Pitch on roof, condensation from metal roofing

[Danaputnam]

I am building a 16x24 pole barn sugar house with wood and tank storage off the back. It will have a steam cupola in the center. I am boiling with a 30" by 8' evaporator.

I will be using steel roofing - any concerns about condensation and therefore do I need to put plywood under the roofing or can I simply attach to pearlings?

Also, what pitch have people used - I am currently planning 6/12 pitch but can still change.

Any input appreciated.

[tcross]

i would probably use plywood underneath, but it is not necessary! Probably use a little steeper pitch so the water runs off easier (like an 8/12)! the only concern with not using plywood would be, you'll have to strap the roof so you have something to attach the steel to! if that is the case, the water will run down your steel and hit the strapping and more then likely drip off of that onto you? at least I would imagine it would! if you use plywood, you may want to use treated plywood or paint it since the water will be on it and could rot it over time! if you go the strapping way, you could also run plastic panels on the under side so the water wouldn't drip off the steel! they make a few different products that would work... some look like steel panels but are a milkhouse fiberglass or plastic and some look like just sheet stock! my .02 anyways! hope it gives you a few ideas... and doesn't confuse you further!

[whalems]

There is a underlayment that the builders around here are using now on steel buildings to help combat condensation issues. It is similar to tyvec and goes over the perlins before you put down your steel. Don't know how it would work with an evaporator putting off that much steam though.

[upsmapleman]

I built my sugar house 19 years ago with steel roofing and just boards to fasten it to. works great with some dripping but not a lot. Some days are worse that others. went with steam hoods several years ago and this solved most of the problems of moisture. A couple of things to think about if you don't use steam hoods you may get drips back in the evaporator and what is in plywood especially treated. Also I put a 1 to 5 pitch on mine because sooner than later you will want to get on the roof to work with stacks, covers ect. The steeper it is esp. in winter it gets hairy. If you do not have steam hoods you may want to plan on them sometime down the road as it is my feelings from talking to inspectors with new regs that are coming that having pans covered will be a hot button. Just think about it, just by covering your pans you greatly reduce your chances of contamination by something falling from the roof.

[Scribner's Mountain Maple]

Dana,

tcross had the right idea with just strapping it. Why use plywood at all? Other than the fact the stuff is expensive and unnecessary, it is laced with chemicals. I wouldn't be putting plywood above my arch if I could help it, certainly if I thought it might get wet and drip into it. Especially PT plywood. They don't even want you burning plywood, so I wouldn't suggest using it.

The steeper the pitch, the more space you have inside for shelves, storage, etc. 8 or 9/12 would be my suggestion. 8 is a good number and just not steep enough so you can still walk on it while you work on it. At 9 and above, you need to be using a harness or ladder to be safe. Really you should always wear safety gear when working on the roof. Another benefit of the pitch is snow load, the steeper the pitch, the less chance of snow building up. With a 5 or 6 /12 pitch, you will be shoveling.

If your building is 16' wide, a 9/12 will give you 6 ' of rise at the center, the top of your ridge should be 6' above end wall height. This is a more traditional sugarhouse pitch too. Good luck. I just built a 24 by 30 pole barn w/ a 9/12 pitch, so if you have any other questions, fire away.

Ben

[Flat Rock Farmers]

Dana,

Our sugar house is 16' x 16' with, I believe a 10/12 pitch steel roof. We didn't use anything under our roofing just 2" x 4"s for strapping.
On some days you really can see the condensation on the steel but the drips are minimal. We've got a 2' x 8' evaporator a bit offset from
the center of our cupola and it seems to drip some from the cupola supports and cross members. It can be a bit annoying especially if you
get a drip down your collar on the back of the neck!
We only had a couple of days when it dripped noticeably but it's not too bad. I imagine a hood would remedy that but I don't see that in
our future too soon. For the cost of extra roofing material I don't know if it would be worth the extra expense especially if you're on a tight budget.

Jay

[Danaputnam]

Thank you all for the great advice, much appreciated.

[Shawn]

no plywood on ours and we joke each year who gets the first drip on them:cool:

[maple flats]

I also built my sugarhouse with spaced roof boards as purlins and the steel roofing screwed to that. The first year I had no hood and there was lots of dripping. I think they all landed on the back of my neck. The next year I made hoods and had almost no dripping. With each new evaporator or set of pans, hoods were a first priority. With my current set I get no dripping, the flues pan is total cover, and the syrup pan is full cover but raised about 16-18" above. Each has a 15" stack to pull the steam in. The only drips now come off the condensate gutters at the bottom of each hood, that channel the condensate out, but the drip a little from the sweat beads that form on their outer surface.

[markreid]

I have a 20'x30' steel buildings colorado (http://amfsteel.com/) which was built 2 years back. We faced condensation and mould problem after few weeks of its completion, then a steel roof professional advised to add insulation. We ended condensation problem after installing foam insulation.

[Mark-NH]

Put down the plywood or it will rain inside the sugar house. Notice how everyone who hadn't has added a steam hood. We skipped the plywood and fault the drips until we added plywood.

[bees1st]

Ah yes. But for the cost of the plywood , could you have a nice steam hood made ?

[sugarwoodacres]

Doesn't the condensation still collect on the plywood ?

[Thompson's Tree Farm]

I sheathed mine with one inch pine hemlock and poplar. No condensation! There is not the temperature differential with wood as there is with metal.

[lpakiz]

I used 1 inch boards on the rafters, then steel. Not one drip. The wood IS insulation of sorts, compared to steel.

[BreezyHill]

1" of wood is on R value of insulation. The wood is porous and the condensation is absorbed rather than beads up and falls. When the FDA regs come into affect the ceiling will need to be dust proof and washable.

Remember that the bugs in the evaporator wood like moist warm spots to thrive. Powder post beetles love moist warm wood to lay eggs in.

Ben

[sugarwoodacres]

Question for those who have put down plywood. Did you put tar paper down in between plywood and metal roofing ? And do you still use purlin 1x4 spacers to screw metal to ? Thanks for any help

[sugarwoodacres]

Just wondering if you built it yet, we just did a 7/12 pitch and im debating what to do on roof . QUOTE=Danaputnam;233536]I am building a 16x24 pole barn sugar house with wood and tank storage off the back. It will have a steam cupola in the center. I am boiling with a 30" by 8' evaporator.

I will be using steel roofing - any concerns about condensation and therefore do I need to put plywood under the roofing or can I simply attach to pearlings?

Also, what pitch have people used - I am currently planning 6/12 pitch but can still change.

Any input appreciated.[/QUOTE]

[WI Sugarpop]

Question for those who have put down plywood. Did you put tar paper down in between plywood and metal roofing ? And do you still use purlin 1x4 spacers to screw metal to ? Thanks for any help

I built mine with 7/12 pitch with cupola. I put plywood on the rafters with felt, then 2x4 purlins with 1 1/2" foam in between, then steel over that. Someone told me that I would have problems with moisture if it is heated but it is not heated, only when the evaporator is running but then the cupola is open.

[sugarwoodacres]

I built mine with 7/12 pitch with cupola. I put plywood on the rafters with felt, then 2x4 purlins with 1 1/2" foam in between, then steel over that. Someone told me that I would have problems with moisture if it is heated but it is not heated, only when the evaporator is running but then the cupola is open.
Thanks for help ful info . I think the steam will get out through cupola. I really don't want a steam hood . I also have a 7 pitch on roof

[Clamer33]

I run a roofing company and can tell you guys a few tips to avoid ruining any of your roof decks. The best way to avoid condensation is to have the moisture hit the vapour barrier first. We just built a brand new sugar house this year, with a 6/12 roof pitch. And prior to installing the strapping I vapour barriered the top of the roof truss. It is a little more work but you can support the trust from moving by tacking a few straps to the underside of the roof trust first. Then as apply vapour barrier and the roof straps on 16" or 24" you can line up the trust and knock off the lower straps. I would strongly advised not to install plywood. Plywood doesn't like moisture. Roof boards are a better option. However installing any of these first and the vapour barrier after, will create a barrier on top of the wood. Keep in mind the vapour barrier is a preventive measure to stop moisture from penetrating the roof from the outside of the building. And unless the product has what is called a "PERM" factor higher than 1 it will trap moisture from the inside as well. 15"lb felt paper will not allow moisture to pass either way. In our roofing business we use a product called Titanium UDL 50, it a commercial grade vapour barrier. It can breath a little from the inside. Anyways in closing if you apply the vapour barrier on top of the wood, the wood will act like a sponge and suck up the moisture. If it is dripping it will rot in time. And will need replacing in the future. I will try to post a few picture of our building.

1109111092110931109411095

[Clamer33]

1109611097

[sugarwoodacres]

1109611097
The clear panels are a great idea. Nice work

[Cedar Eater]

Thanks, Clamer33. In the interior picture, it looks like you put a vapor barrier on the underside of the ceiling joists and used furring strips to hold it on. What's up with that?

[Clamer33]

We put 6 mil poly up to keep the heat in because we poured the concrete on Jan 20 of this year. I think that night went to -25C. Then I decided to install a cedar T&G ceiling, because I knew the moisture wouldn't effect the cedar like it would pine etc. Also all of our roof truss are 44" centers. So the strapping is 24" centers. Just help support the ceiling materials better.