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David J. Wyatt, CDT
Senior Member
Username: david_j_wyatt_cdt

Post Number: 13
Registered: 03-2011
Posted on Monday, August 19, 2013 - 02:14 pm:   Edit PostDelete PostPrint Post

Some architects for whom I have written roofing specifications use the terms weather-tight and water-tight without much distinction.

The NRCA Roofing and Waterproofing Manual only uses the term "weathertight" in one instance I have been able to find, and there is no definition for it.

I found this definition of weathertight on a website dealing with marine elements:

"An industry definition of marine closures indicating that they could be exposed to the elements, with the probability that only small amounts of water, wind or rain would pass thru the closure."

It sounds like an accurate definition.

Going further, however, I see the term weathertight more often used when describing windows and doors - vertical elements in the building envelope.

So, it seems that "weathertight" is less favored than "watertight' when applied to roofing.

Have any of you had this semantic problem? If so, how have you dealt with it?
George A. Everding, AIA, CSI, CCS, CCCA
Senior Member
Username: geverding

Post Number: 674
Registered: 11-2004

Posted on Monday, August 19, 2013 - 05:01 pm:   Edit PostDelete PostPrint Post

I wonder if you could draw an analogy from below grade "waterproofing" which must withstand intrusion by water under hydrostatic pressure, and "moisture-proofing" which doesn't? In a roofing system, you have watertight conditions (one roofing ply sealed to another)which must resist wind driven or standing water, and a weather resistant flashing which might shed moisture, but wouldn't necessarily stop wind driven water from penetrating?

I don't have any standard backing this up - just making it up as I go.
George A. Everding AIA CSI CCS CCCA
Ingersoll Rand Security Technologies
St. Louis, MO
Jeffrey Wilson CSI CCS
Senior Member
Username: wilsonconsulting

Post Number: 107
Registered: 03-2006
Posted on Monday, August 19, 2013 - 06:06 pm:   Edit PostDelete PostPrint Post

This might be case where more than one term is well-understood, and therefore either can be used validly. Performance requirements in MasterSpec's roofing sections refer to roofing & flashing having to "withstand exposure to weather … and remain watertight" -- both terms used in the same paragraph. LEED credits refer to adhesives and sealants used inside the weatherproofing system, with respect to roofing systems as well as vertical cladding systems and glazing. I don't see any conflict, since the terms have the same essential meaning.
Lynn Javoroski FCSI CCS LEED® AP SCIP Affiliate
Senior Member
Username: lynn_javoroski

Post Number: 1680
Registered: 07-2002

Posted on Tuesday, August 20, 2013 - 11:59 am:   Edit PostDelete PostPrint Post

"Water-tight" to me implies keeping out water, while "weather-tight" means keeping out weather, which would include cold and heat as well as water (in the form of rain or snow).

Hence, "weather-tight" would be more stringent than "water-tight".

I want my building, including my roof, to be weather-tight and maintain the interior conditions I choose while not allowing the exterior conditions to bother me. My foundation/basement walls can be water-tight and keep the water out without necessarily keeping out weather (to which they may or may not be exposed).
ken hercenberg
Senior Member
Username: khercenberg

Post Number: 581
Registered: 12-2006

Posted on Tuesday, August 20, 2013 - 12:57 pm:   Edit PostDelete PostPrint Post

I don't know of any standards that define weather-tight, though I suppose one could argue that groups like ABAA and AAMA offer weather-resistant systems criteria that can be measured.

My concern with using either of these terms in Contract Documents is the lack of definition. Use of vague or undefined terms leave the definition to the reader (ie: The Contractor). I believe your designers may want to find terms that are better defined if they are to continue using them.

I spec both waterproofing and weatherstripping. Both are useful items but they are hardly interchangeable.
Steven Bruneel, AIA, CSI-CDT, LEED-AP, EDAC
Senior Member
Username: redseca2

Post Number: 403
Registered: 12-2006

Posted on Tuesday, August 20, 2013 - 02:36 pm:   Edit PostDelete PostPrint Post

I can think of traditional roofing systems that did a good job of keeping the weather out (for the location they originated from), but were hardly watertight.

Spanish clay tile roofs were originally attached to wood members perpendicular to the roof joists with no continuous sheathing or water barrier, but if your "rain in Spain is mainly on the plain", and only a few inches a year to boot, they worked fine.
ken hercenberg
Senior Member
Username: khercenberg

Post Number: 584
Registered: 12-2006

Posted on Tuesday, August 20, 2013 - 04:17 pm:   Edit PostDelete PostPrint Post

Great point Steven. So if the first law of waterproofing is "If the water isn't there, it can't leak" does that mean that slope and drainage are forms of waterproofing even if the assembly isn't weather-tight?
Steven Bruneel, AIA, CSI-CDT, LEED-AP, EDAC
Senior Member
Username: redseca2

Post Number: 404
Registered: 12-2006

Posted on Tuesday, August 20, 2013 - 06:07 pm:   Edit PostDelete PostPrint Post


Raised seam metal roofing manufacturers regularly require a minimum slope so I guess that is true.
Paul Sweet (Unregistered Guest)
Unregistered guest
Posted on Thursday, August 22, 2013 - 01:15 pm:   Edit PostDelete PostPrint Post

I'd consider "weathertight" as resisting rain (or snow) more intense than a spring shower, but short of a hurricane.

"Watertight" implies standing water.

Siding (including windows, doors, louvers, etc.) or sloped roofs can be "weathertight", but flat roofs or decks over inhabited areas have to be "watertight".
Brett Scarfino (Unregistered Guest)
Unregistered guest
Posted on Friday, August 23, 2013 - 12:44 pm:   Edit PostDelete PostPrint Post

No one has mentioned 'air' as part of weather.
With this in mind (and from an exterior wall consultant's perspective), when I hear 'weather barrier', by default I think air/water barrier (absolutely needed and code required)...and ask for clarification on water vapor performance (not necessarily needed or code required).

While an official code definition may not exist, the accompanying performance criteria should paint a clear picture on what is textually implied.

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