Truss Spacing and load question?

[City Farmer]

Thanks for the help everyone, I appreciate it.
In no specific order:
1) Foil backed insulation over purlins
2) new metal roof
3) metal ceiling with blown insulation
4) ridge vent
5) wall insulation
Can someone recommend a quality foil back insulation I can install over the purlins?

Eave venting might be a problem because whoever built it hardly anything for the overhang, there's only a few inches.

 

[RNeumann]

If eve vents will be an issue consider turtle backs when the roof is redone. Their is a science to venting- both size and locations so read up on that or have someone do those calcs.

Insulation is a whole other topic and your data isn't sufficient to weigh in.

The foil back insulation is something your local building supply will have. Telling you a brand is near useless as most building supplies only carry one brand. If you are after the foil backing- they also make roof sheathing that has it preinstalled. I personally haven't seen the science that supports the cost but I have seen it installed a few times when speced.

Snow loads aren't calced differently for metal vs comp shingle- that isn't an issue. You can google "psf snow loads by zip" or something similar for your own edification but remember these calcs were done when the building was built and changing roofing won't change the load- unless you decided to put a 6" concrete slab up there for a roof- that's sarcasm!

It's nice to see the concern and forethought with this project! It sounds like this will turn out nice!!

 

[jfh28]

if these are engineered trusses then odds are a building permit was required and taken out when it was constructed....that means you should be able to go down to your local building department and have them pull the permit jacket.......most building departments require a copy of the engineered truss drawings to be submitted as part of the permitting process........so you will be able to look at and maybe even get a copy of the truss design drawings which will have all the design criteria that was used to design them......in general trusses are designed based on span, spacing, dead loads (weight of the truss, sheathing, purlins, roofing material) and live loads (wind load, snow load).....in your case adding sheathing and shingling will only change the dead load.......typically around here trusses are designed using a dead load of 7 - 10 psf which if you think about it is quite a bit of weight and more then usually found in most construction......so if you can get a hold of the truss drawings you can bring them to a structural engineer who can quickly advise you on the suitability of what you want to do.....its a very simple calculation........they will also be able to tell you what thickness sheathing to use as it will depend on the span rating of the sheathing........the 3/12 roof pitch falls in the minimum slope for asphalt shingles and will require a double underlayment.....personally I like to use full coverage ice and water shield on low slope roofs as the underlayment......especially in areas where snow will be sitting on the roof.........keep in mind even metal roofing will have minimum slope requirements which will vary from manufacturer........Jack

 

[Sawyer Rob]

Generally, in Michigan you don't need a building permit "IF" the building was/is built for farm use.

SR

 

[KennyG]

My building was not set up for eave venting so I put a couple of wall vents in the end walls above the ceiling. Works fine.

 

[Billrog]

I see no value in foil for insulation under the metal spend the money wisely else ware. With metal roofing you have an approx.1" every 8" alone with gable vents and continuous ridge venting you'll have plenty of vent. If you calculate the space the ribs give you for venting it = 's more than you acquire with 2' aluminum sofeting.

 

[gzfrt9]

In Chesterfield your going to need a building permit. Because I would bet your not zoned Ag.
That pole barn will handle a singled roof. I have a very similar 30x40 here in Fair Haven, MI.
If you need a builder let me know. I have Mark Bonser in Marine City build all our stuff here on the farm

 

[TomSeller]

Generally, in Michigan you don't need a building permit "IF" the building was/is built for farm use.

SR

Now that is good regulation !!

 

[Tractor Seabee]

I vote for replacing the metal roof. A lot of metal roof and siding builders are using the plastic cellular insulation. High R, light, easy to handle and install, and provides an excellent vapor barrier to prevent condensation. Based on many tears in military construction and maintenance. We tried many insulation schemes for pre-engineered buildings and I was impressed with cellular the most. On an older building; unless you did or had it done originally you have no idea what the previous owner(s) did or had done. Play it safe unless you are an practicing engineer instead of an arm chair engineer.

Ron

 

[LD1]

With metal roofing you have an approx.1" every 8" alone with gable vents and continuous ridge venting you'll have plenty of vent. If you calculate the space the ribs give you for venting it = 's more than you acquire with 2' aluminum sofeting.

Was going to say the same thing.

Unless you use NON-vented closure strips across the eaves and non vented at the ridge.......you have plenty of ventilation. Most use nothing at the eave and vented closure at the ridge.