The unforgiving North

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The unforgiving North

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The Unforgiving North

by R.W. Chill and J.K. Latta

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Proceedings Fourth Canadian Building Congress

Learning from Experience / Avoiding Failures

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Session 5, p. 157

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LE NORD IMPARDONNABLE

Les desordres dans les batiments construits dans le Nord sont souvent le resultat d'un manque de discernement dans l'application des techniques de construction couramment utilisees dans le sud du pays. Un certain nombre de facteurs environnementaux propres au Nord doivent etre pris en consid6ration pour assurer la durabilite des bltiments. Cette communication propose des solutions _B divers problsmes au niveau de l'enveloppe, des fondations et de la ventilation, problsmes qui sont associ6s aux grands vents, au pergelis01 et aux longues periodes de temps froid caracteristiques des regions nordiques.

THE

UNFORGIVING NORTH

R.W.C. Chill, Indian and Northern Affairs Canada, and J.K. Latta, National Research Council Canada, Ottawa

Building failures in the North have often resulted from indiscriminate application of standard southern construction practices. A number of environmental factors unique to the North must be taken into consideration before durability can be achieved. This paper proposes solutions to a variety of envelope, foundation and ventilation problems, which are related to the high winds, permafrost and long cold periods characteristic of the North.

THE UNFORGIVING NORTH

R.W.C. Chill1 and J.K. Latta2

l~ndian and Northern Affairs Canada

*~ivision of Building Research, National Research Council of Canada

INTRODUCTION

Everyone is well aware that the North is cold; what really distinguishes the North from the South is the duration of the cold season, rather than the extreme low temperatures. Saskatoon has a 1% January design temperature of -V°C and 6077 heating degree days below la°C, whereas Frobisher Bay, with a 1% design temperature only S°C colder, has 9844 degree days Celsius.

A profound distinction between the North and the South arises out of this. In the South, when condensation occurs in the fabric of a building because of some minor defect, only a relatively small amount of condensate accumulates before conditions moderate and the water has an

opportunity to dry out. In the North, condensate accumulates over a long period and the summers may be too short for this larger quantity to dry out completely; this leads to a progressive buildup of water from one year to the next.

For many'years, the North has been designated as those areas north of the southern limit of scattered, discontinuous permafrost. Since permafrost is a temperature condition, any

disturbance of the natural ground cover may upset the natural thermal balance and cause the ground to thaw. This problem may be compounded by heat loss from a building. With soils that are permeated with ice lenses, this can lead to a complete loss of strength and to serious settlement, which can rip a building apart.

The North is also characterized by strong winds together with long periods of intense cold; drafts that would be considered minor in the South can cause major problems in the North. In addition to the discomfort, pipes and even water and sewage holding tanks may be frozen.

An

airtight envelope is thus essential in the North, but airtightness accentuates the problem of ventilation of the building itself. The chimney may be back-drafted if it becomes the principal entrance for air to replace that sucked out of the building by wind action through a poorly placed vent.

Buildings in the North have been afflicted with these and many more problems because designers have failed to appreciate the differences between

northern and southern conditions. There are no easy solutions transferable from southern

experience. Would-be designers and builders of northern buildings rmst take pains to discover the problems before adding to the already massive cost of building failures.

Despite the harshness of the climate (and also because of it),,Northern buildings m s t work in all respects. Aesthetically pleasing designs are possible but technology is paramount, for the North is unforgiving of error.

THE BUILDING ENVELOPE

Deterioration of the envelope occurs when water accumulates within its thickness without being able to dry out again.

In the North this accumulation collects as hoarfrost (Fig.

1)

and goes unnoticed until a moderation in the outdoor temperature causes it to melt. Then it flows out of the envelope and may appear temporarily as icicles (Fig.

2)

or as a stain on the ceiling. In a worse case the weight of accumulated water may cause the ceiling to collapse or, worse still, the water stays trapped in the envelope to soak the wood members and promote rot or corrosion of nails and other metal fasteners. Sometimes evidence of this trapped water appears on the outside as staining of the siding material.

To stop the outward movement of air that carries the water vapour to the location in the envelope where it condenses, the building envelope uust be made airtight. This is essential for the durabil- ity of the envelope and is not just for energy conservation, as is often thought. Saving energy is important, especially in the North, but not as important as the durability of the building.

Air leaking out of the building must be replaced by an equal amount of outside air, which will, as a minimum, cause discomfort for the occupants if it enters through uncontrolled leaks. In more severe cases, clothes in closets against an outer wall, or even beds against outer walls, can become frozen in place. Wind can blow through the envelope from one point to another without entering the building and may cool the interior finish to below the dew point temperature of the room air, leading to

In many p a r t s of t h e North, v e n t i l a t i o n of a t t i c s and roof s p a c e s i s n o t a f e a s i b l e way t o c o n t r o l moisture accumulation, s i n c e very f i n e powder snow and i c e c r y s t a l s i n t h e a i r a r e blown through even small openings and deposited i n t h e a t t i c . The whole concept of c o n t r o l l i n g moisture accumulation by v e n t i l a t i o n is l a r g l y based upon a f a u l t y premise. For t h e system t o work, t h e flow of a i r through t h e a t t i c must be a b l e t o absorb a t least a s much moisture a s l e a k s i n t o t h e a t t i c from t h e house. A t t h e very low temperatures t h a t p r e v a i l f o r long p e r i o d s i n t h e North, t h e a i r is not capable of holding much water and is c l o s e t o s a t u r a t i o n a l l w i n t e r long. On t h e o t h e r hand, even r e l a t i v e l y small l e a k s from t h e house, s i n c e they a r e much warmer, can c a r r y l a r g e q u a n t i t i e s of water. Thus, i t i s v i r t u a l l y impossible t o remove enough moisture from t h e a t t i c t o prevent

condensation.

The only e f f e c t i v e approach i s t o s t r i v e t o e l i m i n a t e a l l a i r l e a k s from t h e house i n t o t h e roof c o n s t r u c t i o n and t o reduce vapour d i f f u s i o n t o a n e g l i g i b l e amount by means of a good vapour b a r r i e r . Even so, some p r o v i s i o n should be made f o r moisture t o escape. F i r s t , any r e l a t i v e l y l a r g e q u a n t i t i e s of water should be drained t o t h e eaves, which i n d i c a t e s t h e use of a sloped c e i l i n g r a t h e r than a l e v e l one. Second, v e n t i l a t i o n can be provided i n summer but should be closed off during w i n t e r , which w i l l r e q u i r e a r e v i s e d d e t a i l a t the eaves t o provide drainage t o t h e o u t s i d e without allowing t h e wind t o blow through t h e i n s u l a t i o n . The roof i n s u l a t i o n could be i n closed-ended compartments, but t h a t would i n h i b i t summer v e n t i l a t i o n u n l e s s p r o v i s i o n is made t o open t h e compartments a t t h e ridge. Truly, t h e r e a r e no easy s o l u t i o n s i n t h e North.

WINDOWS AND EXTERNAL DOORS

Openable windows and e x t e r n a l doors a r e i n many ways comparable items and s u f f e r from a number of s i m i l a r problems, mainly due t o t h e accummulation of snow, f r o s t o r i c e between t h e frame and t h e movable s a s h o r door. It i s e s s e n t i a l t h a t a door be operable a t a l l times, but i t i s n o t e s s e n t i a l t h a t a window should open. Fixed windows e l i m i n a t e most of t h e major problems and should be t h e choice f o r t h e North. V e n t i l a t i o n can be provided by o t h e r means.

Air l e a k i n g o u t from t h e house p a s t t h e door o r window s a s h w i l l flow over t h e cold o u t e r p o r t i o n s of t h e frame and some of t h e moisture i t is c a r r y i n g w i l l probably condense o u t a s f r o s t (Fig. 3). Snow can be blown i n t o t h e gap between t h e frame and t h e movable s a s h o r door. Some of t h i s f r o s t o r snow w i l l melt and then r e f r e e z e i n t o s o l i d i c e o r i t may be packed s o l i d by t h e opening and c l o s i n g of t h e door o r window. Condensate t h a t runs o f f t h e g l a s s may f r e e z e between t h e bottom of t h e sash and t h e frame. Thus a t some time a closed window o r door w i l l be f r o z e n s h u t and an open one prevented from c l o s i n g properly. A door must, however, be opened f o r people t o pass i n and o u t ; sooner o r l a t e r i t w i l l be damaged a s i t i s forced

open. I f windowe a r e used t o provide v e n t i l a t i o n , t h e n they t o o m e t be f o r c e d open; s i n c e they a r e much l e s e r o b u s t than doors they w i l l soon be damaged s o badly t h a t they w i l l have t o be

replaced. The t h i n s a s h t v i e t e e a s i l y and breaks t h e g l a s s . Weatheretripping i e o f t e n encased i n t h e i c e and g e t e ripped o f f .

Because of t h e i r h e i g h t and c o n s t r u c t i o n , doors have a more s e r i o u s problem than windows w i t h warping due t o temperature o r humidity d i f f e r e n c e s b e t w e n t h e i n e i d e and o u t s i d e faces. Gaps may open a t t h e t o p and bottom of an outward opening door on t h e l a t c h s i d e , allowing convective a i r flow with e x f i l t r a t i o n a t t h e top, even i n calm weather, t o compound t h e problem of condensation

(Fig. 4). &I t h e hinge s i d e , s e v e r e s t r e s s e s w i l l be imposed on t h e h i n g e s a s they r e s i s t bowing. Four hinges should be used r a t h e r than t h e t h r e e r e q u i r e d by b u i l d i n g codes. On an outward opening door t h e l a t c h t o o may be s u b j e c t e d t o c o n s i d e r a b l e

f o r c e s t h a t can lead t o e a r l y f a i l u r e and t h a t make i t d i f f i c u l t t o o p e r a t e , e s p e c i a l l y by a c h i l d wearing heavy m i t t s . Lever type handles can overcome t h i s b u t t h e y m e t be very r o b u s t t o withstand t h e f o r c e s on t h e mechanism.

Conventional w e a t h e r s t r i p p i n g ( r u b b e r , p l a s t i c o r s p r i n g metal s t r i p s ) i s t o o f r a g i l e and o f t e n poorly located. All s e a l i n g d e v i c e s must be placed on t h e i n s i d e t o keep them warm. This may l e a d t o t h e use of an outward opening door, which is

c o n t r a r y t o conventional s o u t h e r n p r a c t i c e f o r houses. Gaskets should be ueed i n preference t o w e a t h e r s t r i p p i n g and, t o accommodate any warping, t h e g a s k e t should be of t h e f l e x i b l e magnetic type. The hinges must be placed s o t h a t t h e door moves away from t h e g a s k e t on t h e hinge s i d e i n s t e a d of wiping a c r o s s i t and p o s e i b l y pinching i t (Fig. 5).

The g a s k e t should be placed i n a pocket on a l l s i d e s t o p r o t e c t i t from damage. With t h i s

arrangement t h e r e i s no c l o s e f i t t i n g rabbet a t t h e hanging jamb o r s i l l i n which snow could pack. A pocket mst be l e f t under t h e door f o r snow and d i r t o f f boots t o f a l l i n t o r e g a r d l e s s of whether t h e door opens inward o r outward (Fig. 6). With an outward opening door t h e r e should be a s t e p down i n t h e p l a n e of t h e i n n e r f a c e of t h e door w i t h an open g r i l l l a n d i n g below i t t h a t w i l l not accumulate snow. Northern b u i l d i n g s a r e mostly r a i s e d o f f t h e ground t o maintain t h e permafrost and, because of t h e f r e e flow of wind under t h e b u i l d i n g , snow w i l l not accumulate below t h e platform. In a l l c a s e s t h e bottom g a s k e t mst be p r o t e c t e d by a s t r o n g t h r e s h o l d p l a t e .

Compressible type g a s k e t s should be mounted between heavy metal f a c i n g s t h a t have t h e major p o r t i o n of t h e i r a r e a exposed t o t h e i n e i d e s o ae t o c o l l e c t and conduct h e a t t o them. The gap between t h e frame and t h e s a s h o r door nust be s h i e l d e d t o keep o u t wind-driven snow. E x t e r i o r doors can be

i s o l a t e d from t h e humid, heated i n t e r i o r of t h e b u i l d i n g by means of an unheated and u n v e n t i l a t e d v e s t i b u l e with an a i r t i g h t i n n e r door with a s e l f c l o s i n g d e v i c e mounted s e c u r e l y on t h e warm s i d e . A l l hardware needs t o be much s t r o n g e r , be more s e c u r e l y mounted and have b e t t e r r u s t p r o o f i n g t h a n conventional equipment used i n t h e South.

Hold-open devices for windows (Fig. 7 ) and large fissures full of ice, or well drained coarse retainers and hinges on outward opening doors rmst gravel) or on permafrost that remains frozen. In be strong enough to withstand the high winds that the former caee more or less conventional southern prevail in the North. Hinges should have riveted practice can be followed.

In

the second case two pins and modified leaves to maintain security general techniques can

be

followed, each of which against unauthorized entry. Iatches for windows attempts to stop heat from the building from should be replaced by clamping devices to ensure

airtightness.

A

window designed to meet these conditions has been tried over the wlnter of 1984185 in Frobisher Bay, and has worked well. Glass breakage is a serious problem in the North because of a high incidence of vandalism and also because of the wind, thermal stresses, and abuse of the sash when jammed by ice formation. Acrylic

and

polycarbonate glazing would tolerate this abuse, but they are expensive. Also they are banned by many fire departments as difficult to break through for entry into or escape from a burning building. Tempered glass has been used successfully and, though costlier initially, it is cheaper in the long term. It can be broken for fire exit or emergency entry and rescue.

Thermally, windows and doors are weak points in the building envelope. Windows must be kept free of condensation and ice formation that would obscure vision and may damage the sill and wall below. With the extensive duration of low outside temperatures, condensation on windows is inevitable, even with moderate indoor relative humidities, unless special provisions are made to prevent it. One way ie to blow air over the

window. If this air is heated it nay not

be

cooled to its dew point temperature while in contact with the glass. Heated or not, the added turbulence will reduce the thickness of the inner air film, thus warming the glass slightly. More importantly, it will sweep away cooled air in contact with the glass that is nearing its dew point. Recirculated air from the house will suffice, provided the air flow is continuous.

FOUNDATIONS

The majority of buildings in the North are founded on permafrost, which is defined as the thermal condition in soil or rock of temperatures below O°C

persisting over at least two consecutive winters and the intenrening summer. Moisture in the form of water and ground ice may or may not be present; rock can be permafrost, as can silt that is permeated with ice lenses. Above the permafrost, an active layer thaws in summer and freezes in winter. This layer can vary from a few inches to several feet, but with large local variations.

As most of northern Canada was glaciated, fine-grained soils, which are generally frost- susceptible, predominate. When perennially frozen, they contain large quantities of ice and when thawed they turn to a slurry with little or no strength.

To avoid failures due to settlement, buildings must either be founded on material that does not become unstable when it thaws (e.g., solid rock with no

reaching the permafrost.

Wherever possible the building should be raised off the ground so that the wind can blow underneath it. Naturally, the floor =st be insulated and airtight to maintain satisfactory internal conditions and reduce the cost of heating, but a skirting around the building to save energy by blocking the wind must not be installed. Allowing free pasage for the wind has the further benefit of preventing snow from drifting on the leeward side. The building can be supported either on piles anchored in the permafrost below the active layer or on footings on a pad of granular material that is not frost- susceptable.

Piles are usually inserted in holes drilled or steamed in the permaforst and then frozen in place. The length of pile below the active layer must be great enough to support the load from the structure by adhesion in the permafrost, aided by

end-bearing. Steel and concrete piles have a high heat conductivity and so will melt the permafrost in summer to a depth greater than that of the active layer. Wood piles have a better insulating value. Also, the strength of frozen ground

increases with decrease in temperature and, in general, with increase in moisture (ice) content. The pile will

be

subjected to an uplift as the active layer refreezes in the fall. The ground freezes to the pile near the surface and the frost heave forces caused as the material in the active layer freezes will jack the pile out of the ground if it is not .sufficiently well anchored in the permafrost below.

When one is relying on adhesion to resist both the applied loads and uplift, a rule of thumb is that the length of pile in the inactive permafrost should be twice the length in the active layer, allowing for any increase in depth of the active layer around the pile.

A

pile that relies on end-bearing on rock a short way below the active layer may not be sufficiently well anchored to resist uplift unless it is anchored into the rock. The alternative to a pile foundation is a pad of granular non-frost-eusceptible material over the existing active layer. This pad must be thick enough to keep the original ground frozen and to contain the active layer entirely within the thickness of the pad.

A

pad made of granular q~aterial will not lose strength as it thaws in spring nor will it heave as it refreezes in the fall. It may be difficult to obtain suitable non-frost-causceptible, granular material in an area that is overlain with silty material.

Drainage must be arranged to deflect water away from the pad and to remove water from snow or rain that may fall on the pad. In northern areas surface water is conspicuous in the summer, despite the generally low precipitation. Because

water-bearing permafrost soil is relatively impermeable, drainage is generally poor and movement of water can only occur above it. For this reason materials in the active layer are often saturated. Accumulation of water on the ground surface can be a serious problem because of its thawing effect on the permafrost. Drainage is therefore vital. If natural drainage is impeded or

:

proper drainage structures are not provided, construction operations can be seriously

complicated by intensified frost action during the winter and accelerated thawing during the summer. Construction of the granular pad will normally be carried out in summer when the active layer is thawed. Thus some of the silty material may be squeezed up into the bottom layers of the pad, making those layers frost-susceptable. Over the following winter the ground will refreeze and heaving will occur in the original soil. Some settlement will take place in the granular material of the pad although this can be minimized by

compacting it with loaded dump trucks. Thus the surface of the pad will move during the first winter at least. If possible the erection of the building should be delayed until the next summer, to allow time for the permafrost table to establish itself in the granular pad.

In

any case, because it is difficult to ensure stability of the

foundation pad, the footings supporting the main beams of the building should be made adjustable. This is usually done by means of hardwood wedges. Levelling of the house structure by means of these wedges is a somewhat tedious chore and in some cases screw jacks are used instead, with a locking device to prevent movement in the jack itself. If the task is not carried out annually, the

accumulated movement could split the airtight components of the building envelope, leading to poor performance and rapid deterioration.

High winds in the North pose a problem of lateral displacement or overturning. These have to be resisted by tying together the building, its supporting beams and the footings or piles. Then the whole must be firmly anchored to the ground. With piles this usually presents no problem, unless they are short end-bearing piles founded on rock. With spread footings on pads the sill members must be set with their top surface flush with the top of the pad to resist lateral movement and the building tied down against uplift with long bolts anchored by deadmen below the pad.

Racking of the superstructure must be minimized by making the main beams very stiff and continuous over the supports. This requires very deep beams of steel or glulam construction, well braced to prevent sideways collapse.

With larger buildings, and those such as garages or warehouses that must carry heavy loads, elevated floors are not practical and it is necessary to construct a slab-on-grade.

In

this case, too, heat from the building must be dissipated to the air to prevent thawing of the permafrost. The rate of heat flow from the building can be reduced, but not stopped, by insulation placed below the slab. With narrow buildings, this reduced heat flow can move

sideways through a thick granular pad to be carried away by the air around the building. With wider buildings it will be necessary to provide vent pipes through the pad. If natural ventilation is to be relied upon, large ducts of at least 600 m

diameter must be used. Otherwise fans can be used to blow outside air through smaller ducts.

Considerable skill is needed to select the correct combination of inrulation, fill and ventilation.

VENTILATION

Because the building envelope must be as airtight as possible, natural air infiltration and

exfiltration cannot be relied upon to provide adequate ventilation. Openable windows should not be used for ventilation in cold weather, since they are subject to a multitude of problems.

Ventilation must, therefore, be provided through a specially designed system.

The simplest way to provide controlled ventilation is by means of a mechanical system using

electrically driven fans. Ikrfortunately, with the very high cost of electricity at some locations in the North (up to 7OSlkW-h) this imposes an extra financial burden. Even with mechanically driven fans, the pressure distribution within the building and the location of the intake and exhaust are of crucial importance. Merely placing the intake and exhaust openings on the same facade so as to be exposed to approximately the same wind pressure is no guarantee of satisfactory operation. The fan characteristics of flow under various pressure regimes must be taken into account and the fans must not be selected solely on the basis of rated capacities under standard pressure conditions.

A

reduced or increased flow for a day or two is not likely to create a health problem or to increase the heating energy consumption seriously. If a suction is created by a powerful exhaust fan, or even by wind action on a poorly located outlet for a non-mechanical system, combustion equipment will be back-drafted.

Ideally the ventilation air should be warmed to at least room temperature before it is introduced into the building, but with non-mechanical systems this is usually not possible. With a mechanical

ventilation system and a forced warm air heating system, the outside air is often fed into the return air duct. If so, the two air streams must be well mixed before they reach the furnace heat exchenger, otherwise a cold spot will form on the heat exchanger, leading to condensation and

preqture failure from corrosion. Furthermore, the suct4on of a furnace air circulation fan is

considerably greater than the delivery from a ventilation unit, which will be overwhelmed. Thus

the fresh air should be distributed in a separate system or introduced in a space in the house where

it will be picked up and mixed with the return air before distribution. This latter solution has been tried successfully in a house in Frobisher Bay. To reduce the cost of heating the ventilation air and to temper it to a reasonable extent before

introducing it into the building, heat recovery ventilators are being used in new houses in the North. Their effectiveness levels are often much lower than expected. One installation in Frobisher Bay was monitored at between 21 and 60% in cold weather, which was attributed to the heat exchanger being iced up enough to interfere with heat

transfer but not badly enough to initiate the defrost cycle. Air exhausted by such a unit should not be taken from bathroom or kitchen areas, because of the high moisture content.

CONCLUSION

Just because something works in the South is no guarantee that it will do so in the North. Every detail of construction must be thought out with great care to ensure that it is based upon sound technical principles and can be built with the available labour in the short construction season. Anticipate the worst; then plan to prevent it, for surely "if something can go wrong it will".

Non-mechanical ventilation systems are difficult to

design because of the great variability of the ACKNOWLEDGEMENT

driving forces: wind and stack effect. However,

in the North there are long periods when these This paper is a contribution of the Division of forces are more than enough to provide adequate Building Research, National Research Council of ventilation. The system would have to be installed Canada, and of Indian and Northern Affairs Canada. in the tightest possible envelope to ensure

controlled ventilation at a specified, but variable rate, with proper distribution of air throughout

the building. An electrically driven fan would be e

needed for those periods when stack effect and wind forces did not suffice.

-9

PLUMBING

Piped water supply and sewage disposal is not the norm for most communities in the North. Most modern houses are equipped with a water storage

tank, and water is delivered by tank truck. Similarly sewage is held in a storage tank until extracted by a suction pump on a sewage truck and taken away for disposal.

The suction pumps on the sewage trucks can cause a considerable vortex and draw-down of the surface of the sewage in the holding tank if a simple dip pipe . . -is used. With shallow tanks, the suctibn may be broken indicating an empty tank long before all the

sewage has been removed. A wide mouthed suction Fig. 1. Frost formation under the roof and on intake cone of about 450 mm diameter will reduce insulation.

the loss of head due to vortex formation. The suction can draw water out of the traps of the fixtures in the house, or even collapse the tank, unless adequate tank venting is provided.

The vent pipe must pass to the outside of the building and so the tip will be exposed to the cold outside temperatures, with the danger that vapour from the warm water in the tank will condense as frost (Fig. 8) and ultimately block the pipe. The buildup of frost at the tip of the vent pipe must be reduced by increasing the temperature of the pipe; this can be done by minimizing the surface area of pipe exposed to cold temperatures,

increasing the area exposed to warm temperatures, and using a highly conductive material, such as copper. Any pipe that must be run through a cold attic should be heavily insulated. In order to keep the area exposed to the cold to a minimum, the diameter of the pipe should not be increased after it passes through the insulated envelope. As a

last resort a heat trace can be used to feed more Fig. 2. Icicles from melting hoarfrost under

Fie.

-

5. Horizontal section, modified jamb and hinging for steel doore with magnetic gasket.

Fig. 3. Frost deposition from warm, moist air leaking past windau sash.

Fig. 4. Frost deposition from convective air flow allowed by bowing of door.

D O U B L E F R A M E W A L L D R I P L I N T E L O U R B A R R I E R Y P S U M B O A R D R E T U R N E D S T A I N L E S S STEELi

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-I N S U L A T E D S T E E L D O O R A L U M I N U M ... - ~ P A C K I N G H A R n W O O D M A G N E T I C G A S K E T D I R T P O C K E T ,--FLOOR

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Fig. 7. Heavy duty hold-open device and hinges an Fig. 8. Frost blockage of plumbing vent