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I purchased a house with a relatively new roof installed (2 years). Climate: mild winters that sit around or just below freezing, can get moderate snow fall and mild accumulation, summer wind/thunderstorms.

The roof starts flat (torched roof here), then transitions on both sides to a large 3/12 sloped area (shingles), and finally transitions on both sides to a smaller steep 20/12 sloped area (shingles).

The roofer only installed ice and water shield only at the terminal ~3 ft of shingled areas on both the low slope and steep slope shingle sections (per building code). There is no underlayment beneath the low sloped roof otherwise. I know this is not best practice. Is it an acceptable practice or am I just waiting for my roof deck to rot?

Second question about box vents. While I was in the attic I noticed evidence of small leaks coming through two of these along the low slope area (drip pattern on the insulation below). I know when installing these, sealant is applied around three sides but no sealant is applied to the "downhill side" to allow for potential water drainage by gravity. In the case of my low slope roof, I think wind has on occasion pushed water through this unsealed side and allow it to drip into the attic. Is there a different installation technique for these box vents on slop slope roofs?

Thank you for the input..
 

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If your in Ontario, manitoba or sask it's still acceptable to install shingles onto the wood without underlay. On a 3/12 it probably isnt a good idea,though if it isnt leaking
If they are installed properly it wont be an issue,though you probably wont get a shingle warranty.
If your vents are leaking applying sealant under it may help
 

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Read your shingle mfg instructions, and you will find they likely require underlayment. And on a low slope roof, (anything 2:12-4:12) they usually require double coverage by lapping the underlayment 19".

Box vent louvers, such as Lomanco 750's typically dont need sealant, but are often installed incorrectly. With no photos, we are only guessing.
 

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^^ This. Most manufacturers will require the underlay and ice shield and ridge vent etc. to honor any warranty (and they'll probably still try to get out of any claims even with all the stuff they say needs to be installed).
 
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