ᐅ We are planning to build a house. Is what has been offered to us acceptable?
Created on: 15 Apr 2015 19:47
L
LittleWulf
Hello, we would like to start building our own home this year with a general contractor, a complete package.
Since I am not very knowledgeable about this topic despite a lot of research and cannot properly assess such matters, I wanted to ask what you think about the offer we have received. We are currently strongly leaning towards this provider.
We are curious whether this is more or less "standard" or if it is rather on the lower end. Also, what could possibly be improved without immediately having to pay several thousand more.
First of all, many items are listed as “insulated,” such as the lowered ceiling in the bay window, the roller shutter boxes, or the solid knee wall.
Floor:
Reinforced concrete slab foundation including frost protection edge strip and waterproofing against rising damp instead of strip footings. Thickness about 20cm (8 inches) and concrete quality C 20/25.
Steel reinforcement and slab thickness according to the assumed ground pressure as per the homeowner’s specification sheet (I can provide that if needed). A foil is laid under the slab as a clean layer.
Walls:
The exterior walls are executed with a total thickness of about 44.5cm (17.5 inches) as follows:
1.5cm (0.6 inches) fine plaster
17.5cm (7 inches) masonry of porous, fired clay brick
14cm (5.5 inches) cavity insulation, thermal conductivity class (WLG) 035
approx. 11.5cm (4.5 inches) facing brickwork
Interior walls on ground and attic floors are constructed with brick (Poroton).
(Now the addition for KfW 70)
The piping for the warm water underfloor heating is designed for a supply temperature of 35°C (95°F) by installing the pipes closer together.
Extension of roof insulation to 26cm (10 inches) with WLG 035
(Credit of 4,216,- if omitted)
[Is that reasonable for slightly better insulation and closer pipe spacing?]
For an upgrade to KfW 55 (20k-21k):
Different heating system with more solar input.
Ventilation system.
8cm (3 inches) insulation with WLG 035 under the slab.
Exterior walls then apparently no longer face brick but rendered, consisting of:
1.5cm (0.6 inches) fine plaster
17.5cm (7 inches) masonry of porous, fired clay brick
20cm (8 inches) external thermal insulation composite system (ETICS) with WLG 032 including silicate facade plaster.
Now my question is: since I would like a ventilation system, should I improve the insulation somehow even if I do not aim for KfW 55? And isn’t the masonry thickness of 17.5cm (7 inches) rather thin?
I skimmed a forum where this exact wall build-up (by the same contractor) was heavily criticized.
Since I am not very knowledgeable about this topic despite a lot of research and cannot properly assess such matters, I wanted to ask what you think about the offer we have received. We are currently strongly leaning towards this provider.
We are curious whether this is more or less "standard" or if it is rather on the lower end. Also, what could possibly be improved without immediately having to pay several thousand more.
First of all, many items are listed as “insulated,” such as the lowered ceiling in the bay window, the roller shutter boxes, or the solid knee wall.
Floor:
Reinforced concrete slab foundation including frost protection edge strip and waterproofing against rising damp instead of strip footings. Thickness about 20cm (8 inches) and concrete quality C 20/25.
Steel reinforcement and slab thickness according to the assumed ground pressure as per the homeowner’s specification sheet (I can provide that if needed). A foil is laid under the slab as a clean layer.
Walls:
The exterior walls are executed with a total thickness of about 44.5cm (17.5 inches) as follows:
1.5cm (0.6 inches) fine plaster
17.5cm (7 inches) masonry of porous, fired clay brick
14cm (5.5 inches) cavity insulation, thermal conductivity class (WLG) 035
approx. 11.5cm (4.5 inches) facing brickwork
Interior walls on ground and attic floors are constructed with brick (Poroton).
(Now the addition for KfW 70)
The piping for the warm water underfloor heating is designed for a supply temperature of 35°C (95°F) by installing the pipes closer together.
Extension of roof insulation to 26cm (10 inches) with WLG 035
(Credit of 4,216,- if omitted)
[Is that reasonable for slightly better insulation and closer pipe spacing?]
For an upgrade to KfW 55 (20k-21k):
Different heating system with more solar input.
Ventilation system.
8cm (3 inches) insulation with WLG 035 under the slab.
Exterior walls then apparently no longer face brick but rendered, consisting of:
1.5cm (0.6 inches) fine plaster
17.5cm (7 inches) masonry of porous, fired clay brick
20cm (8 inches) external thermal insulation composite system (ETICS) with WLG 032 including silicate facade plaster.
Now my question is: since I would like a ventilation system, should I improve the insulation somehow even if I do not aim for KfW 55? And isn’t the masonry thickness of 17.5cm (7 inches) rather thin?
I skimmed a forum where this exact wall build-up (by the same contractor) was heavily criticized.
BeHaElJa schrieb:
If you are very environmentally conscious, you will meet people who are "afraid" of aluminum—whether in water bottles or deodorants—because it is suspected to contribute to Alzheimer’s disease (not proven or confirmed). For this reason, they also reject aerated concrete blocks, which get their pores through the roasting of aluminum. There are also people who dislike reinforcement steel because it is said to interfere with radiation fields, and so on... But there is no aluminum in it?!
Asks Yvonne
L
LittleWulf17 Apr 2015 07:19Yes, we had additional offers. We narrowed it down to four providers (Viebrockhaus, Helma, Fibav, Fischer), and now only two of them remain. We have received an offer from each (Helma’s will be available from Saturday).
B
Bauexperte17 Apr 2015 10:02Hello,
This is a typical example of what I call “dangerous half-knowledge.” Once published online without further explanation, the message gets distorted like in a game of “broken telephone”; the original facts shrink while imagination gradually takes over...
Aluminum has recently come under scrutiny because it is blamed for causing yellow stains under the armpits of light-colored T-shirts, shirts, and blouses. Manufacturers have responded by offering deodorants without this ingredient; it is interesting in this context that aluminum is also present in cosmetics, yet so far women have been using these products without much concern.
***The main raw materials or precursors should be specified as mass percentages, separated into sand, cement, quicklime, anhydrite/gypsum, foaming agent, water, reinforcement steel for prefabricated elements, and others (to be specified).
Example:
Sand 60 – 70 mass-%
Cement 15 – 30 mass-%
Quicklime 10 – 20 mass-%
Anhydrite/Gypsum 2 – 5 mass-%
Aluminum 0.05 – 0.1 mass-%
Additionally, 50 – 75 mass-% water (relative to the solids) is used.
Further explanation of the materials used:
Sand:
The sand used is a natural raw material containing mostly quartz (SiO2) along with natural accessory and trace minerals. It is an essential component for the hydrothermal reaction during steam curing.
Cement:
According to DIN EN 197-1; cement acts as a binder and is mainly produced from limestone marl or a mixture of limestone and clay. The natural raw materials are calcined and then ground.
Quicklime:
According to DIN EN 459; quicklime serves as a binder and is produced by calcining natural limestone.
Anhydrite / Gypsum:
According to DIN 1168; the sulfate carrier used influences the setting time of the aerated concrete and comes from natural sources or is technically produced.
Aluminum:
Aluminum powder or paste is used as a foaming agent. The metallic aluminum reacts in the alkaline environment, releasing hydrogen gas that forms pores and escapes completely after the foaming process is finished.
Water:
Water is necessary for the hydraulic reaction of the binders. It is also required to produce a homogeneous suspension.
Mold release oil:
Mold release oil is used as a separating agent between the mold and the aerated concrete mixture. Polycyclic aromatic hydrocarbons (PAH)-free mineral oils with added long-chain additives to increase viscosity are used. This prevents the mixture from running off in the mold and allows economical application.
The manufacturing process should be described and may be illustrated with a simple graphic:
The ground quartz sand is mixed with lime, cement, and crushed recycled aerated concrete, together with water and aluminum powder or paste, in a mixer to form a watery suspension, which is then poured into molds. The water dissolves the lime with heat development. The aluminum reacts in the alkaline environment, producing gaseous hydrogen that creates pores in the mixture and escapes without residue. The pores typically have a diameter of 0.5 – 1.5 mm (0.02 – 0.06 inches) and are filled only with air. After initial setting, semi-solid raw blocks are formed, from which the aerated concrete components are cut mechanically and with high precision.
The final properties of the components develop during subsequent steam curing for 5 – 12 hours at approximately 190°C (374°F) and a pressure of about 12 bar (175 psi) in pressure steam boilers, called autoclaves. Here, calcium silicate hydrates form from the raw materials, corresponding to the naturally occurring mineral tobermorite. The reaction is complete when the product is removed from the autoclave. This means, unlike concrete hardening, the reaction only takes a few hours. The steam is reused for further autoclave cycles after curing. The condensate generated is used as process water. In this way, energy is saved and environmental pollution from hot exhaust steam and emissions is avoided.
***Source: Institut Bauen und Umwelt e.V.; PCR Aerated Concrete (this document is available for download to any interested homeowner by the institute)
It is true that aluminum is suspected of accelerating Alzheimer’s disease; some researchers even speak of a causative role. Anyone unwilling to wait for ongoing research results and concerned about aluminum should avoid all aluminum foil in their household, buy aluminum-free cosmetics, and avoid drinks from cans.
However, there is no need to fear aerated concrete because after completion of the manufacturing process, this foaming agent is no longer present.
Best regards, Bauexperte
BeHaElJa schrieb:
Aerated concrete is expanded using aluminum, it’s more about residues (in my opinion, still somewhat esoteric)
This is a typical example of what I call “dangerous half-knowledge.” Once published online without further explanation, the message gets distorted like in a game of “broken telephone”; the original facts shrink while imagination gradually takes over...
Aluminum has recently come under scrutiny because it is blamed for causing yellow stains under the armpits of light-colored T-shirts, shirts, and blouses. Manufacturers have responded by offering deodorants without this ingredient; it is interesting in this context that aluminum is also present in cosmetics, yet so far women have been using these products without much concern.
***The main raw materials or precursors should be specified as mass percentages, separated into sand, cement, quicklime, anhydrite/gypsum, foaming agent, water, reinforcement steel for prefabricated elements, and others (to be specified).
Example:
Sand 60 – 70 mass-%
Cement 15 – 30 mass-%
Quicklime 10 – 20 mass-%
Anhydrite/Gypsum 2 – 5 mass-%
Aluminum 0.05 – 0.1 mass-%
Additionally, 50 – 75 mass-% water (relative to the solids) is used.
Further explanation of the materials used:
Sand:
The sand used is a natural raw material containing mostly quartz (SiO2) along with natural accessory and trace minerals. It is an essential component for the hydrothermal reaction during steam curing.
Cement:
According to DIN EN 197-1; cement acts as a binder and is mainly produced from limestone marl or a mixture of limestone and clay. The natural raw materials are calcined and then ground.
Quicklime:
According to DIN EN 459; quicklime serves as a binder and is produced by calcining natural limestone.
Anhydrite / Gypsum:
According to DIN 1168; the sulfate carrier used influences the setting time of the aerated concrete and comes from natural sources or is technically produced.
Aluminum:
Aluminum powder or paste is used as a foaming agent. The metallic aluminum reacts in the alkaline environment, releasing hydrogen gas that forms pores and escapes completely after the foaming process is finished.
Water:
Water is necessary for the hydraulic reaction of the binders. It is also required to produce a homogeneous suspension.
Mold release oil:
Mold release oil is used as a separating agent between the mold and the aerated concrete mixture. Polycyclic aromatic hydrocarbons (PAH)-free mineral oils with added long-chain additives to increase viscosity are used. This prevents the mixture from running off in the mold and allows economical application.
The manufacturing process should be described and may be illustrated with a simple graphic:
The ground quartz sand is mixed with lime, cement, and crushed recycled aerated concrete, together with water and aluminum powder or paste, in a mixer to form a watery suspension, which is then poured into molds. The water dissolves the lime with heat development. The aluminum reacts in the alkaline environment, producing gaseous hydrogen that creates pores in the mixture and escapes without residue. The pores typically have a diameter of 0.5 – 1.5 mm (0.02 – 0.06 inches) and are filled only with air. After initial setting, semi-solid raw blocks are formed, from which the aerated concrete components are cut mechanically and with high precision.
The final properties of the components develop during subsequent steam curing for 5 – 12 hours at approximately 190°C (374°F) and a pressure of about 12 bar (175 psi) in pressure steam boilers, called autoclaves. Here, calcium silicate hydrates form from the raw materials, corresponding to the naturally occurring mineral tobermorite. The reaction is complete when the product is removed from the autoclave. This means, unlike concrete hardening, the reaction only takes a few hours. The steam is reused for further autoclave cycles after curing. The condensate generated is used as process water. In this way, energy is saved and environmental pollution from hot exhaust steam and emissions is avoided.
***Source: Institut Bauen und Umwelt e.V.; PCR Aerated Concrete (this document is available for download to any interested homeowner by the institute)
It is true that aluminum is suspected of accelerating Alzheimer’s disease; some researchers even speak of a causative role. Anyone unwilling to wait for ongoing research results and concerned about aluminum should avoid all aluminum foil in their household, buy aluminum-free cosmetics, and avoid drinks from cans.
However, there is no need to fear aerated concrete because after completion of the manufacturing process, this foaming agent is no longer present.
Best regards, Bauexperte
B
Bauexperte17 Apr 2015 10:24Hello,
I think we all need to be more careful with what we say or write, especially in the fast-paced world of the internet.
Regards, Bauexperte
BeHaElJa schrieb:I believe you, but...
I’m not saying that I believe it,
BeHaElJa schrieb:... you simply included the claim that aerated concrete contains aluminum in a reply, without explaining what the aluminum is used for. This stirs up unnecessary fears based on hearsay; there are many quiet readers of the forum as well. That’s why I referred to reputable institutes’ websites and tried to provide a clear explanation of the manufacturing process; after all, I’m not a scientist. Anyone now searching online for information on the topic will also find the other side of the story; from my subjective point of view, this is the only way to enable an objective formation of opinion.
...we have already been confronted with this twice (once even by an eco-architect who said, "you never know what residues might still be present").
I think we all need to be more careful with what we say or write, especially in the fast-paced world of the internet.
Regards, Bauexperte
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