ᐅ Floor structure and subfloor construction in the attic with loose fill?
Created on: 20 Dec 2017 19:40
M
Markus31Hello dear forum members,
As part of a renovation, we are currently refurbishing our attic. The new roof is now in place, and we are starting with the interior work, beginning with the floor. Below the attic is an occupied apartment. The attic will eventually house various rooms (office, bathroom, living room, etc.).
We have already installed 20cm (8 inches) high joists. Beneath the joists, there is a layer of clay from earlier construction that we want to keep as it is (see image 2). The next step is to fill the gaps between the joists so we can then build up the floor structure (OSB boards, etc.).
1. Question:
Right now, we are unsure about what to use to fill the spaces between the joists.
- Loose fill?
- Mineral wool?
- Something else?
As mentioned, the height to be filled corresponds to the joist height of 20cm (8 inches). The total attic area is 60 sqm (8 m x 7.50 m / 86 sq ft), and the spacing between the individual joists is 55cm (22 inches).
What would you recommend here and why?
2. Question:
How thick would you make the floor build-up?
We plan to install OSB boards (screwed) onto the joists, followed by impact sound insulation and then the final floor covering (e.g., vinyl, hardwood, tiles in the bathroom, etc.).
- What thickness of OSB boards would you recommend for this situation? (They need to support considerable weight, such as a bathtub in the bathroom.)
- How much impact sound insulation?
We are extremely grateful for any answers and recommendations.
Greetings from Würzburg,
Markus
As part of a renovation, we are currently refurbishing our attic. The new roof is now in place, and we are starting with the interior work, beginning with the floor. Below the attic is an occupied apartment. The attic will eventually house various rooms (office, bathroom, living room, etc.).
We have already installed 20cm (8 inches) high joists. Beneath the joists, there is a layer of clay from earlier construction that we want to keep as it is (see image 2). The next step is to fill the gaps between the joists so we can then build up the floor structure (OSB boards, etc.).
1. Question:
Right now, we are unsure about what to use to fill the spaces between the joists.
- Loose fill?
- Mineral wool?
- Something else?
As mentioned, the height to be filled corresponds to the joist height of 20cm (8 inches). The total attic area is 60 sqm (8 m x 7.50 m / 86 sq ft), and the spacing between the individual joists is 55cm (22 inches).
What would you recommend here and why?
2. Question:
How thick would you make the floor build-up?
We plan to install OSB boards (screwed) onto the joists, followed by impact sound insulation and then the final floor covering (e.g., vinyl, hardwood, tiles in the bathroom, etc.).
- What thickness of OSB boards would you recommend for this situation? (They need to support considerable weight, such as a bathtub in the bathroom.)
- How much impact sound insulation?
We are extremely grateful for any answers and recommendations.
Greetings from Würzburg,
Markus
Hello
I have a similar structure in my house. I filled the gaps with loose fill and placed a membrane underneath as a protection against particles falling through. On top of that, I did not use OSB panels but installed dry screed instead. This does not make any noise when walked on. It was installed as a floating floor.
I had to fill about 10cm (5 inches). In thicker areas, we were advised to add some expanded polystyrene (EPS). It is more cost-effective than loose fill when considering the volume.
Best regards
I have a similar structure in my house. I filled the gaps with loose fill and placed a membrane underneath as a protection against particles falling through. On top of that, I did not use OSB panels but installed dry screed instead. This does not make any noise when walked on. It was installed as a floating floor.
I had to fill about 10cm (5 inches). In thicker areas, we were advised to add some expanded polystyrene (EPS). It is more cost-effective than loose fill when considering the volume.
Best regards
Yes, there are different opinions (even so close to Christmas ).
1. I like the relatively small spacing of the load-bearing beams!
2. It is definitely possible to leave a clay infill in the existing panels.
3. It is a bad idea (nelly190) to use styrofoam in the panels just for cost reasons. Styrofoam does not belong there; instead, either a mineral loose fill or, for fire protection reasons, mineral wool or glass wool should be used. The latter only applies if the entire building is timber frame.
A mineral loose fill on paper acts as mass, which we absolutely need for sound insulation.
4. We have to abandon the idea that, with timber construction of a floor, the same impact sound insulation as in a solid construction can be achieved.
5. In addition to the mineral infill of the panels, I would lay the impact sound insulation (if it deserves that name) on the load-bearing beams when there is no build-up height available; and this is exactly what can be seen in the photos.
Here, sufficiently thick felt underlays should be fixed in strips on the load-bearing beams (nailed or glued) before the OSB boards at least 19mm (3/4 inch) thick are laid floating and glued in tongue and groove.
6. When using a bathtub, it gets critical!!! In this case, definitely contact a carpenter and have them advise on where and how the bathtub will be installed. Under no circumstances should OSB be laid without proper consideration and just hoping for the best!
7. Instead of OSB boards, gypsum fiber boards with tongue and groove suitable for bathrooms can also be used. That would be my favorite. Take a look under BRIO!
8. No bathroom in timber construction without a full-surface waterproofing of the floor!! Also think about the transitions between floor and walls and the sealed execution at internal and external corners with suitable prefabricated corner elements and molding.
----------------------------------------------------------------------------
What you plan to do yourself is a complex matter.
One must know what he or she is doing and not only know the technical rules but also apply them.
Remember: Anyone installing as a private person has the same testing and duty of care obligations as a professional company. They must know and apply them. Otherwise, it will become very expensive once the interior is furnished and there are construction-related weak points.
Correcting these later involves not only enormous costs but is always very time-consuming—if it is even possible.
Best regards and good luck with the construction project: KlaRa
1. I like the relatively small spacing of the load-bearing beams!
2. It is definitely possible to leave a clay infill in the existing panels.
3. It is a bad idea (nelly190) to use styrofoam in the panels just for cost reasons. Styrofoam does not belong there; instead, either a mineral loose fill or, for fire protection reasons, mineral wool or glass wool should be used. The latter only applies if the entire building is timber frame.
A mineral loose fill on paper acts as mass, which we absolutely need for sound insulation.
4. We have to abandon the idea that, with timber construction of a floor, the same impact sound insulation as in a solid construction can be achieved.
5. In addition to the mineral infill of the panels, I would lay the impact sound insulation (if it deserves that name) on the load-bearing beams when there is no build-up height available; and this is exactly what can be seen in the photos.
Here, sufficiently thick felt underlays should be fixed in strips on the load-bearing beams (nailed or glued) before the OSB boards at least 19mm (3/4 inch) thick are laid floating and glued in tongue and groove.
6. When using a bathtub, it gets critical!!! In this case, definitely contact a carpenter and have them advise on where and how the bathtub will be installed. Under no circumstances should OSB be laid without proper consideration and just hoping for the best!
7. Instead of OSB boards, gypsum fiber boards with tongue and groove suitable for bathrooms can also be used. That would be my favorite. Take a look under BRIO!
8. No bathroom in timber construction without a full-surface waterproofing of the floor!! Also think about the transitions between floor and walls and the sealed execution at internal and external corners with suitable prefabricated corner elements and molding.
----------------------------------------------------------------------------
What you plan to do yourself is a complex matter.
One must know what he or she is doing and not only know the technical rules but also apply them.
Remember: Anyone installing as a private person has the same testing and duty of care obligations as a professional company. They must know and apply them. Otherwise, it will become very expensive once the interior is furnished and there are construction-related weak points.
Correcting these later involves not only enormous costs but is always very time-consuming—if it is even possible.
Best regards and good luck with the construction project: KlaRa
Regarding point 3: I will probably use mineral wool here. For mineral wool, I would likely choose the cheapest option (wl040), since I don’t need special thermal insulation there because there will be heated rooms both below and above the ceiling.
Regarding point 4: I am aware of that. Which type of impact sound insulation would you recommend? And what thickness?
Regarding point 5: Should the OSB panels be installed as a floating floor only? Can such a construction provide sufficient stability, or should I screw the OSB panels down (of course with tongue and groove joints and glued)?
New points:
10. Should I use dry screed anywhere in the floor structure? If yes, where and what would be the purpose/benefit?
11. Is there a way to install underfloor heating in at least the bathroom within my construction? If yes, what type?
Regarding point 4: I am aware of that. Which type of impact sound insulation would you recommend? And what thickness?
Regarding point 5: Should the OSB panels be installed as a floating floor only? Can such a construction provide sufficient stability, or should I screw the OSB panels down (of course with tongue and groove joints and glued)?
New points:
10. Should I use dry screed anywhere in the floor structure? If yes, where and what would be the purpose/benefit?
11. Is there a way to install underfloor heating in at least the bathroom within my construction? If yes, what type?
I had already mentioned impact sound insulation under point 5.
Dry screed—this term technically falls under prefabricated screed elements. OSB, wood chip, or gypsum fiber boards all fall under this technical term!
If the supporting beams are widened by attaching battens on the sides (this method is also excellent for leveling out unevenness in the beams), then it is possible to install the flooring monolithically on felt underlays.
Every screw and nail connection between the prefabricated panels and the supporting beams will negatively affect structure-borne sound.
Underfloor heating is also possible with timber construction.
However, this becomes very complex, and a greater overall build-up height is required.
This would be achievable using gypsum fiber boards with milled channels for heating pipes. A special screed with a thickness of about 6mm (1/4 inch) and a load-bearing, flexurally stable base are necessary!
At this point, a layperson will likely reach their limits!
Dry screed—this term technically falls under prefabricated screed elements. OSB, wood chip, or gypsum fiber boards all fall under this technical term!
If the supporting beams are widened by attaching battens on the sides (this method is also excellent for leveling out unevenness in the beams), then it is possible to install the flooring monolithically on felt underlays.
Every screw and nail connection between the prefabricated panels and the supporting beams will negatively affect structure-borne sound.
Underfloor heating is also possible with timber construction.
However, this becomes very complex, and a greater overall build-up height is required.
This would be achievable using gypsum fiber boards with milled channels for heating pipes. A special screed with a thickness of about 6mm (1/4 inch) and a load-bearing, flexurally stable base are necessary!
At this point, a layperson will likely reach their limits!
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