Comprehensive Guide to Flat Roofs: Materials, Installation, Maintenance, and Repair

Flat Roof Types To Consider

Most roofs of this kind use single ply sheets, asphalt layers, or metal and liquid coatings. Flat roof types in the first two groups cover most house, garage and small commercial jobs.

• EPDM: black rubber sheet with taped or glued seams. The easiest to patch.
• TPO: white or gray plastic sheet with heat welded seams.
• PVC: a sheet which can be heat welded like TPO, and it is resistant to grease and chemicals, which is why restaurants use it.
• Hot-mix asphalt: asphalt treated with additives and mixed hot, with layers of asphalt and reinforcement (polyester or fiberglass) joined together and torched or mopped down.
• Built up roofing: alternating asphalt and felt, usually four plies deep.
• Over a solid deck; interlocking panels used for new work: Standing seam metal
• Liquid coating: an elastic layer, which restores a sound membrane.

The hardest case among flat roofs is a low slope addition tucked against a taller wall. Runoff from the upper roof pours onto the flat section, so the wall flashing does more work than the membrane itself.

Best Material For A Flat Roof In Tacoma

EPDM or TPO offers the best price/leak resistance and PVC earns its premium for near cooking exhaust or chemicals.

Comparing flat roof materials here means weighing months of drizzle, fir needles piling at the drains, and summers that rarely run hot enough to make reflectivity the deciding factor.

Typical lives are industry ranges, not guarantees.

Sales sheets for white membranes on flat roofs lean on reflectivity. The EPA says cool roofing products can stay about 50 to 60 degrees Fahrenheit cooler than conventional materials at peak summer heat.

It also notes reflective roofs can raise winter heating use, though summer savings usually outweigh that. With mild Puget Sound summers, count reflectivity as a bonus.

Flat Roof Costs In Tacoma

Expect $6 to $15 per square foot installed, which puts a 600 square foot roof between $3,600 and $9,000.

These assume one old layer torn off and a sound deck. After a wet winter, almost always one finds rotted plywood on hand. The flat roof costs more per sq.ft. for small flat roof areas than for a large flat roof area, because the setup and edge detail does not reduce with the flat roof.

How Long Does A Flat Roof Last?

Plan on 15 to 30 years, and let drainage decide where in that range your roof lands. A roof that clears water within a day or two ages slowly.

The reason is weight. About 5.2 pounds per square foot equals 1 inch of water, and a puddle that is 10 feet by 15 feet (or 150 square feet) is approximately 780 pounds. Tacoma receives about 40 inches of rain annually, with November typically being the wettest, so a slow drain can handle that amount for months at a time.

The first failures of membranes on Tacoma flat roofs typically occur when fir needles and litter clog scuppers before the membrane failure occurs. That is a housekeeping problem, and it costs the least to prevent. Check that your roof falls at least a quarter inch per foot toward its drains. Anything flatter than that will pond.

Flat Roof Installation Process

A house size replacement usually takes one to three days and follows one order: strip, repair the deck, insulate, install the membrane, flash, test.

Flat roof installation goes wrong at the details, so each step below is a place to ask for a photo.

1. Remove the old membrane and any wet insulation down to the deck.
2. Replace soft or stained sheathing.
3. Lay tapered insulation so water has a path to each drain.
4. Add a vapor retarder if the assembly calls for one.
5. Adhere, weld or fasten the membrane, depending on the system.
6. Probe every seam and reseal any gap.
7. Flash walls, vents, skylights and edges.
8. Flood test the drains and confirm water leaves the roof.

Do You Need A Permit To Reroof In Tacoma?

No permit is needed if the old roof is removed, the new material is under 2.5 lb per sq. ft., and the framing stays unchanged.

Laying new roofing over one existing layer is different: the city lists a roof overlay permit, and its over the counter list notes a pre inspection must be completed first.

Owners of commercial flat roofs need a separate strip and reroof permit. Structures with more than six dwellings or more than three stories also go through commercial review. Changing the roofline or framing, which happens when someone wants to add a deck, needs a permit no matter the building type.

Most Common Flat Roof Problems

Water rarely gets in through the middle of the membrane. Most flat roof problems start at seams, flashing and drains, so check those first.

On older flat roofs, the last row is the expensive one. However, wet insulation will not dry on its own under a sealed membrane and each patch placed over it will only cover up the problem.

Flat Roof Leak Repair Process

Find where water enters, dry that spot, patch it with a material that matches the membrane, and test with a hose.

The first step to flat roof repair is a search, as water runs along with the roof before falling down, leaving the stain some distance from the hole.

1. Take measurements from two walls to the stain inside then extend those measurements to the roof.
2. Work uphill and sideways from that point, checking seams, flashing and drains.
3. Dry the area completely. A patch over damp membrane traps the moisture.
4. Clean the surface and patch with a product made for your roof. Asphalt roof cement can damage single ply sheets.
5. Press out air, seal the edges, then run a hose to test.

Resist stacking thick coats of mastic over a leak. Each coat builds a small dam, and the roof was designed to shed water toward its drains. Small patches typically run $250 to $800 in Tacoma (estimate).

Owners of flat roofs can clear drains and patch a small puncture on a dry EPDM roof with the maker’s kit. TPO and PVC repairs need heat welding, which is a pro job, and so is anything near an edge.

Flat Roof Maintenance Schedule

Twice year round, and after large windstorms. In Tacoma, the fall visit is at the beginning of October, prior to rain.

The primary principle of flat roof maintenance is to maintain a flow and trap any opening before the next rainy season makes it a stain on the ceiling.

Choose A Flat Roof Contractor In Tacoma

Review Washington L&I registration; compare written scopes versus price. GCs require a $30,000 bond, specialty contractors require a $15,000 bond and $250,000 liability insurance.

Ask each bidder:

• What is the manufacturer’s warranty and how is the workmanship warranty?
• How is rotted deck priced?
• Who pulls the permit, if one is needed?
• Will you send photos of each step?

Ask how many flat roofs the crew installs in a typical month, and watch how the office handles change orders. A contractor who dodges that talk before signing tends to create a dispute after. Put three quotes side by side and compare material and thickness, insulation, deck pricing, warranty terms, permit handling and cleanup. A low total with a thin scope is usually the costly one.

Frequently asked questions