Monthly Archives: February 2011
Just what is it that double-height spaces speak of? How does one get them and why?
High expectations: Home owners should not assume that high ceilings will keep the place cool
The old-world wisdom stating how one action leads to another has proven true for the recent write-ups of this column, where the last two essays were prompted due to reader reactions of the previous write-ups. The present one follows suit, after dozens of mails in reaction – both agreeing and arguing with the earlier contents!
There apparently are houses with double-height spaces which are not so cool. Why is the factory with high roofs warm inside, though it has no heat-generating production inside? There is this master bedroom in the vaasthu-specific south-west corner. It has a high ceiling and ventilating windows up to the 0roof, still the room is hot at nights. Can we introduce a double-height space in a four-storeyed public building? In an existing building how can we introduce these ideas?
How do we react to such comments and contexts?
Idea vs application
An idea like height, however great it is, cannot succeed by itself. Building design and construction demands clear knowledge of the concept, careful application and appropriate locations. In case the applied idea is not so effective, maybe the reason lies in the context than the idea itself.
If the first floor master bedroom has walls exposed to both south and west, with no shading at all, it is bound to face the wrath of the sun. Additionally, the cement plastering and chemical-based paints contribute to heat absorption. However, maximum heat gain comes from the roof, receiving direct solar radiation whole day long. Vented roof with higher ceiling may help, yet to keep bedrooms in the south-west corner stay cool, we need to combine and apply many rigorous modes of passive cooling together. Alternately, we can try choosing between vaasthu-friendly home and eco-friendly design!
A mere tall space with no option for the hot air to escape will only result in increased quantity of hot air warming up the building. The case of the factory quoted above possibly suffers from this syndrome! Double-height spaces need to be strategically located to get the best out of them.
Often, staircase areas go high up with closed flat roof above, trapping heat, which then moves down into the house! Anyway, we need to discuss double-height spaces in more detail, especially as an integral part of the related design elements and concepts.
While many such common eco-mistakes occur, we also need to remind ourselves that not always do we need an eco-friendly idea. Not all of our homes exhibit eco-friendly ideas, but they could be cool and nice!
Most new buildings being built nowadays have low roofs with no ventilation, which does not necessarily make them hot boxes!
The answer to the puzzle lies in the specificity and context of building. Anyway, we know that ideas like shaded walls, insulated roofs, vented ceilings, cross ventilations, shorter spans, heat-reflective surfaces, proper orientations and many such small ideas together can make a difference.
The most visible reason for the popularity of double-height appears to lie in the expanse of space it create
During a family trip, while passing by a factory, every kid is excited by the tall towers. When asked about it, how do we answer them? If we take a tour of old European towns, the rooftop chimneys dominate the skyline. Do we really know how do they work? Why are the civic buildings with the tall cloak towers airy inside? What has prompted large hotels and offices to employ central atrium space?
The answer to all the above is a single theme – these tall narrow towers work as hot air chimneys, using technically what we call as stack effect, where hot air rises up along a tapering vertical column. Before the days of mechanical ventilation, people realised they could force air movement using these simple laws of physics! If not for this discovery, the European fire places would not have existed and factories would have billowed smoke all over the place.
Adapting the stack effect
Can all our houses today have a tall, towering chimney? That would be ridiculous! However, it’s possible to adapt the stack effect to a reasonably effective degree by having a common space going high. Then, this room would have the ceiling at the same level as the first floor, at a clear height of 20 ft. instead of the normal 10 ft. Termed today as double-height space or high-ceiling room, most owners prefer it in the living room, dining hall or the family space. In case the final roof is also flat, the clear height would be 20 ft while by designing sloping or curved roof we can reduce the effective height to 15-16 ft. In the last essay we discussed how a high ceiling of 12 or 14 ft. is not needed all over the house unlike in the past. Retaining clear floor height at 10 ft., we can still effect air movement by having one double height space, carefully positioned to draw hot air from all over the house. Only the toilets and bedroom escape from this drag effect, which need their individual modes of displacement ventilation in the form of ceiling-level vents.
Towards multiple advantages
Ideally, the double-height is part of the three-fold design solution including skylights and internal courtyards, which together do wonders to the house micro-climate. While the vertical space distributes light from the sky all over the house, making it bright, and suck the hot air upwards to ventilate, the floor below acts as a passive court or as an active part of the house plan. Double-height spaces chip in more value-added advantages, like the possibility of looking down and talking to people therein.
While the major intention of this idea is green and eco-design, the most visible reason for the popularity of double-height appears to lie in the expanse of space it creates. Even a small house in a 30’x40′ site may look as if it’s in a bigger plot!
Room volume as a way of cooling is definitely a valid method, largely discovered by the British
FOR A BALANCE: Ceiling height decides functional and aesthetic aspects
For all of us, visiting the grand old home of a distant aunt is an unforgettable experience. Stepping into the living room, we notice the large volume, with high ceiling, often with light pouring in from the roof. In summer, the cool inside cannot go unnoticed, more so if we walk in just in time for lunch!
Where is the magic? Commonly it’s attributed to high roof, which is rather unfair to all other aspects of passive cooling. Anyway, room volume as a method of cooling is definitely a valid method, largely discovered by the British. They would insert a horizontal window in the roof called as clear storey which had openings in the sides. Sometimes, there would be louvers at the top of walls or window shutters fixed in their centre to be operated by long ropes or steel rods.
Impressed by all of this, when we plan for a new home now, we insist that the rooms be at least 12 ft. high. This decision could be useful or a waste of money – so, let us try to understand this phenomenon first.
Old time solution
High ceiling does not reduce the heat gain at roof level, but decreases its effect during floor-based activities. However, room air also gets heated up, hence the high level openings which are provided are to let hot air escape. The British tried up to 15 or even 16 ft. high rooms, and ensured these rooms were proportionately spacious in plan. The resultant volume of the room would create different aesthetics, but more importantly, create a sense of coolness.
It is not worth blindly copying these designs today; we need to realise our project contexts to apply these principles. If the building has a first floor, high ceiling on ground floor has no climatic effect, though it may create spacious looks. Height without displacement ventilation could be detrimental to the cause, since the air and heat trap zone above the lintel level increases! Added height would increase the run of the staircase, volume of wall and length of service lines, all adding to the construction cost. With the present set of electrical gadgets adorning the roof, higher the roof, lesser the effect of fan and light, besides the problems of replacement.
We cannot stop atmospheric heat, but can reduce its ingress and let it escape again. Passive cooling ideas offer many options, where indoor temperatures can be reduced, compared to normal construction systems. In case of minimal indoor air movement discouraging ventilation, thermal currents can be created by letting heat inside through skylights, resulting in displacement ventilation. As such, today there are simpler and more economical solutions, without taking the roof to great heights.
If the house has no natural air movement, the only option left is to have exhausts and ceiling fans and keep them on all the time.
Let all rooms open into the garden
The Green Sense column explores just one theme in each essay, which makes it easy to read and comprehend. In the process, it singles out issues, which ideally cannot be so separated, being part of the whole process of building. Material cannot be discussed without reference to external elevation; windows affect internal functionality; and semi-open spaces need to relate to the building plan at large.
As such, without the opportunity of an inter-related narration in long text, this column is limited to information coming in bits and pieces, and it is hoped that the reader would connect them together. Often, it may be difficult to inter-relate the topics, where the specific eco-theme stands in isolation, and may never get applied. Hence all of the above explanation and the following text to illustrate the case of window positions and plan form.
One of the reader inquiries mentioned about a newly built house, wondering how to increase air movement. Look at most of city houses built within a specific rectangular site. The building form too happens to be a rectangle, add two floors with a flat roof, imagine a balcony or some terrace – at first look it is a rectangular box.
Most rooms have only one external wall, where we end up having one big window in the centre of wall, hoping the size of window would solve all our problems of light and air! In addition, all rooms would have walls and doors, which block the little light and slight air that may filter into the room, resulting in no air movement across the house at all.
We are not criticising the conventional approach, but hoping to learn from it. We realise, enabling air and light is also a function of the house plan; hence there could be one plan that increases air and another that hinders it.
If the house is already built with no thoughts on natural air movement, the only option left it is to have mechanical means like exhausts and ceiling fans and keep them on all the time.
Don’t get rigid in your plans
Instead, let us imagine a house plan where the external wall is not one straight line, plan not a rigid rectangle and the whole house not a box. Imagine one bedroom jetting out by 3 or 4 feet where the window can happen in three directions. Automatically, air movement increases. In case we insert a small garden within the rectangle plan, it would get three walls around it and accordingly there could be three rooms or spaces opening into this garden. Since this open space is within the rectangle, it will not be visible from the road, providing privacy during the use of garden.
Even if the neighbour builds close to the compound wall, there would be light filtering in from this private garden setback.
If such ideas get extended further, what do we get? It would be a building with walls projecting or receding and an attractive overall form. There would be more light and air, achieved not merely by the windows, but by the plan itself.