Tips for replacing old garage roof?

[DIYBham]

Hi there, I'm a first-time home owner with zero roofing experience. My partner and I have decided to save money and DIY our architectural roof shingle install project. It's a detached garage building from the fifties, approx 28x28' with a simple 6/12 pitch gable roof & original redwood 2x6 planks underneath. There are numerous leaks through what seem to be LAYERS of old asphalt shingles. I'm not sure how to proceed with replacing the rotten deck boards. Is it necessary to use redwood boards again, or would a different, less expensive species of wood work? I'm also not sure what grade of lumber is required for roof planks. Finally, do I need to surface the deck with plywood? Thanks for reading my questions, and for making the awesome YouTube videos.

[A. Spruce]

with a simple 6/12 pitch gable roof & original redwood 2x6 planks underneath.

IMHO, there is nothing "simple" about a 6/12 pitch. While I'm sure you meant it's just a simple gable style roof, a pitch of that magnitude is not easy to work on and will require roof jacks (scaffold brackets) to provide a safe working platform. Safety first!!! Do not do anything you're not comfortable with.

There are numerous leaks through what seem to be LAYERS of old asphalt shingles.

Code allows for two to three layers before stripping is required. In reality, the more layers there are, the less longevity the roof will have because it can't dissipate heat. Old layers of roof also do not provide a very good base for the new roof.

I'm not sure how to proceed with replacing the rotten deck boards. Is it necessary to use redwood boards again, or would a different, less expensive species of wood work? I'm also not sure what grade of lumber is required for roof planks.

Remove the existing damaged materials and install new, simple as that. Species of wood doesn't matter, matching the thickness of what you have is what is important. With repairs made, you want a reasonably flat surface. The only reason to go back with the same species is if this is your finished ceiling inside and you want it to look good, which is probably not the case in a detached garage. As for grade of lumber, so long as it isn't tweaked and twisted or full of large knots, it doesn't matter, your typical framing grade lumber will suffice.

Finally, do I need to surface the deck with plywood?

You will only need to sheet the deck if it is significantly uneven, has large gaps between the boards, or large knots that have fallen out over the years. If you've got large knot holes, it will be faster/easier/cheaper to replace those sections than to sheet the roof.

[DIYBham]

IMHO, there is nothing "simple" about a 6/12 pitch. While I'm sure you meant it's just a simple gable style roof, a pitch of that magnitude is not easy to work on and will require roof jacks (scaffold brackets) to provide a safe working platform. Safety first!!! Do not do anything you're not comfortable with.

Thank you A. Spruce! You're right of course; this is quite a steep slope on a simple garage roof. Although I am somewhat experienced with rooftop safety due to previous occupation (illuminated signs and lighting maintenance), this is a challenging project for a beginner, so I really appreciate your suggestion for the roof jacks. We will take the utmost care!

Remove the existing damaged materials and install new, simple as that. Species of wood doesn't matter, matching the thickness of what you have is what is important. With repairs made, you want a reasonably flat surface. The only reason to go back with the same species is if this is your finished ceiling inside and you want it to look good, which is probably not the case in a detached garage. As for grade of lumber, so long as it isn't tweaked and twisted or full of large knots, it doesn't matter, your typical framing grade lumber will suffice.

That's a relief! Now I can price out estimates for replacement lumber.

You will only need to sheet the deck if it is significantly uneven, has large gaps between the boards, or large knots that have fallen out over the years. If you've got large knot holes, it will be faster/easier/cheaper to replace those sections than to sheet the roof.

The framing inside the garage is quite solid, and the boards are tightly placed and seem very uniform. The original builder seems to have taken great care with the construction details and used high quality wood.

Again, thank you for all the information and useful advice. I'm confident that I can move forward with this project now.

[A. Spruce]

Hopefully the roof deck isn't T&G, not a big deal, really, but it will add to the expense of the lumber and a touch more difficulty on install, nothing major.

If you've got enough space around the garage, you might consider a boom lift to get you up where you need to be and more around more easily.

[Shannon]

Most architectural shingle manufactures will not warranty shingles placed over strip board surfaces. You would need to cover the roof surface again with OSB or plywood before shingling. If you are not worried about the warranty go ahead.
In my roofing videos you will see that i went right over old shiplap strip boards. My own house so I was not concerned. I believe I mention that in the video.

[A. Spruce]

Most architectural shingle manufactures will not warranty shingles placed over strip board surfaces.

Has anybody ever been successful in getting a roofing warranty honored? Even if you do, they only cover the cost of the shingles, not any of the other materials involved nor the labor, so you're really not getting enough back to bother, IMHO.

I suspect that single boards are going to move around a whole lot more with heat expansion and contraction, as opposed to sheathing that is more dimensionally stable.

[DIYBham]

Most architectural shingle manufactures will not warranty shingles placed over strip board surfaces. You would need to cover the roof surface again with OSB or plywood before shingling. If you are not worried about the warranty go ahead.
In my roofing videos you will see that i went right over old shiplap strip boards. My own house so I was not concerned. I believe I mention that in the video.

You did indeed mention that, however I'm more concerned with the integrity of the roofing surface than the warranty in this case. If I stay long enough, I might reroof the house and garage both with metal, which is extremely common in my neighborhood. The only reason I didn't bother to look into that option yet is because the house was recently reroofed with asphalt shingles. What drives me crazy is that like most homes on my street, no one ever bothered to install drain troughs. I honestly wouldn't have considered those optional, but then again it is an older residence.

[DIYBham]

Most architectural shingle manufactures will not warranty shingles placed over strip board surfaces.

Has anybody ever been successful in getting a roofing warranty honored?

I have to wonder how the shingle manufacturer would investigate product failure in the first place. Would they just ask for pictures and a sample, or would they talk to your insurance company, etc.

I suspect that single boards are going to move around a whole lot more with heat expansion and contraction, as opposed to sheathing that is more dimensionally stable.

That's definitely one of my concerns. I haven't actually torn off the old shingles yet, so I'm not entirely sure what I'll find. I still haven't ruled out plywood, though.

[Shannon]

Has anybody ever been successful in getting a roofing warranty honored? Even if you do, they only cover the cost of the shingles, not any of the other materials involved nor the labor, so you're really not getting enough back to bother, IMHO.

I suspect that single boards are going to move around a whole lot more with heat expansion and contraction, as opposed to sheathing that is more dimensionally stable.

Exactly! that is why I did not worry about it on my house.

[Shannon]

I have to wonder how the shingle manufacturer would investigate product failure in the first place. Would they just ask for pictures and a sample, or would they talk to your insurance company, etc.

I have never even heard of anyone going after warranty so I could not say what they actually do.