Replies

1. 
   rez | Sep 05, 2004 09:21pm | #1

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   Greetings norsky and Welcome to Breatime.

   I see you are a first time poster here so I took the liberty of listing a few old threads that dealt with the subject.

   Clicking on these numbers will take you to those posts.

   Cheers.

   be dead on or that quarter inch is going to haunt you

1. 
   norsky | Sep 06, 2004 12:52am | #2

   Hey, thanks,  rez, for the quick reply!  I read over the threads you listed, and  couldn't quite find a situation quite the same as mine.  Maybe if I got a little more specific about my situation:  My new rafters will be 2x8s, beveled on one end, and attached to the top of the existing roof to a nailer plate just back of the eave.  Can't attach them to a ledger bolted to the house bearing wall, due to lack of height to have a minimum3:12 pitch on the addition.  Otherwise, I might consider a "half" ridge vent at that end of the new roof.  My rafter tails on the new roof will be exposed (no soffit) to match the eave on the house.  I wonder if leaving a screened gap at the top of the blocking between the rafter tails,  with two or three attic vents up near the junction of the two roofs, with holes drilled in the rafters to allow circulation between rafter bays, would work?  I live in snow country ( South Dakota) so would snow blockage of the attic vents on such a low slope roof be a problem.

   Thanks, norsky

1. 
   RichBeckman | Sep 06, 2004 04:28am | #3

   "My new rafters will be...attached to the top of the existing roof to a nailer plate just back of the eave."

   Seems to me that all you need to do is drill a bunch of holes in the nailer plate, drilling all the way through the original roof (which I assume is vented).

   Caveat: Mine is not the voice of experience. This is just the thought of someone who has read a bit about ventilation.

   Rich Beckman

   Another day, another tool.

1. 
   DANL | Sep 06, 2004 05:56am | #4

   Yeah, I wondered the same thing about just drilling holes to tie the new rafter bays to the old, but thought I'd play it safe and see what someone more experienced thought.

2. 
   rez | Sep 06, 2004 06:24am | #5

   To vent or not to vent, that is the question. Whether 'tis nobler...

   Venting seems to be a good controversial subject. A lot of different pro and con information floating around out there.

   Speaking as a homeowner and not a professional roofer my recommendation is to eliminate the thought of adding roof vents near the junction of the new roof tie in. Low slope, snow country, more holes in your roof surface. To iffy increasing the odds of potential future problems.

   If it were mine I would seek a way to continue the air flow thru the bays formed by the new rafters into the attic area of the original roof.

   Is it possible to make your vent channels at the new/old junction in the old roof instead of the nailer? 1 1/2 inch minimum height across the bay is normally recommended.

   Maybe extending the length of the new rafters a tad to increase your slope a bit more, thus providing room to cut into the old roof.

   Since your adding vent space by the building of the new addition you might want to check inside your old attic to make sure you have enough vent space there to handle the out flow.

   Maybe a ridgevent if you haven't already.

   I take it your old space is an attic and not cathedral.

   be dead on or that quarter inch is going to haunt you

2. 
   Dinosaur | Sep 06, 2004 07:27am | #6

   With open soffits on the new eaves and a roof-top tie-in, you will need to get a little creative.

   I'd suggest strip vents set into the sheathing above the top plate on the face wall of the addition. You might want to back these up with HD window screening to keep the smaller bugs out, too.

   To vent the top end, see if you can find a decent looking triangular gable vent that matches the slope of the new roof. If not, build youself a couple out of 1x pine and screen them with ¼" wire mesh backed up by HD window screening. Check the code for your area to see how many sq. inches of venting you'll need for that roof.

   If your new laundry room has got a cathedral ceiling, things are a bit more complicated. You can still use the strip vents on the face wall, but make sure they feed into a vent space created by nailing 2x2 blocking to the side of each rafter flush with its top edge, and then nail black joe under the 2x2s spanning each rafter bay. Stuff your insuslation between the black joe and the ceiling.

   You will still have to vent the top end; with this scenario, it will be necessary to bore or notch each rafter to allow free air circulation among the bays just before they tie into the nailer plate you mentioned. If you don't want to do that, you'll have to open up the existing roof deck, tie your new rafters to the existing ones, and vent out through the existing roof's upper vents, which may have to be enlarged.

   The other way to approach this whole thing would be to insulate the new roof on the outside with rigid foam board on the roof deck, furring on the foam board, and either a second roof deck or steel roofing on the furring. This gives you a cold roof surface without venting the attic space at all.

   In any event, at 3 in 12, you need to lay IceGard membrane on the lower 6 feet of the roof.

   Dinosaur

   'Y-a-tu de la justice dans ce maudit monde?

3. 
   DANL | Sep 07, 2004 12:19am | #7

   I vote for any of the things Dinosaur said. I knew we'd get a good reply if we waited a bit. :-)