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.



40 thoughts on “Building walls with the rat trap bond

  1. Excellent post. My house is built of this Rat trap bond from the Victorian era (English) and its still standing strong touch wood! Its 2 stories with a attic above.

  2. Is it possible to construct a first floor using this method when the ground floor is already constructed 13 years back using traditional bonding method . How to reinforce steel in the walls it self.

    • Yes Asheesh, it is perfectly allright to have the the second level in rat-trap bond. Just make sure you have decent quality bricks and an equally good mason.

      You cannot reinforce the rat-trap walls with steel – it wouldn’t make sense. If you really need to have reinforcement, just put columns at the wall junctions.

  3. Hi There,

    I am planning to construct house in 2/3 years from now. My plan is to build 2 two bed room houses in the ground floor and a duplex on top of it.

    Is it OK to used rattrap method for my house?

    Suppose in future i want to do some construction on top on duplex, will the walls be able to support it?

    Regards,
    Balu

    • Yes Balu, you can add a second level but make sure you have good quality bricks. I don’t think it would be wise to add a third level, though.

  4. hi! I am building my home in ratrap bond and would like to know how can we calculate the number of bricks that will be needed? Any suggestions about calculations would be very helpful!

    • Hi Gauri. Theoretically, you’d need about 75-80 of standard sized bricks per square meter of wall. Practically, though, it would depend a lot on brick size and quality (reject rate). You might want to make a test wall (boundary walls are great not only for this but to get the masons used to working in rat-trap). All the best and I would love to see some photos when it’s done!

      • Hi! Thanks for your help! I have started the construction of my house and will surely be sharing the pictures very soon! I also had this doubt about lintel bricks. Since im using a solid course for the lintel over which i will be using an RCC band, i am in doubt if this could stay put without support till the time i use window/door frames after the monsoon. What is the right method? Will the brick course stay?

        • You could also make reinforced brick lintels if you want to save on the cost of a ring-beam. On the other hand, ring-beams will make the structure more resistant to earthquakes. Depending on the quantum of rainfall at your site, leaving unfinished brickwork exposed to an entire monsoon could be problematic. The brick course will probably stay, but the integrity may be compromised if it soaks up too much rainfall.

          I don’t know if this fits with your schedule but how about leaving the lintels until after the rains and put them in after fitting the door/window frames?

          • Okay. So the site is in Uttrakhand. It experiences a good amount of rainfall. But, the bricks that we have brought up from dehradun have a good compressive strength and we have asked previous owners who have left their brickwork exposed and the bricks are in good shape even after 3-4 years of experiencing the same amount of rainfall. We will have to stop construction for atleast 2-2.5 months and then restart which will elongate our timeline to complete this. Do i need to use some kind of protection for the walls during the halt? I wanted to bring up the walls till roof level before rains start.

          • Hi Gauri,

            If you’re using good quality bricks, you should have far less problems. However, remember that, while the face of a brick wall can be protected by sealing the joints (pointing), an unfinished wall is exposed at the top. From here, water will tend to percolate down inside the wall, thus damaging its integrity. If your pointing is completed before the rains, all you need to do is to somehow protect the upper surface.

  5. Pingback: @robert_bolduc

    • What are you thinking of using it for Prithvi? Even standard walls cannot be of unlimited length unless they have supports at regular intervals.

  6. I am keen to build this wall for the servant room on the terrace. However I wish to know if I can build this rat trap bond with cement blocks as well Which commonly they call as solid blocks used for apartment construction etc.

  7. My house is old as 40years.i want to build 1st and 2nd floor on it with this rat trap bond.is it possible? My 2nd asking is how is it build when the very first level,lintel level n roof level wl come?i hav seen on net but there is cotradiction regarding this matter.with thnx.

    • Raja, I’m afraid I cannot answer such a specific question without complete information. Ideally, you should consult a local civil engineer who should examine your existing house to determine if it is possible.

  8. Pingback: Walls – 2 – Nick's blog (mainly photos)

  9. Hi, thanks for the article, but i like clarify a doubt, these kind of walls are able to handle the load of slab? i mean these are load bearing walls? any framed structure is required? idf anyone knows pls reply..

  10. Hi,
    I am constructing bungalow and want to use this method and it is in city and very hot during summer. I want to reduce the power bill during such time. Will it is be useful to reduce my power bill?

    • As you will notice in the article, the cooling load for a theoretical model reduced by about 8%. The actual difference will depend on the location, orientation, external shade, and a whole host of other things.

      • Actually the location / City where i stay is surrounded by mountains, it has very heavy rain fall, very cold in winter. But now a days due to constructions everywhere and increased number vehicles making summer unbearable. I want this method especially for summer time only

        • The rat-trap walls will be more insulating than regular brick walls for both summer and winter. To protect you from the heavy rainfall as well as the heat, it would be advisable to keep your roof overhangs fairly deep.

    • You could, but it may not be advisable to use bricks below plinth level (except in areas with very low rainfall) because bricks tend to suck up ground-water by capillary action.

  11. Dear Sir ..

    First of all , hearty thanks for providing very useful info , in your website ..

    Keep continuing Sir ..

    Planning to construct our home in Trichy , Tamil Nadu …

    Need clarification on the following, reg rat trap bond sir ..

    1. U value of rat trap bond , in W/m2K ..

    2. What are the limitations & drawbacks in using rat trap bond ?

    3. Is it difficult to use concealed wiring & plumbing in rat trap bond wall ?

    Thanks for your time and consideration.

    • Hi Albert,

      This was quite a while ago and I can’t find the figure I’d saved but, if I remember right, it was around 1.4W/m²K or so. You can do the calculation yourself here: http://thermalcalconline.com/u-value-calculator/u-value-opaque/u-value-opaqueExcel.html

      You will need good quality bricks and, of course, masons with above-average skills. Another thing you need, is to plan everything out well in advance because, concealing wiring and plumbing is preferably done during construction itself as opposed to cutting the brickwork and embedding the conduits/pipes afterwards. An option in the bathrooms is to make one of the walls, which will take all the plumbing, a solid one (use bricks on edge so that the courses match the rest).

      All the best with your home-building. Do share your experiences with everyone here if you choose to use the rat-trap bond for construction.

      • Really very thanks for your reply and wishes Sir ..

        And very sorry for this much delayed reply , from my side , Sir ( Due to my personal issues ) ..

        Wishes for your upcoming works Sir … Keep continue to write more articles Sir ….

        Regards,
        Albert Abraham R

        • You’re very welcome Albert. This site hasn’t seen any updates in a long while, but I hope to get back to writing more articles soon.

          Thanks again for stopping by.

  12. It seems to be great with the construction Rat Trap Bond. But which type of brick is preferred for construction and where it was available. Please clear my doubts.
    Regards,
    Chandra

  13. Very interesting thread. Fascinating to find that this very old bricklaying method is still popular in India. My 1897 Victorian terraced house in Wiltshire, England was constructed using rat trap bond. The unusual and interesting feature associated with this is the use of a clay tile hung exterior. I recently had to make some repairs to the tiling and was very nervous about how the tiles were attached. I discovered that the rat trap bond provides excellent spacing for nailing the tiles directly into the lime mortar bonds, so no tile battens to go rotten. Carrying out tiling repairs has been very straightforward…

    • Thanks so much for sharing your experience, Vince. The rat-trap bond isn’t nearly as popular as it should be, unfortunately. If we want to reduce our footprint on this planet, this is a great way to start.

      I’m sure readers will also be happy to know that a 120 year-old house built with this method is still going strong.

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