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

[tomrscott]

Eddie,

Not sheating "ON" a metal roof, we're talking about the sheating "UNDER" a metal roof; the stuff you srew the metal to that goes over the top of the insulation.

Let me answer your questions the best I can:

1) First, what is a "perlins?" Not familiar with the term.

2) There is almost no insulation currently.

3) I have described this in some detail above, but current roof is roughly like this:

a) The 2x6 T&G cedar ceiling boards are laid on-face spanning 4x12 beams. Each span is only about 6 feet.
b) Probably some roof felt on top of the 2x6s, but I haven't opened it up to see
c) There are 1x4 stringer boards running E/W spaced wide apart as support and air space for the shake shingles (is this what you are calling a "perlin?")
d) It looks like there is a small amount of 1x? styrofoam insulation, old stuff that looks like molded ice chest in between the 1x4 stringers. Not very complete fill, not sealed, not very thick. Sometimes a little chunk of this blows off in the wind, falling out the open sides.
e) Very thick old cedar shake shingles, I don't think you can get them this thick anymore. More than an inch thick. Twenty seven years old and still not leaking, but they're so old and brittle I won't touch them until I can replace them for fear of causing a problem. Even the rain gutters were hewn out of cedar beams.

4) As I said, the roof is not leaking rain, but wasps and flys can find their way in through the T&G gaps up under the shingles.

5) There is no hollow space of any kind under this roof except the gap under the shingles created by the 1x4 stringers. There is no venting unless you mean this space, but no gable vent, no ridge vent, just open spaces along the sides of the roof between the 1x4s. There is no attic, there are no rafters on edge.

6) When I pull off the shingles and the 1x4 stringers all that will be left is the 2x6 T&G ceiling boards and maybe a layer of roof felt that needs to be replaced.

Does that make better sense? /forums/images/graemlins/smirk.gif

I don't want to give the wrong impression, it is a beautiful home, and generally very well built, but the roof could definitely be improved. /forums/images/graemlins/smirk.gif

 

[BillG_in_TX]

Tom,

Meuller is big in metal roofing down here in Texas. They have their installation manuals online. Maybe this will give you some guidance.

By the way, "Mueller, Inc. recommends our metal roofing systems be installed over CDX plywood wooden roof decking with a minimum thickness of 15/32”.

 

[EddieWalker]

I'll try to be more clear. You don't use ANY sheething with metal roofing. NONE. No plywood, no ASB, CDX or anything else that comes in 4X8 sheets.

If you really want to spend the extra cash, you could use it, but all your doing is adding more weight to your roof. The amount of benifit you might recieve is so minimal that there's no point in doing it.

It's just like I was hoping. The ceiling is attached to the 4X12 beams. This is your support.

On top of the ceiling, on edge are 2X6's. This is what will support your roof. The space between these 2X6's needs to be filled completely with insulation. People have said not to use fiberglass due to the amount of air that will remain in the cavity. I don't agree with this, but it's up to you. You can buy expensive solid foam and use that or go with the fiberglass.

The 1X4 "stringers" are the perlins. Only in your case I'd guess they are evenly spaced with about a 3 to 4 inch gap in between them. This will work perfectly just as it is for the metal roof.

Just lay your felt over the 1X4 and screw your metal down to them. You honestly don't even need the felt, but I got a feeling you'd feel better having it.

The metal roof is the water barrier here. Felt paper is what keeps water out on shingle roofs. Both wood and tar shingles are only to protect the felt. They are not water proof even though they help to shed the water. It's the felt that keeps the water out.

On a metal roof, it does everything.

Look for an "R" panal for roofing. 26 or 29 guage with galvalume for protection. You can't get the good stuff at the box stores, and for your house, you need quality. Start looking for a metal building supplier. They will sell you the metal roofing along with all the accesories you need.

Be sure to use quality screws and don't over tighten them. Just enough to start to squeeze the rubber gasket.

As for the bugs that are getting through your T&G ceiling, use clear silicone to seal it from the outside, NOT the side you can see. Walmart has the cheapest silicone I've priced anywhere, and it works really well.

 

[tomrscott]

Eddie,

Okay, you've added some interesting points and expanded my vocabulary with "perlins"!

With respect to the 2x6 insulation frame:
1) Pressure treated? Or should I try to go for Cedar? ($$$) I think I want something that is going to be unattractive to wood eaters.

2) Would you build this frame -- as I've been envisioning it -- in a fully blocked and enclosed frame, angled end cuts, maybe even screwed and glued (I'm willing to over build when it is my labor). The equivalent of a wall frame layed down on the roof, except that the sill plate and headers would be angled to the roof slope. I guess it would need to be done in three sections on each side of the ridge, for the three slope angles of the roof. I think I would be inclined to use some sort of nail clip with short exterior deck screws and a screw gun to attach the frame members to the ceiling boards?

3) Then it sounds like you are talking about putting perlins E/W on top of the 2x6 frame? With air gaps between each perlin? You actually said the existing ones would do, but they're directly on top of the ceiling boards, so that doesn't work, I need to build the insulation frame. That is where I would use the plywood sheathing to seal up the solid insulation chamber, since the sheet metal is not flat. It has corrugations to it that allow air flow and bugs to get into the insulation chamber. Also, the steel isn't really strong enough to walk on between cross boards. Inevitably you have to get up there for something and you end up deforming it. With some 1/2" plywood sheathing underneath it, you have something stiff enough to span the 24" or so between the insulation frame members. Also the winds will buffet the sheet metal viciously causing it to vibrate and try to come loose from their fasteners (I am at the very top of a 1000' ridge line with nothing to obstruct the wind for miles). With some 1/2" ply sheathing behind the metal, it can't flex in the wind. I understand that you could use perlins to back the steel and accomplish nearly the same thing, but since that creates air gaps, we're back to the discussion of whether it is better for the insulation frame to be closed or open. Also, it seems like plywood sheathing is just a bit more support to walk on and to resist wind-induced vibration, pretty easy to install, probably more dimensionally stable than boards, and allows me to completely seal up the insulation frame.

4) Clear silicone caulk from the top side was what I was planning for sealing the T&G ceiling boards. Lot of caulking, but I know the whole family will appreciate the effort. We'll learn to live without the "rustic charm" of wasps, flys, and box elder bugs dropping in unannounced whenever they feel like it. You can always count on it. when it has been cold and we either heat the house a bit extra, or the weather suddenly warms up, something living in the roof decides that river of warm air escaping past their nest must lead to someplace appealing. I've actually watched a wasp "coming out" after hibernation. The good news is they are usually still groggy for awhile and easy to kill, but that's small solace. No, the family won't miss what we give up by sealing the roof tighter. /forums/images/graemlins/grin.gif

5) As for fiberglass versus closed cell foam. I have seen soggy fiberglass from the dampness against a poorly sealed basement wall. You wouldn't think the glass fibers would be very hygroscopic, but take some fiberglass and soak it and then see how long it takes to dry out. Then do the same thing with a piece of closed cell foam. With our thick fog and damp air, I think the closed cell foam makes sense. That is also why I am very tempted to seal up the insulation frame completely.

I must say this discussion has been very helpful and I really appreciate everyone's contributions (even when we disagree). I will be sure to post some step by step pictures of this project when it actually comes together. Maybe that will be as helpful to someone else as this has been for me.

Thanks all! (and please continue if you have something else to add) /forums/images/graemlins/smirk.gif

 

[EddieWalker]

We're not comunicating. I'm gonna try and address you last email one step at a time.


</font><font color="blueclass=small">( With respect to the 2x6 insulation frame:
1) Pressure treated? Or should I try to go for Cedar? ($$$) I think I want something that is going to be unattractive to wood eaters.</font><font color="blueclass=small">(


Neither. Didn't you say there is alread a 2X6 frame on top of the cedar ceiling? That frame is already done. They are acting like rafters, even though you have 4X12 beams that are really doing that job. Your soffits and trim boards can be PT or cedar. Either will work fine.


</font><font color="blueclass=small">( 2) Would you build this frame -- as I've been envisioning it -- in a fully blocked and enclosed frame, angled end cuts, maybe even screwed and glued (I'm willing to over build when it is my labor). The equivalent of a wall frame layed down on the roof, except that the sill plate and headers would be angled to the roof slope. I guess it would need to be done in three sections on each side of the ridge, for the three slope angles of the roof. I think I would be inclined to use some sort of nail clip with short exterior deck screws and a screw gun to attach the frame members to the ceiling boards?</font><font color="blueclass=small">(


Your describing an aweful lot of work building something you don't need. The 4X12 beams are doing all the work holding up your roof. Anything else you put up there is just extra weight.


The beams are going across the span of the ceiling from wall to wall. On top of the beams rests the 2X6 T&G cedar that is your ceiling. On top of the T&G rests some 2X6's that are spaced apart. The gap inbetween this space is for your insulation. On top of these boards are your perlins. Currently they are 1X4's that has felt then your shingles.


Adding another layer of framing on top of what you already have is way beyond overkill. It's a total waste with no benifit. Even the added R value you might get is minimal as aposed to the extra weight you'll be adding to your beams.


</font><font color="blueclass=small">( 3) Then it sounds like you are talking about putting perlins E/W on top of the 2x6 frame?</font><font color="blueclass=small">(


No. you can use what's already there. If it's not broke, don't fix it.


</font><font color="blueclass=small">( With air gaps between each perlin? You actually said the existing ones would do, but they're directly on top of the ceiling boards, so that doesn't work, I need to build the insulation frame.</font><font color="blueclass=small">(


Again, are there 2X6 boards fastened on edge on top of your 2X6 T&G cedar ceiling. I'm hitting a mental block here. Either there is an existing cavity with framed above the cedar, or the existing roof is nailed directly to the cedar and the the only space is the 1X4 you mentioned earlier, which makes no sense.


</font><font color="blueclass=small">( That is where I would use the plywood sheathing to seal up the solid insulation chamber, since the sheet metal is not flat. It has corrugations to it that allow air flow and bugs to get into the insulation chamber. Also, the steel isn't really strong enough to walk on between cross boards. Inevitably you have to get up there for something and you end up deforming it. With some 1/2" plywood sheathing underneath it, you have something stiff enough to span the 24" or so between the insulation frame members. Also the winds will buffet the sheet metal viciously causing it to vibrate and try to come loose from their fasteners (I am at the very top of a 1000' ridge line with nothing to obstruct the wind for miles). With some 1/2" ply sheathing behind the metal, it can't flex in the wind. I understand that you could use perlins to back the steel and accomplish nearly the same thing, but since that creates air gaps, we're back to the discussion of whether it is better for the insulation frame to be closed or open. Also, it seems like plywood sheathing is just a bit more support to walk on and to resist wind-induced vibration, pretty easy to install, probably more dimensionally stable than boards, and allows me to completely seal up the insulation frame.</font><font color="blueclass=small">(



OK, here is where we're having our biggest problem. You are considering useing corrigated tin for your roof. This would be a HUGE mistake. Your right when you mention all the problems you will have with it. Even if you build it to the max, you will still have problems with it. DO NOT USE it!!!


You need to learn about R Panels. They are basically flat with ribs at the ends that overlap to seal out the water. There are little ridges that run the length of it for strength. This is the ONLY material you should consider to use if you want a metal roof on your house.


Go to www.muellerinc.com and click of metal roofing on the left hand side of the page. Again on the left side, click on panel types. Click on R Panel.


This is a local company that I buy from. It won't do you any good in Oregon, but it will show you what I'm talking about and give you a place to start your research.


</font><font color="blueclass=small">( 5) As for fiberglass versus closed cell foam. I have seen soggy fiberglass from the dampness against a poorly sealed basement wall.</font><font color="blueclass=small">(


You are comparing a basement wall with a ceiling. This isn't a good comparison. Compare it to the wall of a house that is properly sealed and not damp all the time. Compare it to a wall that isn't in direct contact with wet soil days on end and probably built without being properly sealed.


It's your call on what insulation you decide, but don't get too carried away with overdoing it. You can spend ten times the amount of time and money doing things that wont do any better job then what you actually need as oposed to what you want to add to it "just in case."


Did you ever know any kids when you were growing up that put 20 to 50 nails into a board to hold it to another when two would have done the job? Don't be that kid with your roof. Spend the money on some quality metal, not on overdoeing all the things that wont make a difference.

Eddie

 

[Jagmandave]

Tom,
My 2 cents.........
Investigate SIPS, they've been mentioned here a couple of times but not by name. You can have them made exactly to size, screw them down to the existing T&G after youve taken everything else off. That's your closed cell insulation, and your metal roof backing all in one. Then just add your metal sheathing over the top, be sure to flash everything properly, and you're home. You've got a solid surface you could walk on under the metal, you've got your R value, and it's all in one piece already cut to size. Fast, easy and it works.
They'll also engineer your dormers for you, and you can build them with SIPS, too.

 

[bugstruck]

Eddie, I have to agree and disagree. On the purlins with rigid foam insulation between the purlins and the metal roof directly on top. Bingo, we agree. That works as well as applying sheathing over the entire structure from a condensation standpoint. That is good advice on how to economically and sensibly meet the task at hand. You have not violated the open (trapped is the key word here ) air-space rule. So no condensation should occur. That rule applies to timber frame or stick frame construction. No difference worth mention as a condensation problem is achieve by similiar bad designs on either type of construction. However, bear in mind that with your solution you have no 30# felt over sheathing as a backup to minor leaks. Nearly any metal roof with penetrating fastners has or develops them over time as the fastners back out or the gaskets deteroiate. They are seldom enough to cause any major problems and the leaks are generally small and dry themselves out. However even a small leak becomes an issue if it has nearly direct (easy) access to the interior of the structure. Now if your talking properly installed true standing seam metal roofing.... No problems there as that system should be nearly impervious to leaks (no thru fastners).

Here is where we part. On the OSB versus plywood durability. I hear what you say but I gave you my observations over time. Is is far inferior to quality plywood in passing real world wet tests. You can probably dig up some ASTM or other 6 or 12 cycle wet test that say it passes. So does moisture resistant MDF pass a 6 cycle test. OSB is better at hanging togeather than moisture resistant MDF. Most people don't know such a product even exists. But OSB absolutely will not come close in wet cycle durability to quality fir plywood with exterior glue. Do the tank test. It's simple. You won't hardly recognize the OSB but you will the fir plywood. Also, OSB is heavier, harder on saw blades and your lungs. and generally has more deflection than decent (same thickness) plywood. So unless its used for wall sheathing or interior floor sheathing (I can barely tolerate it on interior floors) why use it? We are not talking the bones (framing) here but the skin (sheathing) of the structure. Both are important. Not to brag I have some experience on the sheating, but as I walked through the shop today I passed every type of sheating home depot has except pressure treated plywood and about 30 others they don't carry. Units (hacks) of them. Granted most are interior products, but not all. It's my old experience as a Carpenter and Superintendent that gives me the real world background on exterior sheathing and water. Your just going to have to trust me on this, or not. If I'm moving dirt and trees in incredible ways, I'm calling you! I'm pretty sure you have some amazing posts and knowledge on that. /forums/images/graemlins/shocked.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

Good posts though. I haven't spewed this much info. in a long time. /forums/images/graemlins/blush.gif /forums/images/graemlins/crazy.gif /forums/images/graemlins/smile.gif

 

[jinman]

Tom, I've been reading this thread with interest, because you are planning on doing almost the exact construction that I have on my roof. My house has no attic and is a loft ceiling (even in the closets). I'm not going to agree or disagree with the advice you have been given, but rather, I'm just going to show you how my roof was done. The first picture is of the inside of my house showing the 2x6 tongue and groove layed down over 4 x 10 beams on 4' centers.

 

[EddieWalker]

Chris,

I'm not disagreeing with you that plywood is better then OSB. There's no doubt of it's superior strength or durabilty, even CDX of the same size is better quality then OSB.

It's all we used to use in California, but now it's all gone to OSB. If it passes code there, then I'm comfortable with it in my own use.

You have a good point on the felt. It's cheap insurance and wont hurt anything. Getting it one hundred percent right when he has no experience workig with it might be un-realistic. Hopefully he'll have some help. For me, the hardest part is getting it all lined up.

 

[jinman]

This next picture shows the eaves and the ribs (purlins) on top, but from this angle it is deceiving. The ribs only extend a short way up the roof.