruin materials in the room before or, at worst, a build-up of pressure that caused large sections of the roof to collapse. Now, manufacturers sell flat roofing materials with greater durability and quality.

Before attempting to repair a flat roof, homeowners should research common problems that crop up on flat roofs. Leaks remain the most common problem, but a myriad of ways to patch up leaks exist. Homeowners should also read up on materials, such as felt roofing; tools for repairs, such as ladders; and safety precautions.

Identifying Problems

Most problems with flat roofs manifest as leaks; however, it is imperative to understand how leaks occur and just how to identify specific problems.

How Leaks Occur

Oftentimes, homeowners fail to notice the leak themselves; instead, they notice wet spots in carpeting or furniture below the leak; however, this does not indicate that the leak occurred directly above. Various layers of materials make up a flat roof. Most often, water seeps in through the top layer and winds its way downward, zig-zagging until it permeates the lowest layer, which sits above an interior room.


Ponding remains the most common source of leaks in roofs. Ponding occurs when water gathers in one place. Ponds greater than 25mm cause water stains and sustain plant life. Between plants, water weight, and the deterioration of roofing materials caused by the pond of water, leaks occur quickly.

Damaged Materials

Whether through ponding or simple wear and tear, roofing materials accrue damage and let in leaks. Look for signs such as cracks in corners and at joints, ventilation slits, and cracks around chimneys skylights and lights.

Repair or Restore

After inspecting their flat roofs, homeowners need to decide whether they should repair the roof or replace the entire structure. Homeowners can remedy damages caused by tears and ponding using roof repair kits. These kits include materials such as adhesive that seal away leaks, and kits designed for a specific type of structure, such as fibreglass, include specialised materials as well. Try using do-it-yourself repair kits in conjunction with other materials, such as waterproof paint, for extra protection.

Choosing Materials

After deciding to repair a flat roof, homeowners should choose the material they want to use.





Felt Roofing

Layers of tar and roofing felt

Most common type of material

Lifespan: 10-20 years

Low cost

Poor ventilation

EPDM Rubber

Layer of rubber applied to decking

Lifespan: Up to 50 years



Fibreglass GRP

One-to-two-layer finishes able to match any color

Lifespan: 25-30 years


Poor ventilation

Most expensive option

Homeowners who feel uncomfortable repair their roofs or applying a new roofing material should ask professionals for help.

Making Repairs

Certain types of damage require specific methods of repair.

Removing Felt

Homeowners should inspect their flat roofs at least twice a year to check for signs of damage. When felt begins to break down, homeowners can remove it easily by starting at a corner and peeling the material away. Below, homeowners should see an expanse of wooden substrate. Check it for stability by applying light weight. If it sinks, it needs replaced by professionals. In most cases, though, sweeping it off should suffice. With the wooden substrate clear, homeowners can apply a new roofing material.


Blisters occur when moisture builds up in roofing material, and do not require the homeowner to repair the entire roofing surface. Use a utility knife to cut blister right down the middle, exercising caution not to penetrate the roofing beneath it. Now, cut around the blister's edges and place thumbs at the edges of the blister. Apply pressure and move thumbs toward the blister's center to squeeze out water. Mop up excess moisture with a rag.

To finish up, apply generous helpings of roof cement on the lower edges of loose felt and press down on the blister. Seal the blister by nailing each edge of the slit closed using galvanised roofing nails.


Condensation can cause rot to build up in layers beneath the top layer. Homeowners can protect against condensation and rot by improving ventilation between layers. Add an outer layer of roofing membrane on top of external insulation, leaving a gap between the timber decking and the ceiling.

How to Buy Materials to Repair a Flat Roof

eBay offers new and used versions of the equipment and materials homeowners need to repair flat roofs. To look up a product, go to any eBay page and locate the search bar. Enter a keyword phrase designed to narrow down results to specific products, such as "Cromapol Acrylic Roof Coating." Homeowners who prefer to browse a more extensive, albeit general list of products, should try entering "flat roof sealant."

After making repairs, many homeowners may want to consider taking advantage of their more stable roof to add new structures and decorations. Many manufacturers build skylights large enough to flood an entire room with light. Gutter trimming, another practical investment, can catch water and debris, lessening the amount of soggy weight on the roof.

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