Well, the weather is clearing up so I need to start thinking about re-roofing my garage. Looks like it will be a total tear-off to the rafters, possibly some repair to them if necessary.
Garage exterior dimensions are 19w x 18d, 6/12 pitch roof measures 12w x 21.5 deep on each side. There is a front to rear support wall about 10 ft from one side, 8 from the other. According to the permit history the garage was built in 1924. The entire inside is finished with toungue and groove 1×4 planking, so I can’t tell what the rafters look like except at the eave overhang. There was a leak in the small room but when I inspected the roof (i.e. I poked it with a stick), it was clear that major work was needed so I covered the roof with a blue polytarp for the winter. As far as I can tell, the roof is tightly planked with 1×4 toungue and groove, then a layer of shakes, then two layers of asphalt shingles, and finally about a half inch of moss. The boards exposed at the eaves are nearly completely rotted. I eyeballed the material at less than 2 inches thick, so at 520 sq ft we are talking about 90 cu ft of debris. The garage is down a narrow driveway, too narrow for a truck to drop a box, so I’m thinking of starting with one of those 4 cu yd rolling dumpsters, and getting a second if necessary. IIRC it was like $100 for a few days rental and up to 1000 lbs of material.
Over the last week I looked up a number of threads on roofing in these archives, and read through 4 books on roofing so I’m fairly up to speed on what needs to be done, but I do have some more questions. I’m in the Pac NW so moisture is an issue, which I suppose affects the OSB/CDX choice.
The big issue right now is rafter spacing, which is variable at best. Center to center up one side goes 14.5, 22, 24.25, 24, 23.75, 25, 22, 26, 27.25, 31.5, and 14.5. The two 14.5″ represent overhanging eaves on the front and back. I’m not quite sure yet how to stagger the sheathing without wasting material and/or getting poor coverage of multiple rafters. Of course, if I find myself sistering damaged rafters, this spacing variance might not be such an issue. I will put in horizontal blocking and figure that 3 sheets from bottom to top, 3 sheets front to back, 9 total, should cover each side.
The rafters are 2×4, most likely full dimension old growth doug fir. Until I open up a corner and peak in I’m not sure what type of internal trussing is present. I know the ceiling joists are on a 24″ center. If the area above the ceiling is open, I plan to cut an access panel through the ceiling to use it for storage and/or the dust collector system. I may also splurge and put in some insulation to make it a bit cosier in the winter.
I went to the local plywood warehouse today and they have 4 ply 1/2″ CDX for $20 a sheet and 5/8 for $25 a sheet. Is 1/2″ adequate? I’ll be using clips, or is that redundant with blocking? Shingles were $11 a bundle for 25 year that match what is on the house. I guess I’ll need about 6 square. I will likely rent some 5 ft scaffolding to make it safer/easier to get materials up to the roof.
I’ll be doing all the standard stuff including drip edge on eaves, felt, drip edge on rake, and then shingles. Once I get inside I’ll figure out how to handle attic and roof ventilation.
Because I anticipate running into lots of problems and delays, I most likely won’t be renting a coil nailer since it might not get used much, or at all some days. More than likely I’ll be doing most of this myself over the course of a week when the imp is at daycare. Can coil nailers be used to nail the sheathing down as well? None of the 4 books covered sheathing very well. It would certainly make that task faster and easier rather than nailing by hand. I did a rough calculation of 55 nails per 4×8 sheet of sheathing and 300 per square of shingles. If so, I might consider buying a PC for $250 and then selling it once I’m done as opposed to renting one for $30 a day for a week. What length of nail would one use to secure sheathing? Ditto for the actual shingles. One source said the nail should barely penetrate the sheathing to reduce interior condensation, while another said the nail should penetrate the sheating by at least 3/4″. Nothing like consistency. 🙁
So, anything I missed? Suggestions. Even if we don’t continue to live here and convert the place back to a duplex for rental, I anticipate keeping the garage for myself since doubles are so hard to find.
Replies
Man, you're covering a lot of ground here.
Before you start, check your local codes. They may have some specific requirements we don't know about here.
Since your rafters have odd spacing, I'd suggest 5/8 plywood or OSB if you strip it to the rafters. But if you can leave the 1X boards on top of the rafters, just lay 7/16 OSB on top of those. That saves you the worry of trying to make the edges of the plywood butt on rafters.
I always nail plywood down with 8D CC sinkers. I don't think coil nails are long enough for this.
I just wish once someone would call me "Sir" without adding, "You're making a scene."
After searching through the building department web pages, I found one reference to a permit being needed if the sheathing is replaced. Don't know if this means a complete replacement or a repair to a small section. I'm assuming that I'll need to do a complete replacement based on boards at the edges, but that might not be the case. Would there be a weight issue associated with adding the OSB on top of the original 1X sheathing? No permit is needed if only roofing materials are being replaced, max of two layers. I think I currently have 3 or 4. ;-) I couldn't locate any fee forms or instructions, and they aren't answering the phone today, so I guess I'll have to waste some time and tromp down there.
In the residential section, they do reference that they use the Uniform Building Code (UBC), Volumes 1 through 3 1997 Edition and amended by the Building Codes Division of the Oregon Department of Consumer and Business Services, including Appendix Chapter 5.
as far as covering unevenly spaced or crooked rafters i can help there, it is the same technique you should use to be a very efficient sheeter anyway, when you lay the ply or osb just worry about one end on the starting sheet, and the top and or bottom being parallel to the fascia. mark on both top and bottom of end of sheet where the center of the rafter/joist is at the other end. make sure you overlap this rafter/joist with next sheet. it continues in a dominoe pattern. after each row snap lines for the cut.(you bring the mark on the center of the rafter up to the top of the sheet and snap across before covering mark or rafter) then you just go back and set saw depth to cut either 2 sheet thickness, or 1 depending on need, and cut on the lines. start from the bottom, and be carefull you don't slip in the sawdust.
The rafter spacings on both side of the garage are withing a 1/4 inch, so I think they are consistently square. I'd just not sure I can offset the sheets since the spacings between 5 rafters sometimes exceeds 96 inches.
I'm not sure how you value your time vs. budget, but you might consider (or need to depending on condition and load) tearing the rafters off and starting with new trusses. Wouldn't hurt to get a price.
Ditto..........get rid of the low pitch and the odd spacing in one shot.
This reminds me of one I did last year. It was framed with 2x4 and a 5/12 pitch. The rafters and sheathing were sound, except at the tails in the overhang. I used a sawsall to remove the tails, and then framed a new roof up over the old. new ridge beam, 2x6 rafters, sheathing, etc. The old tails cut off got trimmed with a frieze board.
Since the price os osb and ply is so high now and you could ened up with waste, look into using boarding boards. Here, it is sold as #4 pine, finished one side 7/8" thick.
This all depends on whether or not the existing raftes are rotted out. I would think you need to know that before you start to know if you are getting in over your head.
Buying a nail gun to resell is a good idea, A lot of guys do that.
Bostich better than PC for guns, but one thing important is service and selection available in your area.
Coil roof guns and framing guns are two different animals.
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
I'm in agreement with Boss Hog...use an 8d sinker for nailing off your sheathing to your rafters...if rafters are still good and most sheathing can be saved, sheath over with 7/16 if you feel the need. And in doing so, don't worry about whether the ply ends land on a rafter or not. Just be sure and stagger your rows.
I think you should look into buying, renting, or borrowing a coil roofing nailer. Normally, if you rent by the week, the cost is much cheaper than when renting by the day ( ie...renting the coil nailer may run you $30 per day, but possibly only $70 for the entire week) Use 1-1/4 inch nails for nailing down asphalt shingles over wood sheathing. Use 1-1/2 inch nails for nailing roof caps.
Also, after a normal roof tear-off, we always go back over the entire roof with nail gun in hand and renail existing sheathing. You'll be surprised how many boards your roofing tool will loosen during a tear-off. Sooo, with this in mind, I'd beg, borrow, steal or rent a regular stick nailer too....way faster than hand nailing. Case of coil roofing nails will set you back around $30...and around $25 for a box of 8d stick nails.
Hope you got some buddies and some beer handy...you're gonna need both!
Davo