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Building Technology
 
Addition above load bearing walls
My house is a 25 year-old load bearing wall structure. It is in a fairly good condition. No bad structural cracks, seepage, etc.

I now intend to construct a duplex (1st plus 2nd floor) on the existing ground floor. I have been consulting engineers and architects and have received mixed solutions for this. While some say that it is safe to go for 2 floors above, as the ground floor load bearing walls are 16 inches thick (13.5 inch walls + 1.5 inch plaster), others advise against going even for 1 floor, saying that the ground floor will develop cracks in a couple of years, being unable to take the additional load.

My civil contractor, however, was ok with 2 additional floors but turned down my idea of going for cavity walls on the first and second floors. He says that cavity walls don't work with load bearing walls and should be used only in case of column and beam construction.

He opines that cavity walls are not good enough to take heavy loads and hence should not be used as load bearing walls. I had suggested cavity walls to make the building more climate friendly.

Yet another engineer suggested raising columns on the sides and inside the building such that the load of the new floors is transferred to the columns sparing the walls of the ground floor. While this is the most sound one, I am not inclined towards this as this will eat up a lot of additional space and damage the existing flooring of the ground floor - something that I want to preserve.

What would you advise? How can one make sure that the walls can take two additional floors? Also keep in mind that I would like to go for cavity walls considering the oppressive temperatures in Hyderabad.

Additional info: the foundation of the ground floor walls is 4 feet deep.
Pawan Jeedigunta
Responses
 
Addition above load bearing walls
Dear Pawan,

I deem it unprofessional to give advice to a situation like yours (with a possible application of the proposed solution) without any structural study. Therefore, I abstain from giving my opinion vis-a-vis the solution. Maybe others will be more forthcoming.

However, I must stress that your house walls are 13.5" thick (or one and a half brick walls as claimed in architectural parlance) and not 16". Plaster is not counted in wall width since it is a non-structural entity.

This becomes all the more crucial in your case since the walls are load bearing. So steer clear of professionals who treat your house walls as 16"; they obviously don't know their craft.

Best of luck. Hope you find an apt solution.
Shubhru Gupta
Addition above load bearing walls
Thanks Shubru.

I was curious to know how a problem like this is generally approached. Is there any technique to determine the load bearing capacity and decide if the building can take two additional floors? What should an engineer or architect be doing to decide this?
Pawan Jeedigunta
Addition above load bearing walls
Dear Pawan,

Ideally, there are mechanical instruments available to ascertain strength of old standing walls. But these are expensive tools unless your engineer or contractor already has them.

Otherwise, there are complex mathematical calculations involved but you won't be able to review them being a non-professional.

Your safest bet right now would be to refer to BIS standards for brick masonry construction.
Shubhru Gupta
Addition above load bearing walls
Cavity walls are not load bearing? Here in the UK it is common if not universal practice to build housing with brick, load-bearing cavity walls. These cavity walls are secured to each other with `butterfly`(shape) wire ties.

Today, modern built brick wall houses have cavities fitted with solid fibre-glass insulation batts (battens?) and the older houses are retrofitted with insulation foam pumped into the cavity.

I once visited an old early Victorian brick built house which had canvas `walls` mounted on battens inside solid brick walls, because the inside surface of the brick wall ran with moisture in the cold weather.
Frank John Snelling
Addition above load bearing walls
Everyone,

There was an architecture show at Hyderabad yesterday where they had a helpline. I sought their opinion on the issue.

I was advised to approach the civil engineering department at Osmania
University, where they apparently have instruments that measure the load bearing strength of a wall. A good suggestion, no doubt, but practically difficult.

So with all options of some kind of a test and confirmed report (I was eager to have this before going ahead with the construction) I have decided to repose my trust in the architect/structural engineer who says he can give in writing that the structure can take two additional storeys.He says that the structure looks excellent and there is no need to conduct tests as there is absolutely no sign of problems.

He is also happy with the 4 feet depth of the existing foundation. Hmmm- let's see how it goes.
Pawan Jeedigunta
Addition above load bearing walls
Shubhru,

What could be the reasons for cavity walls not being popular in India ? Surprising since it would work excellent in the extreme climates of the plains. Is it due to lack of awareness or the addtional expense in contructing two walls in place of one? Or is that cavity walls have some inherent disadvantages?

I suggested to my arch'l engineer to consider cavity walls purely to make the building more climate friendly. The temperatures in Hyderabad are getting more oppressive by the year and I am looking for natural ways to counter this.
Pawan Jeedigunta
Addition above load bearing walls
Dear Pawan,

Am glad to know you sought professional advice, and hope the solution works for you.

There could be many reasons for cavity wall construction not being popular among the masses. I don't think it has much to do with lack of awareness, but more to do with the manifold increase in the cost of construction, not just for walls but also for spanning of floors, roofs and fenestration (doors, windows and other opening) that have to go across two wall sections. Then there are additional costs for wall ties, etc. Consult your engineer for details of this.

Besides, a cavity wall takes up more floor area than a standard 9" wall, which is unacceptable from the real estate's exploitative point of view, where every inch of usable floor space matters.

Besides, there are other mechanisms for combating extreme weather that are extremely effective and add to the richness of architectural vocabulary as well, like internalised planning, courtyards, the play of openings for effective ventilation, et al.
Shubhru Gupta
Addition above load bearing walls
Pawan,
I am surprised that no one so far asked about the soil condition on which your house was constructed. Though the house was constucted 25 years ago, it is essential for one know the type of soil.
Also, I am surprised that none enquired about the longest unsupported span of the roof in the ground floor.
The strength test for the walls is no doubt helpful, but would take a lot of time and also money. It would cost more than having a pillar in the center to reduce the span and transfer the load directly through the columns instead of walls.
Your contactor/architect may say that the walls would take the load. The same was done by an architect who is not a civil engineer to my brother's house six years back in Eluru. Now,the walls in the gound floor and first floor and some portion of roof in first floor developed huge cracks. Now, my brother is planning to get the entire house repaired with the help of the civil engineer who initially suggested that the house needs additinal columns to support the load.
Please review this again, before you take a decision.
Ratnam Jeedigunta
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