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Thermal mass and staying cool

  • 15-08-2022 4:20am
    Registered Users Posts: 2,473 ✭✭✭

    Thermal mass is a broad term that describes several material characteristics that determine a material's capacity to absorb, store and release heat. A material like plasterboard has a low function in this regard, while concrete has a higher mass and performs better. At the same time, water performs even better again. It is widely appreciated that it has a substantial impact in evening out internal temperature fluctuations in hot or cold weather. It is often noted that traditional cottages are excellent at staying cool in Ireland due to the large mass of their walls. However, this is not the case in countries where temperatures are hot for long periods of time, in such countries eg. India or Japan, wood rather than stone has been a preferred construction material traditionally. In terms of exploiting this characteristic, such thick stone walls are hard to use in modern construction, but concrete block walls are widespread in Ireland. My question is, is hot weather ever long enough to make the thermal mass of concrete blocks a disadvantage? I don't think stone walls are ever a disadvantage in this regard, but they are far thicker than a modern cavity block wall and have higher density and don't have insulation in the middle.


  • Moderators, Home & Garden Moderators Posts: 10,123 Mod ✭✭✭✭BryanF

    NoT really

    thermal mass is generally an advantage in our climate

  • Registered Users Posts: 9,401 ✭✭✭Flinty997

    Kinda ignoring the cultural (tradition) influences on construction choices or cost or technology. Or space (area) constraints.

    It would be interesting to see what could be achieved on cheap land with cheap materials and low tech in terms of building energy efficient building.

    Straw and Mud thick walls, passively cooled larders etc.

  • Registered Users Posts: 2,473 ✭✭✭Yellow_Fern

    Yes. Mud is a marvellous material. Mud external walls and stone internal chimney. Water is also a great material for mass. Rarely used for this.

  • Registered Users Posts: 31,193 ✭✭✭✭listermint

    No idea. But in this weather our house with 200mm eps has managed to avoid any extremes. It avoids the extremes year round tbh. I don't think there is a blanket situation but we are south facing with enough external walls direct to the sun all day long it would be very uncomfortable without the insulation outside.

  • Registered Users Posts: 2,473 ✭✭✭Yellow_Fern

    I see thanks. Is the benefit sufficient enough to replace a wall of dry wall on steel studs on block with wet plaster? This is a three story, and it gets too warm upstairs, even outside heat waves.

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  • Moderators, Home & Garden Moderators Posts: 10,123 Mod ✭✭✭✭BryanF

    So this is an existing 3 storey house? That’s very different. your not adding much concrete at this stage..

    heat rises etc so in the hot weather if your ventilating the ground floor, the top floor is going to be warm..

    id probably install cellulose insulation where possible (search decrement delay)

    but you may need to look at air-tightness, as well as insulation and of course ventilation/ air-movement.

  • Registered Users Posts: 2,473 ✭✭✭Yellow_Fern

    The concept is to exploit the mass already present in the outer leaf, which is partially cut off via the drywall.

  • Subscribers Posts: 39,466 ✭✭✭✭sydthebeat

    I think you need to clarify what exactly youre asking here.

    There was no mention in the OP that your looking to resolve an existing issue, nor any details regard the existing situation.

  • Registered Users Posts: 30,896 ✭✭✭✭Lumen

    My question is, is hot weather ever long enough to make the thermal mass of concrete blocks a disadvantage? 

    Hot weather in Ireland or anywhere? In a sufficiently hot climate a building needs to be actively cooled. In that situation you have the same thermal mass trade-off as you do with an Irish house in winter, which is that if it's discontinuously occupied you are pumping heat for when there's no one home.

    For instance, if you live in Athens where the day-night temp in August averages say 32/23C, and you're out at work all day in an office where someone else is paying the air con bill, you come home in the evening and your concrete house will be full of heat from the day. The air con will be fighting that heat, resulting in higher cooling costs overnight. On other hand, if your concrete house is externally insulated and you have solar powered air con, you can keep the house cool all through the day and get through the night without using grid electricity.

  • Subscribers Posts: 39,466 ✭✭✭✭sydthebeat

    Thermally massive houses in warm climates actively work against solar gain by using large overhangs, awnings, shutters etc. These reduce the heat coming into the dwelling in the first place, reducing the need for energy intensive cooling.

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  • Registered Users Posts: 2,473 ✭✭✭Yellow_Fern

    Thanks for the feedback. I am referring to Ireland in this case. The reason I asked is as I was interested in ways to make my home my comfortable. I like the idea of overhangs and awnings but it is not so practical in my house. As a three story house, it seems particularly prone to overheating. The walls are plasterboard over two leaf block cavity wall. So I was investigating whether replacing some of the plasterboard with wet plaster, probably just a table wall, to exploit the the thermal mass of the inner leaf, currently isolated by the drywall. Now I know it means a cooler wall in winter and I understand it is a expensive project though. So I am trying to understand would it make any difference to comfort. Other ideas would be change some of the attic insulation to wood fibre blocks.