Building walls with the rat trap bond

Just in case I’ve got you visualising rodents scurrying about where they’re not wanted, ease your mind; the rat trap bond I’m talking about is simply a method of laying bricks when building a wall.  It’s similar to the common “Flemish” bond but instead of putting the bricks on their face, they are placed on their edges. This leads to cost savings because less bricks and cement are needed which, in turn, reduces the embodied energy of the wall.

The Rat Trap Bond

Bricks are laid on edge to create an air gap between two layers

Laurie Baker took every opportunity to try and make people realise the value of this method but, by and large, the 20-25% saving in brick doesn’t seem to have been appealing enough.  The rat trap method of construction was popular in England until the start of the 20th century but sustained lobbying by the brick-making industry convinced people that that it was not strong enough to build load-bearing walls.

That is rubbish of course; it’s strong enough for one and two storey buildings as has been proven over and over again by Laurie Baker’s lasting work. But masons too are not usually happy about adopting this system and come up with all sorts of excuses to try and avoid it. I have to admit that, till date, I have not pushed hard enough against their inertia but now I’ve just got one more reason to do so.

For the ShKo bungalow at Karjat, I plan to use the rat trap walls and wanted to know just how much difference they would make thermally. Nobody seems to have done a calculation of the difference — at least there was none that I could find. So, armed with some data from thermal calc and the energy evaluation component of ArchiCAD, I tried to do just that.

Taking just a simple 3m x 3m structure with no openings, I ran a calculation for both types of wall. Result: average U-value of the structure’s outer shell dropped about 15% compared to conventional walls and the energy required for cooling also fell by about 8%. The difference was exaggerated because the model had good roof overhangs to shade the walls.

Still, when you think about it, 8% is nothing to scoff at.  In addition, the embodied energy is reduced quite dramatically and, of course, Laurie Baker’s original reason for using the rat-trap bond still stands — the wall is simply cheaper to build.

Now, I just have to go and steam-roll the masons into learning a new technique.

Karjat Resort

Entrance aangan to a cottage

Entrance aangan to a cottage. The overall design was meant to create the ambiance of an Indian village.

Satya Health Farm, now Satya Resort, is situated in the Karjat region — about two hour’s drive from Bombay. With the river Pej flowing past the northern edge of this 50 acre (20 Hectare) property and surrounded by the ranges of Matheran, Dhak and Bhimashankar, it is an excellent spot for either purpose.

The brief given by the developers was to recreate an Indian village. Not in the literal sense of course – Indian villages are generally short of water, electricity and telecommunication infrastructure. What the clients really wanted was, for the design to generate a feeling of rustic community. A place where time flows slowly and you are not under any kind of stress. No deadlines, no schedules — just a feeling of well-being.

Courtyard around which are some rooms and suites

Some of the rooms are in arranged around central open-to-sky courts

The layout makes full use of the variable slopes with clusters of ground-hugging cottages following the contours of the site. A monsoon stream flows through before joining the river to the north. The river itself is a perennial one since it comes from the Bhivpuri Power Station which generates electricity throughout the year.

The requirement for peace and tranquility is reflected in the choice of building materials and the overall aesthetic appearance. Rooms are arranged around courtyards or as part of a larger cluster – a Mohalla. With their front Aangans and rear Otlas every room gets as much space outside, as within. The idea is to draw people out – to cajole them into shedding the attitude that makes city folk hesitate to speak with their neighbours.

The cottages are arranged in clusters

The cottages are built very close to each other without sacrificing privacy.

Locally made burnt bricks were used to erect a load-bearing structure resting on a foundation of local black (basalt) stone. This is topped by a traditional wooden roof with Mangalore tiles. The entire roof planking was done with treated rubber wood which is not just economical but ecologically friendly too, being a by-product of the rubber industry.

The design needed to have a feeling of softness. This was achieved by avoiding sharp edges and by the use of warm colours on the walls. The flooring too, is of red terrazzo tiles with patterns and borders in green and yellow marble. For the detailing, traditional forms and patterns have been drawn upon – in the archways connecting cottages for example.

Click on any of the thumbnails to see the gallery.

The lighting, especially for the exteriors, has been deliberately kept at low levels not just because bright lights would attract insects from miles around but also because harsh illumination would shatter the tranquillity and obliterate much of the night sky.

You may also want look at the list of materials, consultants and contractors.

Download GDL Cookbook 4 [PDF]

A couple of months ago, I was telling you about a free download of David Nicholson-Cole’s “GDL Cookbook 3” and saying how I was looking forward to the updated version. Well it’s out and it’s a free download as well. You can get it either as a single concatenated file or as 48 individual chapters. Alongside, you can also get his brilliant “Introduction to Object Making”.

Download it Here

Free Beta of SpecifiCAD

CADalytic Media has released a free beta of SpecifiCAD for ArchiCAD 10/11, AutoCAD, ADT, Revit and Sketchup. SpecifiCAD allows you to click on a building component within each of these programs and access its CAD details, 3D models, specifications and Green information using the Sweets Catalog network and the Sketchup 3D warehouse depositories.

Download SpecifiCAD from http://www.cadalytic.com/index.php?dir=downloads

Edit: Sorry to say the site seems to be no longer available.

Barebones ArchiCAD

Graphiosoft are offering a stripped down version of ArchiCAD 11 for way below their normal price, the target market being small architectural firms. On the face of it, it’s a good move because small firms may be able to get by without features like teamwork, markup tools or even a printed manual. However, if you look at the comparison, there are way too many essentials that have been removed. I mean, how can you do without something as basic as rendering (lightworks & sketch rendering have been knocked out), profile manager for making custom wall/column shapes or the ability to open normal ArchiCAD files?

I think, if they tweak the feature set a bit, they might have a winner but in its present form, they’ll get little response.

ArchiCAD Start Edition 2008 v/s ArchiCAD 11

Download GDL Cookbook 3 [PDF]

I could have sworn this page didn’t exist when I searched for such a download some months ago. I’d found some sites selling the book for a few bucks but now the author himself is giving it away.

“The GDL Cookbook 3 is out of print and I am unable to get Cookbook 4 out, so I am providing a free download for the PDF (no print, no edit) copy.”

It’s over 7 years old but still useful today and, hopefully, David Nicholson-Cole will be able to bring out the version 4 soon. I’m waiting to buy it.

Go to :: GDL Cookbook 3

GDL Toolbox only in Hungarian

This is was a plugin that worked as a 3D object editor within ArchiCAD 9 but was never updated for v.10 – or so we thought. In fact, the original link referred to in an older post – [[gdl toolbox – freeware]] doesn’t work any more. Just when I’ve started to learn GDL, one of the finest tools made for it is no longer usable. Unless you know Hungarian.

Go to :: http://www.eptar.hu/eptar_letoltes_toolbox.php