Naturally-Ventilated House Construction for Hot and Humid Climates

One of the ways of reducing  heat stress in naturally-ventilated poultry houses during hot weather is making sure that outside air can easily flow in and out of the chicken house. The easier it is for outside air to flow through a house the less build-up of heat in the house which will minimise the outside temperature differentials. Increased air exchange rates also result in increase of air movement around and over the flock inside the house ensuring heat loss due to convection. There are 3 primary factors that help with air movement through a house. They are: width of house, the openings in the and obstructions around the house.

How wide should the house be?

In the past poultry farmers have disovered that natural ventilation works best in houses which are 12m in wide or less. Wider chicken houses have lower air exchanges and much less natural air flowing towards the center of the house. Because air exchange rates need to be reduced significant temperature differences can happen between the upwind and downwind sides of the poultry house especially during colder times of the year. Using circulation fans in poultry houses helps to reduce the problem, The width should be kept to 12m or less in most hot places..

What are Best Curtain Openings and Curtains to use in a poultry house?

All naturally-ventilated houses must be equipped with some type of adjustable side wall curtains to control the flow of air into the house during cooler times of the year or when small birds are present. In order to facilitate the rapid exchange of air during hot weather curtain openings should generally account for between 50% to 80% of the side wall height. The hotter the climate, the wider the house, the greater the percentage the curtain opening should account of the side wall.

It is very important that there are solid portions of wall above and below the curtain opening. The lower solid wall portion of the wall serves a number of important functions. First, a solid lower wall helps to reduce the amount of rain that can enter the house during storms as well as prevent outside water from running into the house. The solid wall stops  the direct sun light entering the house when the curtains are fully opened and also provide a surface for the bottom of the curtain to overlap stopping wind in colder periods.. The wall also helps to stop rats from entering the house as well as reduces contact between the flock in the house and wild birds outside the chicken house. There is no best height but generally it is best if the wall is at least 40 cm high.

A solid wall above the curtain opening allows enough of the surface for the side wall curtain to seal against cold weather. In hot places it is vital to be able to seal a poultry structure well when brooding so as to minimize heat loss as well as wind. It is also important to have a wall above the curtain to allow installation of the side walls air inlets during cooler temperatures or during brooding. It is bbetter that the wall above the curtain opening allows the side wall curtains to overlap the wall by a at least of 30cm

The side wall curtain should be made from clear, non-breathable material to reduce air exchange during when you wish to conserve heat. A stiff curtain rod at the top of the curtain opening can be used to more control the amount the curtain opens during you wish to retain heat. It is best if the bottom of the curtain opening is also has a curtain rod to reduce drafts when closed.As with the top of the curtain, the bottom of the curtain should overlap the bottom wall by at least30 cm or more.

Translucent curtains are ussualy good for allowing the maximum amount of light in the house. When the curtains are closed or half closed the light will enter the house.. When blackout curtains are used to control light (mostly for layers) it is good that the outside surface is silver or white color so as to reflect suns radiation.

What should the House Spacing be?

House spacing can significantly affect the environment in poultry houses during hot weather. A structure creates a zone on the downwind side where wind velocities are reduced. If an adjacent house is placed in this zone it can be subjected to decreased air exchange rates as well as heat, moisture, dust and microorganisms emanating from the upwind house.

Though there are a number of factors that determine optimal house spacing (prevailing wind speed, direction, topography, etc.) a minimum recommended spacing can be calculated from the following formula (Timmons, Cornell University):

D = 0.4 X H X L0.5
These represent:
D= separation distance - (ridge to the closest wall of the next house) in meters
H=Height - obstructing building in meters
L=Length - obstructing building in meters

Should one have trees and vegitation near a house?

All vegetation should be cut right down around a chicken house to help stop rodents and to allow air flow into and around the house. Do not remove or cut all the green vegetation around the house, but rather cut it down as this is much beter than bare ground because green vegetation temperatures can lower the temerature as much as 3 degrees C. Also green vegetation reflects less solar heat into the house than bare earth. I have also seen poutry farms which keep the tree around the chicken house so that the shade helps cool the house - your call ....

Tall trees planted next to a poultry house are a bonus during hot weather. If the tree has a canopy above a houses side walls it will shade the poultry house roof from the sun, reducing heat from the ceiling and the ground around the house, canopy trees can also help to push air into the chicken house. It is important that the trees do not affect air flow into the house that the trees are trimmed so that  the branches are not below the eaves of the chicken house because this will hinder the flow of air in and out of the  poultry house.

Are Ridge Openings Needed?

Ridge openings are used in naturally-ventilated chicken houses and are only really effective in chicken structures that have uninsulated roofs. Air collecting next to an uninsulated roof can easily go above 55C. Because the hot air is hotter than the other air in the house it will rise to the highest point of sloped roof. When you have an opening at the peak of the roof (ridge) this very hot air will flow out of the chicken house. If you do not have a ridge opening the hot air will collect causing an increase poultry house temperatures. In a steel structure with an insulated tin roof the air temperatures next to the ceilings are not that much warmer than those next to the floor of  the house and there is no need to get rid of the air next to the ceiling.

Which way should the house face?

Naturally-ventilated houses should always be orientated in an east-west direction. The reason for this is to minimize the possibility of direct sunlight entering the house. Direct sunlight striking upon a bird can dramatically increase the effective temperature a bird is experiencing. Direct sunlight can increase the surface temperature of a bird to well above 38oC creating a heat stress situation at air temperatures that wound not normally be thought of as problematic. What is more often is the case when sunlight enters a house is the birds will move away from the side wall where the sun is entering the house thereby dramatically increasing the effective density of the birds. The higher density significantly decreases the amount of air movement over the birds body as well as puts in direct contact with other hot birds.

Though it is true that orientating a house east-west direction may not take full advantages of winds blowing from east or west this is typically not a problem for narrow houses (12m or less) with proper house spacing and curtain openings.

What is the best Roof overhang?

A properly designed roof overhang helps to reduce the direct and indirect sunlight entering a poultry house during hot weather. For most places in the world the sun will travel slightly to the north or south of an house facing in the east-west direction. Without a large enough roof overhang the sun will be able to shine directly into the houses. In a naturally-ventilated chicken house this means the sun will shine into the poultry unit and increase heat stress related issues.

The length of the overhang is important. The taller a houses side walls the longer a houses roof overhang should be to stop the sun from entering the chicken shack. The closer the side wall opening is to the ground the longer the roof overhang needs be. Roof overhangs should ussualy be a minimum of 0.6 meters in most cases but some houses with taller side walls and large curtain openings could produce better results from a roof overhangs of 1.25 m or more.

Roof overhangs can also help stop rain from coming off the roof of a house and into the house as well as keep rain directly from entering a house.

What should the Roof Slope be?

Though there are structural considerations related the most desirable roof slope for a chicken house, the best roof slope is determined by level of roof insulation. In poultry houses with uninsulated rooves a steep roof slope (45 degrees) is best for the following reasons. First, a steep roof slope tends to collect less radiant heat from the sun than does a flat roof. Second, a steep roof maximizes the distance between the birds and the hot ceiling which reduces the amount of radiant heat the birds receive from the hot uninsulated roof. A steep roof also encourages the super heated air immediately next to the ceiling to quickly rise towards the peak of the ceiling far from the birds. If the house has some type of open ridge the heated air will quickly leave the house. A steep roof tends to create a more open environment for beter for air flow into and out of the house.

If a ceiling is correctly insulated it creates almnost no radiant heat and the need for steeply sloped roofs is . It is still advisable in a naturally-ventilated house to have a sloped roof to easy the flow of air into and out of the houseIt also allows equipment to be lifted out of the way when cleaning the house.

What is the best Insulation?

To reduce heat stress hassles during hot weather it is good to insulate the chicken house roofs and ceilings. Many chickebn house roofs are made from galvanized sheet, which will sometimes reaches temperatures of up 50 to 70oC on a hot day. A hot roof can cause raised chicken house emperatures and can also increases the amount of thermal radiation the flock is exposed to. Like direct thermal radiation from the sun which can increases the surface temperatures of things inside the house by 25 degrees or more above ambient temperature, also the radiant heat comming off by a hot roof.

The most effective way to stop heat from a roof is using a good insulation. Insulation is a barrier that keeps heat from a hot roof tin from coming inside the chicken coop. Many types of insulating materilas exist for a chicken structure.

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