| Author |
Message |
Wayne Yancey
Senior Member
Username: wayne_yancey
Post Number: 386
Registered: 01-2008
| | Posted on Friday, December 10, 2010 - 02:05 pm: |    |
Yesterday, I attended a good product knowledge seminar on exterior insulation. From several questions from the audience, it is clear there are different opinions between AHJ's enforcing the energy code and designers as to what "continuous" means. Typical wall assemblies that use metal wall panels incorporate continuous Z-girt or other girt shape, horizontally or vertically, between the joints in the single layer of the insulation. One attendee stated that Seattle AHJ considers continuous as not using horizontal or vertical girts. This AHJ's opinion was noted by several as not practical unless the continuous exterior insulation is SPF which is not common the PNW.
Anyone know of a metal wall panel support system over exterior continuous insulation that mitigates the thermal bridging of the girts and collateral fasteners?
OR
A more rational meaning of continuous? The typical exterior insulation product come in panels, therefore there are joints every 16-24" vertically and 96" horizontally. This is not continuous regardless of girts or no girts. |
Paul Gerber
Senior Member
Username: paulgerber
Post Number: 47
Registered: 04-2010
| | Posted on Friday, December 10, 2010 - 02:25 pm: | |
Wayne,
Interesting how some AHJ's have such seemingly impossible takes on common, everyday architectural/construction concepts that move the "common" into the category of "unattainable".
Following their interpretation of "continuous" I would be curious to hear their interpretation of shelf angles or, for that matter, masonry veneer ties such as RAP ties. It could easily be interpreted that RAP tie or a cavity ladder tie even is a thermal bridge. Where does it end???
Thankfully none of the AHJ's in (presently) snowy ON have taken on the task to further complicate our already complicated existences with nonsensical interpretations...yet...touch wood.
IMHO this is just someone in an AHJ justifying their existence in the name of...God knows what! (I was going to say public safety, but that isn't really applicable in this instance)
Ride it like you stole it!!! |
J. Peter Jordan (Unregistered Guest)
Unregistered guest
| | Posted on Friday, December 10, 2010 - 02:29 pm: | |
The only "continuous" insulation system that I am aware of is EIFS. In masonry veneer construction, if one installs the insulation outside of the sheating (in the cavity), the insulation is still interrupted by masonry ties. If you have continuous insulation under fiber-cement siding, you still have to mechanically fasten back to a metal or wood structural member.
I think the ideas has to be not to completely do away with thermal bridging (not really possible, much less practical), but to minimize it. |
Lynn Javoroski CSI CCS LEEDŽ AP SCIP Affiliate
Senior Member
Username: lynn_javoroski
Post Number: 1165
Registered: 07-2002
| | Posted on Friday, December 10, 2010 - 03:29 pm: | |
Yesterday a Dow rep visited us with a new system. Thermax Wall System: glass fiber reinforced polyiso foam core faced with 4 mil embossed acrylic coated aluminum (aluminium for Paul) on one side and 1.25 mil embossed al. on the other. This is the exterior sheathing. Then styrofoam spray polyurethane foam (2 component) is sprayed on the interior of the stud wall. You'll have to get more particulars from Dow if you're interested. |
Wayne Yancey
Senior Member
Username: wayne_yancey
Post Number: 387
Registered: 01-2008
| | Posted on Friday, December 10, 2010 - 04:24 pm: | |
Thanks Lynn.
I am aware of the Dow Thermax Wall System. The wall assemblies we prefer are more traditional in nature but with exterior insulation. My firms preference is all exterior insulation over an air barrier on any substrate (concrete, CMU, gypsum sheathing). A wall assembly (along with roof assembly) that works in any climate zone from Alaska, to Nevada, to Florida, to Saudi Arabia.
In early 2009, Dow came through Seattle doing their dog and pony show at the same time Seattle DPD was negative on using SPF for most of our building types. Dow was sent back to the drawing board to convince the City of Seattle their fears were unfounded. Dow had to produce more paperwork such as evaluation reports. I have not kept informed as to their success.
The Dow system has promise for certain construction types.
Wayne |
Paul Gerber
Senior Member
Username: paulgerber
Post Number: 50
Registered: 04-2010
| | Posted on Friday, December 10, 2010 - 04:34 pm: | |
LOL @ Lynn...although I spell some things differently than my "neighbours" to the south aluminum is not one of them. However I did have an instructor in college who emigrated from Scotland who still pronounced and spelled it aluminium (Al-YOU-min-ium). Another one of his quirks that made me the butt of a few jokes to my classmates was his pronunciation of the word masonry (May-son-ARY...you have to try and say it with a thick Scottish brogue in your head)...much to my chagrin part way through first semester I discovered that the word was not spelled "masonary". I did however see a pickup truck once that proudly displayed the company name "Doug's Masonary" (or something like that) on the side, at which time I decided that if I ever than a mason with such a company name on one of my projects I would respectfully ask the Contractor to find someone who could actually spell the name of his profession to employ.
Ride it like you stole it!!! |
(Unregistered Guest)
Unregistered guest
| | Posted on Friday, December 10, 2010 - 04:42 pm: | |
In the mid 70's I attended an International MASONRY symposium in Calgary. The opening keynote address was delivered by a UofC engineering prof who used MASONARY throughout his address. Like finger nails on a blackboard. |
J. Peter Jordan (Unregistered Guest)
Unregistered guest
| | Posted on Friday, December 10, 2010 - 03:32 pm: | |
This is a very interesting system; however, it still has the problem of thermal bridging when you anchor the exterior cladding back to the structural wall system. |
Wayne Yancey
Senior Member
Username: wayne_yancey
Post Number: 388
Registered: 01-2008
| | Posted on Friday, December 10, 2010 - 05:20 pm: | |
There seems to be little or no information available about thermal bridging of fasteners into the cold-formed metal framing.
Are fasteners inconsequential?
The metal wall panel is connected to the Z-girt, the Z-girt is connected through the air/vapor barrier and sheathing into the cold-formed metal framing, the cold-formed metal framing is at ambient interior temperature.
I tend to think the thermal bridging is inconsequential when compared to the potential thermal briding thru a curtain wall or a window wall or storefront. Particularly when the mass of the aluminum extrusion is now located outside the insulation plane in the outside ambient temperature. Frost or condensation or both occurs on the glass and sills in the winter.
FERO recognized this potential thermal bridging in the design of their shear stud masonry connectors. FERO simply drilled large and small holes in the exterior portion of the shear plate to reduce the mass of steel beyond the face of the gypsum sheathing. Most of the plate is encapsulated by the exterior insulation.
Wayne |
Joseph Berchenko
Senior Member
Username: josephberchenko
Post Number: 29
Registered: 08-2003
| | Posted on Monday, December 13, 2010 - 02:32 pm: | |
Wayne - Have you considered Centria MetalWrap?
http://www.centria.com/wallpanels/metalwrap2/Pages/default.aspx |
Wayne Yancey
Senior Member
Username: wayne_yancey
Post Number: 390
Registered: 01-2008
| | Posted on Monday, December 13, 2010 - 02:37 pm: | |
Joesph,
Had seen previously but it slipped thru the cracks. Thanks. Seems like a good idea.
Wayne |
John Bunzick, CCS, CCCA, LEED AP
Senior Member
Username: bunzick
Post Number: 1284
Registered: 03-2002
| | Posted on Wednesday, December 15, 2010 - 09:26 am: | |
Actually, the AHJ's definition is not as far-fetched as you may think when you look at the context. When we think of continuous insulation, we usually mean that the studs do not interrupt the insulation. How is the Z-girt that different? It's not really. Maybe that's not what is intended by the code, but .... ?
Of course I agree that for certain types of wall assemblies, like metal panels, the Z-girt is taken for granted as required. Notably, common claddings such as masonry do not have the degree of thermal bridging that Z-girts do. I challenge the assumptions about continuous Z-girts for some systems. A metal composite material cladding system that has continuous extruded aluminum shapes around the perimeter of each panel does not really need continuous Z-girts. Why not individual, spaced (stiffer) clips the way we do with masonry? But the industry won't have it. I got looked at funny more than once when I suggested that. (Come to think of it, maybe that wasn't because of my suggestion about cladding.) |
Brian E. Trimble, CDT
Senior Member
Username: brian_e_trimble_cdt
Post Number: 31
Registered: 08-2005
| | Posted on Wednesday, January 05, 2011 - 05:39 pm: | |
Thermal bridging of metal wall ties is small in comparison to the other types of thermal bridges found in wall assemblies. One of BIA's Technical Notes mentions that the effect of a wall tie on R-value is around 4 percent.
There was a good article on thermal bridging and steel shelf angles in Modern Steel Construction about a year ago: http://www.modernsteel.com/Uploads/Issues/January_2010/012010_Jan10_ThermalBridging_Web.pdf. There are ways to address this as we get more refined in energy efficiency and our envelope.
Also look at NCMA TEK 6-13 on thermal bridging and continuous insulation and their new Thermal Bridges catalog: http://www.ncma.org/resources/design/Documents/Thermal%20Catalog%20Phase%20I.pdf. |
Wayne Yancey
Senior Member
Username: wayne_yancey
Post Number: 402
Registered: 01-2008
| | Posted on Wednesday, January 05, 2011 - 06:12 pm: | |
Brian,
Thanks for the good links.
Wayne |
Wayne Yancey
Senior Member
Username: wayne_yancey
Post Number: 413
Registered: 01-2008
| | Posted on Friday, January 28, 2011 - 03:05 pm: | |
An excerpt of the relevant text from Chapter 2 (2009 Washington State Energy Code is used as the basis of Seattle Code.
CONTINUOUS INSULATION (c.I.): Insulation that is continuous across all structural members without thermal bridges other than fasteners (i.e. screws and nails) and service openings. It is installed on the interior or exterior or is integral to any opaque surface of the building envelope. For the purposes of this definition of continuous insulation, only screws and nails are considered fasteners. Insulation installed between metal studs, z-girts, z-channels, shelf angles, or insulation with penetrations by brick ties and offset brackets, or any other similar framing is not considered continuous insulation, regardless of whether the metal is continuous or occasionally discontinuous or has thermal break material. (See Section 1332 for determination of U-factors for assemblies that include metal other than screws and nails.)
My research revealed: Metal studs, z-girts or any other repetitive continuous metal framing can decrease the effective R-value of insulation by more than 50%. However, occasional continuous metal framing members such as shelf angles are also significant thermal bridges around the insulation. Discontinuous metal elements, such as stand-off brackets are better, but still are a thermal bridging element. Calculations on a stand-off system utilizing 6-inch brackets showed that the brackets mounted at 24 inches on center vertically and 16 inches on center horizontally decreased the effective R-value of the assembly by 25% and the brackets mounted at 48 inches on center vertically and 16 inches on center horizontally decreased the effective R-value of the assembly by 14%. Even isolated discontinuous metal elements such as brick ties have a thermal impact that is too large to be ignored. |
Brian E. Trimble, CDT
Senior Member
Username: brian_e_trimble_cdt
Post Number: 34
Registered: 08-2005
| | Posted on Friday, January 28, 2011 - 03:33 pm: | |
I would have to disagree with the last statement. In our Technical Notes 4 (www.gobrick.com) we calculate the loss due to brick ties at about 3%. I'm not sure I would consider that an "impact that is too large to be ignored". Let's talk about eliminating other thermal bridges in walls first, before we consider small amounts such as these. I would tend to agree with the issue about shelf angles. If anyone has seen a thermal image of a wall with a shelf angle you can see some of the losses at that point. Some of the information in the article I already mentioned from Modern Steel Construction addresses that.
I think the code people need to look at commissioning of the envelope before they start looking for ways to improve thermal resistance 3 - 4%. |
Wayne Yancey
Senior Member
Username: wayne_yancey
Post Number: 414
Registered: 01-2008
| | Posted on Friday, January 28, 2011 - 04:11 pm: | |
Brian,
I would agree the impact is small enough to ignore in wood frame construction but cold-formed metal framed walls is another matter.
Brick anchors such as the Fero Stud Shear Connector (and side mounted Rap Tie) make direct contact with the steel steel studs even with material removed to reduce thermal conductivity. This connector is much more than just screws and nails. The scope, size and complexity prevent us from using wood frame construction other than heavy timber. However, "Even isolated discontinuous metal elements such as brick ties have a thermal impact that is too large to be ignored" may be to subjective.
Do you know of an acceptable (acceptable to the AHJ) % of decreased R-value when using cold-formed metal framing. WA and Seattle seem to have drawn a deep line in the sand. Back to the drawing board. |
Les Cullen (Unregistered Guest)
Unregistered guest
| | Posted on Wednesday, October 09, 2013 - 03:10 pm: | |
The IECC allows foam of multiple planes which overlap to be considered continuous without taping if they overlap at least 1". A company in Idaho named InsulStone and I-Siding manufactures a patented system of interlocking panels which accomplish this purpose. |
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