Roll Roofing on a Shed or Porch Gets Its Own Inspection Line

Roll roofing is the flat-sheet material on many garden sheds, detached garages, back porches and the low covered step over a side door. It comes in long rolls, usually mineral-surfaced asphalt, and it is laid with lap cement and exposed nails rather than with individual shingles. A roof inspection that treats it like the rest of the house misses where it actually fails. If your property has a shingle roof and a roll-covered shed or porch in the same yard, the inspector should write the small roof as its own entry with its own photos.

Why the seams matter more than the field

On a shingle roof, the exposed face of each shingle is most of the roof, and the nails sit hidden under the next course. On roll roofing, the field is one large sheet, and the weak places are the laps where one strip overlaps the next, the edges where the sheet folds over the drip edge, and the rows of exposed nails along the top edge. Lap cement dries out over several St. Louis summers and then cracks. Nail heads back out of the sheet as the deck expands and contracts through freeze-thaw cycles. Once a lap opens, wind can lift the free edge and water gets underneath.

When you walk your own yard before the inspector arrives, look at the seams first. Note whether the lap lines are still sealed flat, whether any strip is curling, and whether the nail rows are straight or have popped. Take one photo from the low side with the light raking across the sheet. Raking light shows lifted seams that look flat from straight above.

What heat and hail do to a flat sheet

Roll roofing on a south or west exposure takes the full afternoon sun in July and August. The surface can blister, which shows as bubbles that have lost their granules. Blisters that crack open leave a dark, soft patch that water can enter. Ask the inspector to measure the affected area with a tape and to note whether the blisters sit in a band near the eave or spread across the sheet. A band can point to heat, and a spread can point to age.

Hail on a flat roll sheet looks different from hail on shingles. A stone can knock granules loose in a round patch and leave a dark spot, or it can puncture the sheet if the hit is large. Many of the dents people expect to see in metal are not there at all. A photo with a ruler in frame, taken straight on and then at an angle, is the record that matters. The hail section of this site explains why one photo is not proof on its own, and that applies to a shed roof just as it does to a house.

Where the drip edge and the gutter meet the sheet

The edge is the other common failure. Roll roofing folded over a drip edge can crack along the fold within a few seasons, especially where the sheet was cut too tight. Water then runs behind the sheet and into the fascia. Look at the bottom edge from the ground with a flashlight in the early morning, when shadows are long and the fold is easy to see. Check whether the gutter sits below the sheet's edge or whether the sheet dumps water onto the outside face of the gutter.

If the shed or porch roof drains onto a walkway or patio, the inspector should note where the water lands. A roll roof that sheds water onto a concrete pad will splash onto siding and the foundation in a heavy rain, and that is a different fix from a leak in the sheet itself.

Questions to put to the inspector

• Does the inspection record each small roof as its own line, with its own photos and measurements?
• How many layers of roll roofing are on the structure, and was the new sheet laid over the old one or over bare deck?
• Are the laps sealed, and is the lap cement cracked or still soft in the seam?
• Are any nail heads backed out, and how many are exposed per linear foot?
• Where does the free edge sit relative to the drip edge and the gutter?
• Is there water staining on the underside of the deck, visible from inside the shed or from the porch ceiling?

A written answer to each question gives you a record to compare against next year. A verbal "looks fine" does not.

When a repair stops making sense

Roll roofing that has been patched several times with lap cement and new nails usually does not improve with each patch. The patches add weight, the old sheet keeps moving, and new cracks open beside each repair. For a shed roof, replacing the sheet with new roll roofing, or with a short run of shingles where the pitch allows, is often a better use of the money than another patch. For a porch roof, the decision often depends on what the porch ties into. A porch roof attached to the main wall can leak at the wall flashing as well as at the sheet. Ask the inspector whether the porch roof ties into the house, and if it does, record the wall flashing as its own item.

Permit rules for sheds and small roofs differ between the city and the county, and they depend on the size of the structure and whether it is attached to the house. Call the municipal permit desk where the property sits before you order material. Keys Roofing can be reached at (314) 220-2333 to talk through the scope. The written scope will list each small roof with its photos and measurements, so you have the record in hand when you decide.

Keep the small roof in your file

The main roof gets the attention because it covers the living space. The shed and porch roofs get forgotten until a ceiling stain shows up on the porch or a shelf in the shed gets wet. Keep a separate page in your roof log for each small roof, with the date of the inspection, the photos and the measurements. That page is the baseline for the next walk, and it is far easier to compare against than trying to remember what the sheet looked like last year.