Hello,
The cedar shingle roof on my father in law’s 16’x22′ unheated garage needs to be replaced. The building was originally a carriage house and is about 100 years old. The current shingles are at least 50 years old. The garage in in Banff, AB which means minimal precipitation and cool temperatures.
The current roof is shingles over 3/4″ ship-lap boards, 2×4 rafters, another layer of ship-lap inside, then tar paper, then tin-test.
Here’s the dilemma, my father in law plans to put 30 lb tar paper under the new shingles, but to me that will trap moisture in the rafter structure. I could install a ridge vent, but there’s cross bracing at the ‘hip’, so there would be no air flow to the eaves. I’m thinking that the building has lasted this long without tar paper under the shingles and once it’s got 5000 nail holes in it how much water resistance does the tar paper offer? Should I just skip the tar paper and let the roof structure breath? I have heard about a Typar house wrap-like product for roofs, but never seen it for sale around Calgary.
I would like to add drip edge, membrane at the eaves and flashing at the ‘hip’.
Am I missing anything?
Thanks,
Adam
Replies
The Cedar Board specifies installation of cedar shakes and shingles over skip sheathing with felt interleaved in each course. This is to allow the shingles or shakes to dry better. If you want to install the shingles over a solid roof deck they recommend you use a product such as 'Cedar Breather' to provide airflow to the underside of the shingles.
That said, the 50-year track record of the existing shingles speaks for itself. In your case, the shiplap siding used as roof decking provides some ventilation under the shingles--I'd normally prefer more, but it looks like it has worked for your FIL (you'll know how well it worked when you strip the shingles and see how much rot is hiding, if any).
Don't use Typar or Tyvek or any similar product.
As to using membrane on the upper roof, the building is unheated and uninsulated. That said, I wouldn't expect any ice dams to form on the upper roof (and the lower roof is too steep even if it were heated). So membrane would be a waste of money.
The transition between the upper and lower roofs of a gambrel (a Mansard is a hipped gambrel) can be blended or highlighted. In the case of your FIL's barn, it looks better to me without highlighting the break...but that's just an opinion (mine). If you want to add drip edge, you'd normally add a fascia as well so you have somewhere to hang it. That would change the look of the roof substantially by making the break stand out much more than it does now.
Use stainless or HDG nails; copper or galvanised flashing and drip edges (if you use them)--no aluminum.
Dinosaur
How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....
Thanks for the input. The climate is pretty dry in Banff. The whole building was sitting on the ground for 100 years. The skirt was damged from water splashing back off the roof, but the bottom plate showed remarkably little damage. The floor boards sat on the ground and were replaced two years ago because a couple had broken from parking cars in there, nothing was rotten. When the skirt and floor was replaced, the building was lifted to sit on 6 inched of crushed stone and a pressure treated bottom plate. Should last another 100 years.All that being said, if I see little to no rot on the roof deck, should I just skip tar paper and use a cedar breather product, if I can find it? I'm concerned about trapping the moisture in the roof space, if I use tar paper.I like the look of the roof transition without the flashing too. How do you ensure a good seal at the transition without flashing? Maybe a layer of tar paper behind the upper course and folded over on top the upper roof deck?As for drip edge, I was thinking more along the sides, where there is a fascia board.Thanks,Adam
if I see little to no rot on the roof deck, should I just skip tar paper and use a cedar breather product, if I can find it? I'm concerned about trapping the moisture in the roof space, if I use tar paper.
I like the look of the roof transition without the flashing too. How do you ensure a good seal at the transition without flashing? Maybe a layer of tar paper behind the upper course and folded over on top the upper roof deck?
The Cedar Bureau publishes a free manual for installing cedar shingles and shakes. I hope you've got a high-speed internet connection, because the document is a 3-meg download. But it'll answer all the questions you could possibly ask about cedar shakes or shingles on a roof. Here's the URL:
http://www.cedarbureau.org/installation/roof-manual.htm
As for drip edge, I was thinking more along the sides, where there is a fascia board.
The drip edge you're proposing to install would be on the gable end; the 'fascia' on the gable is actually called a Rake Board. I'd say Go for it. It makes a nice visual detail. But use copper or galvy, not cheap stock aluminum off-the-shelf 'roof starters'. Have it bent by your local sheet-metal fabricator.
As for the 'Cedar Breather' membranes, I'm not particularly sanguine about their use. This is one of those modern 'convenience' materials designed to avoid the necessity of using traditional techniques (which are often more labour intensive). I have never used it, so I can't testify as to how well it works. And since it hasn't been in existence for that many years, no one can say with certainly how it performs over extended periods of time. It looks good on paper, though....
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
"The Cedar Board specifies installation of cedar shakes and shingles over skip sheathing with felt interleaved in each course."Check yourself.Interweave is for shakes, not for shingles.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Deja Vu--
You, sir, have a persistant habit of being correct!
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
I like to keep my average up anyways
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
For that roof, which is a gambrel rather than a mansard BTW, I would skip the tarpaper.
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!