I agree with Sophie, this is not the time to play with mixed materials. You have come this far and why muck it up now.

One major concern: slate probably wouldn't be installed until spring and winter here is BRUTAL. Is there a way to weatherproof the roof to prevent leaks until then?

I should also mention that the addition (started by previous owners) is clapboard and the original house is stucco. It's what got me thinking of mixed materials.

If the addition was of a different style (as you sometimes see in additions in more urban settings) a different roof material could work. In this case where you have gone with a seamless integration of new with existing it requires the same type of roof. Sophie W. suggestion of utilizing the garage slate is the way to go. Thankfully with careful removal you should have enough material to salvage from the garage for the addition. PS is that bare plywood I see? It should have a synthetic membrane on there right now. These are generally rolled out immediately to protect the plywood before shingling starts.

Here some different trade names...

http://www.gaf.ca/Roofing/Residential/Products/Roof_Deck_Protection/TigerPaww

https://www.iko.com/products/residential/accessory-products/ice-water-protectors/stormshield/

Best of luck!

Thank you. All good ideas though the cost seems like it would be high to remove - and risky if the slate breaks. Perhaps not though. Something to look into!!

If we couldn't complete until winter wouldn't we risk leaks and ice damage though?

Still wondering about Evostar shake slate. It looks pretty good! Hard to resist.

Have you considered recycled rubber shingles made to look like slate? http://inhabitat.com/euroshield-eco-friendly-roof-shingles-made-from-recycled-tires/

You have a source for the slate you need - use it. Rusty Empire is TOTALLY correct in that the new plywood should have been covered immediately upon install.

Perhaps you don't understand the purpose of shingles / tiles / shakes / slate? The roof decking (plywood or boards) are covered with a waterproof material; rolled roofing paper / tar paper / hot asphalt / membrane. THAT material is what protects the roof from water incursion. The shingles etc. are only to protect the underlying material from being damaged by the sun / rain / wind / ice.

A slate roof is a "forever" roof...how I envy you!

Oh geez. Don't worry guys, our builders have used waterproofing material- it's just rust colored and extra durable actually. And yes, of course I know the purpose of slate.

Whew, thanks for clarifying. When you remove shingles from garage - which I hope you do - then you can weigh your choices for doing that building.

heres another source for shake options

http://www.davinciroofscapes.com/products/slate/bellaforte/

Is the addition structure designed to support the weight of a slate roof?

Whatever is on the existing house should match what is on the addition, even if you have to change what is on the existing house.

I have to agree with the suggestions you have been given to carefully remove the old slate from the garage roof to use on the addition and then use a different material (maybe a gray metal?) roof on the garage. You can console yourself, however, that even if you could have afforded it, new slate would not have matched the old slate you have. We have an original slate roof from the 1920's, much like yours. Recently, a house down the street put on a new slate roof (paid for by insurance after a fire), and I am amazed at how different in color and texture the new slate looks. It is much more uniform and a different shade than the rest of the old slate roofs on our street. It would look like a completely different roof material if we put it on an addition and used it next to our older slate.

Great question Mark. Builders think it's slate ready but are double checking.

I have to say, I'm very thankful for all the input. I'm surprised nobody seems to think an alternate material would look good!

I realize that having a material side by side that is trying to match slate could easily look off - that's why I thought a whole different material might stand better on its own.

One last idea: a shake slate that mixes in some variation of gray and green so it is clear different but still works to pair with the old.

I always defer to the original materials, but as the addition is already a different material I think having the roof different isn't terrible. That said a faux wood shingle roof seems so different. Often houses with slate roofs had secondary roofs like porches done in copper, could that work? Still very expensive I realize.

Agreed! faux wood shingles = too much contrast. Lots of beautiful copper sadly might have the same issue I think.

I think we might go for shake slate. Removing all of the perfectly maintained carriage house slate seems like a historic building no no. If it looks bad we could redo the main house with more shake (instead if repairing the ice storm damage). So hard to pick a color though.

Pulling the slate off the garage and reroofing it will cost nearly as much as buying new slate or more. That is a really foolhardy idea in my view. The slate itself is not expensive (relatively speaking) it is all the labor. A good slate guy can find stuff to match. Salvage slate is available and not expensive at all. There are some options I have seen (but have no personal experience with) that can reduce labor cost. There is the slate system that uses hangers, for example.

There are options.

One other issue to evaluate is the condition of the slate that is on the house. Some slate is good for only 80-120 years particularly grey PA slate.

You need to evaluate the condition of the roof and make decisions from there.

If you know where to look, you can match anything and that is, no offense intended, a rather pedestrian slate roof. Slate comes in red, green, purple, and every shade of grey from middle to near complete black.

I highly recommend the slate roof bible. Read it. Interview some slate roofers in your area after you do, and find a good one. Mine matched my slate so perfectly -- using salvage slate -- on patches, you can't even tell which slates he replaced (there were not a lot, but I know where each of them were).

Evil, very good points - but it sounds like our homeowner was set on synthetic from the start.

Yes, looking for validation. Now has a new dilemma up on same. We did not provide the strokes!

Look at Certainteed Symphony, pic below

How old is the slate roof you have? Slate roofs do not last forever and eventually you will have to replace the whole thing - so you need to find out how many years you have left on it before you make a decision on mixing roofing materials. I think you are making a huge mistake to do so, it will look silly. So either pull it all off and put one roof on, find a similar but close enough matching material or put slate back up. Do not mix materials.

perhaps in different areas the available slate wears down faster/differently than in others? i've been taught that slate roofs DO in fact last forever; and what starts to fail after a century or so is the nails holding the slate on begin to rust out. to that end, in areas where slate has been used extensively (as I would guess has been the case in the area in question), slate roofs are often removed and pitched in a bin...making it somewhat easier and cheaper to access used slate than one might have expected.

Myth about the nails. Not only does the book say that it is a myth, but every broken slate I have seen is cracked -- usually at the nail hole, sometimes laterally in half. Nails still need to be ripped out to repair and are fine.

Slates will eventually crack and fail. You can nurse a failing roof "forever," but it becomes a ship of Theseus type situation which is cost prohibitive. Everything you may want to know about slate roofing is in this book. The slate roof bible. Great website too.

http://josephjenkins.com/books_slate.html#

The other issue is things like flashing, underlayment, gutters. Whoever said the underlayment keeps the water out is wrong. If that is what is happening, the roof is installed wrong. Slate itself installed properly with proper headlap will keep all
water out. Valley flashing, which thankfully you don't seem to have a ton, also fails and is expensive to replace because the slates have to be removed and refitted. Use 20#?copper. Anyway, I don't know where you are located, but there is someone near you know knows how to do it right. Find them.

it appears evil that you have much more knowledge surrounding this than i, seems we're on the same page regarding salvage slate being the way to go though. i also raised my eyebrows at the sentiment that shingles don't do the job of keeping water out.

i think a standing seam metal roof that matches the color of the existing roof could work.

If a metal roof on garage or addition then use one that will patina such as copper or zinc. A painted roof will not have the natural variation you need to compliment your slate. This also goes for fake slate which seems like a nice product for new builds looking for more character than asphalt but it will look ludicrous next to your slate. Some things are simply worth the money and you will never ever regret doing the right thing for your home.

Cchute has a real life dilemma - someone started this addition (and perhaps it broke them) before he got here. His budget is a real issue.

Architecturally, keeping the carriage house historic and intact is not as big a priority as keeping the house intact. Architecturally, and value wise for the home, if the slate has 25 years left on it, moving the slate from the carriage house over is the best answer. Now, what if that is cost prohibitive or the new structure wasn't engineered to carry the slateweight? Once again we are looking at the downside of DIY (and I don't mean you cchute) - this is a house that deserved an architect. Whoever designed this addition wasn't too thoughtful - they tucked the new roof line in under so the eave bounces down, the stucco is actually an easier material to match /more appropriate architecturally than siding / no more expensive / even less expensive .. so not sure what that was about. Builder addition?

Must be because cchute has inherited it and trying to make some good decisions.

If you can move shingles from the garage (and no doubt it can be done, if they wait until spring, then you can probably get away with a slate look alike over there.Go to the lightest gray option if you do so. My guess is that any good roofer would want to keep that slate going - and finding some reclaimed to patch the garage roof back after you scavenge what you need might be theticket (or it might be a ticket to the poorhouse in cchutes mind).

Sadly, the architecture doesn't lend itself to using the slate for part of the roof and something else for part of the roof. I mustagree that if you can't afford to pull the roof from the garage, or it isn't engineered for that, then you need to pull the whole roof off (talk about expense). Then standing seam metal (still an expensive choice) is probably best. Even if you have to cover the roof with a tarp for the winter (and it is winter now most places), take your time making this decision. Investigating what you have will be worth the trouble. Could be the underlayment on the carriage house was about to go and you would be back in there in the next 5 years anyway. This might turn out to be a blessing in disguise.

I will say this again. You will save no money pulling slate off the garage.

If you don't have the budget for slate (even salvage) on the back addition, it is sufficiently hidden that I would just use architectural asphalt shingles in a close color and size match to the slate and LEAVE EVERYTHING ELSE ALONE. Ripping off slate is a sin. There are asphalt shingles that can come close enough to a match that it won't look terrible (they are popular around me for people who want a slate look, but do not want to pay slate prices). I would not go with metal, or other product, but rather just the run of the mill asphalt shaped like your existing slate. It will be most cost effective and will match best.

I have very little experience with slate roofs. I'm pretty sure Evilfij has sufficient first hand experience with slate roofs that his advice should be well heeded.

I have much experience with slate roofs after working on dozens of Yale's gothic dorms and other buildings, which are fabulous treasures. The slate bible mentioned above is the best reference around. There is also a Slate roofing organization you can google, call, and feel free to get pro unbiased advise. They love to help!

As for underlayments, Certainteed, manville, and others, but grace makes a new product that is meant for preventing ice damns and to be left exposed for months. You really should not pinch pennies on the roof. Above all do not mix asphalt or composite, rubber or other types of shingles. It is hard enough to get slates to match. If you can find where the original source is, call them. The quarries are usually Vermont, other new england states, pennsylvania and i believe north dakota.

Many original slate roofs have no underlayments and the old guys (installers) will tell you if installed correctly slates do not need anything below the furring strips. The whole industry has become more complex because of energy codes and "experts" who really are not. Take the time to track down an experienced architect in this field. Or call a roofing consultant (i can name a couple for you if you like) who only do that... provide details, specs and inspections on slate roofs.

I agree with the idea of considering changing material of the addition to metal. Red copper would be my first choice, as it will patina wonderfully. Yes it is $$$$. On a house like yours consider it an investment and it will pay you back. If you cut corners and mix inferior grade materials your home value will plummet!

SLATE ROOFS is a book by the national slate association is another great guide book along with the bible. They just issued a revised edition of the bible, by the way.

National slate association: 866-256-2111 You can get the SLATE ROOF book there.

814-786-9085 is where the author of the SLATE BIBLE can be found.

Slateroofcentral.com ; Traditionalroofing.com ; Slateroofers.org and Joseph-Jemkins.com are all great references. The last one is that of the author.

Make sure your designer has allowed for the extra weight of slate. It is far heavier than the heaviest asphalt composition shingles. Usually, requires double the size of normal rafters, or if your home has an open attic, use it as a guide. Check the spans and your areas code requirements for snow loads too.

The best thing you can do is to get sound advice from one who knows!

I hope I did not put anyone to sleep!