Reinforce floor slab insulation, reduce heat entry into the upper floor

Hi,

Adding more insulation does not help with summer heat protection.

You hear that now and then, but I would actually be interested in the physics behind that claim. If this statement were completely correct, there could be no passive (Styrofoam) coolers or the like.
It is clear that insulation only slows down the "heat transfer" between two media and does not stop it. After an infinite amount of time, the temperature would be the same on both sides, no matter how thick the insulation is. But the days are not infinitely long here...

Apart from that, it is strange why one chooses a lower U-value for the roof, which is responsible for the greatest losses, than for the walls, at almost zero additional cost.

Yes, the question is not entirely unfounded. The general contractor simply installed only what was necessary. Since we consume about 15,000 kWh of gas per year for roughly 270 sqm of heated area (including hot water), the design is not entirely wrong from an economic perspective. Whether it would have made sense to add insulation for another 1,000 € to save 50-80 € heating costs per year is debatable. Today, however, I would have it done more generously from the start. But you’re always wiser afterwards.

Best regards,

Andreas

Hi,

Why don’t you insulate the roof? That way you wouldn’t heat up the airspace in the attic, which is probably hardly ventilated, in the first place.

Sure, we’ve thought about that too. But for that, we would have to change the entire roof structure and the effort would be much, much greater. And then you wouldn’t have 50 degrees in the attic during the day and 15 degrees at night, but probably a constant 30 degrees. Over 24 hours, that probably doesn’t gain much.

An active ventilation of the attic in summer might possibly be the best solution. Simply to reduce the heat buildup up there. But then you start with active windows, sun and rain sensors, etc. Or does anyone have a good solution there? Just installing a few ventilation bricks probably won’t help much because the underlay membrane prevents ventilation.

Best regards,

Andreas

why would you have to change the entire construction? A sub-rafter insulation is quite common, after all? And blown-in insulation, for example, insulates extremely well against heat. Glass wool is of course not as efficient there.

Hi,

the majority of the heat in summer comes from the window areas,
even when shaded it is only a reduction of radiant heat by several kW daily,

I would really and honestly be interested in the exact calculation.
In our case, the windows and walls of the upper floor are always half in the shade during summer due to the roof overhang. In addition, our windows are consistently shaded by roller shutters. Direct sunlight does not hit the windows in summer. The roller shutters heat up, of course. However, they emit the radiant heat again as long-wave radiation, which glass cannot penetrate. What remains is pure heat transfer through the warm air between the roller shutter and the window.

We have roughly about 20 sqm of windows on the upper floor.
Our Ug is 0.6, let’s assume Uf 0.8.
With that, even with a 20-degree temperature difference (25 degrees inside and 45 degrees between roller shutter and window - note the roller shutter must not be fully closed, otherwise heat buildup occurs), I calculate
0.8 * 20 * 20 = 320 watts.
That is barely half of what comes through the ceiling. But sure, that adds up easily to 3-4 kWh daily.

Best regards,

Andreas

Hi,

We have currently had various calculations made regarding roof insulation. It turns out that you eventually reach your limits and adding more insulation only changes the result slightly or the heat/cold enters somewhere else, as already mentioned here. Ergo, it would only make sense as an overall concept, including windows, timely shading of walls, personal behavior, etc., yet the heat will eventually get inside the house.

Sure, you are of course right, there is a limit. The effectiveness of additional insulation decreases more and more with increasing thickness. That’s why my idea is to at least insulate the ceiling as well as the walls, but not significantly more.

And yes, again you are right, the overall concept is important. But we have largely exhausted that:

[*]The windows have a Ug value of 0.6,
[*]also a G value of 53%.
[*]The windows are shaded very consistently with roller shutters (automatic control with sun position sensors – this initially required some persuasion here but is now accepted)
[*]Ventilation only takes place early in the morning when it is cool outside.
[*]Otherwise ventilation is via controlled residential ventilation, which can at least "cool" the air to 21 degrees using a ground heat exchanger.

I really can’t think of much more....

What is difficult for me to estimate is the heat input through open front or terrace doors. That of course immediately rises. But with us, they are only open briefly. But generally, the living room with its large windows will probably still be quite a heat collector despite the external blinds. We will probably now also install an air conditioner there.

Best regards,

Andreas

If this statement were comprehensively correct, there could be no passive (Styrofoam) coolers or similar.

Well, that's a different principle.
On the one hand, you have active cooling there (the ice block), and on the other hand, no window where the sun shines in. Put the box without the battery in the sunny garden and you can cook something inside.

The system of the house in summer is infinite heat input from outside. Thicker insulation slows it down slightly, but whether it heats up after 3 or 5 days doesn’t really matter. In addition, the heat brought in by the sun is retained even better inside.