ᐅ Reinforce insulation of the ceiling between floors to reduce heat transfer to the upper floor.
Created on: 8 Mar 2021 13:18
A
andimann
Hello everyone,
We built our house in 2016, and the floor/ceiling construction between the upper floor and the attic is as follows:
This assembly achieves a U-value of about 0.234. The attic is therefore an unheated roof space. Not a fully conventional cold roof, since there is also a vapor-permeable underlay membrane beneath the roof tiles, but close to it.
This U-value is clearly worse than the U-value of the walls on the upper floor (about 0.15), but so far everything is fine: no moisture issues, and adding more insulation would hardly pay off in terms of heating costs.
However, in extreme cases the upper floor can reach temperatures up to 26°C (79°F) in summer, and we have considered installing air conditioning. We will likely do this, but only on the ground floor, as it would be a huge construction effort on the upper floor.
A rough estimate shows that about two-thirds of the heat gain into the upper floor in summer comes through the ceiling from the attic. This is due to the approximately 92 m² (990 ft²) of surface area and the temperatures above 55°C (131°F) up there. (At 55°C, the LCD thermometer display turned black, so it may well get even hotter.)
The plan is now to reduce the heat transfer from the attic to the upper floor by improving the insulation. An additional 120 mm (4.7 inches) of EPS 035 insulation is planned, resulting in the following total assembly:
This should produce a U-value of 0.130 for the ceiling. This lowers the heat flow from the attic to the upper floor from about 650 watts to 350 watts, which accounts for approximately 30% of the total heat gain.
I hope this will slow down the temperature rise on the upper floor and reduce the maximum temperature from 26°C (79°F) to 25°C (77°F) or better, 24°C (75°F).
Question: Could this work, or am I missing something fundamental?
Thanks and best regards,
Andreas
We built our house in 2016, and the floor/ceiling construction between the upper floor and the attic is as follows:
- 180 mm (7 inches) concrete
- PE foil as a vapor barrier
- 160 mm (6.3 inches) EPS 040 insulation
This assembly achieves a U-value of about 0.234. The attic is therefore an unheated roof space. Not a fully conventional cold roof, since there is also a vapor-permeable underlay membrane beneath the roof tiles, but close to it.
This U-value is clearly worse than the U-value of the walls on the upper floor (about 0.15), but so far everything is fine: no moisture issues, and adding more insulation would hardly pay off in terms of heating costs.
However, in extreme cases the upper floor can reach temperatures up to 26°C (79°F) in summer, and we have considered installing air conditioning. We will likely do this, but only on the ground floor, as it would be a huge construction effort on the upper floor.
A rough estimate shows that about two-thirds of the heat gain into the upper floor in summer comes through the ceiling from the attic. This is due to the approximately 92 m² (990 ft²) of surface area and the temperatures above 55°C (131°F) up there. (At 55°C, the LCD thermometer display turned black, so it may well get even hotter.)
The plan is now to reduce the heat transfer from the attic to the upper floor by improving the insulation. An additional 120 mm (4.7 inches) of EPS 035 insulation is planned, resulting in the following total assembly:
- 180 mm (7 inches) concrete
- PE foil as a vapor barrier
- 160 mm (6.3 inches) EPS 040
- 120 mm (4.7 inches) EPS 035
This should produce a U-value of 0.130 for the ceiling. This lowers the heat flow from the attic to the upper floor from about 650 watts to 350 watts, which accounts for approximately 30% of the total heat gain.
I hope this will slow down the temperature rise on the upper floor and reduce the maximum temperature from 26°C (79°F) to 25°C (77°F) or better, 24°C (75°F).
Question: Could this work, or am I missing something fundamental?
Thanks and best regards,
Andreas
Hi,
It’s clear that insulation only slows down the heat transfer between two media; it doesn’t stop it completely. After an infinite amount of time, temperatures on both sides would equalize, regardless of insulation thickness. But here, days are not infinitely long…
Yes, that’s a fair question. The general contractor (GC) only installed what was required. Considering we consume about 15,000 kWh of gas annually for roughly 270 m² (2,900 ft²) of heated floor area (including hot water), the design isn’t entirely wrong from an economic perspective. Whether it would have made sense to invest an extra $1,000 in insulation to save 50 to 80 dollars in annual heating costs is debatable. Today, I would definitely opt for better insulation from the start. But you always know better in hindsight.
Best regards,
Andreas
Lumpi_LE schrieb:You often hear statements like that, but I’m genuinely interested in the physics behind this claim. If that were entirely true, passive coolers made from materials like Styrofoam wouldn’t exist.
Adding more insulation does not improve summer heat protection.
It’s clear that insulation only slows down the heat transfer between two media; it doesn’t stop it completely. After an infinite amount of time, temperatures on both sides would equalize, regardless of insulation thickness. But here, days are not infinitely long…
Lumpi_LE schrieb:
Besides, it’s strange why the roof—which is responsible for the biggest heat losses—has a lower U-value than the walls, especially with almost no additional cost.
Yes, that’s a fair question. The general contractor (GC) only installed what was required. Considering we consume about 15,000 kWh of gas annually for roughly 270 m² (2,900 ft²) of heated floor area (including hot water), the design isn’t entirely wrong from an economic perspective. Whether it would have made sense to invest an extra $1,000 in insulation to save 50 to 80 dollars in annual heating costs is debatable. Today, I would definitely opt for better insulation from the start. But you always know better in hindsight.
Best regards,
Andreas
Hi,
Sure, we’ve considered that as well. However, that would mean redesigning the entire roof structure, and the effort involved would be much greater. Then, instead of having 50 degrees during the day and 15 degrees at night in the attic, you’d likely have a constant 30 degrees. Over a 24-hour period, that might not result in much improvement.
Active attic ventilation in summer might be the ideal solution to reduce heat buildup up there. But then you start dealing with automated windows, sun and rain sensors, and so on. Does anyone have a good solution for this? Simply adding a few vent bricks probably won’t help much because the roof underlay prevents air circulation.
Best regards,
Andreas
Myrna_Loy schrieb:
Why don’t you insulate the roof? That way, you wouldn’t heat up the airspace in the attic, which probably has little ventilation anyway.
Sure, we’ve considered that as well. However, that would mean redesigning the entire roof structure, and the effort involved would be much greater. Then, instead of having 50 degrees during the day and 15 degrees at night in the attic, you’d likely have a constant 30 degrees. Over a 24-hour period, that might not result in much improvement.
Active attic ventilation in summer might be the ideal solution to reduce heat buildup up there. But then you start dealing with automated windows, sun and rain sensors, and so on. Does anyone have a good solution for this? Simply adding a few vent bricks probably won’t help much because the roof underlay prevents air circulation.
Best regards,
Andreas
M
Myrna_Loy8 Mar 2021 21:01Why would you need to change the entire construction? Installing insulation beneath the rafters is quite common. Blown-in insulation, for example, provides excellent thermal resistance, especially against heat. Glass wool is naturally less efficient in this regard.
Hi,
I would honestly be very interested in the exact calculation.
In our case, the windows and walls of the upper floor are shaded about half the time in summer due to the roof overhang. In addition, our windows are consistently shaded by roller shutters. There is no direct sunlight hitting the windows in summer. The roller shutters heat up, of course. However, they release the radiant heat as long-wave radiation, which glass cannot transmit. So, what remains is the heat transfer through the warm air between the roller shutter and the window.
We roughly have 20 sqm (215 sq ft) of windows on the upper floor.
The Ug value is 0.6, and let’s assume the Uf is 0.8.
With a temperature difference of 20°C (25°C (77°F) inside and 45°C (113°F) between the roller shutter and window—note that the roller shutter should not be fully closed to avoid heat buildup), we get:
0.8 * 20 * 20 = 320 watts.
That’s only about half of what comes through the ceiling. But of course, it adds up to easily 3-4 kWh daily.
Best regards,
Andreas
Nida35a schrieb:
Most of the heat in summer comes through the window areas,
even when shaded, it’s only a reduction of the radiant heat of several kW daily,
I would honestly be very interested in the exact calculation.
In our case, the windows and walls of the upper floor are shaded about half the time in summer due to the roof overhang. In addition, our windows are consistently shaded by roller shutters. There is no direct sunlight hitting the windows in summer. The roller shutters heat up, of course. However, they release the radiant heat as long-wave radiation, which glass cannot transmit. So, what remains is the heat transfer through the warm air between the roller shutter and the window.
We roughly have 20 sqm (215 sq ft) of windows on the upper floor.
The Ug value is 0.6, and let’s assume the Uf is 0.8.
With a temperature difference of 20°C (25°C (77°F) inside and 45°C (113°F) between the roller shutter and window—note that the roller shutter should not be fully closed to avoid heat buildup), we get:
0.8 * 20 * 20 = 320 watts.
That’s only about half of what comes through the ceiling. But of course, it adds up to easily 3-4 kWh daily.
Best regards,
Andreas
Hi,
Sure, you’re absolutely right, there is a limit. The effectiveness of additional insulation decreases as the thickness increases. That’s why I’m considering at least making the ceiling insulation as good as the wall insulation, but not significantly more.
And again, you’re right, the overall concept is important. But for us, that is mostly maxed out:
One factor that is hard for me to estimate is the heat gain through open entrance or terrace doors. That naturally causes the indoor temperature to rise quickly. However, these doors are only open briefly here. But generally, the living room, with its large window areas, will likely be quite a heat collector despite the external blinds. We will probably install air conditioning there now.
Best regards,
Andreas
pagoni2020 schrieb:
We have currently had various calculations done regarding roof insulation. It turns out that you eventually reach a limit, and adding more insulation only changes the result slightly, or the heat/cold simply enters somewhere else, as already mentioned here. Therefore, it would only be effective as part of an overall concept, including windows, timely shading of walls, personal behavior, etc., but even then, heat will eventually get inside.
Sure, you’re absolutely right, there is a limit. The effectiveness of additional insulation decreases as the thickness increases. That’s why I’m considering at least making the ceiling insulation as good as the wall insulation, but not significantly more.
And again, you’re right, the overall concept is important. But for us, that is mostly maxed out:
- The windows have a Ug-value of 0.6,
- and also a g-value of 53%.
- The windows are consistently shaded with roller shutters (automatic control using sun position sensors – which took some convincing at first, but is now accepted)
- Ventilation is only done early in the morning when it’s cool outside.
- Otherwise, ventilation is managed by a controlled residential ventilation system, which can at least “cool” the air to 21°C (70°F) using a ground heat exchanger.
One factor that is hard for me to estimate is the heat gain through open entrance or terrace doors. That naturally causes the indoor temperature to rise quickly. However, these doors are only open briefly here. But generally, the living room, with its large window areas, will likely be quite a heat collector despite the external blinds. We will probably install air conditioning there now.
Best regards,
Andreas
andimann schrieb:
If that statement were entirely correct, passive (Styrofoam) coolers or similar products wouldn’t exist.Well, that’s a different principle. On one hand, you have active cooling (the ice block), and on the other, there’s no window letting sunlight in. Put the cooler without the battery in a sunny garden, and you could actually cook something inside it.The system of the house in summer is continuous heat influx from outside. Thicker insulation slows this down slightly, but whether it heats up after 3 or 5 days doesn’t really matter then. Additionally, the heat brought in by the sun is retained even better inside.
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