Replacing Roof Shingles On A Garage Home Improvement
My new shop is a detached garage that was built nearly twenty years ago – I know this because the lumber stamp on the OSB used for the roof is dated 1994. Although it is half the size of my old one, about 13′ x 27′, it should be ok until I get a bigger one built.
My original plan was to build the new workshop from the ground up in about a year, but I have decided that it would be better if I concentrated on getting my house renovations finished before starting that. I’m not sure how long it will take to complete the renovations on the house, so the garage will have to be my workshop for the foreseeable future. To make it easier to heat (and to cool) and more comfortable to work in, I have started to insulate and drywall the walls and ceiling. That work came to a halt when I ran into a problem: the roof was in very bad condition, especially the south facing side:
I already knew it was in rough shape, but thought I could put off redoing it until later in the fall. I quickly changed my mind during a rain storm when it started to leak. In fact, in the picture above, you can see daylight through the roof (middle of the picture). Judging from the water stains, I would say it has been leaking for quite some time.
With the weather forecast calling for clear skies over the next three day, I thought there was no time like the present to get the roof done. I bought the material and started stripping the old shingles off the bad side. As shown, the deck is still wet from the recent rain:
The stripping is easily done with a garden spade. The shovel is used to pry the shingles off and can also be used to pull the roofing nails out. One thing to watch for are the “H” clips (red arrow in photo) that are sometimes used instead of solid blocking at edges of the sheathing. These connect the sheets together and should be left undamaged.
With the south facing side completely stripped, I can get it ready for the new roofing. The roof sheathing is mostly 7/16″ OSB, but two of the panels are 1/2″ plywood. Interestingly enough, the plywood was in much worse condition than the OSB. It was still good enough that I didn’t need to replace it, but was showing signs of delamination and sagging heavily between trusses:
Rather surprising that the OSB was still in very good condition, with only the overhanging edge showing any signs of deterioration. Much has been said about the inferiority of OSB as a sheathing material, but it’s been my experience that it is perfectly acceptable for that purpose, especially if you keep it dry (as any sheathing should be).
Although fairly well built, the garage did have one glaring error in it’s construction: the roof sheathing was left open to the weather. It extended past the rakes and eaves by nearly 2″. This is not the way I would do it, preferring to cover the sheathing with a trim board, as shown in my shed project.
The fix here is to trim back the overhanging OSB and install a drip edge to cover it.
I chalked a straight line across and used a cordless circular saw to cut back the sheathing. The water damage was limited to the very edge of the sheathing and the OSB is like new at the cut (red arrow):
After the edge was trimmed off, a metal drip edge was nailed on, covering the cut edge of the OSB. As shown in the picture above, the drip edge extends out and folds back in to direct water away from the roof and provides even support for the edge of the shingles.
The next step was to roll on a 36″ wide strip of ice and water shield. This is a self sealing continuous membrane that will guard against leaks from water backing up due to ice damming. A starter course comes next, then the roof shingles can be installed. I’m using 1-1/4″ roofing nails in a pneumatic nailer to fasten the shingles:
The drip edge is also used at the rake edges.
Although it is recommended by the manufacturer, I did not put a starter course at the rake edge. I also didn’t using tar paper or roofing felt under the shingles. I can’t see any advantage to using an underlay like felt, as it will be punctured hundreds of times with the nails that hold the shingles on. It’s good for temporary waterproofing until the shingles are installed, but is dangerous to walk on, especially on a higher pitched roof when wet or damp. Of the roofs I’ve stripped, I can’t see any real differences between the ones that had underlay and those that haven’t.
The shingle manufacturer makes a dedicated starter strip for the shingles I used, but the traditional way is to use an ordinary three tab shingle and cut the tabs off:
Sometimes the starter course is an ordinary shingle turned upside down, but cutting the tabs is a better solution. As shown above, the glue tabs are where they are needed: right at the edge of the shingle. The heat from the sun will melt these and seal the first shingle course in place.
With most of the first course done, I went down and took a picture of the eave:
It certainly looks much neater and there should not be any problems with water entry. I extended the starter course 1/4″ past the drip edge, and the first course of shingles 1/4″ past that. Any more than that and the shingles may droop and possibly break off.
I had to do the first four courses from the ladder, since there was no place to stand on the roof. A better solution is to have scaffolding set up to do the first few courses:
It goes quickly after I can stand on the roof. The day was cool, so the risk of damaging the shingles was minimal. During hot weather, the shingles can get hot enough to melt and will be easier to mar. One way to counter this is to hose down the installed shingles with cold water, but you need to be careful not to go past onto the sheathing (and create a leak).
After a very long, very tiring day, the south facing side is finished. The top course of shingles goes up and over the ridge. With no rain expected, I didn’t worry about making the roof absolutely water tight.
The next day, I got some much appreciated help from my brother and we finished the north facing side. We also got the drywall up on the ceiling in the shop. Putting drywall on a ceiling is best done with two people, and this is particularly true when using 10′ long sheets.
The roof was watertight at the end of the second day, but still wasn’t finished. The last thing to do is to put the ridge cap on, and ordinary three tab shingles are used for this.
The shingles are cut at a slight angle into three pieces
They are then nailed on individually, with two roofing nails:
I used a stick to measure the exposure.
Most three tab shingles have locator slits that are used to line up the shingles. Here I’m just eyeballing the centre slit on the apex of the ridge to line it up. If this were more visible from the ground, like a hip ridge cap, I would chalk a line and use that as a guide. For a ridge where there is no line of sight along the length, I skip the chalk line:
The roof complete, good for another twenty years or so.
I made a video showing some of the roofing and a brief update on the progress of the new shop:
Replacing a roof is probably my least favourite do it yourself project, but when it needs to be done quickly to save my workshop tools from ruin, I don’t mind. Saving money and getting it done right is also good, and now I have the peace of mind to continue finishing the inside without fear of water damage.