New roof on a cedar home... Some questions?

[tomrscott]

If you read my post about the workshop roof, here is a related one. The other big project that I really should try to do this summer if we can budget the materials. Our home is a cedar beam home, almost a cabin, but the solid wood walls are tongue and groove beams of cedar 3.5" thick. The roof is over an open-beam ceiling with no attic air space. We don't have terrible cold here like many of you deal with. The house has extra thick cedar shake shingles that were over an inch thick and have lasted for many years (don't know how many, maybe 27?), but they are showing their age and are going to have to be replaced. The shingles are on 1'x4" stringers (not sure the right term for this...) that are spaced about 4 or 6 inches apart, I guess for air space to help the shingles dry out. We are backed up near a large forested area and though we don't have a lot of fire problems here due to the wet, still forests can burn even here, so the shake is probably not a real good idea. Also, the air space in the rool has tended to collect wasps and box-elder bugs. The ceiling inside is tougue and groove cedar 2x6s. These have some gaps between some of the tongue and grooves that are big enough that an occasional nesting wasp or fly finds his way through a gap with the heat rising and gets into the house. A real nuisance.

I have considered many things for re-roofing, but we are probably leaning toward a green metal roof. I've put this stuff up when we did the horse barn lean-to roof and repaired the workshop roof, so I have experience with it. I have also considered some sort of lightweight cement shingle that would look like wood, but I think those are pretty expensive. Asphalt shingles are cheaper, but I'm not crazy about them.

Anyway, if I go with a steel roof, I am trying to decide how to build it, insulate it better, etc. I am no expert at roofing, but here's what I had in mind:
1) Strip the old roof off down to the 2x6 T&G boards
2) Caulk all of the T&G gaps
3) Lay down a vapor barrier of some sort, and maybe a layer of felt.
4) Build a 2x4 frame kind of like a wall section frame laying down on the roof on close enough centers to support the metal roof panels, stagger blocked every four feet or so, clear out to the edges of the eaves with some facia boards to trim it out.
5) Fill this frame with closed cell foam inulation and fill any gaps with the spray stuff to get it real tight.
6) Cover this with another layer of vapor barrier and the metal, or should I put some 1/2 in stranded roof underlayment on first?

I don't really know what I am doing, so feel free to tell me if this is all wrong, I take correction well! /forums/images/graemlins/smirk.gif

Seriously, feel free to make any suggestions at all; different roof material, different insulation, different layup, thicker insulation frame, etc. Just remember that we have a modest temperate climate, high winds, mild summers, lots of rain, and a little bit of snow each winter but usually less than a foot.

The idea is to get several inches of insulation under the roof and to seal the ceiling boards better against bugs getting in. Thinking I don't need the air space if I use something non-porous for a roof.

Further complicating this is that we want to put two dormer windows in when we do it, but that's another matter.

I think I'm going to be real busy this summer. /forums/images/graemlins/smirk.gif

 

[GuglioLS]

Wow sounds like a serious roof. Yea right you don't know what you are doing - you do not lie very well.

Item 6 -
If it were up to me I would use the 1/2" OSB (oriented strand board) some 30# roofing tar paper on top of that then the metal. Plan on a ridge vent as well, there will be condensation under the metal and will need some sort of ventilation air - in at the bottom then out the top.

Be careful up there !

 

[beenthere]

All I can add is to make sure you have good ventilation for that area between the steel roofing and the insulation. Otherwise, the wood will decay real fast, especially in your damp climate.

Check out your ideas with the Oregon St Forestry dept, in Corvalis, OR. They should have some helpful ideas and critique.

Sealed up is probably not good, but I can't quite tell if that is what you intend to do, or intend to not do.

 

[LarryRB]

I would do as you want except, use 2 X 6 instead of 2 X 4's.. By using the 6's you automatically have built in a chase for air to move from soffit to ridge vent,,

 

[EddieWalker]

It sounds like you're going to build a solid roof by filling all your voids with insulation. I'd use 2 X 6's on edge instead of 2 X 4's.

You didn't mention the span your bridging, so you'll have to take that into consideration. Log homes use a beam to build similar type roof systems. You might have to use larger lumber like 2 X 8's or more.

Since it will be solid, then there is no air to circulate, and no need for venting, since you have nothing to vent.

You might want to look at some log cabin roof designs. They build solid roofs like what you described all the time. I've seen it layed out explaining the steps on a website, but I have no idea which site it is.

There is also a company that builds the roof panels already finished and ready to install. You need a crane to pick them up and put them into position. They were very expensive, but just what your doing. Again, I forget the companies name.

Eddie

 

[bugstruck]

Not sure which direction you intend to run the framing. You could run it north/south (up and down). Skip the vapor barrier, unless it's very breathable (I don't like true vapor barriers on the heated side of a wall or ceiling and you can't use a true vapor barrier on the exterior side of a heated wall unless it's breathable tyvek or similiar) , and move the felt to the sheathing on top of the framing if that's how you construct it. You don't necessarily have to do that. The other options are:
1. Frame it east and west. I'd use 2 x 6's and insulate to not more than 5 " thick. Then you would be spanning the framing directly with metal roofing and that can create some real issues if you want to walk on it later. Much of the roof metal is rather light gauge and doesn't fair so well without direct support. The manufacturer should be able to steer you on that. However it breaths better this way.
2. Frame 2 x 4's north and south, insulate full depth, and top strap it east/west with 1x material at fairly close frequency. This works if the metal roofing is not true standing seam but has open folds (most does) that create their own air convection channelways.

Other options exist but these are the first that come to mind.

The latest (5 to 8 years) thinking among some of the expandable foam insulation companies on this, with asphalt shingles at least , which won't work for your fire concerns, is that you can solid foam insulate a cathedral ceiling with absolutely no reguard for air movement (ventilation) and not have any issues at latitudes as far north as the Pa./ New York line. I'm still a bit skeptical on this although many homes with pre-engineered roof panels (sandwich construction) have been doing this for about 25 years with very limited problems. And many are erected as far north as New England, that I know. The old Yankee Barns homes come to mind in using these sandwich construction full foam insulated roof panels. They never created any problems in Maryland that I know. However the trick was to be tightly insulated (foam only) from the living space to the roof sheathing with the roof material directly applied to the sheathing. Bear in mind I never saw it done with metal but I bet a little research will find it has been done. My guess is frequently.

Sounds like your on the right path. Just a little research and some feedback here should clear up any questions. /forums/images/graemlins/confused.gif /forums/images/graemlins/grin.gif

HTH,

 

[tomrscott]

So let's see if I can answer a couple questions, clarify my thoughts, and summarize a bit. /forums/images/graemlins/mad.gif

I have attached a .jpg cropped out of a larger aerial shot of the property to show this roof. It's pretty fuzzy since it is cropped out of a much larger area, but it should help visualize what I'm talking about.

1) The framing I was planning would run N/S

2) There seems to be some disagreement on one of the major points of my concern: Whether a non-porous roof can be built air tight without internal ventilation or not.

3) I can understand how a wood shingle roof would need underside airflow to help the shingles dry out. But I can't help but think that a water tight roof like a good metal roof can be should not need to dry out underneath if you build it solid and air tight.

4) The metal has N/S (meaning ridge to eave) corrugations that could be left open to breath, but I'd really like to close them up at the ridge and eaves to keep wasps and others bugs out.

5) Some have suggested 2x6s for 5.5" of insulation or 4.5" and some air space. I will have to price the insulation, but I'll bet that gets spendy. I am sure it is a good investment in the long run. This would be pretty much a lifetime roof. I will have to do it myself, cause the materials alone will nearly break us. Now way I can pay somebody what it's worth to build it!

6) One thing about this house, it breathes. We don't have the same problem with moisture inside as some contruction types do. The wood walls are tight, but porous too. According to the guy who built it, he used 78,000 pounds of Canadian Red Cedar. It's called a Lindal Cedar Home.

7) The roof is broken up into three slopes with short spans. The 2x6 T&G boards laying on face run N/S spanning some 4x12" beams. From the center ridge beam, a six foot span on a shallow slope (about 28" run in 12" rise), then a six foot span at a very steep 30" run in 48" rise, and then another six foot span at the shallower slope. I think there's a name for this style roof, Swiss Chalet or something, but I' not sure what they call it.

8) With regard to safety, when I work someplace like this, I like to work with a safety line that runs across the ridge and is secured to something on the other side.

9) I would really like to water-proof everything and seal it up tight just like you would a wall. I would think that the 2x6 T&G ceiling boards will breathe plenty underneath, so that I should be able to keep the outside as air and water tight as I can make it.

So this will drive the "you have to have air flow" gang nuts, but this is about what I would like to do:

a) 2x6" T&G running N/S on face (existing interior ceiling)
b) Caulk the grooves as needed on top (some gaps have opened up over the years and the wasps, flys, and box elder bugs can get in there
c) 30# felt
d) 2x6 pressure treated frame on edge running N/S at span equal to metal panel lap width (24" I think) (Need to figure out how to secure this framing to the 2x6 T&G ceiling boards, probably clips and short screws. Don't want to go through, and need to be real secure for these mountain-top winds).
e) closed cell foam insulation filling the whole 5.5" as tight as I can fill it, aerosol can foam fill and trim for any gaps
f) 1/2" stranded roof board or plywood waterproofed both sides
g) 30 pound felt again
h) Green steel corrugated roof sections with washer head screws. Not exactly sure about the right treatment at the pitch changes, downhill overlap of course, but maybe it needs some sort of extra flashing too.
i) Closed cell foam filled in the edges of the steel panel corrugations N and S (ridge and eave)
j) 2x12" facia board around the eaves with matching green steel flashing and gutters

So I am guessing several of you will bite my head off for not wanting air flow, and sounds like some agree that this can work. AGAIN let me reiterate (contrary to GuglioLS's flattery), I don't know much about this, but have just been thinking on it for a long time and trying to figure out what should work.

I would sure love any pointers to roofing concepts like this (open beam ceiling, exterior insulation, etc.)

Thanks! I really appreciate all the discussion and ideas floating around. /forums/images/graemlins/smirk.gif /forums/images/graemlins/smirk.gif /forums/images/graemlins/smirk.gif

 

[tomrscott]

Here's another view from the other direction. In this one you can sort of see a dormer on the right side of the ridge line, we want to put two like it on the left side to push out some space in the loft bedroom and office. Those would face west and pick up the sunrise and a perfect view of Mount Hood. /forums/images/graemlins/smirk.gif

 

[mwood]

Looks like you are on the right track... but with respect to air flow, I have a couple of thoughts.

As much as your ceiling breathes, I would still plan on vents. On my roof, the overhangs have cutouts with a mesh like screen under them. There is a vent running the length of the peak with more screening to keep the critters out. I think this is the best approach but in your case, may not be feasable. I would just hate to see moisture build up in your framed in insulated "roof wall" you are creating.

 

[EddieWalker]

If he makes the roof solid, with no air cavities, then there will be no moisture or heat issues. There will also be no air to move, resulting in no need for vents.

It's even becoming a topic of discussion wether a house with an attic actually needs to be vented or not. I'm not talking about northern homes with snow and ice, but in southern and coastal homes. You guys with snow are outside my area of experience or knowledge.

Years ago in So California during the fire storm there was an article on a house that survived the fire when every house around it burned to the ground. The guy who built the house did three things to ensure his house wouldn't burn down in a fire. He was expecting one to happen one day.

He doubled the thickness of the stucco, used quad paned glass and totally sealed the roof with no vents. His plan was to make the house totally air tite, resulting in no way for a fire to penetrate the exterior protection of his house.

It worked. The photos showed total devastation except for his house sitting all alone on the hill without any fire damage except for his landscaping.

The support for the lack of vents was based on some studies that have been done that indicate they aren't needed on homes with attics. The attic gets allot warmer in summer months, but this doesn't do any damage to anything. With the attic sealed, you also don't get any moisture build up from humidity. You are creating a sealed air pocket when you don't use vents.

I've never done this on a house, nor do I know anybody who has, but just about every builder I know will tell you about it and how it works in theory.

Eddie