The value of insulation is generally recognized in temperate and cold climates, where it’s function is often though of as prirnarily to help keep birds warm in cold weather, with minimal fuel use. However, insulation has a valuable although different function in summer also : protecting birds from heat stress caused by solar heat gain through the roof. This protection is needed in moderate to cool climate areas, and even more in warm to hot areas. It is extremely important for producers and industry personnel in warmer climates to realize that under – roof insulation is essential in both open – side and fan – ventilated poultry houses. If birds are kept in un – insulated houses in hot weather, even with the best ventilation system, bird performance is likely to be very poor and mortality rates of 10% to 15% or even higher should be expected.

Research in the Southeast U.S. in conventionally built fan – ventilated poultry houses, identical expect for having or not having insulation in the roofs, has shown the following mortality rates for market – size broilers when cutside average maximum temperature was only 91 F (32.8 C)

Lack of roof insulation leads to poor performance, high mortalities.

	House with insulated roof	House with no roof insulated
Inside mortality	0.5%	14.3%
Max. Temp. Rate	99 F / 37.2 C	92 F / 33.3 C

Losses are likely to be even higher in lower – latitude conditions, where the sun will be more directly overhead and air temperatures higher. Here’s what you need to know to make the best decisions on warm – climate poultry house insulation.

Effect of Heat and Cold on Bircis
The normal deep body temperature of chickens is over 106 F (41 C). Birds use energy from feed to maintain this internal temperature and operate their internal organs and muscles, Feed energy above that needed or these “maintenance” functions is used for growth and reproductive functions.

The temperature of the birds’ surroundings needed for best performance depends on growth stage and function.
For broilers and pullets, the optimum temperature range from about 92 F (33 C) at birth to about 73 F (23 C) at four weeks, then leveling off. Laying hens perform best in the temperature range from 78 F to 82 F (26 – 28 C). Under normal conditions, fully – feathered birds actually produce excess heat, which their bodies must shed, and which results in warming their surroundings. For this reason, little supplementary heat is usually needed in poultry houses even in cold climates, except in the early brooding period. The birds heat the house. This means that in most cases and most of the time, and even more so in warm to hot climates, the problem is keeping birds from over – heating, not in seeing that they do not get too cold.

If for any reason birds gain heat at an excessive rate or cannot get rid of their excess body heat, they will reduce their feed intake to lower their heat production, and will change both their internal metabolism and their behavior to promote faster heat loss. Birds shed excess heat by respiration (breathing), getting the cooling effect of moisture evaporating from the surfaces of their airways and lugs, and by transferring it to the air circulating over their bodies. Birds feeling too hot, for example, will pant, drawing more air inside their bodies to absorb heat. They will also lift their wings to expose more body surface area to the air, and will alter their blood circulation to pump more blood to surface air – cooling areas such as the wattles and feet.

All of these responses of course lower the feed efficiency and performance of both broilers and laying hens. If the birds are unable to get rid of the excess heat, eventually they will die.

What Insulation Does
Insulation is any material that resists or slows down the rate of heat transfer from one place to another. The function of insulation under cold – weather conditions is to reduce heat loss from the house, whether the heat is produced by the birds or by supplemental heaters. This reduces the amount of supplemental heating fuel that must be burned, and allows the birds to make most efficient use of their feed intake. In cold weather, heat is lost by conduction through both the roof and walls. For example, assuming that the walls are made up of typical un – insulated building materials, if the outside temperature is 40 degree F (22 degree C) colder than the desired in house temperature, an un – insulated house will lose about 27 Btu’s of heat per hour per square foot of surface area (307 kJ/hr/m2). Adding moderate insulation in both roof and walls, for example Thermal Reflective Insulation (5.00 mm), cuts this heat loss to about 3.3 Btu’s/hr/sq ft (37.5 kJ/hr/m2)

The function of insulation in hot weather is to lower the rate of heat gain from the outside into the house and into the birds. Typically, all hot – weather heat gain is through the roof, and the mode is primarily by radiant heat transfer rather than by conduction. Radiant heat is a form of electromagnetic radiation in which heat moves from a warm object to a cooler one through the air but without warming the air. The sun, fires and heaters with glowing elements (such as brooders) are all radiant heaters. The source of radiant heat does not, however, have to blaze or even glow. Any object warmer than another one in sight will radiate heat to the other one, either by visible or infrared rays. Radiant heat may be beneficial, as with chicks kept warm by radiant brooders, or it may be disastrous – typically for larger birds receiving radiant heat from an un – insulated or poorly insulated roof.

Sheet metal roofs on houses may easily be heated to 150 F (66 C) or higher in summertime, even at fairly high latitudes. Research in the Southeast U.S. has shown that a sun – heated and un – insulated weathered galvanized roof will radiate heat into a poultry house at from 30 to 35 Btu’s per hour per square foot (340 to 398 kJ/hr/m2) during the hot part of the day, with the maximum usually occurring in the early afternoon. In latitudes closer to the equator, the rate of solar heat gain will be even higher. This is why under – roof insulation is needed.

Effects of Un – insulated Roof Heat Gain on Birds Ventilation
The magnitude of the problem of radiant heat gain is shown in the following example:
1. For a 40 – by 500 – foot house (12 x 152 m), a 35 Btu’s per hour per square foot (398 kJ/hr/m2) rate of solar radiant heat gain will total at least 700,000 Btu’s per hour (739,000 kJ/hr)

2. Based on the rule of thumb for mature birds of about 5 Btu’s per hour per pound (11.6 kJ/hr/kg), this house with, for example, 25,000 five – pound (2.27 kg) broiler birds would have gain from excess bird heat of about 625,000 Btu’s per hour (660,000 kJ/hr)

3. Modern ventilation systems typically are designed to handle excess bird heat plus a small amount of heat gain from a properly insulated roof or ceiling. For this house, a typical installed system would have a fan capacity of about 200,000 cubic feet per minute (94.4 m3/s)

4. Since the heat gain from the un – insulated roof is even larger than the excess bird heat, a ventilation system designed and installed under the assumption that the roof will be properly insulated would not be able to remove the total heat gain encountered of 700,000 + 625,000 = 1,325,000 Btu’s/hr (1,398,000 kJ/hr).

Ventilation system cannot handle large heat gain through an un – insulated roof!

The Particular Danger of Radiant Heat to Birds
Radiant heat coming from an un – insulated roof is difficult to combat and is especially dangerous for birds because it transfers heat not to the inside air but directly to the objects below the roof – the birds. The air temperature in such a house will rise by the air adsorbing heat from the already radiantly heated birds. Ventilation removes heated air, and ventilating air moving over the birds certainly helps them get rid of heat. But in the radiant heat gain situation the ventilation effects operate only after the birds have already absorbed this heat. Further, poultry personnel who do not spend long period of time in the house and whose clothing (often white) shields from feeling the radiant heat, may become aware of the effects on the birds without realizing the source of the problem, and blame the ventilation system instead of the true culprit, the un – insulated roof.

The particular danger of radiant heat was shown in research conducted in the U.S. mentioned above. In two environmentally controlled chambers with and without simulated roof radiation, with air temperature in both chamber controlled at 105 F (41 C) and the same relative humidity, the bird death rate was 40% in the chamber with simulated roof radiation, almost twice the mortality rate (22%) in the chamber without radiant heat. This test indicates that the effects of directs radiant heat are much more severe than the same heat load without radiation.

Advantages of Under – Roof Insulation
Placing insulation under the roof blocks the downward heat radiation and converts the heat transfer mode from mostly radiation to mostly conduction (at a slow rate) through the insulating material. Because of the heat transfer mode conversion, the exact effects are difficult to calculate, although easily seen in field experience. Installing thermal Reflective Insulation (4 to 8 mm) in the roof of the above