ᐅ Is it worth investing in insulation beyond the standard requirements for new construction?
Created on: 8 Jul 2015 19:25
G
Grym
Concepts like these from the prefab house provider Kampa initially sound quite good, and there are many people in forums who believe that nowadays you shouldn’t build a house with a U-value above 0.15.
On the other hand, when you calculate the raw numbers, I struggle to understand how insulation beyond what is necessary can actually be cost-effective.
Let’s take a 140-150 sqm (1500-1600 sq ft) house with 1.5 stories as an example. This would have an exterior wall surface area of about 170 sqm (1830 sq ft) (excluding roof, top floor ceiling, foundation slab, and windows, with a relatively high knee wall as we plan).
The local provider, in a standard case, offers a U-value of 0.21, while Kampa advertises 0.11. According to a U-value calculator, the local provider’s wall consumes 16 kWh/m² per year, and the 0.11 U-value leads to 7 kWh/m² per year. Calculated over the surface area, that’s 2,720 kWh versus 1,190 kWh. With an air-to-water heat pump with an annual performance factor of 4.1 (yes, these are available for about 4,000 EUR – greetings to the purple forum), this equates to 663 kWh_el versus 290 kWh_el. So, you save about 373 kWh just from the exterior wall construction. Variant A: standard solid construction and Variant B: passive house wall. In strict monetary terms, that’s about 93.25 EUR per year or 7.77 EUR monthly installments.
Over 20 years, the difference adds up to 1,865 EUR. In 20 years!!!
Of course, additional savings come from insulating the foundation slab, roof, and better windows in a passive house, but those also require separate higher investments.
On the other hand, a photovoltaic self-consumption system can save a lot, especially during transitional seasons (self-generated electricity costs less than half compared to grid electricity). This is particularly true for an energy-saving standard house, which benefits significantly from PV power during these periods, unlike a KFW40-level house where heating is mostly needed only in the coldest winter months.
The question in the end is: is it even worth it, or is the current energy-saving regulation standard already so strict that the economic feasibility has long been exceeded?
There’s also a bit of a question between timber frame prefab houses versus solid construction. Only with a timber frame prefab house can you achieve a high insulation value for the exterior facade with a reasonably manageable wall thickness (in cm). In my opinion, this is the only advantage of a timber frame prefab house compared to solid construction.
On the other hand, when you calculate the raw numbers, I struggle to understand how insulation beyond what is necessary can actually be cost-effective.
Let’s take a 140-150 sqm (1500-1600 sq ft) house with 1.5 stories as an example. This would have an exterior wall surface area of about 170 sqm (1830 sq ft) (excluding roof, top floor ceiling, foundation slab, and windows, with a relatively high knee wall as we plan).
The local provider, in a standard case, offers a U-value of 0.21, while Kampa advertises 0.11. According to a U-value calculator, the local provider’s wall consumes 16 kWh/m² per year, and the 0.11 U-value leads to 7 kWh/m² per year. Calculated over the surface area, that’s 2,720 kWh versus 1,190 kWh. With an air-to-water heat pump with an annual performance factor of 4.1 (yes, these are available for about 4,000 EUR – greetings to the purple forum), this equates to 663 kWh_el versus 290 kWh_el. So, you save about 373 kWh just from the exterior wall construction. Variant A: standard solid construction and Variant B: passive house wall. In strict monetary terms, that’s about 93.25 EUR per year or 7.77 EUR monthly installments.
Over 20 years, the difference adds up to 1,865 EUR. In 20 years!!!
Of course, additional savings come from insulating the foundation slab, roof, and better windows in a passive house, but those also require separate higher investments.
On the other hand, a photovoltaic self-consumption system can save a lot, especially during transitional seasons (self-generated electricity costs less than half compared to grid electricity). This is particularly true for an energy-saving standard house, which benefits significantly from PV power during these periods, unlike a KFW40-level house where heating is mostly needed only in the coldest winter months.
The question in the end is: is it even worth it, or is the current energy-saving regulation standard already so strict that the economic feasibility has long been exceeded?
There’s also a bit of a question between timber frame prefab houses versus solid construction. Only with a timber frame prefab house can you achieve a high insulation value for the exterior facade with a reasonably manageable wall thickness (in cm). In my opinion, this is the only advantage of a timber frame prefab house compared to solid construction.
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Username_wahl8 Jul 2015 20:50We initially aimed for a Passive House, but we are now going for KfW 55. That’s a good compromise, don’t you think?
Let's continue with the windows. For standard windows, I assume a U-value of 1.1 (triple glazing is probably standard nowadays?), and for Passive House windows, 0.8. Heat loss is 86 kWh or 63 kWh per m² per year. With 30 m² (323 ft²) of window area, this results in a difference of 690 kWh_thermal or 168 kWh_electric, or 42.07 EUR per year. Over 20 years, that amounts to 841.40 EUR, although I have read that insulated glass doesn’t necessarily last 20 years.
841.40 EUR over 20 years – is there ever a benefit to anything other than standard windows? Especially since such high-performance windows with argon filling and all that might not actually last that long.
By the way, my cost calculations are based on a heat pump running on household electricity at 25 cents per kWh_electricity, without any self-generated photovoltaic power, so more or less a worst-case scenario at the moment.
841.40 EUR over 20 years – is there ever a benefit to anything other than standard windows? Especially since such high-performance windows with argon filling and all that might not actually last that long.
By the way, my cost calculations are based on a heat pump running on household electricity at 25 cents per kWh_electricity, without any self-generated photovoltaic power, so more or less a worst-case scenario at the moment.
Achieving an annual performance factor (Seasonal Performance Factor) of 4.1 is quite challenging even for the Geisha heat pump (although it is a good model from the manufacturer – 3.88 at A2/W35). Please keep in mind that if your insulation is poor, you will likely need two units... just as a side note.
Whether it’s worth it probably also depends on who you build with and how. Our general contractor builds the way he does – typically to KfW55 or KfW70 standards (depending on the heating system) – which means he simply adds 16 cm (6 inches) of mineral wool insulation to the walls. If you work with a large company whose strategy is to maximize the price point using tiered pricing, it usually isn’t worth it.
Whether it’s worth it probably also depends on who you build with and how. Our general contractor builds the way he does – typically to KfW55 or KfW70 standards (depending on the heating system) – which means he simply adds 16 cm (6 inches) of mineral wool insulation to the walls. If you work with a large company whose strategy is to maximize the price point using tiered pricing, it usually isn’t worth it.
smodon schrieb:
Rising energy costs and resale value might be worth considering. In my opinion, a higher standard should also be reflected in a potential resale.Insulation is actually relatively unimportant when selling in 10-15 years. A house that is 15 years old today still has reasonable insulation value. No one will really care in 15 years whether it was built to KfW 70 or 55 standards today. In 15 years, the insulation will be technically outdated, the windows will have seen better days, and the heating system might need replacing soon. Depending on maintenance, the house will still make a very good impression, of course.
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Sebastian799 Jul 2015 19:42I doubt that the insulation is really outdated, that the windows have passed their prime, and especially that the heating system needs to be replaced.
But I suppose this reflects the mindset of a throwaway society...
But I suppose this reflects the mindset of a throwaway society...
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