Rain leakage tests on vertical through-joints

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Rain leakage tests on vertical through-joints

NATIONAL RESEARCH COUNCIL CANADA

DIVISION OF BUILDING RESEARCH

RAIN LEAKAGE TESTS ON VERTICAL THROUGH -JOINTS

by

R. E. Platts and J. R. Sasaki

ANAL

VZED

Internal Report No. 323

of the

Division of Building Research

OTTAWA October 1965

The satisfactory performance of prefabricated

wall systems depends lar gely on the joint detail. The

joint must accommodate construction tolerances and

building movements while maintaining an adequate

barri-er to heat, air and watbarri-er. Many jointing arrangements

have been found inadequate in resisting rain penetration. Early in 1964, the Division of Building Research assisted the Department of Northern Affairs and Na-tional Resources in the design of a prefabricated north-ern hut which utilized wood panels with stressed plywood skin. A joint of the open rain -scr een type was suggested

for joining adjacent wall panels. The results of

explor-atory water leakage tests performed on a number of joint arrangements evolving towards the final design are now reported.

The fir st author is a civil engineer and research officer with the Housing Section with special interests

in prefabrication practice; the second author is a

me-chanical engineer and research officer with the Building Services Section with responsibility for rain leakage

studies. Ottawa

October 1965

N. B. Hutcheon Assistant Director

RAIN LEAKAGE TESTS ON VERTICAL THROUGH-JOINTS

by

R. E. Platts and J. R. Sasaki

The performance of pr efabricated exterior wall systems depends to alar ge extent on the performance of the joints between

adjacent wall panels. These joints are usually through-joints,

with a single continuous gap leading from the interior wall face

to the outside. Ideally, through -joint details should be simple to

manufacture and assemble, and should tolerate flaws in dimensions

and workmanship. At the same time, the joints must be capable

of accommodating building movements due to thermal and struc-tural stresses while preventing the entry of outside air, rain and snow.

Early in 1964, the Division of Building Research assisted the Department of Northern Affairs and National Resources in the

design of a pr efabricated northern hut, the "An gir r aq", which utilizes stressed plywood skins on both interior and exterior faces

of the wall, floor and roof panels. This report describes

exploratory rain penetration tests on through-joints of the "open

rain-screen'! type as suggested in the design of this hut. It shows

the wetting and air pressure patterns of various joint arrangements that evolve toward the final approach, and notes the differing

effects of two types of rain simulators used in the laboratory

pro-gram. The design and field testing of the "Angirraq" and its

special joints will be reported separately.

With its long interest in the functions of building enclosures, the Division of Building Research has become familiar with

problems associated with through-joint design and with the leakage

problems found in modern buildings. It is general field practice

to render through -joints weathertight by applying caulking material or a gasket at the outer surface of the joint, a location invariably

wetted by rain. As the sealant also sustains the total wind pressure

difference that can occur across exterior walls, it has the difficult task of preventing the leakage of water when an air pressure

difference exists. As wall panels become larger and buildings higher, the sealant must be capable of withstanding greater panel

movements and wind pressures. Improved performance has been

won at high cost by improvements in the sealing materials used. The main disadvantage in the outer -seal design of present through-joints is that minor flaws in the contact between joint surface and sealant will permit the free entry of wind-driven rain.

For some time, it has been appar ent that a change in

approach to the through -joint design was r equir ed; one which

would allow indefinite trouble-free performance, greater working

tolerance and lower cost. A design concept presently arousing

much interest is the open rain-screen principle developed by the

Norwegian Building Research Institute. The Division has studied

the principle and discussed its possible application in the design of

joints in windows and walls (1). Briefly, the design principle

involves the placing of a loose shield or " r ain-screen" over the exterior fac e of the j oint, with an air spac e in the j oint gap behind the shield having free access to the outside, followed finally by a

relatively tight air seal placed at the inside face of the joint. When

subjected to wind action, the air space pressure is essentially the

same as that of the outside. Little or no air pressure difference

can exist acros s the wet portion of the joint, so that the shedding

of rain by the shield is greatly simplified. The joints tested

and described in this report range from simple open joints to modified open rain-screen joints, such as used in the "Angir r aq", The tests were performed in the DBR rain leakage apparatus. Some additional tests wer e performed using a spray system

suggested by the Architectural Aluminum Manufacturers Association, Inc. (AAMA) (2).

TESTING EQUIPMENT

The DBR rain leakage apparatus consists of alar ge air-and water -tight chamber with an 8 -by 8 -ft opening in one wall

(Figure 1). The test specimen is mounted in the opening with its

weather sid e facing the interior. Ninety-six rain sprays move

up and down in front on the specimen, wetting it uniformly. Each

rain spray consists of a water dripper mounted over a 5/8 -in. air

nozzle which blows the water as droplets against the specimen. The

3

-distance from the specimen, and the nozzles can be turned

horizontal! y and vertically. The wall wetting rate can be varied

up to 2 in. of water per hour, corresponding to 1-1/4 U.S.

gallons per hour per square foot of specimen surface or 50.8 mm

of water per hour. (Rain storms with an intensity of 2 in. per

hour lasting longer than 15 min and accompanied by moderate to

high winds, although severe, are not uncommon in Canada.) The

air used to drive the water droplets against the specimen is also used to create the static pressure in the chamber, simulating wind

pressures on a building. The apparatus can provide air pressures

equivalent to winds as high as 100 mph (25 pounds per sq ft or 4.8 in. of water column).

The DBR apparatus was also used to house the water spray system used in the water resistance test specified by the

Architectural Aluminum Manufacturers Association, Inc. For

the AAMA test, the DBR apparatus only provided the static air

pressure in the chamber; the air nozzles were baffled to prevent

direct air impingement on the specimen and the water drippers were turned off.

The AAMA spray rack consists of water nozzles placed on

a square grid with 12-in. centres. The nozzles have a 1200 _spray

cone angle and deliver 1 -1/4 U. S. gallons per hour.

The wetting characteristics provided by the AAMA spray

system and the DBR apparatus differ in two respects. The water

delivered from the spray nozzles is much finer and slower than the

droplets blown onto the specimen by the DBR apparatus. Random

air motion at the specimen face prevents much of the water

discharged at the sprays from reaching the specimen. For the

same water delivery rates, the wetting rate at the wall surface is about 25 per cent less with the AAMA system than with the DBR

apparatus. The second difference in performance is in the air

pressure distribution obtained with the two systems; the air

pressure over the specimen face is fairly uniform with the AAMA test configuration, whereas local high pressure regions occur at the face immediately in front of the moving air nozzles with the

DBR configuration. The additional tests performed with the AAMA

system wer e made in or der to determine whether this peculiarity of the DBR apparatus affected the performance of the test joints.

A Betz projection water manometer was used to measure the air pressures in the chamber, at the test panel weathering

face and across the joint battens. It is capable of reading

differ-ential pr es sur es as lar ge as 400 mm of water column (15. 7 in. of

water column) and is sensitive to ｾ O. 02 mm of water column.

TEST SPECIMENS

Five panels were mounted in the 8-by 8-ft opening of the rain simulator, forming four vertical test joints between them

(Figure 2). The three central panels were 4 in. by 2 ft by 8 ft

while the two end panels wer e 4 in. by 1 ft by 8 ft. Two panels

had their adjacent edges grooved to be used in testing chambered

joints; all other edges were left plain for tests on plain-gap joints.

The panels were positioned in such a manner that all joints had a

nominal 1/8 - in. gap. Stud bolts were positioned near the panel

edges to allow easy adjustment and removal of interior and exterior

battens with wing nut clips. The battens were 3/4-in. by 1 3/4 -In,

cedar strips. The battens and the weather side and edges of the

panels were coated with alkyd enamel.

Some battens were prepared with folded film gaskets

lightly stapled to them. The gaskets were formed from 4-mil

polyethylene film fo l de d into 6 layers, with the folds running along

the length of the joint. This gasket was proposed for and used in

the Angirraq northern hut, primarily on the assumption that a low hut with small, fixed panels does not need a high -pr es sur e elastic

gasket able to withstand lar ge deformations. The folded film form s

a limp filler between batten and panels, accommodating movement

through multi-layer slip rather than material distortion. Incidental

to the main purpose of the laboratory tests, it was hoped to obtain some information to assist in the assessment of this inexpensive

approach to air -seal gasketting.

The test assembly allowed variations in joint configurations, from wide open to battened to gasketted on either or both sides; joint gaps and batten and gasket clearances were also adjustable. TEST PROCEDURE

In the normal water leakage test, the joint was exposed to wetting at a rate of 2 in. per hour for a 15 -rn in period while a

5

-static pressure difference of 13.5 mm water column (total pressure equivalent of a 35 mph wind) acted across the joint

from the exposed face. A few tests were run at both higher and

lower pressure differences.

When testing with the DBR apparatus, the water sprays

were normally located 14 in. from the specimen face. Two

tests were run with the sprays located 22 in. from the specimen. When testing with the AAMA system, the sprays were

placed 5 in. from the specimen face; static air pressure differences

of 13. 5 mm and 43. 5 mm water column (equivalent to winds of 35 and 60 mph) were used.

The rain leakage test program was designed to explor e

the general wetting patterns found in joints of varying configurations, evolving in steps from simple open joints to open rain-screen types. Air pressures outside and within the joints were measured, but no quantitative measurements of water leakage were taken.

Evaluation of joint performance relied on observations of

through-leakage during the test and on visual inspection of the joint gap

from the interior side (room side) following the test, with any

inside batten removed. Tests on anyone joint configuration were

generally repeated three times before the completion of the program. RESULTS AND DISCUSSION

1) TESTS IN DBR RAIN SIMU LATOR

Figure 3 shows the details of the joints tested, and their

performance is shown diagrammatically in Figures 4 and 5. The

sketches show the wetting pattern in the joint gaps as seen from the room side with the test stopped and the inner batten removed; water on the wetted face or in hidden chambers is not shown.

Working from left to right in Figure 4, the performance of batten and gasket in the outer position was first explored, and then

the joints evolved to the rain - scr een approach. The folded-fi Irn

gasket, described before, performed well under all conditions. No leakage occurred even when the batten gap was repeatedly varied from 1/8 in. to tightly closed and the air pressure was increased to simulate 60 mph winds (Figures 4 and 5, A3).

Configurations 7, 9 and 10 of Figure 4 have the outer batten mounted more loosely than the inner batten and can be

considered rain-screen joints. If uniform air pressure exists

over the wall face, very little pressure drop should be present across the outer batten and the air in the joint space should remain

substantially stagnant and no rain penetration should occur. The

plain-gap "A" series of joints did not perform in this way. Water

droplets were dispersed through the space as noted in A7, A9 and

AI0 of Figur e 4. Little or no wat er leaked thr ough to th e inner

wall surface (none where gaskets were used) but air currents were obviously coursing through the joint space and pulling water in. The simplest open rain-screen joints did not work.

These air currents were set up by the DBR rain simulator;

the pressure on the panel surface is non-uniform. The first part

of Table I shows that the air nozzles used to blow "rain" produce velocity pressures of about 4 mm water column (. 16 in. water

column) above the mean static pressure in the box. The nozzles

move up and down over the specimen surface every 10 sec. The

second part of Table I records the pressure differences measured

across the outer batten. These cycled at 10-sec intervals, and

from this Figure 6 was prepared to indicate the probable moving pressure pattern in a typical joint, producing in/out air flow that deposited water throughout the gap.

The severity and close spacing of these local pressure

effects of the DBR apparatus are probably not indicative of conditions

in practice. Some non -uniformity of pr es sur e, however, would be

expected on a building joint, and the geometry of the rain-screen

joint must accommodate the resulting air currents without harm.

Further, the air nozzles of the rain simulator caused the water droplets impinging on the specimen to be blown out radially from

the high pr es sur e ar ea in fr ont of the nozzle. The radiating droplets

were able to penetrate under the loose outer batten in much greater

quantities than would be expected with just the IIspatter" of

impinging drops. Such lateral travel and even upward travel of

raindrops occur on the face of high buildings, and the drops should

be barred or accommodated by the rain-screen joint. The

unsatisfactory performance of the plain-gap rain-screen joint in the DBR rain simulator should have some relevance to practice, at least in high buildings.

7

-(a) Air Chambers

Figure 4 shows that the internal geometry of the rain-screen joint can be readily arranged to accommodate internal

air currents while preventing deep penetration of water.

Com-parison of B7 to B 1 0 with A 7 to AIO indicates that the in/out air flow probably short-circuited along the first air chamber of the former, leaving the inner lands dry, while the air flow in the

latter swept the plain gap and wetted the entir e depth. This

chamber effect depends on certain size and location relationships

to handle the air -water flow. The air chamber must be quite

large in relation to the constriction between it and the wet surface,

or the surface water film must be diverted, or both. For example,

B9, CIO and E9 worked well with their outer chambers, whereas

C7 and F7 did not; the air-water stream overflowed the chambers.

The more complex outer dams of G9 worked well even without a sub stantial chamber.

In addition to channelling the in/out air curr ents, the

chambers apparently act as settling basins for any through-streams of air, allowing water to drop out where the air slows down on

crossing the chamber. Comparison of BO, Bl, B2, B6, B7 and

B8 with their counterpart plain-gap "A" joints supports this

conclusion. The chamber must, of course, be terminated in a

suitable drain detail.

(b) Gap Width

Figure 5(a) shows the wetting in joint A7 when the gap

widths were 1/16 in. and 1/4 in. (normal width, 1/8 in.). The

joint with increased gap width showed little difference in wetting

from the normal joint; wetting was still in the form of droplets.

The leakage through the joint with the smaller gap increased, due

to the water bridging the gap. Where dimensional tolerance or

thermal considerations preclude the use of a consistently wide gap, the discr ete air chamber as mentioned above has the desir ed

effect of br eaking the water film.

(c) Effect of Slanting Rain

Joints E9 and G9 were tested with the water directed 30°

depended on shallow surface grooves and vented barriers showed an increase in wetting (Figure 5(b)), while joint E, with a generous outer chamber, remained dry.

(d) Effect of Gasket Failure

Figures 5(c) and (d) show the effect of intentional gasket

failur es on the wetting characteristic of joints. When sealing

flaws were introduced under the outer gasket in A3, which was

previously dry, large water leakages occurred. When similar

flaws were introduced at the inner batten of rain-screen joints, no water leakage occurr ed even though air leakage was gr eatly incr eased.

These tests illustrate the need for flawless sealing in single -seal joints and the tolerance permissible in the seal of rain-screen joints.

2) AAMA WATER RESISTANCE TESTS

To better establish the extent to which the wetting

characteristic of joints is affected by the local pressure variations of the DBR apparatus, a secondary test program was performed

on some of the joints with the AAMA sprays. The air pressure at

the specimen face and the air pressure difference across the joint

were uniform, as shown by Table I. The water applied to the

specimen was of a very fine size and the velocity of the impinging

droplets was small; random air motion scattered the droplets

such that the water reaching the specimen was 25 per cent less

than the water provided by the DBR apparatus. The AAMA test

was much less severe than the DBR test because the pressure difference acting a c r o s s the joint was uniform, the kinetic energy of impinging water was les s, and the quantity of water hitting the specimen was less.

The resultant wetting of the joints reflected the difference

in test severity; all joints tested with the AAMA apparatus were

drier than when they were tested in the DBR apparatus. The

rain-screen joints with gasketted inner battens remained dry throughout even at extreme pressure differences, whether the gaps were plain or chambered (Figure 5 (e)).

9

-SUMMAR Y AND CONCLUSIONS

Neither the DBR nor AAMA water leakage apparatus truly simulates conditions experienced on a building face in a

wind-driven rain storm. The close-spaced air pressure variations of

the DBR rain simulator probably do not occur on a building but, becaus e of contour peculiarities and protrusions and becaus e of the building shape, some pressure variations do occur over the

windward face of a building. The uniform pressure provided

in the AAMA test method is, therefore, also an unrealistic

con-dition. Natural rain does not impinge in local clusters, as in the

DBR apparatus, nor does it always impinge with such low energy,

as in the AAMA system. In general, the DBR test may be expected

to be more severe than natural wind-driven rain and the AAMA

test less severe. This difference between laboratory test

condi-tions and actual condicondi-tions should be considered when assessing the performance of the joints in this exploratory test program.

Many configurations and materials can be used in the open rain -scr een approach to joints, arranging a loos e exterior shield or overlap over a vented air space followed by an interior au

barrier. Wher e the air space exists as a plane -sided gap

extending through the joint, water is dispersed throughout the gap in the DBR rain simulator, due to in/out currents caused by

non-uniform pressures on the face. Where the air space is shaped as

a discrete chamber or enlargement near the wetted face, water does not get in beyond this chamber even with the DBR apparatus. Outer dams or protrusions can reduce the water load in the

chamber but thes e complicate manufactur e. If suitably drained,

the air chamber should allow trouble -fr ee performance under conditions of quite severe non-uniform pressures, slanting winds,

or with some through-leaks of air. It has been shown that flaws in

a gasket in the conventional outer position allow copious water entry, while flaws in an inner gasket in a rain-screen joint do not.

REFERENCES

1) Garden, G. K. Rain penetration and its control. National

Research Council, Division of Building Research, Canadian Building Digest No. 40, Ottawa, April 1963.

2) Procedural Guide. Architectural Aluminum Manufacturers

BATTEN OF JOINTS

Type of Test DBR AAMA

Nozzle Setback 14 in. 22 in. (Nozzles Baffled)

Box Pressure 13.5 25 13.5 13. 5 43.5

(mm of water)

Pressure on Wall 13-17.5 25. 5 - 29. 5 13.4-16.5 13. 5 43.5

(mm of water)

Joint Type Pressure Difference 6P Across Outer Batten, mm Water

Al dry 12. 5 - 16. 0 wet 12. 0 - 15. 0 A6 dry 3. 7 - 7. 0 wet 7.5 - 11. 0 A7 dry 1. 0 - 2.0 1.4 3. 1 wet 1. 0 - 3. 0 1.5 - 2.5 4. 5 - 5.7 B7 dry 0

-

1.0 0.6 1.5 wet 4.5 - 5. 3 1.0 - 3.0 4. 8 - 6.0 A9 dry -0.7 + 1.0 -1.0+2.5 -0. 4 + 1. 0 0.2 wet -0.7 + 1.0 -1. 0 + 2. 5 -0. 4 + 1. 0

O.

2 B9 dry -0.8 + 2. 0 -1. 0 + 2. 5 -0.4+ 1.0

O.

2 wet -0.8 + 2.0 -1. 0 + 2. 5 -0.4+ 1.0 _, 0.2 A2 dry 13.0 - 16. 0

I

wet 16. 0 - 18. 0 i B8 dry 4.0 - 6. 0 _j wet 9. 0 - 12. 0

I

, A10 dry 0.2 - 3. 0 0.4 I wet 1.0- 4.0 2.20 B10 dry 1. 0 - 3. 0 1.2 wet 4.0 - 9. 0 3. 0 - 5.0

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