| Author |
Message |
Anonymous
| | Posted on Tuesday, January 08, 2008 - 01:55 pm: |    |
I was asked a question regarding extended exposure gypsum sheathing and would like everyones help. Can the joints be taped and sealed in lieu of using building wrap? This allows the exterior sheathing to also act as the air and/or water barrier in the wall system. This installation method is allowed by IBC 2003 and 2000 (and earlier) building codes and Georgia-Pacific had joint treatment methods and written installation guidelines in their product literature. However, the 2006 IBC no longer allows this and now there must be a separate water-resistive barrier over exterior sheathing. What would a specifier want from a manufacturer in this application? |
Marc C Chavez
Senior Member
Username: mchavez
Post Number: 266
Registered: 07-2002
| | Posted on Tuesday, January 08, 2008 - 02:17 pm: | |
In the IBC 2508.2 in both the 2003 and 2006 code it states
"Gypsum wallboard...shall not be used in any exterior surface...exposed directly to the weather...Gypsum sheathing shall be installed in accordance with ASTM C 1280"
Is this what you are speaking about? I see no discussion of "joint solutions" are they in ASTM C 1280?
Could I please have the code ref? |
William C. Pegues, FCSI, CCS
Senior Member
Username: wpegues
Post Number: 692
Registered: 10-2002
| | Posted on Tuesday, January 08, 2008 - 02:41 pm: | |
Anon,
No standard gypsum sheathing should be permitted to be used as a weather barrier. They don't hold up. Some special products like the DensGlass products hold up, but even there should have some kind of material over them.
And unless something rather recent has changed, none of the gypsum products can be used as an air barrier material. Some have anecdotal application, like the Dens products, but the manufacturer will not certify them for permeability. So, you are still going to have to come up with an air barrier if you need one at that location in the wall (depends on the code being used as well as the climate zone and the wall type construction).
William |
David Axt, AIA, CCS, CSI
Senior Member
Username: david_axt
Post Number: 960
Registered: 03-2002
| | Posted on Tuesday, January 08, 2008 - 04:40 pm: | |
FYI
Georgia Pacific has modified their glass mat facer and upped their exposure warranty on DensGlass Gold to 1 year. Prior to that you could only have DensGlass uncovered and exposed to the elements for 6 months. No joint compound or tape necessary. |
Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP
Senior Member
Username: specman
Post Number: 599
Registered: 03-2003
| | Posted on Tuesday, January 08, 2008 - 04:54 pm: | |
I agree with William. Best not to leave gypsum sheathing, whether permittable or not, as the weather barrier. The IBC (2006 edition included) will allow it, but it must be suitable for contact with moisture, such as the DensGlass products (this assumes the gypsum panels will be covered by another suitable material for weather exposure such as metal panels). If this is done, the joints aren't taped and finished, they're sealed with a joint sealant.
However, that leaves many locations susceptible to failure and potential leakage. Best to stick with an approved weather barrier or air barrier material over the gypsum panels. |
randy_cox (Unregistered Guest)
Unregistered guest
| | Posted on Wednesday, January 09, 2008 - 08:15 am: | |
If a sheathing material meets the necessary requirements for air resistance, it can be used with taped or caulked joints as part of the air barrier assembly. A separate moisture barrier assembly would also be required. |
William C. Pegues, FCSI, CCS
Senior Member
Username: wpegues
Post Number: 693
Registered: 10-2002
| | Posted on Wednesday, January 09, 2008 - 11:42 am: | |
The problem with this is that its typically not published what the perm rating is for the sheathing, especially the gypsum sheathing products. There are some sheathing products, especially in stick built construction, that come with a air barrier rated 'sandwich' of materials or skin.
When one says 'air barrier', that's only part of the requirement. What is really needed is whether it is a water vapor barrier air barrier or a water vapor permeable air barrier. Sheathing products you would use in highrise projects do not come with manufacturer's certified usage as an air barrier product. Yes, there is anecdotal evidence that it does work, but they are not marketing it as that.
Maybe they don't want the liability.
Most air barrier products, and all the best ones, act for all 3 effects...
1 air barrier (movement of air is blocked)
2 moisture barrier (movement of water is blocked)
3 vapor permeable or impermeable (water vapor it either blocked or permitted to be passed through depending on your wall design requirements)
DensGlass even works as a moisture barrier as well, but they don't market it as such and recommend the use of other products as air and moisture barriers.
William |
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