Ripping a board with a circular saw

Factual Questions
1

I’m thinking about redoing a flat garage roof, adding a little slope to it in the process.

I want to take flat, rectangular, roof roughly 24 feet long, currently very level, and add a slope starting 8 inches up on one side and sliding gently to the original roof height at the other side. That gives me about a 0.25" rise per foot from side to side which is supposed to be about the minimum for shedding rain (something it doesn’t do today).

My thought is to take a 2x10 board and rip it lengthwise, starting at the corner of one side and ripping a straight line cut to the middle of the other side.

If I can pull it off, I can place the two pieces together, equal sides touching, and have a long, gentle ramp that’s twice the length as the original board. Make sense?

Is this possible or am I fooling myself that it’s possible to pull this off with a circular saw and a snap-line?

2

[QUOTE=Belrix]
Is this possible or am I fooling myself that it’s possible to pull this off with a circular saw and a snap-line?
[/QUOTE]

With a snap-line? No way. With a straight-edge? Yes, it can be done.

Sorry, but I can’t remember which woodworking magazine of late recently ran an article on how to use a handheld circular saw and a straight-edge to rip 4x8 plywood sheets about as well as a table saw. I’ll dig to find it but I make no promises.

3

Can you cut such a cut freehand? Depends on how good you are with a saw. I doubt you are that good, but I have met guys that could.

Actually you could build a saw guide that would allow you to do this with not too much trouble.
You will need a piece of thin plywood (1/4" is fine) with one absolutely straight edge. Rip that piece of plywood into a strip about 5" wide. Rip a second strip that is 6" wider than the wide side of the sole plate of your saw (edge of the plate to the edge of the blade)
Attach the two pieces of plywood together so that the absolutely straight edge of the 5" wide piece is on top facing the lower piece of plywood.
Take your saw and run it along the guide, it will trim off the excess plywood from the lower piece.
You now have a saw guide that will allow you to make a perfectly straight cut eight feet long.
Snap a line on your work, and lay the saw guide on it. You will need to attach the saw guide, you can use small nails, screws or C-clamps. Because you are cutting on a diagonal you will probably need to secure the work and perhaps put other pieces of wood under the guide to support it.
You can probably figure out a way to make a table that holds the guide and piece of wood being cut in place, and set it up like a mill where you are just making repetitive cuts.
ETA: If you could find two pieces of 1X 12’ long you could make a 12’ long saw guide out of them.

4

Sure, you can do this by hand.
Remember, it’s a roof, not a Birds-eye Maple hutch. If you are off 1/4" somewhere in the middle of the line, and correct it later on, you’ll never see the difference once you nail your decking down. I’m always amazed at the absolute crap (warped) lumber that houses are made from…

5

[QUOTE=Belrix]
If I can pull it off, I can place the two pieces together, equal sides touching, and have a long, gentle ramp that’s twice the length as the original board. Make sense?
[/QUOTE]
I’m having a hard time pictureing this.

How are you going to nest/sister one cut 10’ long board into a 12 foot slope that doesn’t have a dip in it(assuming there is going to be a peak)?

10’ - 2x10s? 24 foot roof?

I’ve ripped 2x8s down to 2x6s with a circular saw and a chalk line. Really not that big of a deal if you have a good saw.

I gotta stress the good saw part. Worm drives are best (I’ll never buy a direct drive again). They are bigger, and heavier and longer than a direct drive. But, IMHO, they allow you to find the best line. About $200 for a Milwaukee. You’ll never need another circular saw.

I would agree. It’s gonna be sheathed and shingled. I’d be a little concered about 1/4 inch off, but you should be able to do this with no more than a saw curf off.

6

Absolutely you can do this.

Don’t be cheap with your saw blade though. A good blade will make this job easier. Two if you have a bunch of them to do. Set the blade depth to go through the board to the depth of the notches made by the teeth.

You will need to watch the crown though and perhaps cut the crown side on one board and not the other and then mix the pairs.

If you are going to use treated lumber be careful how wet it is cause it will go in all kinds of directions once it dries and you have already cut and placed your pieces.

Are you thinking of any overhang?

7

You can always rent a table saw for a few bucks, which is what I would do. When I laid flooring and had to rip rows of boards, I borrowed my boss’s table saw, and it was wonderful…I’m so glad I didn’t have to try and do it with my circular saw.

8

[QUOTE=Belrix]

If I can pull it off, I can place the two pieces together, equal sides touching, and have a long, gentle ramp that’s twice the length as the original board. Make sense?

[/QUOTE]

 Maybe my coffee hasn't kicked in yet,but no, it doesn't.

1/4" rise p/f is too little in my experience, especially with wind factors.

Leaving aside saw gymnastics,why couldn’t you set your normal parallel rafters on angled compression blocks ( end grain SPF ),using nail plates, if deemed neccessary?

9

[QUOTE=Mongo Ponton]
Don’t be cheap with your saw blade though. A good blade will make this job easier. Two if you have a bunch of them to do. Set the blade depth to go through the board to the depth of the notches made by the teeth.
[/QUOTE]

I can’t emphasize this enough. For years I suffered with trying to use my circular saw for ripping. Never had much luck, and usually reverted to the jigsaw – talk about painfully slow! There was a little respite with lots of pre-planning, in that both Lowes and Home Depot (and any lumber yard) will rip full sheets for you to your specified dimensions, and often free of extra charge. But… I recently discovered I had the wrong, damned blade on my circular saw for ripping wood all these years. As soon as I fitted a proper blade to it, it was like cutting through butter! No more binding/stalling. No more going off at odd angles. I still want to kick myself in the behind over it.

10

[QUOTE=Belrix]
My thought is to take a 2x10 board and rip it lengthwise, starting at the corner of one side and ripping a straight line cut to the middle of the other side.

If I can pull it off, I can place the two pieces together, equal sides touching, and have a long, gentle ramp that’s twice the length as the original board. Make sense?

[/QUOTE]

The original 2x10 now becomes two pieces. One piece tapering from 10 inches down to 5 inches. The other - which is the cutoff piece from the first tapers from 5 inches down to zero. He will then reverse piece #2 so he has a continuous slope, 20 feet long, tapering from 10 inches down to zero.

It’s not rocket science. Use a sharp carbide blade. Take your time. Use a sharp carbide blade. Make sure your table or sawhorse is secure before you start cutting with any powertool. Use a sharp carbide blade. Wear safety glasses, the dust is a real bitch.

Oh, and did I mention, use a sharp carbide blade?

11

What Rick said, with emphasis on using the factory edge, and not being shy about screwing your piece down to your sawhorses or worktable. In most cases, I would just use C-clamps to attach the guide, but you’re not going to have much room to work with on at least one side, so screws will probably work better.

On the side you have less room on, use a scrap piece of 2 X under the unsupported part, and just screw everything together. (the guide to the piece to the table or horse).

12

[QUOTE=Fir na tine]
The original 2x10 now becomes two pieces. One piece tapering from 10 inches down to 5 inches. The other - which is the cutoff piece from the first tapers from 5 inches down to zero. He will then reverse piece #2 so he has a continuous slope, 20 feet long, tapering from 10 inches down to zero.

[/QUOTE]

   Makes sense now.Apologies for not being a rocket surgerist.For all the time involved in sawing though,straight 2x elevated one end would make faster work.
13

[QUOTE=Fir na tine]
The original 2x10 now becomes two pieces. One piece tapering from 10 inches down to 5 inches. The other - which is the cutoff piece from the first tapers from 5 inches down to zero. He will then reverse piece #2 so he has a continuous slope, 20 feet long, tapering from 10 inches down to zero.
[/QUOTE]
Ahhh, got it.

Well then, a 2x10 (actual 9 1/4) won’t work. He’ll need a 2x12 (actual 11 1/4). A pitch of 1/4"/ft will normally shed water (although it is not a desired roof pitch - 2"/ft would be about the minimum I’d like to see). So over 24 feet, 1/4"/ft comes to 6". He won’t be able to get that with the 2x12, but he’ll be close.

14

[QUOTE=Plynck]
Ahhh, got it.

Well then, a 2x10 (actual 9 1/4) won’t work. He’ll need a 2x12 (actual 11 1/4). A pitch of 1/4"/ft will normally shed water (although it is not a desired roof pitch - 2"/ft would be about the minimum I’d like to see). So over 24 feet, 1/4"/ft comes to 6". He won’t be able to get that with the 2x12, but he’ll be close.
[/QUOTE]

The roof is pancake flat right now - it has to be squeegeed off after a snow or rain. It has a layer of roll roofing and a semi-applied layer of white sealant on it.

I just wanted enough slope to shed water. Snow load might be an issue, and I was thinking about putting some beams and jack posts in the inside of the garage to help with that.

There’s a door in the wall of the house that adjoins the garage: a second-floor door opening onto the roof the the garage. They previous occupants had the idea of using the roof of the garage as a deck, a mistake, in my opinion, if the roof integrity is to be protected.

By keeping the rise of the roof low, though, I don’t have to alter that wall much - just remove the lower course of siding and attach a ledger board to hold the ends of the new “joists”.

If I go much higher than 10" or so, then I have to remove the door, probably install a window in the upper part and close off the lower part of the opening. Now I’m repairing a much larger section of siding, too.

I was trying to keep it simple.

I talked with a guy this morning who owns a roofing company “specializing” in flat roofs. He said, for a roof this size, he should be able to lay down a new layer, a “modified torch stone roof”. Properly applied, he said, a flat roof could have four feet of water standing on it and still be waterproof. Price on the order of $2000 or so for around 500 square feet.

Any thoughts?

15

[QUOTE=Belrix]
I talked with a guy this morning who owns a roofing company “specializing” in flat roofs. He said, for a roof this size, he should be able to lay down a new layer, a “modified torch stone roof”. Properly applied, he said, a flat roof could have four feet of water standing on it and still be waterproof. Price on the order of $2000 or so for around 500 square feet.

Any thoughts?
[/QUOTE]

A couple of thoughts. first off if you might be walking on it, at all, ever, don’t use stone. You weight on top of the stones can and will puncture the membrane and you get leaks.
For a data point: In 1994 after the earthquake, I had the roof on my house and garage replaced. My roof is not all flat, but due to the way the house is constructed, It might as well be. I had it stripped to bare wood (roof was 3 layers thick) and a commercial grade roof applied. Three layers of felt hot mopped with a white reflective coating on the top. fifteen year guarantee, and not a drop has leaked since it was installed. Cost for the house and garage was $6500. My house is 1400 square feet, plus a two car garage.