ᐅ Interior insulation using mineral wool and calcium silicate boards
Created on: 1 May 2023 13:35
M
MayoooxHello dear house building forum members,
First of all, I wish you a sunny May Day.
It’s been several years since my partner and I purchased a home. It turned out to be a very old house with land, located outside the city. Just what we wanted. The problem is… it’s an old house… a very old house. Accordingly, the insulation is quite poor.
The previous owner had renovated and finished the lower floor. At least, that was the assumption. However, we have now found out that the renovation was not as advanced as expected, resulting in insufficient insulation in the bathroom and kitchen. We definitely need to address this. It’s frustrating because the renovations on the lower floor were supposedly completed quite some time ago.
Structurally, only internal insulation is really possible. External insulation is hardly feasible. The house has no roof overhang, and according to the roofer, the currently installed roof tiles are no longer produced in this style. Re-roofing with an extended roof and external insulation, as well as insulating the foundation and masonry, would also be practically impossible due to the cost.
For the internal insulation, I have two approaches that I would like to combine if possible and sensible.
This raises several questions that are currently holding me back regarding implementation.
Is it possible to combine traditional internal insulation with calcium silicate insulation? Meaning, would calcium silicate be applied on one wall and mineral wool on the next? What would the transition between the two look like?
Are there additional requirements for the substrate when using calcium silicate? So far I understand that wall paint should be removed and that the calcium silicate boards should sit flush against the masonry. Are there other considerations? Has anyone gained experience working with calcium silicate boards?
Both rooms are separated from the upper floor by a concrete ceiling. Does it make sense to insulate here as well? I don’t have a good sense of how much heat a concrete ceiling transmits. But I suspect that, given the poor external insulation, it acts strongly as a thermal bridge. Therefore, my initial approach would be to insulate here too. Am I mistaken, or would the benefit not be as significant as I hope?
Thank you very much in advance for your time and efforts!
First of all, I wish you a sunny May Day.
It’s been several years since my partner and I purchased a home. It turned out to be a very old house with land, located outside the city. Just what we wanted. The problem is… it’s an old house… a very old house. Accordingly, the insulation is quite poor.
The previous owner had renovated and finished the lower floor. At least, that was the assumption. However, we have now found out that the renovation was not as advanced as expected, resulting in insufficient insulation in the bathroom and kitchen. We definitely need to address this. It’s frustrating because the renovations on the lower floor were supposedly completed quite some time ago.
Structurally, only internal insulation is really possible. External insulation is hardly feasible. The house has no roof overhang, and according to the roofer, the currently installed roof tiles are no longer produced in this style. Re-roofing with an extended roof and external insulation, as well as insulating the foundation and masonry, would also be practically impossible due to the cost.
For the internal insulation, I have two approaches that I would like to combine if possible and sensible.
- Traditional internal insulation: stud frame, mineral wool, vapor barrier, and drywall.
- Use of calcium silicate boards.
This raises several questions that are currently holding me back regarding implementation.
Is it possible to combine traditional internal insulation with calcium silicate insulation? Meaning, would calcium silicate be applied on one wall and mineral wool on the next? What would the transition between the two look like?
Are there additional requirements for the substrate when using calcium silicate? So far I understand that wall paint should be removed and that the calcium silicate boards should sit flush against the masonry. Are there other considerations? Has anyone gained experience working with calcium silicate boards?
Both rooms are separated from the upper floor by a concrete ceiling. Does it make sense to insulate here as well? I don’t have a good sense of how much heat a concrete ceiling transmits. But I suspect that, given the poor external insulation, it acts strongly as a thermal bridge. Therefore, my initial approach would be to insulate here too. Am I mistaken, or would the benefit not be as significant as I hope?
Thank you very much in advance for your time and efforts!
I would always prefer the clearly better option of external insulation.
A roof overhang can also be made with different tiles or materials. Alternatively, you can look for used tiles or leftover stock. Internal insulation is technically always the inferior option. You will probably need a professional (energy consultant) anyway to apply for any renovation subsidies. I would have them suggest options for the necessary (small or preferably larger) roof overhang. One idea that comes to mind is standing seam metal sheets as a wider roof overhang on the gable ends, allowing some tiles to be removed there and installed at the eaves. However, there are probably other, better ideas as well.
A roof overhang can also be made with different tiles or materials. Alternatively, you can look for used tiles or leftover stock. Internal insulation is technically always the inferior option. You will probably need a professional (energy consultant) anyway to apply for any renovation subsidies. I would have them suggest options for the necessary (small or preferably larger) roof overhang. One idea that comes to mind is standing seam metal sheets as a wider roof overhang on the gable ends, allowing some tiles to be removed there and installed at the eaves. However, there are probably other, better ideas as well.
Mayooox schrieb:
Is it possible to combine classic interior insulation with calcium silicate insulation? Meaning calcium silicate on one wall and mineral wool on the next? How would the transition between them look?Yes, you can insulate walls using different insulation materials. Apply one type all the way to the corner and then connect the other to it. Install an expansion joint between them (using permanently flexible PUR insulation material, sealed on the front with acrylic, for example).There are more options beyond just these two.
Vapour-permeable insulation with wood fiber insulation boards. Similar to calcium silicate, but they fit better against the wall, have higher heat storage capacity, and are more affordable. The insulation performance is the same. These boards are reinforced on the interior and plastered (preferably with lime or clay plaster) and painted (with lime/silicate or clay-based paint), similar to silicate boards. The insulation materials must not be covered with gypsum board or wallpapered.
Vapour-permeable does not mean that with internal insulation the wall "breathes" or significantly transports indoor humidity through to the outside. Rather, it allows indoor humidity to be buffered better and released again during ventilation.
Another option: vapour-tight XPS insulation boards or PIR boards (more expensive, better insulation). These are also reinforced on the interior side and plastered with your preferred plaster and painted or wallpapered as desired. Alternatively, they can be glued and covered with gypsum board. The insulation boards can be bonded with PUR insulation adhesive and, on non-load-bearing substrates, also mechanically fastened. The PUR foam/adhesive also seals cavities. These insulation materials are somewhat cheaper than wood fiber or similarly priced (PIR) while offering better insulation and greater flexibility in interior design—but they are not ecological and are vapour-tight.
Mineral wool with a stud frame is the most vulnerable form of interior insulation. The interior vapor barrier is often damaged or has defects at connection points. Indoor humidity can then penetrate (through diffusion or air leaks) and condense, leading to damp spots.
Where exterior walls are not very vapor-tight (usually the case, except with concrete), EPS can also be used instead of XPS and covered with gypsum board. However, the moisture load should be calculated (software such as WUFI by Fraunhofer can be used).
Mayooox schrieb:
Are there other points to consider? Has anyone gained experience with handling calcium silicate panels?They are relatively porous and tend to break easily if pressed too hard or if the adhesive mortar is mixed too thickly or has already started to set.Mayooox schrieb:
I suspect, though, that with poor exterior insulation, these will act heavily as thermal bridges.That’s a correct assumption.Mayooox schrieb:
Therefore, my initial approach would be to also add insulation here.Also a good approach. There are wedge-shaped insulation boards specifically designed for these cases, i.e., for interior walls adjoining exterior walls. These should not be forgotten.Exterior insulation of the gable ends can almost always be done without extending the roof, as @i_b_n_a_n has already mentioned. Flashing sheets as drip edges at the top edge for roof closure are practical.
Hello,
thank you very much for the informative details.
@dertill
Thanks for the many suggestions. I will look into the alternatives and review different options. Using mineral wool in the bathroom also makes me uneasy. Therefore, I would prefer an insulation method here that is less prone to mold growth.
The attic is insulated except for a few spots where cables still need to be installed. Exterior walls have 140mm (5.5 inches) mineral wool, the roof has 200mm (8 inches). About 90m² (970 ft²) of the floor will still be filled and fitted with underfloor heating (old hayloft). Here, I consider the thermal insulation of the intermediate ceiling sufficient. The remaining approximately 60m² (645 ft²) is separated by a concrete intermediate ceiling.
I will gladly reconsider exterior insulation. So far, I had the impression that once you start with exterior insulation, it opens a can of worms and many more problems arise concerning the roof area. An energy consultant has already been on site. Subsidies could be applied for. Whether it will ultimately pay off is still being clarified. Interior insulation only receives subsidies once a certain U-value is reached. This is hardly achievable with products like sand-lime brick panels.
thank you very much for the informative details.
@dertill
Thanks for the many suggestions. I will look into the alternatives and review different options. Using mineral wool in the bathroom also makes me uneasy. Therefore, I would prefer an insulation method here that is less prone to mold growth.
Are all other insulation measures already implemented? In very few cases, such as timber framing with thin infill, interior insulation makes sense. If the upper floor is occupied, the ceiling does not need to be insulated.
The attic is insulated except for a few spots where cables still need to be installed. Exterior walls have 140mm (5.5 inches) mineral wool, the roof has 200mm (8 inches). About 90m² (970 ft²) of the floor will still be filled and fitted with underfloor heating (old hayloft). Here, I consider the thermal insulation of the intermediate ceiling sufficient. The remaining approximately 60m² (645 ft²) is separated by a concrete intermediate ceiling.
I would always prefer the clearly better option of exterior insulation.
A roof overhang can also be made with different tiles or materials. Alternatively, look for used tiles or leftover stock. Interior insulation is technically always the inferior option. You probably need a professional (energy consultant) anyway to apply for possible subsidies for the renovation? I would ask them for suggestions regarding the necessary (small or preferably larger) roof overhang. Off the top of my head: standing seam metal flashing as a roof overhang on the gable sides, slightly wider to then remove tiles there and install them in the eave area. There are probably other, better ideas as well.
I will gladly reconsider exterior insulation. So far, I had the impression that once you start with exterior insulation, it opens a can of worms and many more problems arise concerning the roof area. An energy consultant has already been on site. Subsidies could be applied for. Whether it will ultimately pay off is still being clarified. Interior insulation only receives subsidies once a certain U-value is reached. This is hardly achievable with products like sand-lime brick panels.
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