Re Shingle Low Slope Roof

Tearing Back the Roof and Finding the Real Problems

To properly re shingle the roof, shingles were removed around the vent first. This tells you immediately whether rot is present or if moisture has been lingering long term.

Surprisingly, the wood underneath was in decent shape. It had clearly been wet often but dried quickly due to sun exposure. That happens on some low slope roofs, especially over additions.

The insulation below the vent was soaked. That exposed the real issue. The bathroom fan was not properly vented to the exterior. It was connected to an expanding plastic hose that was not even attached to the roof vent. The fan was dumping moist air into the rafter cavity.

That moisture had nowhere to go.

Flashing Mistakes That Cause Hidden Leaks

Another major issue was how flashing was installed where the roof tied into the house. The flashing had been installed before the shingles, meaning it sat underneath them. Water traveling down the roof hit the flashing and was directed back into the roof assembly.

That is backwards.

The only reason it did not leak constantly was because roofing cement had been layered over it. That is not proper flashing. That is luck.

Drip Edge Problems on Low Slope Roofs

Here is one most homeowners never notice.

The roof was fourteen feet wide. The drip edge was installed in ten foot sections. Two pieces overlapped by six feet. On a steep slope, that might not matter. On a low slope roof, that overlap created a ridge. That ridge caused water to pool.

Under the shingles, everything was wet.

Instead of removing the drip edge completely, the vertical lip was cut down with a hacksaw. Drip edge is useful, but doubling it on a low slope roof can do more harm than good.

Fixing the Roof Sheathing Correctly

Once the roof was stripped, several issues showed up in the sheathing.

There were gaps and transitions between old board sheathing and newer OSB. One area under the chimney had thinner OSB that created a step. That is a guaranteed water trap on a low slope roof.

Those sections were replaced and leveled. Fascia boards that had sagged over time were pulled up tight and fastened through the sheathing with pre drilled screws. This flattened the roof plane and removed another potential water path.

The ends of the boards were cut flush and capped with cedar. The cedar strip was beveled at twenty degrees so water would drip cleanly away from the fascia instead of soaking it.

Correcting the Bathroom Vent the Right Way

The old plastic hose was removed completely. A three inch ABS pipe with an elbow was installed and properly connected to a roof vent flange designed to pass through shingles.

This allows shingles to lap correctly over the flange so water flows down and away naturally. A screen was added to prevent birds and wildlife from entering. Low slope roofs attract animals because they are easy to land on.

Re Shingling a Low Slope Roof Properly

The old roof had no underlayment. That was corrected.

Tar paper was installed as a secondary defense. On low slope roofs, underlayment matters. It is not optional.

Starter shingles were installed correctly with tabs facing up slope so water cannot track between courses. Shingles were woven properly around vent flanges so water flows onto the flange and continues down slope instead of underneath.

Low slope roofs are easier to stand on, but they are harder to waterproof. The flatter the roof, the more precise the work must be.

Final Rows and Chimney Area

The old flashing near the roof edge was left in place because removing it would have caused more damage. The final row of shingles was curved up into the tarred area and sealed along the top edge.

Near the chimney, extra care was taken. Leaks near the top of a roof are less dangerous than leaks near the bottom, but they still matter. A small amount of sealant was used where appropriate, not as a crutch.

Heavy rain came before final sealing was completed. No leaks occurred.

That is the real test.

Final Thoughts on Low Slope Re Shingling

Low slope roofs expose every shortcut. This roof only leaked in one spot, but the potential for failure was everywhere.

Correct pitch understanding, proper venting, correct flashing order, flat sheathing, and proper underlayment are what make low slope shingle roofs succeed.

This roof should last.