I am going to do rolled roofing on my garage and go right over the old shingles, there is only one layer. I know that I should start with the first layer at the bottom, but what do I do from there?
Unsu...Roofing shouldn't be done by novices who want to stay dry.
However if you must do it yourself and are trying to do it fast and on the cheap...
Sheets of asphalt roofing can be torn by wind or by the lumpy old roofing. It's not the much more labor to apply another layer of shingles on top of the ones you already have. Start at the bottom (over lap a bit into the gutters if you have them) that is your starter strip. You will need to use roofing nails that penetrate to the wood sheathing. Next you put another layer right on top of that first layer but stagger the seams by at least 6 inches and work your way up to the top with the next section. The is a nail line is alond a strip of tar that needs to be covered by the next piece. Stagger the seams by at least 6 inches. There are special ridge pieces for the top.
If you must do the rolled roofing: Do the same but you will have to tack the bottom of the first layer too. There are several tar type products (henry's) that let you seal the top of the nails and patch any seams or tears.
I am assuming you have a gable style roof? Do you have dormers or multiple ridge lines? The v's need to be lined with flashing or a layer of roofing material.
This is not how to shingle roof properly. If you have specific questions contact me directly here on Tribe.
Unsu...Roll roofing isn't as tough and long lasting as good shingles.
I've done a roll roof on a low slope in January in the north east.
I got myself some 5 gallon cans of roofing compound ( flashing compound) Spread it out with a home made wood spreader and rolled the roofing material over it.
It worked. But 70 pound mineral felt isn't very permanent.
Rolled Roofing is pretty easy, but I would still read up about it a little if I were you, either on line or from a library book.
I think it will go over your shingles ok, as long as the surface is pretty smooth overall.
I remember something about rolling out the courses and letting them settle in the flat position in the sun before gluing them down.
I used a 5 gallon bucket of roofing tar, but that might just be what I had on hand. Not sure if it's the best thing to use.
Normally you double up the first course in some way, but that might not be necessary if you're going over old shingles. But, if you are replacing or installing flashing on the edges of the roof, you might want to consider installing that first, maybe on top of the shingles, but below the new roofing. - I'm kind of doing this from memory, so you'd want to double check any of that. But, those are some things that come to mind.
Rip that old roof off!!
Whenever I come onto a new job to fix a leak or inspect/repair old work, I nearly always find ridiculous overlayering, patchwork and laziness at the root of the problem.
There's too much to the trade and too many products, details and varying site conditions out there to make online advice anywhere near comprehensive.
*Check out the manufacturer's instructions and specs for the product you are using (and follow them!!)
*Chat with a roofer, contractor, carpenter friend if you have one.
*Get a How to book and read up
Oh, and do this early in the day or when it is cooler: the bituminous sheet is easier to handle and less likely to stick to itself ( plus heatstroke sucks, believe me.)
Grouchosuave does make a good point.
Ideally the "deck" would be smooth as glass, as any imperfection can pop up through rolled roofing when the heat gets on it and it sort of settles down into the shape of whatever is underneath it.
Still, I can understand not wanting to do a tear-off. And I think it will work fine if your shingles are in fairly decent shape.
It may not look great, but I'm getting that you're going for the cheapest and easiest way to get it done here.
More thoughts about the flashing: if you flash over the bottom layer of shingles, you probably want to be sure you have the right flashing for roof edges: I think they call it "Z flash" or maybe just roof edge flash. It has a bit longer nailing surface on one side so you can attach it to the roof easily, and then it has two right angle bends, the bottom one to help guide dripping water into the gutter.
That's important - my house is flashed with stuff that just has one right angle bend, and in some places the flashing just guides water behind the gutter and down the fascia board rather than *into* the gutter.