Field visits to moisture troubled housing in a Maritime climate

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Field visits to moisture troubled housing in a Maritime climate

Scott, D. L.

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ISSN

BUILDING

PRACTICE

NOTE

FIELD VISITS

TO MOISTURE

HOUSING IN

CLIMATE

B Y

D.L.

Division of Building Research, National &search Council of Canada

O t t a w a , September 1984 r N R C - C16T1

BLDG.

RES.

.-

L I B R A R Y

'.?

01-

U -

4

5

FIELD VISITS

TO

HOUSING

IN

MARITIME

by

D.L. Scott*

ABSTRACT

This Mote d e s c r i b e s l a c a l f z e d moisture damage to maritime housing t h a t can b e attributed to a combination ~f inadequate d e t a i l i n g and poor workmanship oz lack of maintenance.

INTRODUCTION

aver t h e p a s t f e w years a number of field v i s i t s have been made t a

investigate the nature and extent a£ moisture-induced damage to wood frame

housing within A t l a n t i c Canada. The number

of

a l l o w a meaningful s t a t i s t i c a l p r e d i c t i o n concerning moisture problems in the overall b u i l d i n g population. It does appear, however, that a

small

can be

a

in the.

~alifax,

M.S.

St.

practice.

CASE ONE

A factory-built s p l i t entry three bedroom home constructed in the fall

of 1982 near Halifax w a s occupied by two adults and one c h i l d . The owners

camplained a f roof l e a k s id rhe v i c i n i t y

of

t h e

warm

An inspectian of the r a o f i n March 1984 found all asphalt s h i n g l e s in

place and a p p r o p r i a t e l y tabbed down. Flashings around the roof caps for

bath

contractor. The a t t i c hatch w a s weatherstripped and the glass f i b r e b a t t s

were

w i t h mold and was saturated over an area immediately above the bathroom and

common plumbing w a l l w i t h the kitchen ( F i g . 1 ) .

No

o.r

*

Figure 1. Saturated roof sheathing

g r i l l was removed, exposing gaps of up to 12.5 mm

(%

housing and adjacent drywall. Similar g a p s w e r e found between the head

l i n e r

of the cabinet above the kitchen szove and t h e range hood fan duct, As air

leakage appeared to be the main moisture c o n t r i b u t o r , these gaps w e r e

caulked. A hygrothemograph w a s installed to record indoor temperature

and h m i d i t y

-

Weekly v i s i t s w e r e made t o i n s t a l l n e w charts and to monitor the

c o n d i t i s n of the roof sheathing. One week after caulking around t h e exhaust f a n housing, the roof sheathing was found to be e s s e n t i a l l y dry above

the bathroom, with some reductian in moisture above the cornon plumbing

0 w a l l . Tcqeratures throughout t h e study period were maintained at 18 C

(65'~) and t h e relative humidity varied between 50 and 6 4 p e r c e n t . The high humidity readings can be a t t r i b u t e d to the clothes dryer (unvented u n t i l

l a t e in t h e study) and low ventilation rates combined with a reasonably

tight house.

By the second week, t h e w e t roof sheathing condition still p e r s i s t e d

above the plumbing wall and a more d e t a i l e d examination of air leakage

sources was undertaken. The kitchen range hood and cabinet were removed,

exposing a substantial gap between the drop ceiling and range hood d u c t ( F i g . 2 ) . When the duct w a s removed, a d d i t i o n a l lacatfans f o r a i r leakage

were discovered at t h e plumbing stack and through several holes drilled in the t o p p l a t e (Fig. 3). These holes to the attic were interconnected

w i t h an uncovered plumbing access hatch located behznd a false f r o n t o n the

Figure '3.. Air leakage past plumbing and electrical services

Figure 4. Uncovered plumbtng access

allows moisture to enter

A f u r t h e r check

in

barrier

5).

Figure 5. Ductwark in a t t i c untaped

Several clear air leakage paths had now been confirmed for moisture- laden a i r from the kitchen area i n t o t h e

a t t i c

the attic the moist air would rise until it hit the cold sheathing, where

frost would form, init-iatlng the cycle leading t o " a t t i c rafn" during

mild

to the plumbing chase. The remaining wet sheathing

then

week. The

was encouraged

to increase the use o f exhaust fans in an effort to reduce relative humidities to levels of about

40

A T T I C M A I N FLOOk B A S E M E N T W I N T E R C O N D E N S A T I O N A N D F R O S T U N T A P E D DUCTWORK N O C A U L K I N G A R O U N D D U C T W O R K O V E R S I Z E D E L E C T R I C A L F E E D HOLE PLUMBING A C C E S S W I T H O U T COVER O V E R S I Z E D H O L E FOR PLUMBING S T A C K

CASE

Aluminum s i d i n g installers replacing the s i d i n g on a two storey duplex

discovered water between t h e sheathing paper and 9.5 mm (318 in.) plywood sheathing. The plywood showed water s t a i n s and preliminary signs of rot in

the stud s p a c e s immediately adjacent to the t i l e d bathtub enclosure in the

second f l o o r bathroom, with the darkest p a t t e r n immediately o p p o s i t e the

soap dish ( F i g s .

7 and

Figure

7 .

on bathtub w a l l

Figure 8. Same pattern on

adjacent housing *it

me

30

patches.

me

was

dish

f r i c t i o n fit i n s u l a t i o n removed. The polyethylene vapous barrier had been cut to i n s t a l l t h e soap

d i s h

of mildew

moisture had accumulated between the polyethylene and the gypsum drywall

Figure 9 . Sheathing cutback behind

soap d i s h

The vapour b a r r i e r stopped at t h e rim of the bathtub, leaviug friction f i t glass fibre insulation exposed t o the area under the tub. Since the house occupants noted the soap d i s h had been loose for some time, it becomes d i f f i c u l t to assess t h e relatllve moisture contribution from direct leakage during showers, a i r leakage at the soap d i s h and d i f f u s i o n and air leakage

through t h e unprotected insulation below the bathtub. These factors did, however, combTne to overcome the natural drying potential of the w a l l in the

area immediately around the bathtub. The remainder of the sheathing in the

These houses were constructed to currenr practice fur the day w i t h respect to insulation and vapour barriers. The plumber r o u t i n e l y roughs i n

the bathtub in advance of the application of insulation,which makes i n s u l a t i n g

below

barrier

i m p o s s i b l e . Consideration

should

a s i n g l e sheet

of

rim

reduce

buildup

wall by

limiting a i r

and

the wall

In

d r y w a l l is almost i n e v i t a b l e

ff the

Surface mounted f i x t u r e s wauld

at leasr

gypsumboard, which would assist in maintaining air and vapour tightness ( F i g . 10). SURFACE MOUNT

F I X T U R E S

T I L E

S U C H

CASE THREE

A s i m i l a r case resulted in m o r e serious damage before the owner w a s alerted to t h e pxoblem. The ,exterior w a l l o f a second storey bathroom was

composed of aluminum s i d i n g , asphalt b u i l d i n g paper, 9.5 mrn (318

in.)

sheathing, 38 x 140 rmn (2 x 6 in-) s t u d s , RSI 3.52 (R20) insulation and a

polyethylene vapour

barrier

rim.

in October

l i n e

plywood

filler end of the bathtub had deteriorated below the v i n y l

floor

that water spillage during childrens' baths and showers was common

and

m o s t water would d i s a p p e a r at the open joint between the v i n y l flooring

and bathtub. Considerable damage w a s caused by

t h i s

( F i g . 11). At the time af inspection t h e w a l l sheathing had a l m a s t n o

structural c a p a b i l i t y and the fibreboard backerboard installed w i t h the aluminum siding w a s saturated (Fig. 12).

Figure 11. S u b f l o o r damage Figure 12. Deteriorated wall

sheathing

In t h i s example, a i r in the Eloorlceiling cavity picked up moisture

spilled i n t o t h e cavity. T h i s moist a i r was able to migrate up through the subfloor, where a l a r g e hole w a s cut for the trap on the bathtub and out

into the

outer

Damage to the exterior w a l l

and

e l i m i n a t e d by controlling water s p i l l a g e , Although most houses up until

r e c e n t l y have been constructed without an air or a vapour barrier b e l o w

the bathtub rim, this problem w o u l d have been greatly reduced if both had

CASE FOUR

A two-storey duplex l o c a t e d in

the

investigazed in March. The exterior

wall system consisted

polyethylene, paper clad

E I

plywood with vertical and

horizontal

temperature and moisture conditions maintained in this u n i t .

The plywood cladding on the SE comer w a s removed, revealing a w e t

stain b n

the panel

13 and

Figure

13.

by a i r leakage at

electrical box

Figure 14. Insulation details

adjacent to e l e c t r i c a l b ox

Moisture-laden air had apparently leaked o u t p a s t h o l e s around and

through

Water

forming

t h e

varied considerably in relation to the proximity of the electrical outlet ( F i g . 15)

.

PLYWOOD CLADDING

Figure 15.

FRAMING ON SE CORNER

VALUES

WITH

TAKEN

75

OUTSIDE FACE

Percent moisture c o n t e n t in

w a l l

Substantial rot w a s found in the

sill p l a t e s

lower r i g h t and upper l e f t hand corners af the panel. Both locations are below an electrical outlet ( s u b j e c t

to

horizontal j o i n t

in the c l a d d i n g ( s u b j e c t

f i b r e i n s u l a t i o n w a s dry, except where it was wadded

in

electrical

box.

CONCLUSIONS

Hoisture damage in the houses studied w a s l o c a l i z e d and appeared to

result from one of three factors:

1. Information

on

residential warking drawings contain only dimensions and material

napes, leaving much of the detailing to standard trade procedures. T h i s p r a c t i c e , while economical in expediting a b u i l d i n g p r a j e c t , has

been shown to produce long term problems.

mre

conveyed to

the

2.

and rtmely

i n s p e c t i o n , t h e construction process soon conceals the evidence, making

future discovery and correction d i f f i c u l t and costly. A small amount

of

3. B u i l d i n g s m s t

be

warranty p l a n s .

To

Note, the b u i l d i n g owner should identify and a t t e n d to minor

maintenance problems before s e r i o u s deterioration begins.

The