I am considering a 10 x 14 addition on the back of my house. I wanted to use a “shed” type roof with a cathedral type ceiling. My dilemna is how to properly ventilate the area above the ceiling. I can install ventilation channels, but the tall end of the ceiling will be against the existing exterior wall of the house, hence nowhere for the hot air to go. The attachment shows almost exactly what I want to do except the right hand side will be against the existing house. Any suggestions ??
Replies
Ya, I'm in the identical situation. Using 4inches of blueboard form between the rafters tight up against the sheathing covered with roofing paper and shingles. Vapor barrier between the foam and the Redwood 1x6 T&G exposed to interior secured to the rafters. Will I need to vent with this scenario?
Half of good living is staying out of bad situations.
get a regular ridge vent and cut it in half. I'm talking the 5ft long hard plastic sectional type. Just cut thru with a utility knife.
Build and leave the sheathing about 1 1/2" shy of the ridge ledger for an air gap. Shingle. Place the vent with the cut edge against the existing wall........and flash above running the flashing under the existing siding and over top of the new vent.
Done. Jeff
.......Sometimes on the toll road of life.....a handful of change is good.......
U DA MAN!!!
Ditch
Jeff,
Seems like I am always overlooking the simple solution. Thanks for the help !
That's one way, Cor-a-Vent makes a product specifically for this application.
The easiest way, don't vent it. In this application, there are many climates where drifting (snow) will occur. This can render the vent ineffective, or cause leaks. There are approximately one billion unvented shed roofs thoughout the land that have not resulted in any problems. It is typical for shingles on a shed roof to have a shorter lifespand than the rest of your typical house. Primarily to to shed roofs typically being of a low pitch which results in more uv damage.Tom
This is one of the hardest venting details to do - just as likely to cause leaks as to prevent condensation. Better to pack full of insulation and use vapour bar to prevent migration of moisture in this case - IMHOExcellence is its own reward!
We’ve been faced with a number of these in our area, which includes wind-driven snow. Here’s the basic approach we’ve used………..Depending upon the width of the rafters and how much insulation you want to tuck up there, you can either use FG insulation allowing a minimum 2” of free air space above, or use wedge- fitted foam board, also allowing at least 2” of free air space above. Vapor barrier, of course. Then apply however many pan vents are appropriate to vent the entire area, spaced accordingly on the roof. Because this will leave rafter bays that have no access to the vents, we drill angled 1” holes, thru the side of each and every one of these rafters, in the free air space, near the top of these bays. This gives all bays access to the pan vents. Supply ample soffit venting to every bay. No problems yet and you can definitely feel the hot air exhausting from the pans in the heat of summer. Before we retrofitted this arrangement, several of these roofs suffered from ice-damming problems, but no more.
Mr.Bill-You'll have to excuse me for jumping in on your thread like I did. It's just I've been mulling over that same question for several months now and was planning to post the question whenever I got around to learning how to place a picture. So when I saw your post I dangburn got excited. I feel more comfortable with the pan vents and two inch space with angled holes. I saw a large new log home being built and was talking with the builder about the roofing system. He told me at the log home building course for this particular manufacturer they instructed him to fit the foam boards tight up against the sheathing. I don't know but like the idea of venting better. Will you be using a gutter system or large overhang?
Half of good living is staying out of bad situations.
If you ask them nice,cor-a-vent will send you a nice spiral bound manual detailing the application Jeff Buck described and quite a few others. Cor-a-vent also makes a new vent with a flange that lifts up in winds over a certain speed to block infiltration. don't know if that flange would work in this application due to the location of the wall.
Use the double strap technique.
first layer of straps goes on vertical right over rafters.
Second layer goes horizontallly saced at whatever your exposure will be on the cedar shakes. (adjust so you are nailing in the center)
Be careful wthi the vapor retarder on the interior, and you will not need to vent at the top edge.
But you probably already made up your mind so vent away.
Mr TDo not try this at home!
I am a trained professional!
Just a thought....ut oh...Not sure what size rafters your using but what about drilling 1 1/2" or so holes at the peak and side vents at each end?
Just a dumb flash
BE well
NAmaste
Andy
It's not who's right, it's who's left ~ http://CLIFFORDRENOVATIONS.COM
Ya, I was wondering if that side venting approach was what Mr.T was making a reference to. Seems like it might be plausible seeing the short width of the roof.Half of good living is staying out of bad situations.
I didn't think of that, but it would certainly work!
Missed 'er TDo not try this at home!
I am a trained professional!
OK Rez...being that I wasnt cut down here with my suggestion..heres what I would do if its just a short run..(or even a long one....Use 2x8's and up at the tekos or ledger at the house real tight to the END of the 2x8 notch in a good two inches in the top of each rafter and put a nice 2-3" vent at each end. that'd work way fine bro IMHO.....and if anyone says no then put a lil damn fan in to blow it through with a thermostat...just coverin myself....lol
BE well
Namaste'
AndyIt's not who's right, it's who's left ~ http://CLIFFORDRENOVATIONS.COM
For all U non-vent shed-heads....the lower pitch of a shed is why I've had to use think up this madness in the past.
Most shed additions do seem to be lower pitch. And on the very first one I ran into like this.......all the pitch I could get out of it was a 2.5/12.
So.....as the customer wanted/needed the new slpoe to match the existing gambrel roof......I was trying really hard to make dimentional shingles work. The building inspect said OK...as long as the shingle manu said OK. They said OK..as long as ice shield was run over the entire roof deck. The building dude said that was OK...as long as the deck was then vented......as the ice guard would hold heat........the shingle guys said OK...and that actually sounded like a good idea.....additional venting. I had to have continuous intake and exhaust or everyone to be in agreement..........so.........
if yer shed roof is a lower pitch........under 4/12....and yer gonna shingle......make a call to all parties involved....and bet ya gotta vent...whether ya like it er not!
......and that paragraph above was pretty much how the game of phone tag went for the first week.......he said...then they said...then he said....so if I.....then U need......OK, now how 'bout if...........finally......bang....done!
Had a chance to check back on it about 2 years later....shingles still looked good....no obvious signs of water.........even where the crazy dude insisted on sky lights over the outside deck portion........that ice guard can be an amazing thing. Jeff.......Sometimes on the toll road of life.....a handful of change is good.......
Rez,
Dont mind you jumping in at all....thats how we all learn. I was planning on 2x8's for the roof, with 4" insulation. That leaves 4" above for ventilation. Actually, I am starting to like the idea of the vents on the ends with holes in the 2x8's to let the airflow through all of them. I will also look at the Corovent system.
Mr T...the roof will be 4-12 pitch with "normal" composition shingles over tarpaper. The pic was only for reference to the general layout. I am not using cedar shakes. I have not decided on the gutters yet, there are a lot of trees and a good overhang might be enough. There is no basement to worry about as far as water goes.
Thanks for everyones helps and suggestions....this site is great !
Jeff- Thanks much for your input. I've a question over a thought I had and was wondering if I could get an opinion.
In regards to venting the shed roof against the house wall. What if... instead of a vent at the top of the roof as you conveyed, instead of pan vents and angled vent holes in the framing members, what if a 1 foot deep flat ceiling would be built at the high part of the roof, inside joining rafter to wall leaving an air space intersecting the airway of each rafter bay flowing thru from one side of wall/roof to the other being fed by lower eave soffits and sidewall vents or an upper peak soffit configuration. I would think the small amount of directly unvented air that would gather between rafters at extreme top would dissipate enough to be non consequential. Just don't like making holes in roof if I can keep from it. What sayeth tho?Half of good living is staying out of bad situations.
I have an addition on my house built as you are describing, triangular vents on the sidewalls at the peak fed by soffit venting on a 3/12 pitch. Got 24 years out of 20 year shingles on the wet west coast.
Mr. Bill,
I reccomend leaving a 1" continuous gap in the roof sheathing approximately 18" down from the top of your shed roof. This will allow the 16" sheathing bays to ventilate between each other. Then install standard hood vents, two for this size room, in two bays overlapping the gap in the sheathing. Hope you like the idea! Let me know.