ᐅ Continuous insulation above rafters desired with existing photovoltaic system
Created on: 18 Apr 2021 21:16
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Proeter
Hello everyone,
I have been reading along for years and recently created my own profile. Here is my first real question.
First of all: Does anyone know how to display more than 5 posts per page? Clicking through long threads is quite tedious.
Now to the actual question. It is quite interdisciplinary (roof, insulation, photovoltaic), so I hope I have chosen the right subforum. There isn’t a dedicated roof subforum...
We are considering buying a house built in the late 1970s. The roof is covered with concrete roof tiles, and the south-facing roof surface is almost completely covered with a photovoltaic system. The attic is barely insulated. In the 1980s, some DIY work was started with insulation between the rafters, but it was abandoned halfway through. That insulation is still partly hanging there, tattered. The attic is suitable for expansion, but again, due to waning motivation from the owners, nothing was done.
The building savings contract now recommends adding insulation above the rafters to ensure sufficient summer heat protection (bedrooms are planned). After extensive research, I found some information about photovoltaic systems combined with above-rafter insulation, but only in cases where the insulation was already in place and the photovoltaic system was installed later – with discussions focusing on the more complex mounting on the roof structure.
But how do you proceed in the opposite case?: The photovoltaic system is already there, and then above-rafter insulation is added “underneath”? Has anyone had experience with this?
The photovoltaic system is over 10 years old, so it might be difficult to obtain the correct mounting materials if they have to match the exact installed type. Or is this standardized enough that I don’t need to worry?
Finally, I have another question on the topic: Online sources give very different estimates about the lifespan of concrete roof tiles. Lifetimes between 30 and 80 years are mentioned. When adding above-rafter insulation, would one generally always replace the roofing? Especially with roof tiles that are about 40 years old?
Thanks and best regards from
Pröter
I have been reading along for years and recently created my own profile. Here is my first real question.
First of all: Does anyone know how to display more than 5 posts per page? Clicking through long threads is quite tedious.
Now to the actual question. It is quite interdisciplinary (roof, insulation, photovoltaic), so I hope I have chosen the right subforum. There isn’t a dedicated roof subforum...
We are considering buying a house built in the late 1970s. The roof is covered with concrete roof tiles, and the south-facing roof surface is almost completely covered with a photovoltaic system. The attic is barely insulated. In the 1980s, some DIY work was started with insulation between the rafters, but it was abandoned halfway through. That insulation is still partly hanging there, tattered. The attic is suitable for expansion, but again, due to waning motivation from the owners, nothing was done.
The building savings contract now recommends adding insulation above the rafters to ensure sufficient summer heat protection (bedrooms are planned). After extensive research, I found some information about photovoltaic systems combined with above-rafter insulation, but only in cases where the insulation was already in place and the photovoltaic system was installed later – with discussions focusing on the more complex mounting on the roof structure.
But how do you proceed in the opposite case?: The photovoltaic system is already there, and then above-rafter insulation is added “underneath”? Has anyone had experience with this?
The photovoltaic system is over 10 years old, so it might be difficult to obtain the correct mounting materials if they have to match the exact installed type. Or is this standardized enough that I don’t need to worry?
Finally, I have another question on the topic: Online sources give very different estimates about the lifespan of concrete roof tiles. Lifetimes between 30 and 80 years are mentioned. When adding above-rafter insulation, would one generally always replace the roofing? Especially with roof tiles that are about 40 years old?
Thanks and best regards from
Pröter
pagoni2020 schrieb:
But you don’t actually have planed rafters for an exposed roof structure, do you? How are you going to do that? I have only done very basic research on this so far and read that it can probably be done with a belt sander. But in general: it’s not uncommon to add an external rafter insulation layer during energy renovation measures. How is this issue usually solved?
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pagoni202018 Apr 2021 23:50Proeter schrieb:
So far, I have only researched this briefly and read that it can probably be done with a belt sander. You’ll probably first need to find a volunteer willing to sand or plane the underside of the roof by hand, overhead.
In my opinion, this is almost impossible or at least not very practical.
Either you manage to properly treat the rafters and the sheathing, which I doubt, or you install drywall, wood, OSB, etc. from the inside against it. The main question is what you want to achieve in terms of insulation value and interior appearance, as well as what you are able or willing to invest.
When renovating, it’s often the case that once you open something up, you quickly face the next problem.
It also depends on the condition of the roof, whether it actually needs renovation.
I also don’t quite understand why proper interior insulation wouldn’t be sufficient to achieve a good insulation value. What exactly is the goal you or the specialist have in mind?
M
Myrna_Loy19 Apr 2021 09:04We completely redid our roof (including replacing the sheathing and rafters) and, after consulting with experts, chose blown-in insulation. This option is better at keeping heat out, dampening noise from the street, improving indoor air quality, and is more environmentally friendly in the long run.
pagoni2020 schrieb:
Either you get the rafters and the sheathing done nicely, which I doubt, or you install drywall, wood paneling, OSB, etc. on the inside. How do others handle this when applying above-rafter insulation during an energy retrofit but have rough-sawn roof beams? Do they simply cover them up? Or in such cases, is it common to use both above-rafter and between-rafter insulation?
pagoni2020 schrieb:
The question is especially what level of thermal insulation you want to achieve. To put it simply (this is also what I told the building savings contract advisor): When it’s above 32°C (90°F) for weeks during the day and about 20°C (68°F) at night, I want to keep the indoor temperature consistently below 25°C (77°F) without air conditioning—just by ventilating at night. In my current attic apartment from the 1970s, that’s a disaster. Even if I close the windows and external blinds in the morning during midsummer, the indoor temperature still rises faster than outside. Poor insulation. …and the roof tiles reach 70 - 80°C (158 - 176°F).
pagoni2020 schrieb:
It also depends on the condition of the roof whether it needs to be renovated. We have already discussed the lifespan of roof tiles – but what typical damage can be expected on other components after about 40 years?
Myrna_Loy schrieb:
We completely renewed our roof (including replacing sheathing and rafters) and after consulting decided on blown-in insulation. Does blown-in insulation provide a higher thermal resistance than between-rafter insulation with mineral wool or similar materials?
M
Myrna_Loy20 Apr 2021 22:10Proeter schrieb:
How do others handle installing exterior roof insulation (above-rafter insulation) during energy-efficient renovations when the roof rafters are rough-sawn? Do they simply cover them up, or do they combine exterior and cavity insulation in such cases?
To put it simply (this is also what I told my building savings contract): If daytime temperatures are above 32°C (90°F) for weeks and nights are around 20°C (68°F), I want to keep the indoor temperature consistently below 25°C (77°F) without air conditioning—just by night ventilation. In my current attic apartment from the 1970s, this is a disaster. Even if I close the windows and exterior shutters in the morning during midsummer, the indoor temperature still rises faster than outside. The insulation is terrible... and the roof tiles reach 70 - 80°C (158 - 176°F).
We’ve already discussed the lifespan of roof tiles, but what types of damage are typically expected on other building components after about 40 years?
Does blown-in insulation have a higher thermal resistance than cavity insulation made of mineral wool? Blown-in insulation is supposed to provide better thermal insulation due to its greater and denser mass. Therefore, its sound insulation properties are also better.
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pagoni202020 Apr 2021 22:59Proeter schrieb:
How do others handle adding an exterior rafter insulation when doing an energy retrofit? To be honest, I’m not exactly sure what "energy retrofit" means in this context, or what an unenergized renovation would do differently.
Proeter schrieb:
Do they just cover it up? Or do they use both exterior and between-rafter insulation in these cases? As I said, it also depends on the overall condition of the roof structure and your planned budget. If those rafters are old and rough-sawn, I would probably choose between-rafter insulation and wouldn’t see why that shouldn’t be sufficient for insulation. With the right choice of insulation material, a good standard can definitely be achieved. So again, the question is: what standard does your advisor want to achieve?
Of course, you could address each rafter individually by planing, sanding, or covering it, but if a contractor is doing it, you might end up replacing the already older roof frame sooner than expected.
Depending on the rafter thickness, you can install a substantial amount of insulation with a between-rafter solution. If needed, you can also double up from the inside, or add a few centimeters (inches) of insulation on top of the roof. In my old house, we had 14cm (5.5 inches) of glass wool and I additionally cladded the roof with 22mm (0.87 inch) boards. The upper floor stayed comfortably cool even in summer.
You should also keep in mind that the roof is only one aspect to consider regarding heat. My son had a small roof window without shading in his apartment, and that tiny window alone turned the place into a sauna. Since installing shading there, the summer heat has been much more manageable.
Proeter schrieb:
Does blown-in insulation have a higher thermal performance than mineral wool insulation between the rafters? You can check the respective thermal conductivity (WLG) values or similar metrics; in my opinion, exterior insulation like PUR mostly works against cold rather than heat.
If the roof is still in good condition externally and the framing as well, I would keep it as is and insulate from inside; depending on rafter thickness, you can fit in enough insulation material and double up if necessary.
We currently live in an old house with blown-in insulation, although probably not perfectly installed. I still find the insulation performance quite good.
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