Garage, Porch and Sunroom Roofs We Take On
Many older Ann Arbor houses have at least one secondary roof: a detached garage at the end of the drive, a front porch, or a rear sunroom or enclosed porch added later. Each is built differently from the main roof, so each gets its own section here.
Detached Garage Roofs
A detached garage is usually a simple gable or hip, easy to reach, and quick to roof. HomeGuide says most garage roof replacements take one to three days, and a one-car garage can often be done in a day.
The code difference: Michigan's residential code requires an ice barrier along the eaves of houses here, but it makes an exception for detached accessory structures with no conditioned floor area. An unheated detached garage doesn't legally need one. Our view: put it in anyway if the garage has a gutter over the door or a heated workshop corner, because the membrane costs little on a roof this size. An attached garage is part of the house and gets the full eave treatment (see ice dam removal for the rule).
Garages also make sense for a different material than the house. Asphalt shingles to match the house are the default, but a detached garage is the cheapest place to try standing seam or a lower shingle grade on a building you'll replace sooner. HomeGuide's material ranges for garage roofs run from $4 to $9 per square foot for asphalt to $9 to $16 for standing seam.
Garage Roof Repair: Sagging Rafters and Rotted Decking
A sag in the ridge or a dip between rafters means the framing is moving. Common causes are undersized or widely spaced rafters, rot at the rafter ends, and ceiling ties cut out to make room for storage. HomeGuide lists these warning signs for a garage roof:
- sagging areas in the roof plane;
- light showing through the deck from inside;
- curling, cracked or missing shingles exposing the deck.
How the fix goes depends on how far it has moved. HomeGuide notes minor sagging may only need added support such as rafter ties, while severe cases need structural repair and sometimes a full rebuild. It puts sagging roof repair at $1,000 to $5,000 or more and recommends starting with a structural engineer's inspection and plan ($300 to $1,000). Rotted decking gets cut out and replaced at $2 to $5 per square foot.
Our view: if a garage roof is sagging and also due for shingles, do both at once. Straightening rafters is far easier with the old roof off, and new shingles on a bent roof will show every wave.
Front Porch Roofs
A front porch roof is usually a shed or low gable tied into the front wall of the house. Its two weak spots are the line where it meets the wall and the beam along the front edge.
- The wall joint. Water running down the house wall has to be turned out over the porch roof by flashing tucked behind the siding. On a re-roof, Michigan's code calls for replacing flashing that's rusted, damaged or deteriorated, and on an old porch it usually is. Sidewall and headwall flashing details are on our chimney flashing repair page.
- The front edge. Gutters overflowing at the porch eave rot the fascia and the top of the beam. Check the wood when the old roofing comes off.
On houses built before 1978, porch trim and ceilings often carry lead paint, which brings in federal rules for paid work that disturbs it; see soffit and fascia repair.
Low-Slope Porch and Sunroom Roofs
Many porch and sunroom roofs, and the flat-looking roofs over enclosed rear porches, are pitched too low for shingles. Michigan's code sets a minimum pitch for asphalt shingles (explained on our flat roofing page), and below it the choices change:
- Mineral-surfaced roll roofing, allowed down to 1:12 on solid decking. Cheap, and short-lived.
- A membrane: EPDM, TPO or modified bitumen, for slopes too flat even for roll roofing.
- Standing seam metal, which the code allows down to 1/4:12 when the panel is rated for it (see standing seam metal roof).
Sunroom and enclosed-porch roofs are often heated space, which brings condensation and ice into play that an open porch doesn't have. Ask the contractor to look at insulation and ventilation along with the roofing.
Why Ann Arbor homeowners call Ann Arbor Roofing Co.
- Written estimate, free of charge
- Shingle line, underlayment and ice barrier named in the price
- Deck repair priced per sheet before the tear-off
- One independent local roofer per request, not a call list
- No fee to the homeowner for the referral
What Does a Garage Roof Replacement Cost?
HomeGuide's 2026 national averages put garage roof replacement at $4 to $12 per square foot, depending on size, pitch and material:
| Garage | National range (HomeGuide) |
|---|---|
| One-car | $1,500 to $4,000 |
| Two-car | $2,400 to $6,000 |
| Three-car | $3,200 to $8,000 |
HomeGuide notes that smaller roofs typically cost more per square foot because most contractors have a minimum project fee, and deck or rafter repair weighs more on a small job. HomeGuide also notes that many cities require permits for roof replacement even on detached garages. How Ann Arbor's permit works is on our roof replacement page.
Repair or Replace a Garage Roof?
Repair when the framing is straight and the problem is local: a few blown-off shingles, a leak at a vent, one rotted corner. Replace when shingles are worn across the whole roof, the deck is soft in several spots, or the roof needs structural work anyway.
If the house roof is being replaced soon, we'd do the garage the same week. One crew, one dumpster and one permit visit costs less than two separate jobs, and the two roofs will match. For a garage or porch roof that's flat or nearly so, compare options on our flat roofing page.