Using Sprayed-In-Place Polyurethane Foam Insulation (PUFI) in Farm Buildings

Agdex#:	714
Publication Date:	01/93
Order#:	93-011
Last Reviewed:	01/93
History:	Original Factsheet
Written by:	H.W. Fraser - Engineer (Horticultural Crop Structures & Equipment)/OMAF; Harold K. House - Engineer (Beef & Dairy Structures & Equipment)/OMAF

Table of Contents

1. Why is it So Popular?
2. What is PUFI
3. Water Absorption Into PUFI
4. Current Construction Techniques
5. Spraying From Inside to Outside Wood
6. Spraying from Inside to Outside Steel
7. Spraying from Outside to Inside Plywood
8. Spraying From Outside to Inside Steel
9. Choosing the Correct Construction Method
10. Building Tips
11. Summary

Why Is It So Popular?

Over the past 20 years sprayed-in-place polyurethane foam insulation (PUFI) has become the insulation of choice for thousands of farm buildings including horticultural fruit and vegetable storages and swine barns. Farmers often prefer the benefits of PUFI since it:

• has a relatively high R-value per unit thickness (at least R-6/inch) compared to many other insulations
• is easy and quick to apply in awkward locations, and on irregular surfaces
• provides an airtight seal, reducing convective heat losses or gains
• provides some increased rigidity to the building
• flows into cracks and gaps that would otherwise not have any insulation
• is a less favourable home for rodents since it is usually not thick enough to burrow in
  
  

PUFI is not without its costs since it:

• is more expensive than traditional fibreglass batt insulation for the same insulation value. However, the cost of PUFI includes applying it, whereas there is still the labour to install other types of insulation.
• is a foamed plastic material and if it is left exposed on the interior of a farm building, it must have a fire-protective covering. Common coverings include plywood; steel; or a cementitious coating material such as *Zonolite 3300, a material commonly used by Ontario applicators. (Always check with your building contractor, building inspector, and insurance agent for suitable materials)
• has traditionally used a fluorocarbon refrigerant as its blowing agent, a substance that has come under fire recently as affecting the Earth's protective ozone layer. New more environmentally friendly formulations are now available.
• can be eaten by rodents or insects, although it has no food value.
• can absorb water vapour and is not a perfect vapour barrier (such as steel cladding or polyethylene sheeting) as many people believe. Although the movement of water vapour through PUFI is very slow indeed, it will pass through PUFI under the right environmental conditions as discussed later. 

* No commercial endorsement is intended

When considering using PUFI or any other insulation, one must take into account all of their financial and environmental costs and benefits.

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What is PUFI?

PUFI is a closed-cell material made up of millions of tiny bubbles less than 0.5 mm (0.02") in diameter. It is very light, usually only 32 to 48 kg/m³ (2 to 3 lb/ft³) in density, compared to more familiar building materials such as spruce wood at 450 kg/m³ (28 lb/ft³), or concrete at 2300 kg/m³ (145 lb/ft³). It is applied in layers using a spray-gun (Figure 1). Application surfaces should be free of grease, oil, and loose particles. Poor adhesion results on surfaces such as plastic or galvanized metal that has an oily film on it.

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Water Absorption Into PUFI

There have been several reports of PUFI absorbing water in bulk potato storages in Ontario, Quebec and New Brunswick. They were sprayed with PUFI using the inside onto the outside steel cladding with a fire-protective coating technique (Figure 3B). Water vapour tries to move through walls and ceilings in order to be at the same concentration on both sides. The greater the amount of water vapour contained on one side of the wall relative to the other, the greater is the incentive to move. Figure 2 demonstrates this concept during winter and summer with the same environmental conditions inside a refrigerated storage.

 Figure 1. PUFI being applied to an experimental galvanized steel wall panel with a spray-gun.

Warm air will hold more water vapour than cold air. In Case I, with typical winter conditions outside, water vapour wants to move towards the outside, because the air inside the building contains relatively more water vapour than the air outside. In fact, in this example, it holds three times as much water vapour as depicted by the number of water drops shown. In Case II, with typical summer conditions outside, the air outside the building contains relatively more water vapour than the air inside. In this example, it holds seven times as much, again depicted by the number of water drops, and water vapour wants to move in the other direction through the wall towards the inside. Depending on the direction of water vapour movement, one has to decide whether a vapour barrier is required or not.

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Figure 2. The direction of water vapour movement changes depending on the temperature and relative humidity on either side of a wall.

Current Construction Techniques

There are 4 main construction techniques used in Ontario

*(Figures 3A-3D). These are:

(A) Spraying from the inside, attached to the outside wood cladding, or concrete/stone walls, with a fire-protective coating

(B) Spraying from the inside, attached to the outside steel cladding with a fire-protective coating

(C) Spraying from the outside, attached to the inside plywood cladding

(D) Spraying from the outside, attached to the inside steel cladding

*(Schematics are not to scale, and are intended for discussion purposes only)

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A. Spraying From the Inside, Attached to the Outside Wood Cladding, or Concrete/Stone Walls, with a Fire-Protective Coating

This construction method (Figure 3A) was very popular in the 1970's for renovating old two-story dairy barns for swine housing. PUFI was sprayed on the old barn boards or the concrete or stone foundation walls from the inside of the barn. It was the only practical method of insulating these barns, and was a key ingredient in the proliferation of swine barns in Ontario during that period. It's advantages are: 

• It tightens up the building considerably, a critical feature in allowing many ventilation systems to work
• One can see if the PUFI is being eaten by rodents
• No support framing is needed
• Since wood, concrete or stone walls are not perfect vapour barriers, water vapour can pass directly through them and the PUFI

The disadvantages are:

•  A costly fire-protective coating would be needed
• The resulting interior surface is rough, dull, difficult to clean and can be damaged by animals or equipment

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Figure 3A. Many older two-story dairy barns have been insulated with PUFI upstairs or downstairs.

B. Spraying From the Inside, Attached to the Outside Steel Cladding, with a Fire-Protective Coating

This construction method (Figure 3B) has been very popular, and involves constructing the building wood frame, putting the outside steel cladding onto the studs or poles, then applying PUFI directly on the steel cladding from the inside of the building. It's advantages are:

• It is very simple, and can be done near the end of construction after the entire shell of the building is up
• It tightens up the building considerably, a critical feature in allowing many ventilation systems to work
• One can see if the PUFI is being eaten by rodents
• For Controlled Atmosphere (CA) Apple Storages a gastight seal is required and it is easier to see where cracks might be if the PUFI is exposed in this manner. 
  

The disadvantages are:

• A costly fire-protective coating would be needed.
• The resulting interior surface is rough, dull, difficult to clean and can be damaged by animals or equipment
• It can result in problems of water vapour absorption under the right environmental conditions
• The PUFI may not adhere well to the outside steel cladding if it is galvanized with an oily film on it. 

Figure 3B. The picture shows a 75 mm thick piece of PUFI with a 5 to 10 mm thick Zonolite 3300 fire-protective coating.  

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C. Spraying From the Outside, Attached to the Inside Plywood Cladding

This method (Figure 3C) is called the 'Inside-Out Construction Method'. It evolved in the 1980's as a result of water vapour being absorbed by PUFI in potato storages using construction method 'B' discussed previously. This method involves constructing the building wood frame, putting on an inside plywood cladding, applying the PUFI on the backside of the plywood from the outside of the building, then installing the outside steel cladding last. Its advantages are:

• It eliminates the need for an expensive fire-protective coating (providing the plywood meets the required fire rating requirements)
• It reduces the danger of mechanical damage
• It provides a smooth, paintable, cleanable surface
• Since plywood is not a vapour barrier, water vapour can pass right through both the PUFI and plywood and not become trapped in the wall. Once the water vapour is in the space between the PUFI and the outside steel cladding, it normally can 'escape'
• The plywood can add considerable rigidity and tightness to the building, a key component in the success of CA apple storages that need to have a gas-tight seal. 

Figure 3C. In the picture, a model of a wall shows how 2" x 4" horizontal wall girts between the studs and the inside plywood allows the PUFI to wrap around the studs.

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The disadvantages are:

• The plywood surface can get mouldy in high humidity horticultural storages
• The PUFI is covered up and difficult to repair if it develops hairline cracks and reduces the air-tight seal in a CA apple storage
• It is perceived to be costly since both a steel and plywood cladding surface are used

D. Spraying from the Outside, Attached to the Inside Steel Cladding

This construction technique (Figure 3D) has only recently been used, where steel is substituted for plywood in the technique described above. Unfortunately, it has been described by some people in the industry as being a method to eliminate the water vapour absorption problems that occurred in construction method 'B'. It should only be used in the applications shown in Table 1.

Its advantages are:

• It eliminates the need for an expensive fire-protective coating (providing the steel meets the required fire rating requirements)
• It reduces the danger of mechanical damage
• It provides a smooth, paintable, cleanable surface
  

The disadvantages are:

• The PUFI is covered up and difficult to repair if it develops hairline cracks and reduces the air-tight seal in a CA apple storage
• It is perceived to be costly since two steel cladding surfaces are used 
• It can result in problems of water vapour absorption under the right environmental conditions
• The PUFI may not adhere well to the inside steel cladding if it is galvanized with an oily film on it 

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Figure 3D. The picture is of an attic in a livestock building. This will tighten and stiffen the ceiling up considerably.

Choosing the Correct Construction Method

The first step in determining the correct building method is to determine in which direction the water vapour wants to travel. In the case of livestock buildings water vapour will always travel towards the outside of the building, as it is always as warm or warmer inside compared to outside. For refrigerated storages used only in warm or hot weather, or for freezers, the water vapour will always travel towards the inside of the building as it is always as warm or warmer outside compared to inside. Both of these examples are fairly straightforward and it is best to use a construction technique that either ;

• Prevents the movement of water vapour into the PUFI in the first place using steel cladding (a perfect vapour barrier) attached to the warm side of the PUFI (construction methods 'B' or 'D', depending on the use), or 
• Allows water vapour to pass directly through without being trapped using construction methods 'A' or 'C'

The more difficult situations are when the movement of water vapour direction will change over the period of the year that the building is used. The main types of buildings that fit into this category are fruit and vegetable storages that are used both during warm and cold seasons. During warm weather, the direction of water vapour movement is always towards the inside of the building, since it is always warmer on the outside of the building. However during cold weather, the direction of water vapour movement may change to be towards the outside of the building, depending on the inside and outside conditions. For these cases, it is best to use construction methods 'A' or 'C' since regardless of the environmental conditions, water vapour can always pass in both directions through the wall or ceiling. Be careful to consider the possible future uses of the building as plans often change.

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* General recommendations assuming; normal Southern Ontario outside environmental conditions during the year; environmental conditions inside are constant; and the building is not used for other purposes in the future. For more specific recommendations, ask a Consulting Engineer familiar with agricultural building conditions and construction methods.

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Building Tips

• Use 1" x 2" or 2" x 4" wall wood girts between the studs/poles and the inside or outside steel or inside plywood, so that the PUFI will wrap around the studs/poles. See Figures 3B, 3C and 3D. This prevents heat from moving in or out through the studs or poles since they are not good insulators. Use wood girts on the ceiling between the trusses and inside steel or plywood for the same reasons. 
• PUFI will attach better to prepainted steel rather than straight galvanized metal, since there can often be an oily film on new galvanized steel.

Summary

Polyurethane foam insulation (PUFI) has many advantages in agricultural construction and is adaptable to many uses. However, it is not without disadvantages. One must be careful to choose the construction technique that is best suited for the intended use.

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