Using Sprayed-In-Place Polyurethane Foam Insulation (PUFI) in Farm Buildings
Table of Contents
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:
PUFI is not without its costs since it:
When considering using PUFI or any other insulation, one must take into account all of their financial and environmental costs and benefits.
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.
Figure 1. PUFI being applied to an experimental galvanized steel wall panel with a spray-gun.
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 2. The direction of water vapour movement changes depending on the temperature and relative humidity on either side of a wall.
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.
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
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. Its advantages are:
The disadvantages are:
Figure 3a. Many older two-story dairy barns have been insulated with PUFI upstairs or downstairs.
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:
The disadvantages are:
Figure 3b. The picture shows a 75 mm thick piece of PUFI with a 5 to 10 mm thick Zonolite 3300 fire-protective coating.
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:
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.
The disadvantages are:
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:
The disadvantages are:
Figure 3d. The picture is of an attic in a livestock building. This will tighten and stiffen the ceiling up considerably.
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:
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.
* 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.
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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