metal roof question

[Joseph Murray]

I was planning on using plywood under my metal roof. I was just quoted $25.29 a sheet and need 78 sheets.
Can anyone tell me about using 2x4 purlins to attach the roofing to instead of the plywood. It would be a considerable savings and I was told that is another way to install metal roofs. Can anyone give me any pros and cons for doing it with the 2x4s ?
Thanks, Joe

[Bob Wood]

2x4's at 18" on centre. It has the added advantage of allowing cross ventilation. I am presuming you are using sheet metal roofing not metal tiles.

bob

[blue eyed devil]

Joe
One thing about plywood is you can hardly beat it for rigidity.
I don't know as much about engineering as I would like to,but my way of thinking is a plywood roof creates a fairly ridgid roof diaphragm.
Might be a concern if your building in an area known for high winds. How much lateral support do you have going with a post/purlin log roof,the way it is now?
Also....
How are you going to deal with condensation if you don't isolate the metal?

[mfritch]

Another consideration is the gauge of the metal used in your selected product. I use a 24 gauge standing seam steel panel that is 12" wide. It would easily go over wood strapping. In fact, when going over a comp roof, the manufacturer recommends putting down 1x4s at about 16" o.c. so that the comp's pattern doesn't 'telegraph' through the metal. If you are running a 26 or 28 gauge roof or using a ribbed roofing with exposed fasteners you might be best of with full plywood sheathing. Personally, I would want to use 5/8 CDX for my sheathing. I try to get all of my clients to go with the best possible products on those items that can't be upgraded. Don't scrimp on foundation, logwork, doors and windows or your roof system. I would rather settle for less square footage or live without some of the flashier things for a while and see that the structure is done well. A proper roof system is the cheapest, one-time insurance policy that you will ever buy for your home. It will cost you more in the long-run than it will save you in the short-term. Blue is correct on the issues of ventilation. If you give a better description of your whole roof structure, we could give you a more complete answer.

[Joseph Murray]

Here's the roof basics. 2 interior trusses with posts on the gable walls. Footprint is 37X33. With overhangs, 6 foot on 1 end, 4 foot on the other and 3 feet on both sides. Next comes 2x6 T&G, vapor barrier then manufactured floor joists. R-31 insulation, roof deck and sheet steel roofing.Full length ridge vent. I'm leaning back to solid surface, osb or plywood. I like the idea of having tar paper over the deck to give me a little time before I have to get the metal roofing down.
I have used 12 inch concrete block, concrete filled and sprayed with a rubberized coating. Anderson windows and doors. Havent skimped on anything yet, not going to start with the roof.

[Tim Bullock]

Joseph, You may want to consider using heavy tarpaper 50# over the tongue and groove pine as you go........to avoid water stains.
The vapour barrier is slippier than heck, I would precut all of the rafters and install the vapour barrier just beforehand........

[mfritch]

Joseph, you didn't mention log rafters or purlins. What does the 2x6 T&G bear on? I agree with Tim on protecting the roof decking, but you might want to check out Tri-Flex 30 at www.flexia.com It is way better than felt paper for this purpose.

[blue eyed devil]

Sounds like a strong roof to me Joe!
How did the I-joist compare in price to 2"x12"s??

[Joseph Murray]

Dont know how I left it out but I am using Purlins on 6 foot centers. Is the heavy felt tar paper over T&G just to make the surface less slippery. Dont I want to have the tar paper over the plywood or osb ? Am a little concerned with working on a roof with a 10/12 pitch. Ladder Jacks ? Any other options ? If I use ladder jacks I'll have all those extra holes in my vapor barrier. Will be picking up a couple of safety harnesses and ropes before I start the roof. With a crane and 5-6 workers I am hoping to have the shell and roof up in 5 days(at least to the point of a tar paper covering over the osb) Will have all the elec. runs done on disassembly. Does it sound do-able ?
Blue, never got prices on 2X12s. Have done so much of the work by myself it is just easier to us manufactured joists with 1 or 2 people doing the work. A lot easier to get a straight and flat roof with the I-Joists.

[Bob Wood]

Vapour Barrier goes on top of the T&G, on the warm side of the Insulation. Are you going to strap your Ridge, Purlins, and Pitch logs with 1x4?

Bob

[Joseph Murray]

Bob, not sure what your asking. My 2X6 T&G will be going vertically connecting the ridge log, 3 purlins and cap log together.
I know where to put the vapor barrier, but Tim suggested that I put felt down on top of the T&G and I wasn't sure why. He mentioned to avoid water stains but if the weather cooperates I hope to have all that done in 2 days with tar paper over the osb.

[Tim Bullock]

Joseph, Felt paper is not a vapor barrier........it is temporary waterproofing for the tongue and groove. Optimism is a wonderful thing.............Just when you think that it wouldn't dare rain....it does.

[Tim Bullock]

Joseph, One other little thing.......it can sometimes be slow going installing the T & G vertically especially in the longer lengths.

[Joseph Murray]

Thanks Tim, I should plan on rain, with my track record. Last 2 winters and springs were coldest and wettest in last 70-80 years. It wont get back to normal until I have my log home dried in.
What are my options for the top of my roof joists on 24 inch centers(MFG). Prices between plywood and osb vary by alot. Should it be T&G and how thick?

[Bob Wood]

Joseph,

To me 2x6 T&G seems a bit of overkill. We usually use 1x6 T&G, normally horizontal. The strapping is what the Roof Joists sit on and the T&G is done after. You could do the same with 2x4 strapping and then fit your vertical T&G after you have the roof on and sealed.

[Tim Bullock]

Bob, That is another way of doing it but I am too old to be nailing t&g upside down.......LOL........Besides there is not too much difference in price between the two. Joseph, whatever you choose, Do NOT use t&g........As a matter of fact, you should be leaving a slight gap between each sheet........a nail thickness. I do like OSB and the code here does accept 5/8" for 24" o/c........I would go with 3/4"........

[Bob Wood]

Tim,

If Joseph were to strap the logs and put his ceiling finish in vertically would he even have to nail it. Also when you say do not use T&G you are reffering to the Roof Sheathing aren't you.

I believe that a TJI Roof Joist system with structural blocking at the Ridge and Pitch logs and then strapped with 2x4 @ 18"(better spacing for the knees) will be more than rigid enough.

Bob

[blue eyed devil]

If you do it the way Bob Wood says he normally does things,you won't have to worry about slipping on vapour barrier or roof jacks tearing the heck out of it.
The strapping sure makes it alot easier to stay up on that 10/12 pitch too.
If you ferr our the tops of of the purlins and plates,run a 2' foot wide piece of six mil under all the straps for continuous vapour barrier.
You said r-31 insulation ,what type??
I also think it might be easier to get all your pots and the rest of the electrical done after the roof is dried-in

[Tim Bullock]

Joseph, Unless you did already buy the 2" X 6", I am going to have to go with Bob and blue on this one.........We do not do it that way...........but it will give you a faster close in which is the objective???? It will take you longer overall but you are doing it yourself so may not be an issue........

[Joseph Murray]

At this point I will stick with my original plan. I think I will get an easier and better seal with the vapor barrier working from the top up. Dont want be putting fiberglass insulation up over my head. With 4 herneated disks, top 2 and bottom 2 it is difficult for me to work over my head for long periods of time an bending backwards is no good for my back. I see advantages to the way Bob does it, but to me the way I have planned I think is best in my case. Definetly more than one way to skin a cat. Thanks one and all. Joe

[Fred]

Hi all
Fairly new to this board. In the early plannning stages of a log home for 2005-2006. Have been following this thread & absorbing some good info. I can see the advantages of putting down the t&g & insulation before sealing up the roof, but the one big advantage I can see in doing the t&g afterwards is being able to do all the electirical after seal up & still being able to have the inspector see it. Blue touched on this subject. I hate to work overhad as much as the next guy but I think this would be the determining factor for me. Any thoughts? I am a designer by trade & have a solid model coming along nicely & I expect to spend the next year or so kicking around a design & anaylizing models, so I will be lurking around here asking questions from time to time

Thanks
Fred

[Tim Bullock]

Fred, Thanks for joining in and welcome. I always like to "bite off" bits of a project without pressure from the next phase. We lay the 2" X 6" t&g and securely cover with tarpaper.....the roof is essentially closed in and I or anyone else can takes days, weeks or even months to contemplate the next phase........vapor barrier/rafters/wiring/insulation and sheathing. We can "wait" for good weather too!!! That is faster than covering purlins with vapor barrier,installing rafters and then sheathing and then tarpaper (if no time to install final roofing material). The other aspect here being that "IF" the t&g is installed horizontally......it provides all of the finish soffit work at the gables........If installed vertically, there are still some lookouts to consider at the gables to protect the log ends but a lot less than doing it upside down. I have been on sites where installing the soffit material can be on a 45 degree slope and 40 feet in the air.........what do you think of installing the t&g soffits upside down now!!!!!!!!!

[blue eyed devil]

Tim
Chester (from "The finishing Touch") came by today.He was telling me about that job or one similar,not even any place to set a ladder !!

[mfritch]

All of this talk about doing things over one's head is making me lose what little balance I had left. The entire conversation brings us back to the point that doing a log rafter system with 2x6 T&G is still about the fastest and least expensive way to do the roof. Yes, rigid foam insulation is expensive, but if you don't like that, consider a spray on urethane foam insulation. We did that on a house years ago and it was one of the sweetest jobs I've ever seen. You put down the decking, the sleepers and spray away. One light covering and you're sealed and waterproofed. You can go back and install the sheathing later if need be. The thing I hate about doing 2x12 or TJI rafters is all of the dangerous, time consuming, expensive finish work in the gables and eaves. When our 2x6 T&G is down...we're done outside and it looks great. We never look back. I've done three houses in the last 21 years that used 2x12's or TJI's and all three were far more expensive than using 2x6 T&G and rigid foam over log rafters. Yes, the log work is more expensive, but you save money on the back end of the project and the house looks amazing with a good rafter roof system. Not a bad deal. Better looking, easier and cheaper to do and it improves your appraised value. It's not hard for me to decide.

[Tim Bullock]

WOW, Mark we agree.....LOL. Always drives me crazy when people look at one little part of a project.....without thinking through the consequences of their actions.......Let's just get the roof on....worry about soffits and trim later..LOL. One unamed log building comapny shipped a house......it was a great price......I couldn't even come close. However, It did have a nice post/purlin roof system but the cost of slabbing the ridges and purlins was not included or even mentioned. Imagine, 30' in the air trying to snap chalk lines and then having to cut it in position.........I bet that cost a few bucks......likely cheaper to call the crane back and take it down and slab it.

[Bob Wood]

Tim,

I can understand putting down the liner first. But it seems that it will only work on a square roof where the pitch logs, purlins, and ridge beam extend right to the facia. What happens to the ends of those logs that are exposed to the elements? What if the client want a prowed roof line, or a stepped roof line?

Bob

[Fred]

Thanks Tim, sealing the outside of the T&G and having the electircal open for rough in inspection from the top sounds good to me, code here says it has to be open for inspection at rough in.

Mark, as of Monday I sold the house I have been living in for over 20 years & it had the exact same roof you describe only with rough sawn beams instead of logs. I remember building it, & you are exactly right about it being easy & fast. Allot of what I am seeing out there now has the rafters & was wondering if the method used on my place was maybe outdated, but I guess not. Any tips for running electrical using the method Mark describes above. The house I just sold didn't have any electrical in the cathedral ceiling, which I would have liked to have , new plan would have lights & ceiling fans.

Thanks
Fred

[Tim Bullock]

Bob, It works on all roofs but you will have to build lookouts to accomodate the soffits that will cover the log ends but a few boards upside down is not the same as doing an 8' overhang upside down.
Fred, Simply do the wiring on top of the roof and through the sleepers which will have to be protected from nail penetrations.
Chester was there!!!!!!!!! lol

[mfritch]

I find that it isn't that tough to call for an inspection the night before you start wiring. We wait until all the sleepers are on and we have all the electrical laid out with the holes cut in for the fixtures. We then start laying the wires without covering them up. When the inspector gets there they can see what you're up to and I have yet to have an inspector not like the quality of the work done. Sometimes we have the electrician on the job and sometimes it is the homeowner who is the responsible party. We've had great luck over the years doing this with the log rafter, 2x6 T&G, rigid foam and 5/8" CDX. The wiring goes fast if you've done your planning before you get to that point.

Another thing that can save a lot of time is the idea of using the Leviton X-10 wiring system and fans that have remote controls. This allows you to run a loop of hot wire from fixture to fixture and then the switching is done electronically right in the box where the fixture is installed. There is no need to run individually switched leads to each light. Time is money here and you can move very quickly with these systems.


P.S. Tim, I think we agree on more that roof systems. Somehow I don't see that you are going to change citizenship, move to the states and vote for G.W.

[Tim Bullock]

Mark, Isn't McGovern still in the running???

[Greg Steckler]

25 years ago, when I built my pump house, I used 2" rigid foam above 2x6 T&G for a small amount of insulation. I have some of those original pieces around the well casing and they are visiable today. I appears to me that they are deteriorating somewhat. I have heard rumors that rigid foam looses its insulating properties over time and there is an anoying "chewing" sound coming from the ceiling to boot. Anybody cast their confirmation or not?:confused:

[Tim Bullock]

Greg, Foam, Foam everywhere and not an R-Value to be found.........Actually, Most of my knowledge is old so going a bit from memory here.......The "good" foam (not eps) does outgas which reduces the R-Value somewhat and most foam manufacturers will give you the "aged" values which are not much lower.....It stabilizes and it is still good.......Now for the bad news........Carpenter Ants "love" the stuff and once they set up home and invite all of their friends and relatives over.........they are very difficult to get rid of........If it is in a roof, Good pest control people will go over the whole inside of the roof with a stethoscope and find them/drill/kill as they do make noise.....Some of the panel guys are aware of the problem and introduce nasty stuff in the foam to keep the "Aunties" away. My "aged' memory here......with few grey cells left!!!!

[dr.]

I've heard the aged value also referred to as "thermal drift".

I keep the camper parked down at the sawmill while at home. It makes a warm breakroom with hot coffee. On more than one occasion I've sawed into an ant home. Nothing bites like an ant coming off a sawblade...although an oldtime neighbor told me of sawing into a bee tree.

At any rate the homeless ants migrated into the blueboard, extruded polystyrene (XPS), in the camper. From my understanding they nest there, their respiration condenses on the walls and forms pools from which they drink. The adjoining wood was dampened and provided food, so they were self sufficient.

The ants did not get into the expanded polystyrene (EPS), white beadboard, although due to a leak it was thoroughly saturated with moisture.

My understanding is that polyisocyanurate has the least thermal drift, but is very toxic in a fire?

You pays your money...

[blue eyed devil]

Rebuilding those campers are fun are'nt they?
I'd rather burn it and start over before I ever do another one!

Cool Fact:
I was reading up on insects that devour dry wood like the Death Watch beetle.They don't need a seperate water source to survive.As each wood cell is broken down in thier stomach,a water molecule is produced.

[mfritch]

Tim, Regarding McGovern (and maybe for G.W., too), I think we need to establish the correct preposition to be used with the word 'running.' Is it running 'from', running 'against,' running 'to,' or running 'for.'

[Tim Bullock]

Mark, I surely do hope that you do not "run" from the bar bill......LOL..........Politics are likely for another forum although I do spend time reading here http://www.smirkingchimp.com/........The world, she is a changin'.........and not necessarily for the good.