Defects in Buildings Envelopes and Jointing Systems

Few comprehensive surveys have been published on the incidence of failure in building joints; there is literature that is of some value, notably that from sur­vey work carried out in the U. K. [1], the results of which are reportedly [2] emulated by a similar work in Japan [3]. The highlights of the survey conducted in 1990 in the U. K. indicated that 55 % of joints failed within less than ten years, and only 15 % lasted more than 20 years.

In North America, interestingly, little has been published on this topic al­though there is information on individual buildings, specifically that published by Huff [4] who provides examples of two surveys, one of which was carried out on a newly constructed eleven-story building and the other, on a twin eighteen- story condominium in Long Beach, CA. It the latter case, a 5.6 % failure rate was detected in the EIFS cladding joints based on 1, 5, and 10 % sampling rates. Interestingly Huff [4] determined from this that the failure rate remained constant irrespective of the sample size.

The former example [4] of the eleven-story building had a total of ca. 10700 m (35 000 ft) of jointing product installed. The survey was conducted on two of 24 grid locations representing an 8.3 % sampling rate. From this study, 14 adhesive failures were detected on one grid section, and 20 on the other, yielding an average of 17 failures per grid section. Based on this information an estimate of the number of failures in adhesion of the entire building was 408 whereas, following a survey of the entire building 427 adhesive failures were uncovered (i. e., a 0.2 % failure rate). The author notes that although the failure rate appears small, there are nonetheless 427 failure locations that represents, based on an average length of failure of 50 mm (2-in.), approximately 21.6 m (71-ft) of product that has failed and through which water can enter.

An investigation of defects and complaints of execution of constructed works in Japan was reported by the Building Construction Society of Japan, results for which are summarized in Fig. 1 [5]. The results indicate that 65 % relate directly to water leakage, of which 44 % can be attributed to water leak­age of the wall system and of this proportion, 32 % of the defects are due to

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leakage at the exterior of the wall, that is, at the jointing system. Hence, based on the results of this study, it is evident that a considerable proportion of de­fects accrue from water leakage alone. Thus understanding the nature of wind – driven rain is important when assessing the loads to which the building enve­lope is subjected. Additionally, considering the relatively high portion of defects attributable to jointing systems suggests that attention be placed not only on the nature of failure at joints but also, the consequences of failure.

In respect to the nature of failure at joints, the Building Construction So­ciety of Japan reports on the different types of failure of jointing products, as summarized in Fig. 2 [6]. The greatest proportion of failures can be attributed to failure due to adhesion (56 %), whereas, the proportion of failures in cohe­sion is reported as 24 % [6].

This may broadly suggests that when attempting to determine the signifi­cance of jointing product failures on the watertightness of joints, defects such as those that accrue due to adhesion failure should first be investigated as these are perhaps the more likely to occur in building joints.

In general then, deficiencies in building facade joints are inherent in any facade jointing system even those for which proper installation procedures have been conscientiously followed. These deficiencies would typically be ad­hesive in nature and could lead to leakage across the wall joint. However, given that openings exist along joints, water leakage evidently can only occur if water is present at the opening and if there are forces driving water through these deficiencies. The presence of water on the facade is in part a function of the climate loads, specifically, the intensity of wind driven rain, that varies, not only in relation to the basic climate parameters of wind speed and rainfall intensity, but also in respect to the height and width of the building, and orientation of the building to the prevailing direction of the driving rain. Features on the facade such as overhangs and balconies necessarily affect local deposition of water on the facade, such features shielding the facade from direct rainfall. Once water is deposited on the facade, it migrates downwards, the concentra­tion of water being determined by different vertical and horizontal features that form part of the cladding proper [7]. In this paper, some basic information

TABLE 1—Characteristic wind speeds and related velocity pressures for different categories of tropical cyclonic events.

Velocity

Category

Wind Speed

Pressurea

(km/h)

(Pa)

WEAK TROPICAL STORM

Speeds/velocity pressures

42-69

82-224

Gust speeds/pressures

64-103

198-515

SEVERE TROPICAL STORM

Speeds/velocity pressures

69-103

224-515

Gust speeds/pressures

105-151

550-1080

Category 1 HURRICANE/MINIMAL TYPHOON

Speeds/velocity pressures

105-132

515-840

Gust speeds/pressures

153-193

1130-1850

Design wind pressure/speed for Southern Coastal U. S.

113

581 (12 psf)

aPv (Pa) =1/2 pv2; pair = ca. 1.2 kgm 3; v (ms 1).

relating to wind speed and rainfall intensity during key climate events is given such that these can be related to test loads used in assessing wall and cladding weathertightness performance.