I thought I knew…. evidently not….
Hello. After 25 plus years in the trades, tons of reading on the trades, and a fair amount of mistakes, I thought a floor system I put together was done properly. That is until some fancy pants union carpenter told me I was a hack. Could it be? Tell me it ain’t so!
Here’s the situation. A deck converted to a sunroom. The bottom of the joists are 30″ above the ground or more and they are 2″ x 10″. The deck was enclosed with a wood structure that had lots of windows. In fact about 30% of all surfaces exposed to outside air are windows with an R value of about 3.2.
The rest has batt insulation ranging from R-13 in the walls to R-23 in the floor and ceiling. The batts in the floor are held in with wires so the kraft facing is toward the heated space. The bottom of the joists are covered with 1/2 CDX OSB with tightly butted joints. Additionally, an underlayment of 1/2″ CDX OSB was affixed to the 2x decking for carpeting.
The union guy says I need another vapor barrier on the bottom of this sunroom – over the plywood. Keep in mind, there is no exposure to the elements underneath. There is a vented apron surrounding the deck and site drainage is good.
So, I can’t find anything in my code books here in North Carolina that tells me this is required. The construction official crawled under there to inspect my wire stays and passed the entire job. Additionally, with the amount of R3.2 in this room, a wind barrier on the bottom might boost the efficiency of the floor, but why bother with all that thermal convection through the glass.
Am I missing something? I’ve built 10 of these over the years the same way and this is how we did it.
Replies
Don't feel bad, you only believed him because he charges more, dresses better than you and has a newer shiner truck than you.
You can start a lot of fights over venting, and air barriers, esp in situations like this. change one of the variables and you might need to change another one. Sometimes less is more when it comes to VB.
IMO, your osb has all the air barrier you need there.
But hey, I might be a hack too.
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
Hacks Of America Unite!AitchKay
new union?
Hmmm... I think I like it.AitchKay
I'm in. I'll be treasurer.
FWIW... can't say I'd have done it any differently.
Exactly as I'd have done, too.
I like this idea of a "Hackers Union". If they get it started, I'm in! =)
~ Ted W ~
Cheap Tools! - MyToolbox.net
Meet me at House & Builder!
I like this idea of a "Hackers Union"
My forum name is proof that I have been chief "Hacker" for years. I need to know how much the graft..er, dues payments I can charge before allowing you guys in.
;-)A La Carte Government funding... the real democracy.
union guy is wrong. the vapor barrier is in the right place and you do not need to have another on the outside of the floor bays. in fact that would trap moisture in the bays and cause rot and mold
union guy is just used to building things that are not designed to last. I'm sure he's a democrat also so you know he's full of BS
if the customers push the issue throw a coat of latex paint under there.
done.
... use white to reflect any solar gain ... that'll confuse the union guy!
mention something about global warming.
Jeff
Buck Construction
Artistry In Carpentry
Pittsburgh Pa
Did you say union guy or onion guy. Makes a world of difference ya know even though they're cut from the same cloth.
Once you're an onion in the union , you know everything that can be known,
And it takes hacks like us to know the rest.
I would definitely NOT put a vapor barrier under the plywood. It would be a good idea to install an air barrier like taped housewrap, or even simpler just caulk the plywood joints.
In our local I believe r 36 is called out.
I've done a few piered addittions where we did r 30 fg with 2'' pink styrofaom with taped joints and perimeters with strapping and vinyl bead material over.
I'm not so sure that the op's solution was the best, but I'm not informed enough nor willing to argue it.
"When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking." — Sherlock Holmes, 1896
The issue isn't so much the R-value as the air sealing. I'm a little sensitive to air sealing because this afternoon I had a two-hour meeting with clients we just did a big addition for, to go over their energy audit with infared camera. Even though we spray-foamed it, there were still LOTS of areas with air leaks. As we all know, fiberglass does not do well with air washing over or through it. That's why I suggested caulking or housewrapping the underside. The layers of taped foam you installed doubled as air sealing.
Howdy. Some clarification on R values... this basically follow the laws of thermodynamics which transends building departments. But all that aside, because it was a 3 season sunroom, the R30 minimum was not needed.
When you have two environments with different temps, the medium between has a tendency to seek an equilibrium between the two. The tendency to do this is measured in R value. When you have a certain % of that medium at a lower R value [and that % can be as low as 10% or less], the lesser R value wins and actually acts as a conduit for transferring heat or cold from one environment to the next.
Translation: a room with lots of windows at R3.2 will need a lot of heating and cooling even if you put R1000 in the floor. It's not going to mean a hill of beans under normal conditions.
I was thinking of putting R-30 between the joists in my crawlspace. Kraft paper face down towards the sand crawl space. Floor above is T&G plywood rated for 24" joist spacing, glued and nailed. Tar paper and finish 3/4" solid oak flooring. Moist enviroment, no good?
moisture barrier always goes to the heated side in your case the floor.which would be up
That is one that can be argued back and forth too.His house is in a hot humid location, so the moisture drive could be up from under at the damp ground.I have taken apart spaces like this many times for various reasons and have seen where it's been installed both ways in floors and never saw a problem result from either, so IMO, this is one place where it is six of one and half dozen of t'other.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Isn't there something on the building science site about hot/humid and predominantly cooling climates having the vb on the outside?
Thats been mentioned here at BT more than a couple of times. OP is in North Carolina, not sure which side of the divide that would be on, probably borderline.
Speaking of whom... where is the skytop guy anyway. Not a single post in this thread, other than startin it.~ Ted W ~
Cheap Tools! - MyToolbox.netMeet me at House & Builder!
Hey Skytop, whey you at? You started this, how's bout a little participation!
=D~ Ted W ~
Cheap Tools! - MyToolbox.netMeet me at House & Builder!
Hey Ted. I was working all day in the field.
I commented on several posts. There is an entry in the code which specifies vapor barriers on verticle surfaces. Nothing about horizontal. My hesitation of putting anything on the underside of the OSB [translation - mold candy] would be the trapped moisture. Also, when you have insulation in an attic and you have the soffit vented you have wash in the batts acjacent to that opening. So a cavity which is sealed would not wash like the attic will... there's no draft. Therefore, why bother with the draft protection.
Hey Ted. I was working all day in the field.
Me too, which translates to sitting here on this computer. =)
So a cavity which is sealed would not wash like the attic will... there's no draft.
Rim joist vents, maybe?
Naw, just kidding. I think the thing to consider is where cool meets hot. If you have the air conditioner cranked up in the room, the floor will get cold in comparison to the great outdoors on a hot summer day. If that hot summer air under the floor meets the cool subfloor, condensation occurs and the insulation gets wet. I'm not sure what affect a vapor barrier will have if installed under the plywood under the joists, as it wont stop heat from rising.
I'm just trying to picture this in my mind. I'm not sure where I'm going with this, but here's a drawing...
View Image
~ Ted W ~
Cheap Tools! - MyToolbox.netMeet me at House & Builder!
Edited 4/15/2009 7:35 pm by Ted W.
Ted, good picture. That's why I suggested sealed plywood but no vapor barrier at the bottom. Same situation as cold climate vapor barriers on walls. The moisture WILL find a way in, so our best bet is to slow it down and let it out again.
I was thinking more about that, maybe a reflective coating under the porch, to deflect the radiant heat.~ Ted W ~
Cheap Tools! - MyToolbox.netMeet me at House & Builder!
Yes, esp important with walls when using AC. Less so for floors and using open windows
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Even in a mixed humid climate, with included Louisville and Kansas City.The first problem is the term VAPOR BARRIER.Vapor retarder is more accurate and can include a number of things.But the 0 perm (plastic sheet) is only recommended in the fridged north. IIRC more than 7500 HDD.In our climate we can have significant moisture drive in both direction.In those cases the best system is one that will limit the amount of moisture that can get in and no surfaces that can condense and trap water..
William the Geezer, the sequel to Billy the Kid - Shoe
you have a point cause when i lived in az it was not uncommon for some to put the paper toward the outside.
I think it has to do with air conditioned homes (which would be most of them). Sort of like a cold can of beer, with the condensation on the outside of the can.~ Ted W ~
Cheap Tools! - MyToolbox.netMeet me at House & Builder!
Actually Paul, it's a humid local but only hot occasionally. We have less than 10 days a year over 100 degrees. Not sure that it makes much difference. My crawlspace has 2x the number of flood vents which are temperature controlled. That's is to say they close in winter and open in summer. My lot doesn't flood under or near the house now, not since the town made me put a curb in. Plus I raised the lot about a foot near and under the house. So overall, moisture would come via the wind, not damp ground.
thanks
What's "CDX OSB"?
If you have a walk-surface of only 1/2" OSB...that's what i'd be concerned about.
Edited 4/14/2009 10:16 pm by splintergroupie
Hey Man,I should have been more clear. There is 2"x decking already as floor support. The 1/2" OSB was for uniform surface for carpet. Thus 2" of flooring, not 1/2". That's twice what's required.J
Thanks for clarifying. It appears you've settled on whether you used OSB or CDX, as well. <G>
Just so you know splintergroupie is all women. :)~
Look for the onion label. <G>
My only worry/criticism would be the "tightly butted joints" on that OSB on the bottom.
I recently had to build a raised storage shed that was going to be conditioned. I need this shed to last five years. I opted to put some radiant osb on the bottom and I put the shiny side out. I will be interested to see how it holds up and I wonder if it will trap moisture and create mold or rot. I didn't use any vapor barrier on the floor insulation. I suppose the OSB will rot off first and be easily replaced if I've made a screwup.
Hi SkyTop,
no exposure to the elements underneath. There is a vented apron surrounding the deck and site drainage is good
Sounds like you have somewhat of a crawl space type ground enclosure. About the only thing I'd consider is a vapor barrier on the ground to limit how much moisture comes up from there but since you're vented, it would be optional.
I find it so nice while crawling around to later run various cabling in these cases to have slightly dusty plastic on the ground vs. damp soil. I expect my prefered comfort in these cases is also related to how much moisture ends up on the bottom side of a room.
As far as the union guy is concerned....he'll eventually die of a heart attack worrying about your hacking abilities so that problem will resolve itself in time. Next time bill him for your listening time.....that's what their used to......everyone pays for everything....the unions stopped volunteers from planting trees on city property in Chicago......they wanted more tax payer $ to pay them to do it!......at least that's what I read from WGN TV......
Pedro the Mule - Hmmm shake off the dry dust or pick mud balls from my furr........
Thanks for the input everyone.
The onion guy... I mean union guy [my bad] will have a heart attach but then be on disability AND be in the job bank [huh huh.. he said job] AND hang around and instruct people AND be able to say he can do everything and not be able to prove it. Life ain't fair.... but, perhaps after looking at this GM thing, perhaps it is.
Hi SkyTop,
The onion guy... I mean union guy [my bad] will have a heart attach but then be on disability AND be in the job bank
I'm sorry to put you in this position, but you're gonna have to steal his aspirin so he'll never make it to the hospital alive....it's a risky proposition but it'll save so many fine home builders from his corruption....
Good Luck!
Pedro the Mule - Only union I want a part in is my union with Mrs. Mule
Hi SkyTop,
Thanks for the input everyone. The onion guy... I mean union guy [my bad] will have a heart attach but then be on disability AND be in the job bank [huh huh.. he said job] AND hang around and instruct people AND be able to say he can do everything and not be able to prove it. Life ain't fair.... but, perhaps after looking at this GM thing, perhaps it is.
Another thought just came to mind.....after his hospital stay we'll all get together to build him a sympathy home....he can be the foreman....and of course with his fine instruction he'll get what he deserves and all of it hehehe......
Pedro the Mule - Oh the pain, must remove nail from hoof