Maybe, maybe not. If the shingles are stapled down, you MAY be able to either pull them out or even cut them where EACH 'end' goes through the shingle. (If you cut 1 end, you'll need to 'bend' the staple straight up so the shingle doesn't rip or tear in any way.) However, if the shingle is nailed, it's probably not worth the effort. The best you can do is try to find out what make and style the shingle is and find the closest match. Personally, I wouldn't worry too much about it matching as long as you can get a close match. If anything, go darker; not lighter.
IF you can reuse the shingles, take some time to put a dab of silicone on the old 'holes'. The silicone will 1) close off the hole, and 2) allow the overlaying shingle to 'stick' to the silicone so the shingle won't be easily lifted by wind or anything. (You may not know this but new shingles have a 'adhesive, tar strip' on the top of the shingle that softens and allows the overlaying shingle to stick to the one below. You'll see the strip on new and old shingles. But on old shingles, you probably won't get the same benefit of the strip unless you dab on some silicone ...)
Be sure you label the shingles you take off the roof that are ODD lengths. Label which row they came off of and which 'side' of the house they came off of. Do this for ALL 'odd-lengthed' shingles. As long as all the other shingles are 3-tabs in size, you can use them anywhere. (It's the ODD length ones you want to put back EXACTLY where you took them off of. I'll spare you the 'why' - Just do it.)
Buy yourself a product like Snow & Ice Shield. Be SURE to read about the product. It's kinda messy and sticky to work with. Make sure you don't have any debris on the roofline when you install it, and be sure you don't end up with any 'waves'. This could be bad news. Just make sure it lies FLAT and SMOOTH. Oh, if you don't have Drip Edge, install that too OVER the Shielding (but under the shingles. The Retailer will tell you how it works and how it's to be installed.)
Make sure you have the right length nails so measure the 'thickness' of the roof's sheathing (or decking or sheets-of-wood.) There are PLENTY of WEB sites that tell you how to install the shingles. Of course, you'll have to 'lift' an additional row of shingles to do this job because you need to be able to 'slip' the final-intalled-row up and under a row that you DIDN'T remove. (That's just the way it is because you're doing a 'retro-fit'.)
My best to ya and hope this helps.
Jay J -Moderator
PS: Did you have a home inspection??? If you did, your inspector SHOULD have written down somewhere what he estimated was either the AGE of the roof, or how many years you had left. If the shingles are brittle, DON'T reuse them. They'll just get busted too easily ...
If you have soffit and ridge vents, make certain that soffit openings have a clear path into the attic (they make special chutes that keep the insulation from blocking the airflow from the soffit openings).
If you don't have soffit and ridge vents, then you should have some other type of vents and/or fans in the attic.
If you have no attic ventilation, then you should consider getting some.
Also, you want to prevent warm air from your house from leaking into the attic during the winter by sealing all light fixtures, chimneys, flues, attic stairs, etc. that are either attached to the ceiling or penetrate into the attic. The sealing is best done by getting in the attic and locating the sources of leaks.
Finally, you should make certain that you have sufficient insulation and coverage on the FLOOR of your attic to help prevent the heat in your house from getting into your attic.
(Jay J, did I miss anything?)
BillyG, you're a savior! It's in my blood to at least address the cause of the problem as well as the solution. Thanks for covering me. Why I forgot to do that this time might be because I'm getting old. LOL
cherylpowell: BillyG is right. Visit this link and read about the cause of ice damming. Don't just install a fan in the attic. Doing just that MAY draw MORE warm air from the inside of the house into the attic, thus, making your problem worst! And please don't go laying down some plastic. Insulation is key, and looking for warm-leaks is key too. Another key is, if you DO have soffit and ridge (or gable) vents, be SURE (as BillyG said) that the 'opening' at the soffit are free and clear of any debris. Also, your roof-rafter 'cavities' (assuming your attic isn't a 'finished room') shouldn't be 'obstructed' by boxes and such that are stacked TOO high. Keep that stuff BELOW the rafters.
See Ice Damming Links and start reading. You'll understand more in doing this.
(Thanks again BillyG.) My best to ya and hope this helps.
Jay J -Moderator
W/A cathedral ceiling, the builder SHOULD have installed soffit vents, chutes, and a ridge vent. If the house is relatively new, then I think that the ceiling MAY have been insulated improperly (meaning, there are no chutes or there is no insulation). If you don't have soffits and a ridge vent (irrespective of the age of the house), it's easy to see why you're getting damming.
The warm air is either 'collecting' where the inside wall meets the leading edge of the cathedral ceiling (and it's SOOOOO warm that it's warm/hot enough to melt snow), or for some reason, you don't have good air circulation to 'move' the warm air around.
Check that you have return ducts and that they're OPEN. If you have a ceiling fan up there, I'd turn it on in Winter, blowing UPWARDS.
After you've gathered all these 'thoughts' and read the links I provided about ice damming, you should have a good grip on the cause of the problem and the fix. My best to ya and hope this helps.
Jay J -Moderator