distance between purlins

[Joseph Murray]

Building a 36X32 log home with a 12/10 pitch to the roof, simple roof with no valleys or dormers.
I plan on placing my white pine purlins 7 feet apart and wonder if that is to wide ? I also plan on running pine 2X6 tongue and groove between them. 1st log home and I just want to know if my plans sound reasonable. Purlins will be supported every 12 feet with king post trusses. I need to order my T&G and need to know lengths to avoid waste. Thanks, joe murray

[Greg Steckler]

Joe,
What are your snow, wind, and seismic loads? Do you intend to have any rafters above your T&G? What kind of insulation and will you need an air space?

Generally, with a 35# snow load, 2x6 pine won't span much past 3-4 feet without additional help. And if you have to use R-38 Batt insulation w/ air space you need at least 11.5 inches in room; therefore, you might as well go with 11-7/8" TJI's (or 2x12's) as rafters and reduce the pine to 1x6's.

If you go with rigid foam some counties want 2x as nailers 2' o.c. on edge then plywood or cdx, paper, then roofing. It really depends on your loads. What are they?

[Joseph Murray]

was planning on using 2X10 with r31 insulation which is 8 inches thick leaving about 1 1/2 inches of airspace.If I go with 1X6 pine I dont see any way to hide the ends, I guess I could butt them on the 2X10's. Building in Southern Ohio, having trouble finding someone who can give me info on snow loads. The County doesnt even inspect buildings, only inspection on my place will be for septic. I called the county engineer and he said, "we dont inspect roofs, only roads and bridges"
The 2X6 span of 7 feet wouldnt really be structual with the 2X10's on top ? Thanks for your help.

[MikeS]

Joe

I'm in northern MN, where code is 40 PSF for snow load. South from here, it gets to 30 PSF snow loading.

Typically for 2 x 6 structural decking, plan view spacing at 6' o/c for purlins is accepted. For loft decking, 4' o/c is what is done. This information comes from lumber tables for 2 x 6 structural decking, which is available at most builder supply lumber yards.

Your rafters, 2' o/c will eliminate the need for the 2" decking, structurally. However, if you are building your roof "from the inside out" it is often a good labor savings plan to use 2" decking, so you can walk on it. The other method is to frame your 2 x 10 rafters at 2' o/c over the purlins. Put 3/4" or 7/8" spacers on the purlins, between the purlins and the 2 x 10 rafters, to raise the 2 x 10's off the purlins. Finish your roof sheeting, shingling, and so forth first. Then come inside and insulate and nail your ceiling paneling on from the inside. The spacers on the purlins allow you to slip the ceiling boards under the purlins.

You need to be aware of and plan for your vapor barrier detail at each rafter, where it crosses purlins and the wall plate. A strip of plastic is typically laid under the 2 x 10 rafter, where it crosses the purlin, to make the vapor barrier continuous across the purlins.

Not doing this detail right makes for a lot of suction in the roof, resulting in a cold and drafty log home. It's the most critical roof insulating detail you should do right. I have 20 years of log home construction and GC experience to go by, and the mistakes of carpenters and owners to learn from.

[Tim Bullock]

2" X 6" decking maxes out at 6'0" o/c for most snow loads.........
Build on top.........waaaaaaaaaaaay easier.

[Bret]

Mike & Tim,
I can see how building up from the 2x6's could really speed things up. I also see how stuffing insulation & nailing 1x6's from scaffolding could be a PIA. (as Mike says)

My question is: Does the labor savings offset the additional wood costs? 2x6 material costs twice as much as 1x6. My interior ceiling cladding will be around $3000. Will I save at least $3000 in labor?

What about rain & snow? When building up, the weather has to be considered. Whatever gets insulated should get covered. Is sheathing & felt paper sufficient until the rain or snow stops?

If you build as Greg describes, rafters...sheathing then roof material you could at least finish the interior on rain or snow days.

Our home will be here the first of April and lots of rain is typical in Indiana for this time of year. I also need to order the wood especially if it is 2x6 instead of 1x6. My builder and I are discussing the best plan of attack. Any suggestions would be helpful.

[Tim Bullock]

Bret, You need shopping lessons from lisa..........LOL
We buy the 2" X 6" at pretty close to the same price as 1" x 6" so this is a no brainer for us........We also buy the 2" x 6" in 12' lengths only which eliminates waste and a lot of cutting.........
Installing the vapor barrier from below and getting it perfect would be one heck of job unless you preplanned and draped the purlins with some but then you gotta walk on it...........
The other advantage being that the 2" x 6" forms the overhang which is waaaaaay simpler. I would have to say that the 3000.00 would get eaten up pretty quickly with the 1" x 6"................
If you do use the 2" x 6"..........caulk the joint (t & g) where it crosses over from the inside to outside.........lots of air infiltration there.................good luck.

[Bret]

Tim,

It's hard to keep shoppin all the time. I don't know how these women do it. But if you or Lisa have a couple of leads on good kiln dried t&g I'll certainly check them out!

Thanks

[Tim Bullock]

Sorry guys, I buy it as a service for my clients........no markup.........works out pretty inexpensive. Look for kiln dried jack pine............