A New Series:
I am starting today a new series which I will call _ Findings _. In it I will show numerical findings about stuff. I will do measurements / collect data, then draw conclusions / find patterns.
How Much Space To Leave Between Buildings For Air
Motivation To Find The Numbers:
I live in a city called Karachi. Its a huge city with over 25 million inhabitants. Like all mega cities its has grown wildly in population during the past 4 decades (i.e. since 1980). As a result, and like all mega cities it has grown vertically in buildings, not much on surface area. Apartment buildings that used to never be over 4 floors above ground are now regularly 12 or so floors above ground. Also, old single family houses of one or two floors above ground have been broken down and converted into apartment buildings.
Karachi is very much near equator. Average temperature is between 30 and 40 degree celsius throughout the air except in very small, two weeks to one month, winter in which it drops to between 15 and 20 degree celsius.
The rise of buildings and fall of houses result in over dependence in air conditioners. While in my childhood in the usual 4 floors above ground apartment buildings fans were enough now you have to have air conditioner if you want to have peaceful sleep at night. Thats in a sea-port city. Moreover, houses and 2 to 3 floors apartment buildings that didnt even need fans now need atleast fans.
This dependence on electricity is ofcourse not sustainable given peak oil and general state of economy. Sooner or later the city and by extension all mega cities in world have to either perish or return to the old state of natural ventilation.
What Data Did I Gather:As stated above I am concerned about mega cities and therefore collected data from a mega city, the one that I could do detailed study of, my own city.
Inside the city I visited the old city area that still have some houses and upto 4 floors above ground apartments. I put close focus on cool areas and attempted to find what makes them cool. Is it greenry, distance from sea, oldness of building, water leakage etc?
I then isolate these factors from the most important factor in my eyes: space left between buildings. I did this by focusing on buildings which have these factors roughly same yet one building is considerably cooler than other.
Following are my conclusions.
The Conclusions:
I made conclusions about how much space at the minimum needs to be left between buildings for sufficient air to be present to properly cool inner areas of the buildings without need of any electrical means for air circulation. Following are my findings:
1. Surface area covered by a building dont matter as long as sufficient space is left around the building for air to flow.
You can have a very large area covered by a building but as long as you leave proportionally enough area around the large area building as around a small area building, that is, as long as the ratio between free space and covered space is same, ventilation is same. This is ofcourse within limits but the limit in which only the lower bound is important is human sized, that is, buildings made for humans.
I promised to give numbers so here are numbers about it. Left and right side of the building, when seen from the entry area, must each be equal to half the left-right length of the building. So, suppose you have a rectangular building that you are seeing from front. It has 2 rooms at left side, 2 at right side and 1 room where you enter in. Its 5 room-lengths long from right to left. Lets say each room is 12 feet long so its 60 ft that plus lets say 4 feet of the 6 walls that would come in your way if you move from right to left. Altogether 64 feet. My first conclusion is that, such building must have free space, that is, open sky space, 32 feet long right to left at the right side of the building and same at the left side of the building. As long as you follow this rule you can make as large in surface area buildings as you want. I said large in surface area because I am not talking about height of the building here. The rule about height is below.
2. Twice as much area must be between the building and the front wall of the plot as the height of the building. Same area must as well be left behind the building, inside the plot.
If you are looking from front, and are standing at the door of the plot, not at the door of the building, that is there is a yard between you and the building, and the building fall towards you then the area covered by the fallen building must cover only half of the total area of the front yard. Same rule for the back area.
Lets say the building is two storeys tall and each storey is 12 ft high inside, and the roof itself is 3 ft thick. Also add 3 ft of stairs at the ground level. The total height then of the building will be 3 + 12 + 3 + 12 + 3 = 33 ft. My conclusion is that such a building must have 66 ft free space in front of the building and 66 ft free space behind the building, all inside the plot.
All my calculations in the conclusions are about the free space around the building inside the plot. I am not counting free space of the neighbouring buildings. I am not counting free space that is in form of roads, foot paths etc.
If I were to count also the free space of neighbouring plots and free space in form of roads and footpaths, then I will say the total free space that is needed in front of a building (same as whats needed behind the building) is 4 times the height of the building, not 2 times. The 2 times is whats needed to be left empty (free space, open sky space) inside the plot. Rest is road and footpath space at the road side of the building, and empty space in the plot of the building that is behind this building.
All plots would have empty spaces in them in all 4 directions. The size of the empty spaces at left side and right side of the building depends on the area of the building. The size of the empty spaces at front side and back side of the building depends on the height of the building.
By free space I mean open sky place. Place that has no roof on it. The place under a hedge, such as under a window hedge or under balcony is in my calculation still a covered space, not free space.
Its easier to understand my conclusions in terms of length, instead of in terms of area. No matter how long your building is left-to-right from seen from front, have half as much long area as free space at the left side of the building and same at right side of building, thats conclusion # 1; conclusion # 2 is, no matter how long your building is, leave twice as much length as free space in front of the building as the height of the building, and same at back of the building.
Why leave so much empty space in front and back of the building? Its because that is what I find from my readings. Old houses and buildings that have very wide front yards and back yards are cooler by a wide margin without exception than both old and new buildings that have narrower front and back yards. Its a decisive factor and therefore very important.
3. For the plots that have buildings on all sides and have a yard inside, covered at all 4 sides by the building, its better to have a long narrow, that is, rectangular yard, than a square yard.
Its because air flow increase by length, not by area, of the yard.
Fundamentally this is not a new and separate conclusion. Its same as conclusion # 2. For sufficient air flow free space length must be atleast 4 times the length of the building that is blocking the air flow. Either remove the part of the building that is at the front side and have free air flow, or have atleast 4 times long yard so air can "jump" the building and reach you at the bottom in the yard. If yard is not long enough then the "jumped" air wouldnt land in the yard, it will land depending on the length of the yard at the first floor above ground or at roof etc.
4. Longer the yard you have better air you get but after 6 times the height of the blocking building it not matter much, and after 8 times it not matter at all.
If you leave a yard that is more than 8 times long than the height of the blocking window then from air circulation point of view you are wasting land.
5. There is a minimum length for air to jump and reach ground. It is 36 ft comfortably and 30 ft with troubles. Troubles here means that most of the time it will work, or most of the time it didnt work before it will work now, but not always. Comfortably means it will work all the time.
Discussion of both comfortably and with troubles above is when it could work. This is to keep the situations away from discussion when air flow is almost fully stopped, like just before rain, when no lengthening of yard as well as no other measure we take can make the air flow.
As always, first find a solution that is guaranteed to work. Dont worry about cost yet. Later work on it to find what fat/cushion can be cut to make the solution efficient. The solution that is guaranteed to work is leaving 36 ft. The efficient, yet effective most of the time, solution, is 30 ft. The efficient, but effective only less than half the time, solution, is less than 30 ft.
These numbers are for front and back yards, not for side yards. Its supposed that the building seen from front i.e. from entrance is wider than its deep. The purpose, therefore, for the side yards are to take the air to the backyard of this building and to the front yard of the building behind it. Remember that your city cannot have only one line of buildings, even villages these days rarely have that. There are buildings behind buildings behind buildings in all human dwellings these days, and always were in cities since the first cities. If there is a wall of buildings, meeting end to end at sides, then sufficient air wouldnt flow to the buildings behind it even if 4 to 8 times the building heights are left between buildings. There would be a number for it, the length that if left as open would be enough for air to reach even behind the wall. I dont know this number. I made no readings for it. All I have is a gut feeling. Its a number of 12 but I am not happy with it. I would be happy with the number 16.
6. Crossing of wind wins the day.
Ofcourse in extreme air flow you dont need the crossing, wind will reach every corner of the room just as well, but we are not talking about extremes, we are talking about just enough plus a little extra to cover all bases, not anything overwhelming.
In all situations where you need air flow for cooling inside of your buildings, that is if you are not living in a cold climate or when its not winter, you need crossing.
Even if you have miles of unobstructed view in the prevailing direction of wind and very wide windows the limit the air go inside your room if there is no opening in your wall at the other end for air to get out, is very low, not even 8ft, I will say its 6 ft in most situations.
Crossing of wind means that behind the in-flow window, at the side opposing that window, there have to be another window, the out-flow window, so air has a free flow across the room. This will cool the room, no other measure will cool the entirety or even majority of the room. The above conclusions about lengths of yards are to have air inside the rooms etc but that dont solve the problem. The air also have to leave the building systematically and in a flow. If you cannot have windows behind windows then only small area of length 2 to 4 feet near the window will be sufficiently cool to be livable in normal situations, not the entire room. Normal as in when you dont have miles of unobstructed view and when no extreme situation such as a thunderstorm is happening.
7. Narrow rooms are needed. Square rooms are for cold climates. Rectangular rooms are for hot climates. Hotter the climate, narrower the rooms have to be.
Again its the length thats your friend here, not the width. Width is the enemy. Wider rooms would be very hot inside.
A rectangular room is a narrow room. It has two long sides and two short sides. The short sides have to be short enough for air to go across the room. If the short sides are not short enough then the air would only reach part of the room, not the whole room, because air pressure would be faded away covering the distance before it reach the other side. The purpose of the short sides is to give air passage to move across the room. The purpose of the long sides is to give air openings to come in the room from one of the sides and to give air openings to get out of the room from the other (long) side.
8. Its not always enough to have air passage. Sometimes the air is needed to go through some treatment before getting passed inside the building.
I said not always and sometimes because its only when the air is hot that the treatment is needed. Cool air is already fit for cooling.
The treatment is: pass the air over building materials. This will cool it.
More mass the air pass over, cooler it become. The issue here is the length over which the air is to pass to reach the inside of building. For a given density, that is, for a given material more is the length the air pass over more is the mass its passed over and so cooler it become; but the more the length the less the air that reach inside the building.
Therefore we have to use dense materials, so that enough mass is available in little length.
Due to the need of dense material we cannot use wood as building material. Our task here is to cool the air that come from outside. If we dont have to cool the air then we can use wood.
We will use earthen materials such as stone, bricks and concrete. They all have same density.
As stated above, we cannot have too thick a wall because then air wouldn't go inside the building in sufficient quantity. We have to have some considerable thickness though to have the air pass over the material in sufficiently long passage. I suggest atleast 1 ft thickness of building walls, 1.5 ft would show the cooling effect considerably, anything upto 2.5 ft will work. Between 2.5 ft and 3 ft its iffy that sufficient air will reach inside. After 3 ft, forget it; its guaranteed at this point that sufficient air wouldn't reach inside the building.
To finish this side topic about building materials I will mention metal and glass. Use as little metal and glass as building material as you can, that is, dont use them. If you want to use them, and remember there is no actual need to use them, shield them. Cover your glass windows by windows hedges and other kinds of covers, point is to reduce exposure to direct sunlight. Similary, put all metals inside other building materials to avoid having any exposure to direct sunlight for them too.
Windows can be made all of wood, no actual need to put glass in windows or anywhere really in your building structure. Glass has this nasty habit of increasing inside temperature when its hot and reducing it when its cold.
Door and window frames can be made entire of wood, no need to put any kind of metal there.
Finally, and to end the discussion about building materials, the age old question: are stones better than bricks as building materials?
I will only talk about their effects and have their comparison with each other with respect to cooling, except this brief mention here about strength. Stones when exposed to pressures such as rams or stones thrown on them themselves take the load and get break to save whats inside. Bricks dont take pressure on themselves, they scatter and remain mostly intact. The mortar between bricks is whats lost. You can always rebuild a brick wall because bricks are still there but you cannot rebuilt a stone wall without getting new stones.
Now about their effect on cooling, its same as long as no organic substance is present in the bricks. If bricks are made by taking material from fertile ground then its somewhat better in cooling than stones.
In all cases, stone is bad material for building as far as cooling is considered. Its also bad for heating. It gets hot too soon and get cold too soon, as long as walls are not very, very thick, like yards thick. Any material, thicker it is, longer time it will take to get hot and longer time it will take to be cold. For a stone wall yards thick its a matter of months. The heat gain from outside will be helpful in keeping the interior cold in winter because it will take a long time by the walls to release that heat, but if the walls are very much thick that time may well include spring and even early days of summer when it will be very uncomfortable to live in such building.
Recap of the main point of this conclusion:If air is hot, then getting it upfront across an open yard would make your rooms hotter than they were before. You have to pass the air through your building materials before it reach your rooms.
Conclusion of the Conclusions:
If the building material is not composite, that is, if same material is used throughout the thickness of walls, the case that we are talking about in this article; then, the inside of the building wouldn't be treated different than outside of the building by the building material. It means that a building that is harder to be cool would also be harder to be warmed. We dont want this. We want control in our hands. We cannot rely on building material much.
We have to use air passage as primary source of cooling. This we can manipulate. We can open and shut windows when we want.
We can decide about thickness of walls. Its a fixed factor, as in once a building is built this factor cannot be manipulated. Its not like a window we can open and close at our whim.
Thick walls, as long as thickness is not more than 2.5 ft as discussed above, would help both in summer and winter. In summer we can have cool air, in winter we can have less air.
Above is long discussion in various conclusions about air passage. Another factor that can be added is upper windows - the windows near ceiling. They are very helpful in putting out warm air. We can also add lower windows - windows near floor. They will help in very useful passage of cool air. Warm air rise, cool air sink, we can use this natural phenomena for our advantage. Higher ceilings would help too, warm air would go up, very up, away from where people are.
Every region has a direction from where the prevailing wind below. In Karachi its west. Wind usually below from west to east through out the year, except in few weeks of winter when the prevailing direction is north.
Thats the only two directions wind blow from in Karachi. The directions may be different in other regions of the world but it will only be two, one prevailing and one that dominate only a few weeks of a year.
Ofcourse its the direction of the prevailing wind that matter. Not only because it covers most of the year but its also when you need ventilation sufficient enough for not only easy breathing but also for cooling. The other direction of wind is always for winter all over the world.
Summary
1. This article is about cooling the building without using any electrical mean. It is not about heating the building, that is, its geared and focused towards hot climates, not cold climates. Also, its not geared towards usage of fans or airconditioners.
2. Rely on air passage, that is, ventilation for cooling. Dont rely on building material. Dont use any special technique such as composite building etc. Only thing that is needed to be done about building material as far as cooling is needed is to avoid using metal and glass; these two building materials can be fully avoided but if they are used atleast avoid their exposure to direct sunlight, by covering it using other building materials if its metal and by putting shades on it and hedges over it if its glass.
3. Use horizontal ventilation only. Dont use vertical ventilation, that is, dont use stacking effect for ventilation. Dont put holes or place chimneys in your roofs for ventilation purpose.
4. Leave enough space in between buildings, at all sides, for air to pass around buildings to reach buildings behind and also to reach inside of all buildings. How much is enough is discussed in detail in numeric terms.
5. Have long, narrow rooms instead of square rooms. Keep the long sides of the room in the direction of prevailing wind.
6. Put upper windows, that is, windows near ceiling; and lower windows, that is, windows near floor - in addition of regular windows that are in the middle. The ventilation proposed in this article is not fully passive, human intervention is required to open and close windows as per seasonal need.
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