How do I lay asphalt shingles on a roof, and what should be under them? Are they self-adhesive? Can I stick them directly onto plywood?
My other answer only answered "what should I put under the shingles". I reread the question and see that @Vebjorn asked how to install shingles. Doing a shed is a good project if you haven't shingled before. Doing a house is harder because of the peaks and valleys.
To shingle your shed, assuming a straight gable roof:
A. Roofing felt.
- Buy a roll of roofing felt: you can get that at Home Depot or wherever.
- Starting at the bottom of the roof, staple down a layer of roofing felt. Just roll it out, then use a staple gun to fasten it at the top, bottom and middle about every 2 feet along.
- After the first layer is put down, add a second layer. Overlap the first layer by about 6 inches.
- Start with a layer of upside down shingles, with the tabs cut off. Ask the person at Home Depot for a knife for cutting the shingles - it'll be so dull and gross afterwards you won't want it for anything else. Position the shingles so the overhang the sides and leading edge of the roof by about 1/2". Nail the 1/2 shingles with the strip of tar at the base of the roof, putting nails in the shingle 4 across, top and bottom, i.e. eight nails per shingle.
- Measure the width of the uncut shingle. Measure that length from bottom of the 1/2 row of shingles on each side of the roof and make a mark. Snap a chalkline between those marks.
- Do the first "real" course of shingles. Again, overhang by about 1/2". Put 4 nails per shingle, about 1" above the cuts that define the tabs. Put one nail on each side, and one above each tab cut. Use the chalkline to keep them straight.
- Now the second course. You want each shingle to be offset by 1/2 tab from the shingles below, and up by 1/2 a shingle width. On the sides of the shingle are little cuts: bend the top part and that will give you a reference to "butt" against the lower shingle. That will keep your shingles level. Likewise, there is a cut on the top of the shingle, in the middle of the tab. Bend that up on the first row of shingle (already nailed to the roof). That will give you a place to butt the new shingle side-to-side, to ensure that the new shingle is well placed horizontally. After the first one is placed you can just butt the shingles against each other, so only the tabs on the new shingle are necessary.
- When you get to the end, cut off the flap as best you can straight with the line you want. Then go back and do the gap at the beginning: you can often use the cutoff from the end you finished to fill in the end you started. (It probably wasn't clear in (4), but I like to start with a full shingle, then come back and fill in the bit at the beginning of the course).
- Continue until you get to the top. The last shingle should fold over to the other side. Then do the other side.
C. The peak
- Now you have two sides of shingles folded over. You need to finish the peak.
- Cut a shingle into three tabs, cutting up-and-down at the tab slot.
- Turn a tab sideways, and fold it over the peak at one edge of the building. Choose the edge away from the prevailing wind. It should be half-and-half on each side.
- Measure how far down the peak it goes, the mark the same distance from the peak on the other side. Snap a chalk line.
- Continue to nail tabs (1/3 shingles) along the peak, two nails per tab, using the chalkline to line them up. You won't have the tabs to help you with the offset now, but by now your eye will be pretty good. :)
- Finish up with a 1/2 tab. Tar the exposed nails.
Asphalt shingles by themselves will keep out the rain. Extra steps increase longevity. You need to follow the manufacturer's directions (take photos!) if the warranty is important to you.
Careful preparation can double the installation time and increase the cost by 25%. Whether it's worth it to you depends on how catastrophic a leak would be. For me, my garage or shed gets minimal preparation since a leak doesn't matter that much - it can be patched when it stops raining. For a house or any finished space like a nice studio, a leak will mean ruined drywall, etc. so more attention is warranted.
In order from minimal work to a complete, nice job:
- Minimum is a double course of shingles at the bottom of the roof. The bottom course should be upside-down with the tabs cut off. This is the minimum I'd do, maybe for a shed.
- Next up is covering the roof with roofing felt before installing the shingles. This increases the longevity of the shingles and helps the nails hold. I'd do this for a garage.
- Best, if you're in a cold climate, is covering the roof with roofing felt then adding a 4' course of ice dam, which is a self-adhesive rubber membrane, at the base of the roof. This helps prevent ice dams from damaging the shingles. I'd do this on any roof over a finished space.
The shingles are not self-adhesive, but you'll see strips of tar on the backside. After you nail the shingles down, the sun will melt these strips and adhere each course of shingles to the one under it.
One thing about the double-course of shingles that you start the roof with. The reason you cut the tabs off and reverse the shingle is to get that strip of tar at the very base of the roof. The tar will melt and glue the first tabs down, helping prevent the wind from getting under the shingles. For some reason many people I know, including my father who I worship, will put an upside-down course of shingles first without cutting off the tabs, to save time I guess. To me this is pointless since it does not do its job, which is to lock down the tabs at the leading edge of the roof.
Depending on your climate you may need some additional material. My roof has an ice guard on it to keep ice from forming at the edges and backing up underneath the roof. I've also got roofing felt as a barrier between the plywood and shingles.
Roofing shingles are nailed down with galvanized roofing nails (at least mine are) and the little roofing work I've done has used a nailgun to nail the shingles through the roofing felt and plywood. The shingles have a compound on them (may be just plain old tar) that seals around the nail to prevent water from dripping through.
Unless they've come out with new self adhesive shingles you're going to have to nail each course to the roof.