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Heat loss through rim joist (14 Posts)
Heat loss through rim joistI recently installed a tube and plate system in a new house. Inch and a half holes were drilled through the joists within an inch to an inch and a half from the rim joist up near the top of the joist, for the loops to cross from one bay to the next. The aluminum plates stop about a foot from the rim joist. Now, it has been brought to my attention that insulation can't be installed between my tubing and the rim joist, and there will be unacceptable heat loss through the rim joist.
I can't argue with that, and now I really wish I had my helper drill the holes a lot further from the rim joist. Am I totally screwed, or can I elongate the holes a little, allow some 2" rigid insulation to be installed on the rim joist, and put some burley pipe insulation on the pipe as it nears the rim joist? There is a code in my state that, if I undertand correctly, requires r-21 between the heated space and the exterior.
Thank you for any engouraging solutions.This post was edited by an admin on March 6, 2014 11:42 PM.
Making stuff up/Crush Blocks:Sounds like someone is making stuff up. Did they install the crush blocks at the ends of the I Joists properly? You drilled through them?
Are they telling you that a 4" long batt, cut in half (2') and doubled up to fill the beginning of the span against the rim joist won't cover it?
WTF, I had a customer that decided to listen to a tale and had all her HVAC metal insulated duct replaces with duct board and flex duct. Part of the job was to spray foam the rim joists all the way around the house. They foamed in every wire and pipe. And all the shut-off valves and toilet mixing valves under the foam so that you can't find anything to work on them,
Is that what they want?
Interesting you bring that up...One option the homeowner gave us was to hire someone to spray foam the rim joist along that whole side of the house (about sixty feet) after moving the tubing away from the rim joist and putting rigid foam against the rim joist as well.
There are no crush blocks in this installation. The I-joist is butted up against the rim joist and sitting on a top plate.
I wonder how effective it would be to calculate and report the actual heat loss from my tubing over a year, as it is installed and with a 1" piece of rigid insulation against the rim joist. I'm not experienced at crunching those numbers, but a wild guess would be a couple dollars of propane per year.
Either way, the homeowner must be satisfied when it's all done.This post was edited by an admin on March 7, 2014 12:43 AM.
InsulationThe rim joist area is a huge area of heat loss, particularly with radiant heat.
I think 3" of well sealed foam board of spray foam is a good idea.
What type of joists do you have?
You may be able to drill new holes and move the tubes over by creating an oval.
Yoou may need to reinforce the joists.
Joist reinforcementThey are "standard" TJI joists. I'm sorry I can't remember the dimensions off the top of my head. If I 'elongate' my hole enough to allow 3" of space to the rim joist, then I will essentially have a 3" long oval hole right over my end support wall. The TJI literature I looked at wasn't very clear about how to reinforce something like that. I guess I could call Weyerhauser and ask them...or just let the contractor deal with that part of the solution.
Read documentation for TJI before you do anything here is the link.
You can drill an 1 1/2" hole about anywhere just below the bottom of the top flange, but not 2" , nor elongation of hole. You should be 1' 6" from bearing point face of wall.
If anything consult factory rep with your question before doing anything.This post was edited by an admin on March 7, 2014 6:28 AM.
TJI/Crush Blocks:Here's more:
I always understood that outside walls that hold the roof/rafter ends were considered load bearing walls. What I don't understand is the kerfuffle over the radiant loops being too close to the rim joists. How close are they? How far back are they saying the radiant tubing must be back from the edge? Are you supposed to give up radiant floor space for the sake of some minor amount of insulation? Most insulators couldn't properly wipe their behind with the stuff, let alone install it properly. Did you say that there is 1" of rigid foam against the rim joist?
If they used an engineered rim joist that matches the TGI's, (which they should), you didn't run the tubing under the wall did you? I doubt it. Its the turning radius they are squawking about.
It sounds like an inspector that was a contractor wannabe and couldn't or didn't make it and now wants to show everyone how badly he can crush gonads.
And that the insulator can't come up with creative solutions for his mistake and wants you to move your installed tubing at your cost rather than the insulator fabricating pieces of foam board between the joists like he should have done in the first place. I've never heard of such foolishness. But then, nothing surprises me anymore.
I knew an inspector like that. He always wore baggy pants with big outside pockets in the back. You were supposed to know what his hand in his back pocket meant.
He had a sign on his wall that he thought was funny.
"Arguing with an inspector is like trying to catch a greased pig. You'll never know how much fun the pig is having".
He thought it funny. I always thought it pathetic. Comparing yourself to a pig.
Interiorend of the joists is where we always make our crossovers . We also use a piece of aluminum to the bottom of subfloor at the outside and as far out on the straight pipe as possible half straps so tubing is in contact with aluminum. This is your area of GREATEST heat loss in any structure and having the tubing not in contact with the subfloor at this location is a bad idea , not having the insulation in contact with it is a worse idea . If the below tubing insulation were in contact with the tubing and subfloor this area would be someone elses responsibility . Figure out what will be more cost effective for you and perform the required task . Maybe removing that tubing and putting the crossovers on the other side is gonna be more economical than hiring a spray foam guy , and your heating system will perform better . At that point you can tell the homeowner to hire the spray foam guy himself as it should be . In either case as our site host always says , Pay your tuition .You didn't get what you didn't pay for and it will never be what you thought it would
More on joistsHere's a pocket guide for TJI/I Joists.
It might be dated, 2005.
Location, Location, Location:" ""Inch and a half holes were drilled through the joists within an inch to an inch and a half from the rim joist up near the top of the joist, for the loops to cross from one bay to the next. The aluminum plates stop about a foot from the rim joist. Now, it has been brought to my attention that insulation can't be installed between my tubing and the rim joist, and there will be unacceptable heat loss through the rim joist." ""
I noticed that.
It was explained to me or I figured it out, that with dimensional lumber (standard 2" X *"), you can only drill in the end third of a joist and only in the middle 1/3 of the joist with a hole no larger than 1/3 of the thickness. My "Rule of Thirds". The exception is when the engineering/code calls for a 2 X 12 as the maximum for a clear span (say 12' for discussion) and you need to drill a 4" home in a 2 X 12 for a 3" PVC pipe. You can't because the joist is probably 11 1/4". However, the only places that the 2 X 12 is needed is on those spans. If you have a room with 6' ceiling joists for the second floor, the joists are theoretically, twice the thickness they need to be in their locations. Therefore, drilling 4" holes in 2 X 12's spanning a 4" hallway is acceptable. Or so inspectors I worked with, agreed when trying to plumb multi-million dollar houses that weren't designed to have any mechanicals in them for aesthetic reasons.
But TJI/I-Joists are different. You can drill pretty much where you want as long as you don't cut into or get too close to the top and bottom chord of the joist. Or, the ends. It was explained or confirmed to me that "The Rules of Thirds (modified) came to play, Take an imaginary line from the point load on the middle end of the joist (crossing a Girt) or the end of the joist at the end/rim joist and draw a triangle from the end of the above sole plate inward. You can not drill or cut any place inside this triangle because this is where the load from above is traveling and it is the need for crush blocks.
Or so I learned at the time.
Back to the original post...I think you should move the tubing. You said it's an inch to an inch and a half away from the rim joist. That means the tubing is looping under the wall of the room above. It didn't need to be that close. I would bite the bullet (if you did it yourself), or have the contractor come back and properly install the tubing-ie, move it.
Depending on your floor covering, someone will drive a nail, or fish a wire down the wall from above thinking there's no way radiant tubing is under the wall, and hit it.
And you'll get to insulate your rim joist properly.steve
I wouldMove the tubing also. I seal the bay ends with silicon then I put 1" or 2" of reflective foam board, and then have the insulation contractor install 6" fiberglass blockers, when he is insulating the floor. There is a huge heat loss through the rim joist, as the Radiant heated bay is the hottest part of the house. Not sure where you live but here in Northern Massachusetts it seems like it is near zero for much of this winter.
Thanks, Bob Gagnon
IceThe installation guide clearly states that you can put an 1 1/2" hole anywhere in the WEB and not in the hatched area over a bearing wall. As soon as you go to a 2" hole you must be no closer than 1' from the FACE of a bearing wall. Clearly what the OP wants to do is not except able per TJI install instructions. PERIOD
TJI or BCI are very vulnerable when you start carving out the web over bearing points. The holes the op wants to elongate are in the bearing area of the joist.This post was edited by an admin on March 7, 2014 7:54 PM.
Splitting hairsIf the rim is gonna be spray foamed even with just a 1" gap at that one spot, the heat loss is gonna be so minimal. If you put a thin piece of reflective metal there then it's spray foamed. It will be near unnoticeable on a Fluke IR camera. Yes more care and TJI drilling knowledge would have eliminated this issue all together. If it were me and this customer well ,,eh hum..... I'd just redo the pipe and look like the man that went the extra mile WITHOUT. Any argument or hesitation. This is what we have minions for and if he does it, maybe he will be more proactive when drilling TJI next time. Either way, I hope both of you are better and smarter from this very minor issue. Better than the plumber paying for a 120' run of engineered trusses that were notched out on the bottom plate to fit pipe flush. OUCH, the employee was a 46 year old journeyman. Chalked lines and all....