little advice please - Contractor Talk - Professional Construction and Remodeling Forum

scott62074 · 08-19-2007, 03:41 PM

Hi guys. I'm new to the site. Not a roofer by trade. Excavation is my thing, but I thought I'd try to save a little by tackling my own roof myself. I have a few questions and just kinda' wanted some re-inforcement on the rest of the plan. Appreciate any ideas you all might have.
Going to be removing 5 layers (just bought it - not my fault)! The bottom layer is wood shakes, which means I'm re-sheathing with 7/16 OSB. Putting back 25 year architecturals.
My big dilemma is ventilation. I've been browsing a couple of your other threads and it seems like this is definitely the place to come for answers!
The roof line consists of 14 different ridges and 10 different valleys. Thus leaving me minimal places for uninterupted venting. There are no vents to speak of right now and the attic space below is finished living space. I really don't want to get into re-sheetrocking the whole upstairs.
I'm not sure what I will find as far as rafter sizing (actually believe they may be 2x4, 2x6 max - 12/12 pitch) ar current insulation. I considered renting an insulation blower and filling the rafter cavities from the bottom up as I put the new deck on. With such shallow cavities, what is the best way, if any to provide ventilation. And is it worth messing with if only 30 - 40% of the roof would actually end up with continuous bottom to top airflow?
Also wondering about vapor barrier. How important is it and would it be acceptable to just cover the top side of the ceiling material and rafters with a plastic film before insulating?
Thanks for any help you can give me!

WarriorWithWood · 08-19-2007, 05:42 PM

If I'm understanding you right, you'll need to install some kind of soffit vent for a cool air intake (there are many different choices) and baffles between the joists (so the new insulation won't block new intake vents) and install a ridge vent for exhaust (once again many choices). Then you can blow in the insulation. If you have a cathedral ceiling (I can't tell from your post, maybe I'm missing something) that's a whole different animal.

I hope this helps

scott62074 · 08-19-2007, 09:19 PM

yes, dennis. you're right on. i've got a whole different animal. the attic space is finished living space, so the bottoms of the rafters have sheetrock/plaster hanging on them. the ceiling line mimics the roof line. with the rafters being 2x6, possibly 2x4, i'm not sure yet, i don't know that i have room to do everything necessary. plus, a big percentage of my rafters end in valleys, where there is no way to put in an "intake" vent.

WarriorWithWood · 08-19-2007, 09:27 PM

Here's a really good article about unvented roofs, it might help. There's alot of reading, but worth it. Poke around the site a little too.

http://www.buildingscience.com/docum...r-all-climates

Grumpy · 08-20-2007, 08:41 AM

First off understand that your roof protects your house and everything in it. Second understand that roofing is very easy until you get to the details which can and willc ause your roof to fail if done wrong. Now ask yourself if this is a risk you are willing to take (which from what you described I highly suggest you hire a roofer).

If so... I've done roofs exactly as you described. You are in luck that you need to re-sheat this roof anyways, so correcting the ventilation is not going to cost you much more. What I have done in the past on roofs like these is to create a new roof deck ontop of the existing spaced decking, using 2x3's and plywood.

You need to create some kind of intake at the eaves, what kind I do not know because I don't know the architecture of yoru home. I am guessing there is no overhang worth mentioning but is some kind of crown molding. You'll have to decide what kind of intake to create, or post some pics.

THen after you have created the intake, you will need to take your 2x3's (laid horizontally, so the roof sticks up 1 1/2" not laid vertically) and nail them directly over the existing rafters, and INTO the existing rafters. Then nail your plywood over the new 2x3's.

Install a ridge vent, and you have now created proper attic ventilation.

Some things to keep in mind. you will probably have to redo all the fascia boards and/or moldings at the edge of the roof. While doing that you may be able to address the intake situation very easily by reworking the over hang.

Other neat tricks are creating ventilation at curbs and valleys, where you need to create sideways ventilation so air can flow from one rafter pocket to the next side-ways. This is done by leaving a gap of about and inch between each 2x3 as it is laid vertically up the roof slope.

tom m · 08-20-2007, 10:34 AM

I like Grumpys thought here adding a air space. Bringing intake ventilation for roof with no eaves has been discussed in the link below. http://www.contractortalk.com/f15/poor-ventilation-advice-670/ If I can add 3 things here it would be that most deck lattice type 12 on 12 are going to have rafters 19.5-24" o/c so if you intend to remove this 1 x material or go over it you will need heavier ply or clips for support or screw additional 1x for support. I would use a power vent over a ridgevent because I hate the sharp bend of material with a 12 pitch and last thing is dormer issues. You will have flashing detail around chimney and dormers adding layers of material. If you find Batt insulation you can just push down slightly to increase air flow and deal with baffles at a later remodel.

theroofinggod · 08-22-2007, 06:23 PM

I AGREE W/GRUMPY

**Ed the Roofer** · 08-22-2007, 08:02 PM

Quote:

Originally Posted by Grumpy

THen after you have created the intake, you will need to take your 2x3's (laid horizontally, so the roof sticks up 1 1/2" not laid vertically) and nail them directly over the existing rafters, and INTO the existing rafters. Then nail your plywood over the new 2x3's.

Other neat tricks are creating ventilation at curbs and valleys, where you need to create sideways ventilation so air can flow from one rafter pocket to the next side-ways. This is done by leaving a gap of about and inch between each 2x3 as it is laid vertically up the roof slope.

I would just like to make sure that Grumpys very accurate and correct description of how to solve this dilemma is not misunderstood. (I took it the wrong way upon my first glance at it.)

(I probably was the only one who misunderstood this point, but just in case, I am adding a clarification.)

When he says to lay the 2" x 3"s "Horizontally, he meant to lay them flat on the wide side, not to lay them fron left side to right side of the roof.

The lengths would get installed "Vertcally", as he stated later on in his post.

Custaom fabricated sheet metal flashings will solve the edge details without having to rework the fascia elevations too.

Ed