ᐅ Roof Insulation for New Hip Roof Construction to Meet KfW 40 Standard
Created on: 8 Oct 2021 14:07
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Dany250
Hello dear community,
we are currently planning our new KfW40+ single-family house with a prefabricated house provider. Although the contract is not yet signed, we are about 98.9% sure that this will be the one. The offer somewhat reveals the manufacturer’s construction method, which leads to my question.
I have absolutely no knowledge of house construction or anything similar, so here is the consideration of a complete layperson. The offer states the following:
For an attic that is not intended for expansion, a nail plate roof truss structure is built in traditional craft-style according to static calculations. The attic space is not accessible with this roof structure.
Construction from inside to outside:
21 x 76 mm and 30 x 80 mm substructure
200.0 mm (8 inches) thermal insulation at ceiling level
solid nailed truss according to calculation
roof underlay membrane
counter battens 40 x 60 mm (1.5 x 2.5 inches)
roof battens 40 x 60 mm (1.5 x 2.5 inches) or 40 x 80 mm (1.5 x 3 inches)
Increase of rafters and insulation: 200 mm to 280 mm (8 to 11 inches) → U-value = 0.14
(for nailed plate roof bottom chord and insulation)
Does this mean that the “standard roof” insulation thickness is being changed from 200 mm to 280 mm?
Can you estimate if this is a reasonable and good level of insulation? Or could you go even further? What confuses me is that the insulation is not applied on the roof itself, but rather only in the uppermost floor ceiling. Does this mean that the roof is not insulated at all?
As someone who grew up in an attic, I am quite sensitive to this. It’s less about the thermal insulation for me and more about summer heat protection. I am approaching my forties and have always slept directly under the roof throughout my life. For the rest of my life, I would simply want to avoid spending summers “cooked” in my own heat.
Our bedroom is upstairs, and I am hoping that with KfW40, underfloor cooling, and of course good shading, my sleep quality will improve significantly in summer.
I am also a bit worried about the:
which is recessed into the attic when not in use
Isn’t this also a “gap” allowing heat to pass through?
I would greatly appreciate constructive feedback. Maybe my concerns are completely unfounded and everything is fine. I just don’t want to save in the wrong place when it comes to the biggest investment of my life.
Thank you very much and best regards
Dany
we are currently planning our new KfW40+ single-family house with a prefabricated house provider. Although the contract is not yet signed, we are about 98.9% sure that this will be the one. The offer somewhat reveals the manufacturer’s construction method, which leads to my question.
I have absolutely no knowledge of house construction or anything similar, so here is the consideration of a complete layperson. The offer states the following:
- Nail plate roof truss, roof pitch => 23°
For an attic that is not intended for expansion, a nail plate roof truss structure is built in traditional craft-style according to static calculations. The attic space is not accessible with this roof structure.
Construction from inside to outside:
21 x 76 mm and 30 x 80 mm substructure
200.0 mm (8 inches) thermal insulation at ceiling level
solid nailed truss according to calculation
roof underlay membrane
counter battens 40 x 60 mm (1.5 x 2.5 inches)
roof battens 40 x 60 mm (1.5 x 2.5 inches) or 40 x 80 mm (1.5 x 3 inches)
- Increase of rafters and bottom chords in nailed plate roofs from 200 mm to 280 mm
Increase of rafters and insulation: 200 mm to 280 mm (8 to 11 inches) → U-value = 0.14
(for nailed plate roof bottom chord and insulation)
Does this mean that the “standard roof” insulation thickness is being changed from 200 mm to 280 mm?
Can you estimate if this is a reasonable and good level of insulation? Or could you go even further? What confuses me is that the insulation is not applied on the roof itself, but rather only in the uppermost floor ceiling. Does this mean that the roof is not insulated at all?
As someone who grew up in an attic, I am quite sensitive to this. It’s less about the thermal insulation for me and more about summer heat protection. I am approaching my forties and have always slept directly under the roof throughout my life. For the rest of my life, I would simply want to avoid spending summers “cooked” in my own heat.
Our bedroom is upstairs, and I am hoping that with KfW40, underfloor cooling, and of course good shading, my sleep quality will improve significantly in summer.
I am also a bit worried about the:
- ceiling retractable staircase as a space-saving folding ladder,
which is recessed into the attic when not in use
Isn’t this also a “gap” allowing heat to pass through?
I would greatly appreciate constructive feedback. Maybe my concerns are completely unfounded and everything is fine. I just don’t want to save in the wrong place when it comes to the biggest investment of my life.
Thank you very much and best regards
Dany
Dany250 schrieb:
You say heat protection and cold protection are two different things. I know you understood me 😉, but could you please explain to me where the difference lies and what I could do better for heat protection. No, I was not talking about heat and cold protection, but about heating energy loss (= wasted money that you don’t want to throw out the window) and thermal insulation in the other direction (= against unwanted heat gain or against the too slow dissipation of gained heat or against the undesired combination of used heating energy and incoming radiant heat). But that is too complex a topic for this time of night and must wait until my not-too-hot night is over 🙂
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
Thank you once again for your very enlightening words 😀.
I’m really looking forward to your fresh reply. I hope this complex topic can be put into words that even I can understand 🤨.
We’ll be out all day again tomorrow, so I probably won’t get a chance to read it until late afternoon or evening, but I’m already excited…
Good night…
I’m really looking forward to your fresh reply. I hope this complex topic can be put into words that even I can understand 🤨.
We’ll be out all day again tomorrow, so I probably won’t get a chance to read it until late afternoon or evening, but I’m already excited…
Good night…
Dany250 schrieb:
Because if the roof is not insulated directly, the attic space becomes like a sauna in summer, and I sleep under that sauna.No, the ceiling of the upper floor will be insulated.If maintaining 25 degrees Celsius (77°F) is that important to you, include an air conditioning system in your plans right away. It wasn’t clear to me either because I’ve always lived in older houses... but the most important thing is:
A new house stays cool for a very long time, but once the heat gets inside—which it inevitably will—you won’t be able to get rid of it just by ventilating. The walls warm up, and as soon as you close the window, it quickly becomes warm again.
Having the bedrooms face northeast helps, as does shading, but there will still be nights when you feel it’s too warm for your comfort.
I also thought I could achieve something with the bypass function of the mechanical ventilation with heat recovery system, but it doesn’t help much.
A new house stays cool for a very long time, but once the heat gets inside—which it inevitably will—you won’t be able to get rid of it just by ventilating. The walls warm up, and as soon as you close the window, it quickly becomes warm again.
Having the bedrooms face northeast helps, as does shading, but there will still be nights when you feel it’s too warm for your comfort.
I also thought I could achieve something with the bypass function of the mechanical ventilation with heat recovery system, but it doesn’t help much.
@Snowy36
I would prefer to install the air conditioning directly and simply see if we need it, and then use it on some days as necessary.
Unfortunately, all the builders agree—including our preferred one—that it’s not compatible with KfW 40 standards, not even the pre-installation. I would have liked to have the pre-installation done to easily add a split unit to the bedroom later, which would surely be easier than doing it afterward.
Nevertheless, I of course would prefer to manage without it, which is why the insulation topic is so important to me.
@ypg
I understand that by now, but I still don’t quite get why this option is better than keeping the heat outside the house by insulating directly at the roof. The hot spot above the insulation in the upper floor ceiling must take even longer to cool down at night, right?
@all
Well, maybe (hopefully) someone here can explain how this works so I can understand it. Until then, I have another question 🙂 I’ve read in some building specifications about combined insulation—insulating the upper floor ceiling plus insulation between the rafters. Could this be a potential option for this?
I would prefer to install the air conditioning directly and simply see if we need it, and then use it on some days as necessary.
Unfortunately, all the builders agree—including our preferred one—that it’s not compatible with KfW 40 standards, not even the pre-installation. I would have liked to have the pre-installation done to easily add a split unit to the bedroom later, which would surely be easier than doing it afterward.
Nevertheless, I of course would prefer to manage without it, which is why the insulation topic is so important to me.
@ypg
I understand that by now, but I still don’t quite get why this option is better than keeping the heat outside the house by insulating directly at the roof. The hot spot above the insulation in the upper floor ceiling must take even longer to cool down at night, right?
@all
Well, maybe (hopefully) someone here can explain how this works so I can understand it. Until then, I have another question 🙂 I’ve read in some building specifications about combined insulation—insulating the upper floor ceiling plus insulation between the rafters. Could this be a potential option for this?
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