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Community and Q&A

Demolishing an existing 150 yr old structure and construct a new home

Girija | Posted in Energy Efficiency and Durability on

Esteemed team,
I have a 150 yr old ancestral home in southern india where it is hot and humid all year around. The house has an 125 x 17 area and shares walls on east and west side with neighbors. These two walls have to be kept in place. These walls are 150 or so years old and built with brick and lime.
To suit the modern comfort the plan is to air-condition all bed rooms using mini split type AC units. In doing so how do I go about insulating the existing walls on the east and west side? I have read articles about insulating old brick homes and the more I read the more I get confused. I don’t have access to exterior side since it is actually the living space for neighbors. I can add insulation on the inside although it will eat into the available area.The north and south side will have new walls and exterior insulation should not be an issue.
The roof structure will be RCC concrete style however I will have a false ceiling with insulation for the air conditioned bed rooms. This specific question pertains to the master suite which will be a two storeyed bed room construction in the first floor. The rest of the building will be a two story structure without basement. I have got the roof insulation part. The master suite faces north and that wall can be insulated on the exterior. It faces south to the living room (living room will be on the ground floor but has a cathedral ceiling)
Is it better to leave the space uninsulated ? If insulating I am thinking about adding a wood wool board as insulation and ceramic tile on top of it.
I would appreciate any feedback you may provide. If there are additional questions you may have, please let me know.
The east and west walls are generally in good shape as no evident leaks / rots exist.

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  1. user-2310254 | | #1


    Are you demolishing or renovating your home? Have you searched for GBA-like sites in your region? This site focuses mainly on the US and Canada. Your local methods and materials (like RCC concrete) are likely quite different from those used here to build energy efficient homes.

  2. Expert Member
    Dana Dorsett | | #2

    Some pictures might be useful for figuring out which methods would be appropriate, and which wood not.

    In general there is a much bigger benefit to insulating the exterior than the interior, since the thermal mass of the masonry keeps the interior temperatures from changing rapidly. This is one reason why very thick masonry walls are used in that type of climate.

    A continuous layer of 2cm or 2.5cm of expanded polystyrene (EPS) insulation on the exterior does pretty well with massive masonry walls. That type of insulation can be finished with a thin cement or stucco should work. It is probably worth doing a lime mortar parge over the exterior of the wall prior to installing the foam board. I'm sure there are many builders in India familiar with this type of retrofit exterior insulation system, but whether any of them are near you depends on the local market for that type of work.

    Key to this approach surviving decades of monsoon seasons is metal flashing to ensure all water hitting the wall and roof gets re-directed to the exterior of the foam layer and not between the EPS foam and brick.

    Air sealing 150 year old houses sufficiently to keep the interior humidity well controlled can be difficult, especially if you are trying to preserve the look and feel of antique windows and doors.

    Are you in Kerala, Tamil Nadu or perhaps not that far south?? (I have friends & aquaintances from both states, though they live in the US now.)

  3. GBA Editor
    Martin Holladay | | #3

    It's always tough to decide how much insulation to add when the insulation reduces the interior floor area. It's a balancing act, and it's up to each homeowner to decide how to proceed. Certainly, some wall insulation is a good idea -- even R-2 or R-4 insulation can make a difference.

    The articles on GBA that raise worries about interior insulation in brick buildings don't apply in your case. The main worry is damage during freezing temperatures, and you are fortunate enough to live in a frost-free climate zone.

    When it comes to choosing your insulation material, you'll have to follow local advice. I have no idea what types of insulation are commonly available in India.

  4. Expert Member
    Dana Dorsett | | #4

    In the US code minimum for that type of climate for masonry or concrete walls would be a continuous R3 on the exterior, which would be ~19mm of EPS. Beyond that doesn't make much financial sense.

    Window glass with low-E heat rejecting coatings would make sense, but it doesn't have to be a double-pane insulated glass unit. In places as far north and at the elevation of Bangalore the average outdoor temperatures or coastal areas such as Chennai or Kochi are pretty moderate in terms of interior to exterior temperature differences,

    Coastal Kerala is a bit like Miami in mid-summer, but the temperatures are pretty much year round.

    At elevation in the Western Ghats temperatures are even more moderate, but the humidity issue is still there.

    Low density EPS molders abound in India- I'd be surprised if EPS sheet insulation in various thicknesses wasn't fairly available.

  5. Girija | | #5

    Thanks for the answers posted here. Much of the local construction simply does not utilize any insulation but in my opinion it is being done that way out of ignorance. The location is southern tamilnadu close to the borders of kerala. The geo co-ordinates are 9.1709 N and 77.53090 E. Mean seal level is about 143 m. The foothills of western ghats are about 40 or so miles. It is humid and hot.
    I do see EPS is available and can be used for exterior walls which will be brand new on the north and south side. Thanks for clarifying low E coating for the window glasses. As someone had asked there is no plan to preserve any old architectural doors and windows.
    Should I then interpret as insulating the existing east / west walls will not be necessary in which case I have a follow up question. What happens when my interior space is air conditioned and the corresponding space in neighbors home isn't conditioned. Since we share common wall, Will the heat from neighbor's side conduct into my conditioned space or am I thinking way too much unnecessarily.
    I wish I had a picture of the existing building but I dont have it at the moment. Unfortunately in those areas, one has to do own research and mandate that construction be done in the best manner and there is no enforcement of codes per se.
    I thought of using wood wool as I thought it was more "Green" compared to EPS. The weather is similar to Miami / Keywest except for the powerful storms. Although there is always the threat of cyclone, the place is away from ocean by atleast 60 miles. This place is unique in that it hardly rains. Rarely we see heavy rainfall.
    So to summarize, Should I just use EPS or can i possibly consider wood wool.
    Should I simply ignore insulating the common wall.

  6. GBA Editor
    Martin Holladay | | #6

    Q. "What happens when my interior space is air conditioned and the corresponding space in neighbors home isn't conditioned? Since we share common wall, will the heat from neighbor's side conduct into my conditioned space?"

    A. Yes, there will be heat flow through the wall. Insulation will slow the rate of heat flow. The heat loss formula for determining transmission losses through floors, roofs, and walls is:
    Q = A • U • ΔT

    In other words, the rate of heat flow through a building assembly (in Btu/h) is equal to the area of the assembly (in ft²) times the U-factor (in Btu/ft² • hr • F°) of the assembly times the ΔT (in F°). The ΔT (or "delta-T") is the difference between the temperature in your neighbor's house and the temperature in your house.

    Bricks have an R-value of about R-0.2 per inch, so if the brick wall is 10 inches thick, it has an R-value of 2 and a U-factor of U-0.5 (since U=1/R).

    If you have a common wall with a neighbor that is 9 feet high and 30 feet long, and the neighbor's house has an interior temperature of 86°F, and your house has an interior temperature of 74°F (meaning a delta-T of 8 F°), the heat flow through the wall would be
    270 • 0.5 • 8 = 1,080 BTU/h

    If you can reduce the U-factor of the wall by adding insulation, you slow down the heat flow rate. Let's say that you increase the R-value of the wall from R-2 to R-10. What happens? Well, R-10 is U-0.1. So:
    270 • 0.1 • 8 = 216 BTU/h

    By increasing the R-value of the wall from R-2 to R-10, you have cut the rate of heat flow by a factor of 5.

  7. Expert Member
    Dana Dorsett | | #7

    The temperature difference between the neighboring space and your space will usually be smaller than the difference between your space and the outdoors. But since you will be putting the insulation between your space and the thermal mass of the wall you won't get the thermal mass benefit- it has to be at least the same or even higher insulation levels than the exterior walls (which DO have the thermal mass on the conditioned space side of the insulation.)

    25-50mm wood wool or stone wool (also available in India) would indeed be greener than using EPS. Stone wool is probably the better choice, since it has the additional benefit of being completely fireproof. It is often marketed for both it's fireproofing and soundproofing properties (another factor with partition walls to neighboring occupied spacing). eg:

    it's available in batts rigid board- most vendors start at 50mm thickness, but it also comes in long, wide rolls. You may be able to get 25-30mm material in long wide rolls. See:

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