# Ceiling Joist Sizing and Distance



## ycanchu2 (Oct 21, 2011)

I am building an ICF home(insulated concrete forms) the kichen and living room area is 20ft wide.
The wall on one side will be 8 ft. and the other wall 10ft high. The roof will be a shed type roof with beams with one inch oak sheathing and insulation then metal roof. i am thinking about cutting 8 to 10 inch popular trees for the beams. The walls will be 6 inch concrete inside the forms. 
I was thinking 3' on center with the beams.....is this doable? or do I need go closer, bigger, or do laminated 2x's? This will be clearspan.
Thanks


----------



## Sebastian C (Jul 23, 2017)

If you're putting down sheathing you'll probably want to keep it some multiple of 8 feet. Either 2ft, 2ft 8in, or 4ft. I'd probably go every 4', with 8-10" round poles. (That is what you mean with the poplar, right?) Structurally that should be plenty strong to hold the roof up. But I live in the tropics with no snow loads or building codes to speak of. You may have to do something different.


----------



## Steve_S (Feb 25, 2015)

Verify that you can use Poplar for structural members in your region (see codes & grumpy inspector). I would certainly not use anything less than 8" or your get bouncy floor. 20' is a long span, any mid wall supports or ? You could overcome such if you wanted say Exposed Beams 8x8 or better running the span. As for your centres your likely better not to exceed 24" but if your "planking" the floor above it, rather than OSB / Plywood you can reduce any flex by using 1" T&G (thicker is better if self milling or if you have deep pockets).

I can tell you, that here, Poplar would not be accepted for structural use, so if you are permit constrained, verify that for your region. Imagine installing all that only to have the inspector order it replaced. I can hear the Blue Air being generated ! TBH, If you have good Oak / Maple, I'd use that for beams and have them exposed to show the beauty & strength of it.


----------



## Sebastian C (Jul 23, 2017)

Steve, excellent points, all of them. But I think we may be talking about "rafters" rather than "joists"...


----------



## ycanchu2 (Oct 21, 2011)

Yes I am talking rafters...the beams will be exposed. There is no buiding inspector only septic tank and electrical inspection.
I have a bandmill to saw any kind of lumber with several acres of timber. I was thinking poplar because i have several in the eight to ten inch size and straight. Oak I'm sure would be better but not as abundant in that size range and easy to get to, but i might could find enough. I just remembered that at about half of that 40 ft length i will have a utility room coming out 7 feet into the 20 ft space....so i will have a support wall at 14 ft on about half of those beams. So I will only have about 7 or 8 beams spanning the whole 20 ft. Also, what about putting braces about 3 ft from the wall to the beam on each side?
Thank you ...please all comment welcome!
Also I have some cherry, hickory, locust, pine, and other species...just finding ones straight enough is the issue. any recommendatios on what or what not to use?


----------



## The Paw (May 19, 2006)

If you have that wall jutting out anyway, I would carry a support beam across the open span to include all the rafters. A 14 foot span is way better than a 20 ft one.

I don't know how to convert the capacity of dimensional lumber to logs, but if you assume a 8 in poplar log is equivalent to a doubled up 2x8 of Doug fir, then 20 feet is a little too far. I would also keep the rafters at 24 inches on center. The 1 inch oak would probably let you use wider spacing, but it will also be much heavier. But we build for snow load up here, it might not be as much a concern for you.

I've never cut my own lumber, but I would be worried about getting it dry enough to avoid any shrinkage problems after assembly.


----------



## ycanchu2 (Oct 21, 2011)

The Paw said:


> *If you have that wall jutting out anyway, I would carry a support beam across the open span to include all the rafters. A 14 foot span is way better than a 20 ft one.*
> 
> I don't know how to convert the capacity of dimensional lumber to logs, but if you assume a 8 in poplar log is equivalent to a doubled up 2x8 of Doug fir, then 20 feet is a little too far. I would also keep the rafters at 24 inches on center. The 1 inch oak would probably let you use wider spacing, but it will also be much heavier. But we build for snow load up here, it might not be as much a concern for you.
> 
> I've never cut my own lumber, but I would be worried about getting it dry enough to avoid any shrinkage problems after assembly.


That is a good idea. i don't want a wall the whole way but I could make a support beam say 6x12 oak ?
On the dimensions of lumber...it looks like an 8 inch diameter log would be stronger than 2-2x8's. given an 8x8 log equals 64 square inches ...whereas 2-2x8's would equal 32...4x8.
I learned in a fencing class that a round post is superior for a brace post over a squared post. They said that a tree grows in rings like one straw over another one and on and on. But when you cut it like 4x4 or 6x6 you cut those " straws" and it allows it to warp more easily. Ironically, I had just done some fencing prior to the fencing school and had used some store bought treated 4x4's as braces....they are all starting to warp...


----------



## AmericanStand (Jul 29, 2014)

I thought the rule of thumb thumb on poplar beams was 1 inch of depth for everyone foot of span on 1 foot centers ?


----------



## mreynolds (Jan 1, 2015)

First, poplar (and cypress) is considered both hardwood and softwood. Meaning that they are at the high end of softwood and the low end of hardwood. You would not be incorrect in calling it either/or. 

That being said, if you used a softer wood like southern yellow pine you would need 9 1/2" thick beam to span that. This is taking into account for a 30 PSF snow load. Kentucky IBC code requires only 20 PSF snow load last I checked. Using poplar you would be ok with the ten inch ones and probably even the 8" ones with using poplar. I would go with the 10" ones though if it was my house. 

Yes, your round beams will be stronger than 2 2x's nailed together. Not as strong as an LVL or other engineered rafter. 

A metal roof weighs about 1/3 less than shingles. 

Disclaimer: I am an engineer. I am not *your* engineer. This is advice only with the info you have provided. Please refer to local AHJ for ordinance and local codes before proceeding. Your building inspector (even if you don't need a permit) is your best friend and wants to help you.


----------



## mreynolds (Jan 1, 2015)

I am not quite understanding your framing plan. Are you planning on running the beans perpendicular to the metal roof or parallel? If perpendicular you can go 4' if using 26 gauge but I wouldn't if using 29 gauge. 

If you are running them parallel you would need to run lathe to screw the metal into.


----------



## Sebastian C (Jul 23, 2017)

mreynolds said:


> I am not quite understanding your framing plan. Are you planning on running the beans perpendicular to the metal roof or parallel? If perpendicular you can go 4' if using 26 gauge but I wouldn't if using 29 gauge.
> 
> If you are running them parallel you would need to run lathe to screw the metal into.


If running them parallel, the sheathing can be screwed into if it's thick enough. But I'd put the rafters at 4' apart, and run 8' long sheet of plywood staggered like across them perpendicular. Then I'd put some 2*4 or whatever nailers perpendicular across the rafters also every 4'. That'd cover the seams like a batten and give you something solid to screw the roofing panels to. Added bonus: put insulation in the void space between the nailers/roofing/plywood. Idle speculation though, I don't really know anything, just make it up as we go along.


----------



## mreynolds (Jan 1, 2015)

I have never used poplar for framing but I did find this that was interesting:


Sebastian C said:


> If running them parallel, the sheathing can be screwed into if it's thick enough. But I'd put the rafters at 4' apart, and run 8' long sheet of plywood staggered like across them perpendicular. Then I'd put some 2*4 or whatever nailers perpendicular across the rafters also every 4'. That'd cover the seams like a batten and give you something solid to screw the roofing panels to. Added bonus: put insulation in the void space between the nailers/roofing/plywood. Idle speculation though, I don't really know anything, just make it up as we go along.


Agreed. It's hard to imagine what's in someone else's mind unless it's on paper. With plywood it wouldn't matter much of course but you would be surprised at the rafters with lathe and metal with nothing else I have seen in my day. I would hope further north they wouldn't do that much but here it's like "Hey, we don't need no stinking plywood." Makes the rain hitting it louder too.


----------



## Sebastian C (Jul 23, 2017)

mreynolds said:


> I have never used poplar for framing but I did find this that was interesting:
> 
> 
> Agreed. It's hard to imagine what's in someone else's mind unless it's on paper. With plywood it wouldn't matter much of course but you would be surprised at the rafters with lathe and metal with nothing else I have seen in my day. I would hope further north they wouldn't do that much but here it's like "Hey, we don't need no stinking plywood." Makes the rain hitting it louder too.


Oh, that's how I live here in the rainforest. Is noisy when it rains. Like shouting indoors in the same room loud. The worst part is the condensation rain inside every morning. Better make sure you don't leave your computer out. One day I'll install a ceiling, there's this pvc plastic beadboard siding type stuff that's the best stuff here. Not affected by leaks or condensation or bugs. One day...


----------



## AmericanStand (Jul 29, 2014)

I’ve done a bit of building with soft hardwood logs. ( poplar and alder)
First off in a 8 inch log the log won’t be as strong as two 2x8s. (22.5 Square inches) 
It will very likely be slightly stronger than one 2 x 8 but not as strong as 2 two by eights. 
The strength In the outer edge. 
Think of the shape of an I beam 
I think the formula for the strength is something like width of the flange times depth of thee beam
In a round pole your width at the deepest point is O!
To get the width of a 2 x 8 to have to come back up a little bit, to get the width of a 4 by you have to come up a lot. 
In other words you could probably cut a 2 inch beam 7 inches from the center of the log but you are going to have a hard time getting a beam 4 inches by 5. 
Cut the logs in half down the center with the flat sides up and down and nail back together and the log will be stronger in your application 
Turn one half end for end and it’s better yet. !


----------



## AmericanStand (Jul 29, 2014)

A note on cutting the logs for horizontal support. 
The Fence post thing about straws is almost correct. 
The rings are more like nesting funnels. 
In the short length of the fence post because it thinks much difference. But in a 20 foot beam it does. 
If you can get your beam on edge from one side of the center follow the surface of the log. 
But if you have to use the center of the log. Cut parallel to the center


----------



## AmericanStand (Jul 29, 2014)

My post above about the rule of the thumb was wrong. 
Rule of the thumb For floor joist is inch depth per foot of span on 16 inch centers. 

Ceilings rafters is much to same 1 inch of depth per foot of Span on 24 inch centers but you measure the beam depth vertically at the installed angle. 
So a 10 inch beam installed at a 45° angle would be treated as if it was 14 in depth.
Just my experience building with raw log in Alaska where the snow loads May be higher.


----------



## Fishindude (May 19, 2015)

If you know the exact species of wood and the grade / quality of it, there are books available at your local library that will provide roof joist size and spacing recommendations, if you know your dead and live loads. This is not something you want to just "wing" or guess at.


----------



## farmrbrown (Jun 25, 2012)

ycanchu2 said:


> I am building an ICF home(insulated concrete forms) the kichen and living room area is 20ft wide.
> The wall on one side will be 8 ft. and the other wall 10ft high. The roof will be a shed type roof with beams with one inch oak sheathing and insulation then metal roof. i am thinking about cutting 8 to 10 inch popular trees for the beams. The walls will be 6 inch concrete inside the forms.
> I was thinking 3' on center with the beams.....is this doable? or do I need go closer, bigger, or do laminated 2x's? This will be clearspan.
> Thanks


I'm building a shop out back with the same basic structure plan and dimensions - a mono slope roof with a 20ft. clear span. I've looked at lots of span tables and engineering tables and they all point you to something like 3 2x12's on 2ft. O.C. or something like 2x14 inch which you won't find on the racks anywhere.
Since I'm by myself lifting beams that size into place isn't going to be easy so I got a new plan - engineered beams, I'll try and put up a link.
Also if you ask in different forums, you'll get the standard answer "Hire an architect and engineer to do this, you can't possibly do it safely and correctly without a license and a degree."

The engineered beams basically are 2x4's with 12 inches of OSB in between, similar to what a steel I beam looks like.
And yes, those will take that span, but not on 3 ft. O.C.


----------



## ycanchu2 (Oct 21, 2011)

mreynolds said:


> I am not quite understanding your framing plan. Are you planning on running the beans perpendicular to the metal roof or parallel? If perpendicular you can go 4' if using 26 gauge but I wouldn't if using 29 gauge.
> 
> If you are running them parallel you would need to run lathe to screw the metal into.


Here is the floor plan I'm talking about. Imagine a rectangle shaped room 20 ft x 40 ft.....one of the 40ft walls will be 8ft high and the other 40 ft wall will be 10ft high. I'll be running beams from the 8ft wall to the 10ft wall across the 20 ft span. on top of those beams will be 1'' white oak nailed solid just like flooring...when you look up , that will be the ceiling. Above that will be 2x4's rough cut that will be perpendicular to the beams and metal on 24 '' centers with insulation in between....then metal roofing screwed to the 2x4's. So the metal will be parallel to the beams. I may do a variation of the last part to make a texas cool roof.
Maybe you have heard of that since being from Texas?


----------



## mreynolds (Jan 1, 2015)

ycanchu2 said:


> Here is the floor plan I'm talking about. Imagine a rectangle shaped room 20 ft x 40 ft.....one of the 40ft walls will be 8ft high and the other 40 ft wall will be 10ft high. I'll be running beams from the 8ft wall to the 10ft wall across the 20 ft span. on top of those beams will be 1'' white oak nailed solid just like flooring...when you look up , that will be the ceiling. Above that will be 2x4's rough cut that will be perpendicular to the beams and metal on 24 '' centers with insulation in between....then metal roofing screwed to the 2x4's. So the metal will be parallel to the beams. I may do a variation of the last part to make a texas cool roof.
> Maybe you have heard of that since being from Texas?


Sounds cool. I understand now. Will the white oak also be milled by you or from a yard? 

Here are a few suggestions. If you use logs you will have an issue with the tops being uneven so you'll have to figure out how to remedy that so your oak will lay flush. 

Maybe if it's not too late raise the other side to 12' to give you a better pitch. That way the snow load wont be as much and less chance of leaks when the snow melts.


----------



## mreynolds (Jan 1, 2015)

Here is a former project of mine. 

https://www.thebarnnac.com/gallery











These rafters are 3x8 and 28' long. They have been there for 7 years now and withstood 2 tornados and one really bad straight line windstorm. 










I designed, engineered, built and installed these trusses. It's next to the main house. They have been through the same storms. 

They are ten foot apart but the decking does not sag. I used engineered decking that works like hardwood floor. There are no splices over the trusses. All splices are away from the truss for added strength. I know that doesn't make sense (and it didn't to me either by the guy that engineered this decking) but it does really work. They have tongue and groove on all 4 sides and are glued all sides. The decking is basically 3 1x6's glued together.


----------



## Bearfootfarm (Jul 13, 2006)

I love those fans.


----------



## mreynolds (Jan 1, 2015)

Bearfootfarm said:


> I love those fans.


So you are a fan then? 

Yeah, I like them too.


----------



## ycanchu2 (Oct 21, 2011)

mreynolds said:


> Sounds cool. I understand now. Will the white oak also be milled by you or from a yard?
> 
> Here are a few suggestions. If you use logs you will have an issue with the tops being uneven so you'll have to figure out how to remedy that so your oak will lay flush.
> 
> Maybe if it's not too late raise the other side to 12' to give you a better pitch. That way the snow load wont be as much and less chance of leaks when the snow melts.


The white oak is already sawn and stacked and sticked and has been air drying about a year or longer.
Yes, I'm going to face one side of the logs either on the bandsaw or with a chainsaw using one of those alaskan mills that attaches to a chainsaw.....the real work will probably be debarking them.
The wall that I said would be 10ft high will actually be 10' 8'' high because the ICF forms will come out to that height using 8 of them 16'' tall. So that will give me a little more pitch.


----------



## melli (May 7, 2016)

ycanchu2 said:


> Here is the floor plan I'm talking about. Imagine a rectangle shaped room 20 ft x 40 ft.....one of the 40ft walls will be 8ft high and the other 40 ft wall will be 10ft high. I'll be running beams from the 8ft wall to the 10ft wall across the 20 ft span. on top of those beams will be 1'' white oak nailed solid just like flooring...when you look up , that will be the ceiling. Above that will be 2x4's rough cut that will be perpendicular to the beams and metal on 24 '' centers with insulation in between....then metal roofing screwed to the 2x4's. So the metal will be parallel to the beams. I may do a variation of the last part to make a texas cool roof.
> Maybe you have heard of that since being from Texas?


Sounds very similar to my home, albeit, 20x36 exterior dimensions. My walls were 10' to 14' (20" span). The 14' wall was 10' of ICF, then a 4' framed wall on top. ICF rule book specified no unsupported wall taller than 10'. Thing is, I am in seismic country, and everything is de-rated up here. I used 2x12 douglas fir for rafters @ 16" OC (clear span was about 18' because walls are about foot thick). I then strapped/purlins top of rafters with 2x4 @16" OC. Sheathing was 5/8" T&G ply (overkill). 
I should add I was aiming for passive house standards. Between rafters, I was able to get R50 in Roxul.


----------



## melli (May 7, 2016)

mreynolds said:


> Here is a former project of mine.
> 
> https://www.thebarnnac.com/gallery
> 
> ...


The hardware (gussets) you have there, is what is keeping that sucker up...lol
I do appreciate fine hardware.


----------



## mreynolds (Jan 1, 2015)

melli said:


> The hardware (gussets) you have there, is what is keeping that sucker up...lol
> I do appreciate fine hardware.


Yes, it is 3/8" steel that I had my local machine shop build. Then they were powder coated to make them pop. Stainless steel grade 5 bolts but that's why there are many of them. Can't get stainless in grade 8. 

This guy had lots of money and he wanted what he wanted. Then turned around and sold it a year later lol. I loved building that though.


----------



## AmericanStand (Jul 29, 2014)

I thought stainless “was” the grade ?


----------



## mreynolds (Jan 1, 2015)

AmericanStand said:


> I thought stainless “was” the grade ?


How so?


----------



## AmericanStand (Jul 29, 2014)

Stainless hardware has certain properties
Just like brass or copper
Steel on the other hand can be alloyed with various things to get different groupings of properties
One of those groupings is to alloyer with nickel to get stainless steel


----------



## mreynolds (Jan 1, 2015)

AmericanStand said:


> Stainless hardware has certain properties
> Just like brass or copper
> Steel on the other hand can be alloyed with various things to get different groupings of properties
> One of those groupings is to alloyer with nickel to get stainless steel


Ok, then let me rephrase. Stainless steel bolts are about equivalent to grade 5 steel give or take. Grade 5 is 125,000 psi. Grade 8 is 150,000 Psi. 

Is that better?


----------



## AmericanStand (Jul 29, 2014)

Sounds good to me. 
Sorry I was kinda picking nits. 
What I should of said is it’s a awesome building and the stainless seems like a good choice.


----------



## farmrbrown (Jun 25, 2012)

Occasionally a topic will come up that I can join in on the "picking". 
@mreynolds you were more right than wrong about stainless.
https://www.boltdepot.com/fastener-information/materials-and-grades/materials.aspx

They only mentioned a few of the different grades stainless comes in, I liked working with 303, but 416 and 440 were so tough that you could count on breaking drill bits, taps and other tools when working with it.


----------



## mreynolds (Jan 1, 2015)

AmericanStand said:


> Sounds good to me.
> Sorry I was kinda picking nits.
> What I should of said is it’s a awesome building and the stainless seems like a good choice.


Not at all. It sometimes is better to spell it out for someone who may not know.


----------



## mreynolds (Jan 1, 2015)

farmrbrown said:


> Occasionally a topic will come up that I can join in on the "picking".
> @mreynolds you were more right than wrong about stainless.
> https://www.boltdepot.com/fastener-information/materials-and-grades/materials.aspx
> 
> They only mentioned a few of the different grades stainless comes in, I liked working with 303, but 416 and 440 were so tough that you could count on breaking drill bits, taps and other tools when working with it.


Cant recall what these were but they were equivalent to grade 5. They were 1" bolts, I do remember that. I loved working on that job and had an offer to go to Arizona to build another smaller one. I didn't go though. Had other fish to fry.


----------



## farmgal (Nov 12, 2005)

Sounds like a salt box design. 

If this building will be heated you must put baffles inside the vaulted ceiling. Where cool outside air can channel through. Keeping that metal cold. Otherwise that insulation will sweat and rot your ceiling.


----------



## mreynolds (Jan 1, 2015)

farmgal said:


> Sounds like a salt box design.
> 
> If this building will be heated you must put baffles inside the vaulted ceiling. Where cool outside air can channel through. Keeping that metal cold. Otherwise that insulation will sweat and rot your ceiling.


Like a coke bottle. 

Glad you thought to bring this up.


----------



## ycanchu2 (Oct 21, 2011)

farmgal said:


> Sounds like a salt box design.
> 
> If this building will be heated you must put baffles inside the vaulted ceiling. Where cool outside air can channel through. Keeping that metal cold. Otherwise that insulation will sweat and rot your ceiling.


Are you talking inside the building or outside in the roof design. I am planning on doing the Texas cool roof which lets air channel up between the roof and insulation and vent out the top. its supposed to keep it cooler in the summer.


----------



## AmericanStand (Jul 29, 2014)

Alternately you can put spray foam insulation directly on the roofing t metal and that will keep it from sweating


----------



## ycanchu2 (Oct 21, 2011)

AmericanStand said:


> Alternately you can put spray foam insulation *directly on the mobile* and that will keep it from sweating


what is on the mobile?


----------



## AmericanStand (Jul 29, 2014)

ycanchu2 said:


> what is on the mobile?


It’s that auto correct again sorry about that


----------



## ycanchu2 (Oct 21, 2011)

AmericanStand said:


> Alternately you can put spray foam insulation directly on the roofing t metal and that will keep it from sweating


How would you get the foam directly on the metal after you screw the metal down? Fill the cavity afterward? Unless you put down styrofoam sheets under the metal.


----------



## AmericanStand (Jul 29, 2014)

I bolted my metal roof directly to my rafters. It wasn’t hard at all to spray the metal before I enclosed the space


----------



## AmericanStand (Jul 29, 2014)

What I did was Spray the space between a rafter and then press in sheets of foam insulation until the already sprayed in foam crawled up around the edges of it


----------



## AmericanStand (Jul 29, 2014)

The metal only touches my rafter for an inch and a half out of every 24. When you spray the foam in just that lets the foam go through the valleys as ridges of the metal sheet from side to side of that rafter. 
Then when you press this foam sheets into the remaining rafter space that presses a small amount of the spray foam under the metal and on top of the rafter the remaining unfilled space is very tiny and the amount of infiltration there does not lead to condensation.


----------



## AmericanStand (Jul 29, 2014)

To be clear the metal on my roof runs horizontally


----------



## mreynolds (Jan 1, 2015)

AmericanStand said:


> What I did was Spray the space between a rafter and then press in sheets of foam insulation until the already sprayed in foam crawled up around the edges of it


Did you use plywood and Ice and Water under the metal first? If not it is not acceptable with todays scientific standards. Often the spray foam will either cause or retain moisture between the insulation and the metal.


----------



## AmericanStand (Jul 29, 2014)

There is no space between the foam and the metal for any moisture to condense. The spray foam is adhered to the metal


----------



## mreynolds (Jan 1, 2015)

AmericanStand said:


> There is no space between the foam and the metal for any moisture to condense. The spray foam is adhered to the metal


I understand that.


----------



## mreynolds (Jan 1, 2015)

AmericanStand said:


> There is no space between the foam and the metal for any moisture to condense. The spray foam is adhered to the metal


Have you ever pulled a beer can out of a coozy? Was it wet or dry inside?


----------



## farmrbrown (Jun 25, 2012)

mreynolds said:


> Have you ever pulled a beer can out of a coozy? Was it wet or dry inside?


It's wet inside when I pull the tab, depending on how thirsty I am, it goes dry inside the can pretty quick.


----------



## AmericanStand (Jul 29, 2014)

Different foams. 
Attic spray foam is closed cell foam


----------



## mreynolds (Jan 1, 2015)

AmericanStand said:


> Different foams.
> Attic spray foam is closed cell foam


Physics are the same. 

You can believe whatever you want but many building scientist are saying it's not a good thing. Many roofs have rusted from the bottom up because of this.


----------



## AmericanStand (Jul 29, 2014)

Moisture doesn’t move through closed cell foam 
It is even used on Yachts for fairing .


----------



## Bearfootfarm (Jul 13, 2006)

> AmericanStand said: ↑
> There is no space between the foam and the metal for any moisture to condense. The spray foam is adhered to the metal


The fact you can't detect the space doesn't mean it's not there.


----------



## AmericanStand (Jul 29, 2014)

Bearfootfarm said:


> The fact you can't detect the space doesn't mean it's not there.


 No actually it does.


----------



## mreynolds (Jan 1, 2015)

AmericanStand said:


> Moisture doesn’t move through closed cell foam
> It is even used on Yachts for fairing .


I'll be sure and tell all those engineers they are wrong then. I'm sure they will understand and agree with you. May even change the new codes coming up and all that. Thank you for helping to straighten this mess out. 

You can argue with me all you want and it still wont change the minds of the ones making the change. I didn't make it. I myself have installed close cell foam under metal roofs because back then they told me it was fine to do so. I do know what close cell foam is as I was a energy contractor for decades. I was using it when everyone else was using open cell. All I am doing is posting the new science coming done the pipes. You don't have to listen at all and build however you want of course. Not my money.


----------



## melli (May 7, 2016)

AmericanStand said:


> Moisture doesn’t move through closed cell foam
> It is even used on Yachts for fairing .


https://www.buildingscience.com/documents/insights/bsi083-mea-culpa-roofs
https://www.buildingscience.com/documents/insights/bsi-063-over-roofing

I'd just be careful about detailing if doing a spray foam job under an unvented roof (whether to tin or under sheathing). 
Personally, I feel the risk of not doing a perfect job isn't worth it. I'd prefer a system where imperfections don't lead to disasters. If you don't get spray foam applied perfectly to the underside of an unvented roof, you risk an unseeable problem, that will fester.


----------



## mreynolds (Jan 1, 2015)

melli said:


> https://www.buildingscience.com/documents/insights/bsi083-mea-culpa-roofs
> https://www.buildingscience.com/documents/insights/bsi-063-over-roofing
> 
> I'd just be careful about detailing if doing a spray foam job under an unvented roof (whether to tin or under sheathing).
> Personally, I feel the risk of not doing a perfect job isn't worth it. I'd prefer a system where imperfections don't lead to disasters. If you don't get spray foam applied perfectly to the underside of an unvented roof, you risk an unseeable problem, that will fester.


Don't bother as he already knows the best way. And he will spew that wrong way to many people who will believe him and they will do it wrong too. 

I also used to help write energy codes (like your links author) from '89 to '95 also. I was perfectly correct on a few (so far anyway) but terribly wrong on many others. The right course of action is to correct your mistakes and try and perfect the code. When you make a mistake you have to own up to it. The problem is the old foggies. They tend to stick with the old ways just because they haven't been bit yet.


----------



## farmrbrown (Jun 25, 2012)

Y'all are still talking about the foam out of the can right?
I like a little, but if you tilt the glass when you pour it, it'll be just right, an inch or less.

I think an engineer taught me that once. At least she said she was, working her way thru school tending bar.


----------



## AmericanStand (Jul 29, 2014)

mreynolds said:


> Don't bother as he already knows the best way. And he will spew that wrong way to many people who will believe him and they will do it wrong too.
> 
> I also used to help write energy codes (like your links author) from '89 to '95 also. I was perfectly correct on a few (so far anyway) but terribly wrong on many others. The right course of action is to correct your mistakes and try and perfect the code. When you make a mistake you have to own up to it. The problem is the old foggies. They tend to stick with the old ways just because they haven't been bit yet.


 Lol right cause you know everything?
I’m sure you have tried my way and found the problems?
There is a company in Mattoon il that makes Roof panels from two sheets of tin with a foam core.
Go explain why that’s wrong to them. 
There’s a lot of information about foaming metal roofs on the Internet the key is it have no dead airspace, direct application and apply enough insulation that the zone where dew forms is inside of the insulation. 
There are a lot of people that have told me that horizontal metal won’t work. 
You the first one that’s told me direct application foam won’t work. 
But if you want to make arrangements I can show you both. 
Given though the application is only 15 years old at this point


----------



## AmericanStand (Jul 29, 2014)

You might want to take a look at this;

https://blog.mbci.com/spray-polyurethane-foam-insulation/


----------



## rambler (Jan 20, 2004)

Just the seat of my pants, no actual real knowledge, I’m really surprised if popular logs can support 20 foot span. I’d be real concerned, that is not a strong wood. I would think they would need closer spacing at the least.

Typically natural logs aren’t all that perfect straight, what is your plant to affix the oak ceiling to the imperfect logs? I guess I envision logs in a U shape, one side planed down to level. Making them weaker and shallower.

It appears you are in the research phase and asking good questions, that is a good thing.

Paul


----------



## ycanchu2 (Oct 21, 2011)

rambler said:


> Just the seat of my pants, no actual real knowledge, I’m really surprised if popular logs can support 20 foot span. I’d be real concerned, that is not a strong wood. I would think they would need closer spacing at the least.
> 
> Typically natural logs aren’t all that perfect straight, what is your plant to affix the oak ceiling to the imperfect logs? I guess I envision logs in a U shape, one side planed down to level. Making them weaker and shallower.
> 
> ...


i have settled on using 4x10x24 yellow pine. There will be a cross brace of the same size at the 13' mark supporting the beams. So i am really just spanning 13'


----------



## AmericanStand (Jul 29, 2014)

Now that sounds plausible.


----------

