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spiragui 07-01-2010 01:40 PM

Replacing a cedar shake roof with asphalt shingles
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New to the forum, so forgive me if I miss some of the finer points of etiquette here... :no:

I am currently in the planning stages of replacing my existing cedar shake roof with laminated 30/40yr asphalt shingles. After getting a few quotes and seeing the labor costs(!), I decided to do the job myself as I have the tools, time and inclination and help. Although the roofers all seemed to really know their stuff, there were some differences in opinion, so I'm hoping to clear those up.

I've surveyed the roof, and a basic layout (ignoring vent caps, chimney stack etc) is attached. The total roof area is around 3500 sqft, with the main section of the house at the top (2500sqft) and the garage is the lower section (1000 sqft). 7 in 12 pitch. Cedar shake over OSB sheathing (which one of the roofers told me contributed to the shakes not lasting very long...).

Anyway, some questions:

1) In the Seattle area, should I be using adhesive underlayment (trying to avoid trade names here)? I don't believe it's code around here, but should I use it as extra insurance along the eaves, rakes and valleys?
2) There are currently five cap vents. The quotations mentioned increasing this to 8 cap vents. No-one mentioned ridge vents as I presume there isn't enough ridge length, maybe?
3) There was mention of reinforcing the hips with flashing to get a nice 'sharp' edge. Is this necessary?
4) Open or closed valleys?

Expecting a few questions back at me, so looking forward to hearing back from you!


seeyou 07-01-2010 05:33 PM

Cedar shake over OSB sheathing (which one of the roofers told me contributed to the shakes not lasting very long...).

He's right.

1) In the Seattle area, should I be using adhesive underlayment (trying to avoid trade names here)? I don't believe it's code around here, but should I use it as extra insurance along the eaves, rakes and valleys?

Ice & water shield (I&WS). If you don't have lingering snow with extended below freezing temps, then there's not much reason to install I&WS at the eaves. If you have infrequent blowing rains, then that lets out the rakes as well. But, I use it in the valleys in pretty much all situations, especially re-roofs.

2) There are currently five cap vents. The quotations mentioned increasing this to 8 cap vents. No-one mentioned ridge vents as I presume there isn't enough ridge length, maybe?

That's likely correct.

3) There was mention of reinforcing the hips with flashing to get a nice 'sharp' edge. Is this necessary?

New one on me.

4) Open or closed valleys?

Personal preference. Either one done wrong will leak and either one done correctly won't.

spiragui 07-01-2010 05:43 PM


Thanks for the reply. I think the explanation for the hip reinforcement was that sometimes the sheathing isn't mitred at the correct angle, resulting in a small gap along the hip join. The flashing would then allow for neater application of the underlayment. New to you guys?

Although the OSB sheathing killed the existing roof fairly quickly, at least it lightens the load on the re-roof! Mixed blessings I guess...


Thurman 07-02-2010 07:56 AM

FWIW---A home near me had cedar shake shingle installed when built in 1961. Only in the last few years did they start having an appearance problem as they were "curling" really bad. On top of all this there is an open breezeway between the home and garage with a common roof which had a "cut-out" area for rain to fall in to water a planter. Within the last six months they had the old cedar shakes torn off, the 3/4" plywood (YEP) decking was just fine, and they had new asphalt shingles put on which do look like the cedar shakes from the street. I know the neighbors slightly and stopped to compliment them on this. They told me they went through seven (7) roofing companies before they found one that would even talk to them about the job. The "cedar look-alike" asphalt shingles were a bit more expensive but really look nice. The roofer did an excellent job of trimming around the opening at the breezeway to prevent rain from getting under the new shingles. So--it can be done. David

Grumpy 07-07-2010 12:51 PM

Cedar isn't what it used to be 100 years ago. The cedar we are installing now was planted 50 years ago to replace the cedar that was cut down. It's no longer old growth wood. Old growth wood is more dense and has more natural resins to keep it lasting a long time. But it's also usually protected from harvestation. Furthermore construction techniques have changed, where as old cedar was installed on roof decks which were often times spaced, the new practice of installing cedar on plywood and osb severely limits the ventilation beneath the shakes. Therefore products like Cedar-breather have been invented which provide this breathe of fresh air beneath the cedar.

Furthermore if you had a deck or fence you wouldn't think it absurd to coat or stain these items every few years, though most cedar roofs go neglected never coated and never treated. A cedar roof is a maintenance roof. The cost of ownership is signifigantly high.

Before you choose to go the route of asphalt shingles keep in mind there may be association or village codes preventing you from installing a roof other than cedar. Look into that for sure.

The cost of labor is not as high as you think. A properly setup company with insurance will pay equal for labor as they will for insurance and taxes. In other words if I pay a roofer $200 for a day, I am also paying about $200 to my insurance company and various government agencies when it's all added up. It's expensive to run a legitimate business. Then there is the necessary markup to pay for the tools trucks and equipment, to have an office someone answering the phone and to be around to fix the roof should there ever be a leak. These things cost money. If you haven't done a roof before it's not as ez as you may think. I guess look at it like this, if you are getting paid $25 an hour, your boss isn't charging the customer $25 an hour for your work... probably $100 an hour or more.

As for your questions...

I would definetly recommend some kind of ice shield in the valley areas and to preflash any pipes penetrations and chimneys, espeically if you will be doing these flashings yourself. This is because the flashigns are critical to the longevity of the roof, and a little added redundancy is cheap insurance, especially if you haven't done flashing work before. I'd just like to stress this paragraph for any DIYer the ice shield will hide alot of your mistakes and when you make mistakes on a roof, it leaks.

As for the ice shield at the gutter line, it appears to me you might be trying to go cheap. If so, and it's not code, this is one place you can cheap out. Though I never recommend cheaping out on a roof. However I do not know the climate of your area, just because it's not code doesn't mean it's not a good idea. If ice damning is a problem in your area you would definetly want an ice shield to start at the gutter line and extend past the exterior/warm wall 24" or more.

If the roof is 3500 square feet at the foot print, I do not think 8 vents is enough. Using the traditional rle of thumb of one square foot of net free area per 150 square feet of attic floor space, I come up with a requirement of 23 net free area, when dividing that for intake and exhaust that leaves us with 12 roof vents and depending on size about 60 intake vents. Simply put, 8 aint enough.

As for ridge vent, a general rule of thumb is not to ridge vent a hip roof. Rules of thumb aside, you would need about 94' of ridge vent, and it doesn't look like you have it.

I never heard of reinforcing the hips, my guess is the salesman was referring to some kind of distincitve hip and ridge shingle.

99% of our valleys with a standard traditional 3 tab or architectural shingle will be closed cut valleys. IMO with a standard 3 tab or architectural shingle the only reason for open metal valleys is cosmetic curb appeal. On high end very thick luxury shingles open valleys become necessary.

spiragui 07-07-2010 02:07 PM

A few more details

Thanks again for the informative reply. Some responses to your questions...

The road I live on is private, and I've spoken to the head of the HOA and he said there are no covenants on roof material. There are a bunch of houses around us and it all varies from concrete tile to clay to asphalt to cedar shake. The HOA guy said as long as we are happy with it, it's fine. Can you buy leopard-print shingles? :whistling2:

The total roof area is 3500 square feet. The garage is an adjoined structure but the roof does not join up with the house roof (it butts up against the house siding). The garage is about 1000 sqft and unheated.

The actual house attic footprint is only about 1300 sqft, due to a multi-level entrance way which eats up a lot of attic space, plus there are sections where the roof actually cuts into room space to give sloping ceilings. The current intake vents are screened holes cut into the eaves, and the output vents are combination of cap vents and a gable vent.

Regarding our climate in Seattle, I thought it was famous for being damp and over-cast! During the winter months it may drop slightly below freezing at night, but it rarely stays below freezing for much of the day. It's fairly temperate, and high-winds are a rarity too. Even if the wind is to blow, I'd be more worried about roof damage from the trees around my house collapsing onto it. Does I&W repel falling trees? :wink:

Phew! I think that's it. Thanks again!


Grumpy 07-07-2010 03:57 PM

You need 3.33, or 4, vents on your garage alone. That's why I am saying 8 total just doesn't seem like enough. You may want to address the intake ventilation too. Those 2" screened holes are next to useless. I wouldn't even know how to calculate how many of those you'd need. I do know you need about 18 or so 4"x16" under eave vents just for the garage, you can use that for comparitive purposes.

I knew Seattle was a wet place, I just didn't know how the winters were. You might not need ice shield at the gutter lines, but I still recommend it for valleys and pre-flashings.

spiragui 07-07-2010 04:53 PM

Vent questions

Winters are fairly mild around here. If you don't mind the rain (and, been a Brit, I don't), then you can play golf all year round here. It's not exactly Miami or San Diego though!

All the areas I've provided (unless otherwise stated) are actual roof surface area, not footprint. The garage footprint is 770 sqft, but I thought that if there is no heating in there that vents aren't required?

Also regarding the ice shield, I was planning on installing it in the valleys for additional insurance. When you refer to applying it to pre-flashings, which flashings are you referring to?


Grumpy 07-07-2010 05:44 PM

I've never heard such a loop hole regarding a conditioned space vs a non conditioned space. However your code may vary from mine. But if you examine your shingle warranty you will see that you will likely void the shingle warranty if you don't ventilate the garage.

For a 770 sq ft attic foot print, you'd need 2.6 vents so 3 vents.

A pre flashing, anywhere you would flash, you first wrap with ice shield. This means your chimney, where the roof meets a wall, around skylights, around pipes, anywhere you would put metal you should first put ice shield. At $75 bucks a roll, or what ever you're paying, it's worth the added investment.

spiragui 07-07-2010 06:25 PM

I&W question

I understand using I&W in the valleys, as a leak would be hit the I&W and then run down the slope to the eaves

If I install I&W around say a plumbing flashing, would that not just direct a potential leak from the flashing to further down the sheathing (unless you run the I&W all the way to the eaves too)? Do I need to think more like a rain drop? :wink:


johnk 07-07-2010 10:19 PM

I've done dozens and dozens of 'cedar conversions'.I know one things for sure,you'll wish you never started it yourself.These are the jobs I despise the most.Well, besides pitch or aspestos tear-offs.If I were you,I would start with doing just the garage or shed .Then see if its something you would want to commit to.All the power to you if you want to do it yourself.It is time consuming.The tear-off is messy,lots of nail pounding and pulling,sheeting and then the underlayment.Then all the shingling.You`ll have to be sure not to bite off more than you can chew in a day.You don`t want to get caught with your pants down.I do wish you the best of luck with it though.Like I said try a small piece first and see what you think.Take care:)

Just to add,your roof is fairly complex for a first timer.There are some things that can be tricky on roofs like that.JFYI.Be glad to help if you run into any problems or had any questions.Just send me a pm anytime

With all of the trees I would suggest an algae resistant shingle.Also high profile ridgecaps.Also I would not get cheap pipe boots(like 5 in 1`s).I prefer to use lead.If you have squirrels though,they tend to chew on them.But that can be remedied.Sorry i could go on and on.I`ll wait for you to ask me,lol.:)

spiragui 07-07-2010 11:32 PM

Approach with caution
Hi John,

Thanks for responding - I know all you salty dogs out there don't have to spend your time helping out the joes like me!

My intention was exactly that - to spend a long weekend doing the garage, and if I absolutely can't take it then turn it over to the pros. I am slightly optimistic, as I have worked construction before (don't let the current pencil-pusher job fool you too much :wink:) and I know only too well that it can be hard, dirty, and treacherous if you don't take the proper precautions. I'm not expecting it to be easy! I do have the advantage of having researched this thing to death, being a rock climber (and therefore pretty comfortable about working at height and yet maintaining safety), having a 'trial run' (i.e. the garage) to help figure things out and callous all the soft squidgy bits, and having help that is construction savvy. I'm even also thinking of building a small mock up out of some 4 by 8's to test valley flashing etc.

I just hope that in a couple of weeks time (I'm not going to start until August) I can start posting pics showing progress, not posting a tail-between-my-legs story as a warning to all the other optimistic DIY'ers out there! I really want to see this thing through, 'cos I am sure that the satisfaction of doing so will outweigh the ache in my back, hands, knees and achilles tendons!

Thanks for the advice on the pipe boots - we've got squirrels and racoons aplenty out here! How do the high-profile ridge caps help out with the trees? I was thinking of adding zinc strips at the top of the roof, or are algae resistant shingles the way to go? Given the amount of trees around us, the roof is actually pretty algae free, maybe because it is so steep?

Really appreciate it you guys who'vetaken the time to help me out!


johnk 07-08-2010 12:07 AM

The high profile caps don`t help with the trees,they are just the icing on the cake.They really make a huge difference appearance wise.Zinc strip is a waste of time,IMO.It is only effective for a handful of courses(4-6)at the most.Anyways,any questions,feel free to ask.Take care:)

racebum 07-08-2010 01:20 AM

small chime in on the work. i re roofed my house this year and have never done a roof before. it's not easy, it's actually pretty hard work. while i don't do it anymore i did work in construction when i was younger doing siding, tear offs and other menial tasks so there's a bit of a background. in my case i ripped off all the old osb and replaced it. if you get into this thing and see damage on your sheathing you should have a plan in place on how to deal with it. the last thing you want is an open deck and you scratching your head. having someone to help is a real blessing. the more experience the better. i hired my step brother who's a union carpenter for $20/hr and it was worth every single penny. everything from the rip off to fixing truss bow to squaring up the new sheathing going down it was a major help. the house is done and everything is great with the new roof but i sure wouldn't want to try to do one solo.

a few things you will need are

1. a coil roofing gun
2. a full round framing gun if you start having to replace sheathing. galv 8d is the common nail for sheathing to truss
3. a cat claw
4. chalk line
5 good tin snips
6. 4ft level and a long string

the level, string and framing gun are really only needed if you have to get into sheathing.

you can check out your favorite shingle but my favorite was from certainteed, they are local to our area as is owens corning. prices are very good on the landmarks here in the NW. they come in a 30,40 and life

if you need nail guns cpo outlets is a great place to check out. they sell factory refurbs for great deals. i paid 149 shipped for a ridgid coil gun and the senco was only 119 but out of stock at the time

DUDE! 07-08-2010 08:02 AM

There will be no tail wagging between the legs. It will be better to call for help then to let hurt feelings get in the way. I've only done two roofs in my time. Your roof pitch is steep, which has helped with the maintainance. I'd certainly need longer then a long weekend to finish the garage area. I'm certainly no roofer but my concern would be to learn how to install shingles and to not fall at the same time. Be safe.

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