Hello all,

yes, I meant roof, not foof....

I'm working out the design of my addition which is based on a 32x40 barn I reclaimed and relocated to my property for reassembly.

The roof details are: pitch=8/12, rafters = 2x5 @ 24" o.c., major purlins (6x6") at mid rafter span, no ridge beam.

My dilema is how to meet code on the roofing insulation, achieve the look I am after and afford it. Western MA code says I need R37 minumum in my roof.

I wish to keep a vaulted ceilings with all the original barn roof structure exposed. I wish to add whatever insulation I need on top of my first layer of roof sheathing so that my roof sheathing, rafters and purlins will remain exposed inside the house.

The two most obvious choices I have come up with are Rigid foam panels (R=7/inch) and fiberglass bats (R3.4/inch) This means I would need 6 inches of rigid foam to meet code or 13 inches of fiberglass to meet code.

Each requires building a second roof structure to secure the insulation into and for attaching the finish roofing too. The rigid foam approach is extremely expensive ($3/ft^2) While the fiberglass approach is a mere .90/lineal foot, it means building up 15" deep cavities over the original roof to fit it in (with air gap). This poses the issue of dealing with how to make a 20" tall facia look unobtrusive.

do any of you have another approach that is cost effective and feasible? Do standard SIP's really meet R-37? How thick are they for roof applications?

thanks,

Shaun

First I’ll thank you for rescueing a historic frame…

You don’t mention the R value for EPS, my preferred core for SIP’s. This is perhaps just as well, in that for R-37 the buns would need be of a thickness which would be proportionally unpleasant, seem out of scale and unappealing to the eye.

But yes, a urethane core panel is to be had and would work, though the price of panels is in a hyper climb at the moment, due to the current volatility in the OSB market.

Your greater issue is that your roof sounds as if it is far too underbuilt to carry such a system and the snow loads your area sees ( I spent a winter hewing timber a town or two over and know your in that Berkshire snow belt ) I don’t have the GSL’s for your area at my fingertips, but don’t think I’m far off in guessing your in the 90 – 100 lb range.

Another guess, you may have to upsize your rafters and purlin plate.

Bear in mind this frame has never carried more than board sheathing and perhaps several layers of roofing as a dead load and the snow loads that fell on it in the past, you are about to ask much more of it.

You need to consult with someone who has done barn / home conversions in your area, or perhaps a structural engineer who knows timber.

Thanks for your reply, Will. I believe the R value of EPS is 7/inch, which is where I came up with the 6 inches thickness required to meet code.

What is the R-value of the SIP's you're using and have you used them successfully in open rafter apps. in this region?

You make good points regarding the loading of my new roof. Believe it or not though, our live load requirement is only 40psf here.

I ran the calculations based on my current roof structure with a dead load of 10psf (5.5psf for original sheathing rafters and metal roofing, then generously guestimating the other 4.5psf for newly added insulation and structure). The math says the current structure has what it takes.

Additionally, I am beefing up the strength of structures tying duties by adding a second floor to this barn which will be supported by two new 7x11 anchor beams added into the two center bents.

This barn was already retrofitted with a second floor before i took it down. While it provided me with 1300 ft^2 of nice plywood and several dozen 2x8 joists, it was not a quality add-in. My anchor beams will be properly joined into the posts and made a natural part of the bents before they go up.

So, while I'm confident with my loading requirements, I'm not so fluent in my knowledge of insulation.

Has anyone else in this region done something similar?

Thanks,

Shaun

Great topic, first of all I'd like to point out that loading in the Berkshires IS an issue, there was a lot more than 40psf of snow there this winter, and a lot of collapsed roofs all over New England. NH has recently changed there GSF map to make allowances for elevation, while I don't believe that its 90-100 anywhere in Mass (but I might just be an arrogant Vermontster), I'm sure its more than 40, regardless of what the code says, which raises another topic, perhaps in a new post.... However safety factors, redundancy and the like usually save us. Nevertheless, the 2x6's make it even if snow load is 50#, and presuming they are actual dimension not nominal then I think they'd be good to 65 or more. However, even using 40# snow loads, those 6x6 purlins can't even make it at an 8' span and I suspect they're going 10ft at least? The old barn most likely had a metal roof and the snow would melt or slide off quickly without insulation. When insulated its just gonna hang around.

Regarding the insulation, EPS is only about r-4.8 per inch, with urethane just over 7. For example a 5-1/2" urethane panel is R-32, when you add interior finish, roofing, and a couple other minor allowances you are really close to 37. But more importantly if this entire frame is wrapped in panels and tighyly foamed you can approach the energy analysis from a whole house model. As I understand it, you can use lower R-values if you demonstrate the superior "tightness" of a panel home. Your panel manufacturer should be willing to help you with this, its in their best interests after all. Since you have strong ties (hopefully very close to the plate and well connected for tension) then I would suggest stiffening those Purlins by increasing size, decreasing span, or adding something...steel perhaps?.... its a pretty good stuff on price/performance ration! Granted its not traditional but if they'd had it they would have used it. After all they weren't trying to build historic buildings, they just wanted them to stop falling down....but i digress....

I have a number of houses in Mass. with 4 1/2" urethane panels all around that passed code. So don't fret that part, but do fret the loading issues! Good luck!

Thanks Paul, I agree, this is turning into a great topic. I am an Engineer, but new to designing houses. I see your point re: real life loading vs, code loading. My 2x5's are full dimension hemlock. I do have the option of upgrading to 3x5 chestnut and oak rafters (from yet another salvaged barn I have), which I may do in light of the fact that they will be exposed and the loading issue.

This won't solve the problem of my 6x6 purlins perhaps being to slight. I suppose I should revisit that part of the structure since both you and Will keyed on it. My purlins span about 12 feet between posts, but only 7 feet between braces. The purlins run 40 feet with a bladed scarf joint dead center, mid span between the two middle bents which did show sag as it had no support. My first impression of the location of this scarf joint was that it was poorly placed. It seems it should have been placed closer to a post....

A steel plate on the back side or perhaps a length of 2x2 steel angle along the back bottom corner, overlapping he scarf joint, where not seem may be a good idea. Or I could upgrade to 7x7 purlins (which I have) and omit the scarf joints by either using a full 40'er or using 3 pieces to span between each bent. Oh, the options......

I did run the REScheck Mass Engery Code program with both R37 and R26.8 (Atlas Nail Base ACFOAM Vent-R) entered for roofing insulation and it passed both ways so I simply need to approach the building inspector and see if this is acceptible.

I am not using SIP's for the walls, but studding and using fiberglass bats.

Thanks for the info and advice guys. I do appreciate and value it.

Shaun