New Roof

[Chris Padilla]

As some of you may know from the Skylight thread several lines below, I am preparing for a new roof to be installed on my house.

It is a 3:12 pitch, currently cedar shakes on skip sheathing. 5 sections of my roof are vaulted ceilings and therefore have rafters as opposed to trusses (which is an attic space, of course).

My roofer will rip off the cedar shakes but leave the 1x8 (or whatever size they are) skip sheathing in place and put OSB (foil on one side) 4x8 panels down on top of it. Then I'll have some nice asphalt shingles (CertainTeed brand) layed down to complete the reroofing.

My question to the collective here is about insulation in the rafter bays for the vaulted ceiling sections:

It seems to me this is the TIME to upgrade/improve the insulation. I could arrange to have cellulose or fiberglass blown into the rafter bays between the skip sheathing or perhaps some skip sheathing could be removed and batts stuffed in the bays.

Now I understand about my roof needing air space for air flow (breathe) especially since the asphalt roof breathes a lot less than my cedar shingled roof right now. I figured if the OSB panels were being nailed to the skip sheathing, that would provide a decent enough air gap per bay.

My roofer claims it would seal things up too much and not allow enough air flow and doesn't recommend I do anything to my rafter bays. I've seen those "trays" that can be placed in the bays that keeps an air-channel open so I figured those could be installed as well.

Any thoughts about this? I'm all ears!!

[Jim Becker]

Outside of using closed cell spray foam, you must have the air gap for ventilation so you can't add insulation to the bays if it takes away that air flow. Those "trays" are called baffles, and would normally be used to keep the insulation away from the roof sheathing. Spray foam can be used right on the deck, although some contractors still prefer to maintain an air gap. (Mine did, but we had 12" rafters to work with...and lucky me, the insulation contractor still filled them which was much more than the R38 we contracted for... :) )

[Chris Padilla]

Yeah, my rafters are 2x6s so I don't have a lot of space but geez, I'd sure like to improve the insulation.

The owner of the roofing company will come out and go over my roof with me step by step so we'll see what he has to say about it.

[Jim Becker]

Chris, with a 2x6 structure, about the only way to really do some "good" retro-fit insulation is to have spray foam done while it's open to the sky. That may also mean they need to rip off the skip sheathing to do it effectively. But you could get yourself to R30 or better that way with closed cell foam in a 2x6 wall.

[Chris Padilla]

Agree...but it'll cost extra to rip off all the skip sheathing...was hoping to keep that to a minimum if possible.

Thinking, thinking, thinking....

[Chris Padilla]

http://www.daviddarling.info/encyclopedia/C/AE_cathedral_ceiling.html

Interesting link.

In the first paragraph titled, "Cathedral celiling ventilation", they have a quote from a lab saying, "Should cathedral ceilings be ventilated? Not if that space is tightly packed with insulation."

Then the paragraph right below that titled, "Insulation techniques for cathedral ceilings", the first sentence says you need an air space! LOL!

So if I spend the extra money to have the skip sheathing removed and that expanding foam insulation sprayed in the rafter bays, it appears that I don't have to ventilate the cathedral ceiling. They can just lay the foil-covered OSB right on the rafters and go to town. Hmmmm...........

http://www.nuwool.com/products/technical/cathedral.html More fodder for reading although it appears to be largely the exact same text in some cases. Interesting, interesting....

[Jim Becker]

Yes, that's correct Chris. At this point, it's an acceptable technique to use spray foam without an air gap. It will also provide a significant increase in structural rigidity...something a 2x6 rafter ceiling will benefit from, IMHO. Do note that you want closed cell foam, not open cell foam. The latter has half the R value and less of the structural and air/moisture infiltration properties that closed cell foam has.

[Chris Padilla]

So I had the skylights installed and was able to see a little bit of my roof from below and above. The skip sheathing is 1x6 spaced 6" apart. My skylight guy said my tar paper has reached the consistency of a potato chip! :eek:

Anyway, with this spray foam insulatin investigation I have going, I'm figuring that maybe every other row of skip sheathing could be removed and that would allow reasonable access to the rafter bays to fill 'em full of gunk.

Oh, I should add that we've discoverd that I have the additional headache of batts AND loose-fill insulation in my rafter bays! :mad: That will make for messy/time consuming (and probably more costly) removal for me should I go the spray foam route. :(

[Lee Schierer]

Just to add to what Jim has said. For the "ventilation" to work you have to have a way for air to get in and for the hot air to get out. Normally this is done with soffet vents and a ridge vent. If the space you are referring to is closed off, or doesn't have both an inlet and outlet, adding insulation may not help the life of the roof much.

[David G Baker]

I don't know if this will apply to your situation because I don't have cathedral ceilings and I have an attic. The attic is not very accessible.
I had a new roof put on. I decided to have the old roofing material removed. During the removal process it was discovered that my soffits were completely enclosed by wood. If there were vents, they would have been useless for ventilation because Fiberglass insulation was crammed into the space between joists and trusses. The old roof was approximately 10 years old and was asphalt shingles over 1/2" OSB and the original 1"X8" boards. The old roofer did not lay down roofing felt, the shingles were on bare OSB. Due to the lack of ventilation the OSB was black with mold and crumbling and the majority of the 1"X8" were rotted. There was no place for the moisture in the attic to ventilate so it stayed in the attic and destroyed the roofing material. There were several of the metal vents in the roof but there was no air source to allow the attic to vent. $14,000 later I had a new roof.

[Chris Padilla]

David,

I do have an attic but only 2 of 7 sections of my roof have such a thing...everything else is a cathedral ceiling. My attic is vented at the gables so no problems there...the "floor" of the attic is the place to insulated well.

[Chris Padilla]

Just to add to what Jim has said. For the "ventilation" to work you have to have a way for air to get in and for the hot air to get out. Normally this is done with soffet vents and a ridge vent. If the space you are referring to is closed off, or doesn't have both an inlet and outlet, adding insulation may not help the life of the roof much.

Lee, et. al. Google with this phrase:

oak ridge laboratory moisture control handbook cathedral ceilings

You'll find some interesting stuff in regards to venting roofs. From what I can discern, if air penetration can be 100% stopped, there is no reason to ventiliate (as ventilating is a form of air flow that can bring moisture in as well as remove it).

You'll also find that the heat gain of a roof is most strongly dependent upon the color of the roof and not the venting methods.

[Rob Russell]

Chris,

I have a personal bias against using OSB for anything structural. I belive in using plywood, even if it is more expensive.

We don't have enough historical data to know how long the glues are really going to hold up. As woodworkers, we all know that the glue will fail. With the manufactured products like OSB, once the glue goes - there is nothing in the panel to provide any structural integrity. At least with plywood, the sheets of ply will provide support even if the glue between the plys fails.

Just my 2 cents.

FWIW, when we did our addition, we used plywood for everything - no OSB.

Rob

[Chris Padilla]

Hi Rob,

I asked my roofer about that but he really prefers the OSB and said he's had success with it for over 20 years so who am I to argue. He has seen the plywood fail/delaminate. I, too, wanted to use plywood but you make a good argument for sure. Hmmmm.......

[David G Baker]

Rob,
I think I may have to agree with you. When my house was re-roofed there was an area that was covered with plywood that was an addition to the old farm house's original structure. The plywood was not as thick as it should have been and it was spongy to walk on but it was still all wood. The OSB, if it did not have the 1"X8" underneath it, when walking on it a person would have fallen through because it was as you described. The OSB sheets were originally 1/2 inch thick but when removed they were closer to 3/4 inch thick due to swelling.
Had the old roof been done correctly I believe that the OSB would have been fine.

[Jim Becker]

My contractor used plywood for all sheathing...you could park a truck on our addition I think...

[Michael Lutz]

I like to use plywood too. We redid a roof that had 3/8" plywood sheathing that had delaminated. You could still walk on it with out falling through. I am not so sure if I could have walked across OSB exposed to the same moisture with out falling through. I have been residing my house and only using CDX plywood sheathing. After sorting through the bundles to find acceptable sheets to put on my house, I can see why the contractors would like to use OSB. There is no differnce between sheets of OSB in a stack.

Mike

[Paul Girouard]

My bias on OSB is it doesn't hold nails worth a crap . I'd use 5/8 CDX on my roof and also on other folks roof IF I can talk them into it.

With skip sheathing under your OSB you'll be fine unless your in a high wind area . But I'd say use 1/2" CDX in your case with the skip sheathing it would be a better substrate IMO. Your roofers seems to vary from mine. Seeing he's the one who's got to stand behind it he may be the one to listen to:rolleyes:

You should have Icynene ( spray foam ) insulation put in.

Link : http://www.icynene.com/

No venting needed , way better R value than any other insulation . I've used it three or four time on remodels like your where there wasn't room for batts .

It will take some coordination effort with your roofer and the insulation sub , IF you can find one in your area it would be the best way to go.

Good luck.

[Jim Becker]

Icynene only appears to be R3.6 per inch if I'm reading the specifications correctly which is not all that different than fiberglass outside of less chance for air infiltration. Closed cell spray foam is R7 per inch and adds a lot of structural rigidity, too. The 2x4 walls in my addition, using the closed cell foam, are at a minimum of R19, although most are higher due to the contractor slightly overfilling. With 2x6 rafters like Chris has, closed cell foam will give R30+ and really stiffen the ceiling up.

[Paul Girouard]

Icynene only appears to be R3.6 per inch if I'm reading the specifications correctly which is not all that different than fiberglass outside of less chance for air infiltration. Closed cell spray foam is R7 per inch and adds a lot of structural rigidity, too. The 2x4 walls in my addition, using the closed cell foam, are at a minimum of R19, although most are higher due to the contractor slightly overfilling. With 2x6 rafters like Chris has, closed cell foam will give R30+ and really stiffen the ceiling up.

Do you have a link to this "closed cell foam"? I thought Icynene was concider a CSF , yes that link I posted say's it's R3.6 per inch , so 3.6 x 5.5 = R19.8 net

I goggled closed cell foam and checked those two links on Chris's post and didn't find anything about CSF. Maybe I was rushing to much / didn't look hard enough:o.

Could be I have my terms mixed up , I did not call and talk to that insulation contractor to set up those jobs. Like I said we've used it three times in the past 7 years , It was expensive but when remodeling you do what best in a small space . I do know it , the spray foam, is the only insulation we can use here in the PNW that does not need , or want , any venting.
Different areas of the counrty have different codes / requirements , I do not recall where Chris lives , I'll check his profile to see if it says after I post this.

[Chris Padilla]

So the spray foam guy came by yesterday. The product they have is an OPEN cell foam and they claim 3.8 per inch (he actually said 3.81 :rolleyes:).

The reason he likes open cell over closed cell is that water can actually penetrate it and that is a good thing because it tells you you have a leak in your roof.

The closed cell allows zero water penetration so if you have a leak, the water will sit on top of the closed cell with no where to go and it'll rot your sheathing and rafters.

The closed cell is also nearly impossible to fish future electrical and what-have-you through the walls although I'm not so concerned about that in a cathedral ceiling but am concerned about that for walls and my crawl space.

I spaced bringing in the material/website info for this firm's stuff so I post it here later for those interested to peruse. Edit: http://www.sprayfoam.biz/default.html (http://www.sprayfoam.biz/default.html) is the place I'm still waiting on a quote from. Here is the foam material they use: Sealection 500: www.sealection500.com (http://www.sealection500.com)

I have the additional problem of both batts and blown-in insulation in my cathedral ceilings. The roofers won't deal with it and my spray foam guy won't deal with it so I have to bring in yet another party to join the "pilfer Padilla party" to clear my rafter bays of material. :mad:

[Paul Girouard]

I have the additional problem of both batts and blown-in insulation in my cathedral ceilings. The roofers won't deal with it and my spray foam guy won't deal with it so I have to bring in yet another party to join the "pilfer Padilla party" to clear my rafter bays of material. :mad:



Do it your self or quit complaining :mad:

Those people are just EARNING a living!

Advice is free here, saying your being "pilfered" by tradesman's EARNING their money just doesn't cut it with me:mad:

[Chris Padilla]

Paul,

It was a joke...you know 3 P's, alliteration.... Well, I enjoyed it! ;) I have a bit of a warped sense of humor as some will attest to around here. Gimme time...I'll have you rolling! :)

[Chris Padilla]

So things are slowly moving along with my roof. I finally have the roofers in order, I got a quote for the spray foam insulaton place that I'm happy with, and tomorrow morning, a guy is coming over to quote me for the insulation removal. He just needs to measure the total area of removal and I should have a number pretty quick thereafter.

Whew, I feel like a GC lining these 3 folks up and they all need to work together, coordinated like to get the job done most efficiently. Thankfully, my roofer is quite used to this and will coordinate the other two folks.

Doing this in the winter in the Bay Area is somewhat risky due to rain but they can do sections at a time on my house if necessary although I'm sure the insulation and insulation-removing guy want to get their job done in a day so we'll see how this all goes. It may cost me more to spread it out over time but if that is how it needs to work, then that is how it needs to work.

I'm just excited to see all this coming together and I really looking forward to see how the room(s) feel with the new insulation!

[Chris Padilla]

Thought I'd update with some pics seeing how the insulation is in, the roof is done, the rockin' is done, and painting is mostly done! :)

[Chris Padilla]

Shots of the roof with the expanding foam insulation in them. These are obviously the rafter bays and a shot of my only attic space. The house looks interesting with a 'white' (CDX plywood) roof!

[Chris Padilla]

And some shots of the interior with the painting mostly done and the new maple floor being layed out.

Ah, the finishing of this room is in sight!!

[Jim Becker]

Wow...I didn't realize this project was this big! Nice!

[Chris Padilla]

Whew! It was quite big...it is the main entrance into the house and it was always somewhat shabby but we've gone ahead and spiced it all up. No longer will we be embarrased to have company over!!

I'll have to get some shots of the new roof...it looks really sharp!! Next time you are in the BA, Jim.... :)

[Jason Beam]

Dang chris ... That came out lookin' dang good!

I hadn't noticed this thing back when you'd started it, but I'm very interested. I'm gonna need a new roof soon and I'm debating some structural and insulation challenges myself. Did you ultimately go with closed cell?

[Chris Padilla]

Hi Jason,

No, OPEN cell is what I have. The reasoning for doing OPEN cell in the ceiling is for leaks. If you have one, it will eventually "percolate" through the open cell and in time, soak the drywall, sag, basically "inform" you that you have a roof leak (BTW, this open cell is unaffected by water...it is back to normal once it dries). The CLOSED cell doesn't allow water through...it just sits on the surface...with no where to go...rotting your sheathing and potentially your rafters.

Anyway, that is what the sales guy told me. The open cell is soft...you can stuff your hand into it fairly easily and rip it out. The closed is like cement. Closed cell will yield higher R-value than open near as I can tell but I'm doing pretty good with near R-4 per inch with the open I had installed. The room is definately more comfortable and definately has milder temp swings than it used to; also it is quieter.

I used a firm that is near you in Folsom: Energy Solutions (www.sprayfoam.biz (http://www.sprayfoam.biz)). Good crew, nice guys, and not horribly expensive IMO.

[Jason Beam]

Thanks for the reply, chris - so did you ultimately end up venting, then? I assume since it wasn't closed-cell, you had to put in the baffles?

[Chris Padilla]

No baffles...the roof is pretty well vented due to the plywood sheathing being placed upon the 1x6 skip sheathing and the roofers vented at the peaks, as usual. I think I'm good...no air movement will get THROUGH the foam so that is the key.

[Jim Becker]

Yes, open cell foam is typically about R3.5 or so per inch. Closed cell like I put in the addition comes in at about R7 per inch.

I do think the salesman's pitch about the leaks is "somewhat" predicated on the fact that he/she had open cell foam to sell... ;)

[Chris Padilla]

I do think the salesman's pitch about the leaks is "somewhat" predicated on the fact that he/she had open cell foam to sell... ;)

I agree and I wouldn't have had a problem with closed cell in the walls but he made some sense in regards to the roof....

[Ernie Starnes]

Make sure your roofing contractor does the extra work it requires to use asphalt shingles on such a low pitch roof. In general, for roof pitches of 2:12 to less than 4:12, two layers of 15# felt applied shingle fashion are required. Starting with an 18-inch wide sheet and a 36-inch wide sheet over it at the eaves, each subsequent sheet shall be lapped 19 inches horizontally.

[Chris Padilla]

Ernie,

My roofer used 30# tar paper...no double layers...dunno the overlap they used. Their work comes with a 10-year guarantee to be 100% leak free so that is good enough for me; I think they know what they are doing. :) They've been around for a long time and carry an excellent reputation.