ᐅ Floor structure and subfloor construction in the attic with loose fill?
Created on: 20 Dec 2017 19:40
M
Markus31
Hello 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 Markus.
Have you ever wondered, when buying something like toothpaste, why besides Colgate there are also other brands offering similar products? Did you then ask what advantages or disadvantages the other products might have?
Probably not. When I said that OSB boards can also be used for the system structure, I’m certainly not opening up a discussion to evaluate options. You can use whatever you prefer.
If OSB boards work, I’ll say so. Whether you choose FERMACELL, KNAUF, wood chipboard, wooden planks, or OSB, that’s up to you.
It’s all a question of marketing, in my opinion.
I’ve heard of men who wear both a belt and suspenders at the same time to keep their pants from slipping. You can do that!
Also, placing softfiberboards over the mineral wool in individual cavities is possible. It’s not harmful and allowed, although completely pointless.
My advice: leave this to a professional who has successfully completed this trade before.
Reading the reactions, I conclude that more damage to drywall construction might be caused by ignorance than cost savings on the other side can justify.
We can offer guidance here (in a public forum) in the form of tips, but this is not the right place for workshops aimed at DIY builders.
Best regards, KlaRa, this time from Augsburg
Have you ever wondered, when buying something like toothpaste, why besides Colgate there are also other brands offering similar products? Did you then ask what advantages or disadvantages the other products might have?
Probably not. When I said that OSB boards can also be used for the system structure, I’m certainly not opening up a discussion to evaluate options. You can use whatever you prefer.
If OSB boards work, I’ll say so. Whether you choose FERMACELL, KNAUF, wood chipboard, wooden planks, or OSB, that’s up to you.
It’s all a question of marketing, in my opinion.
I’ve heard of men who wear both a belt and suspenders at the same time to keep their pants from slipping. You can do that!
Also, placing softfiberboards over the mineral wool in individual cavities is possible. It’s not harmful and allowed, although completely pointless.
My advice: leave this to a professional who has successfully completed this trade before.
Reading the reactions, I conclude that more damage to drywall construction might be caused by ignorance than cost savings on the other side can justify.
We can offer guidance here (in a public forum) in the form of tips, but this is not the right place for workshops aimed at DIY builders.
Best regards, KlaRa, this time from Augsburg
So, we have now made a final decision on the following setup:
- Mineral wool insulation between the joists
- 22 mm (0.87 inch) OSB
- 10 mm (0.39 inch) wood fiberboard
- 18 mm (0.71 inch) Brio board
- Finished flooring (e.g., vinyl)
We still have the following questions:
Thanks in advance for your information and your effort.
Best regards,
Markus
- Mineral wool insulation between the joists
- 22 mm (0.87 inch) OSB
- 10 mm (0.39 inch) wood fiberboard
- 18 mm (0.71 inch) Brio board
- Finished flooring (e.g., vinyl)
We still have the following questions:
- Which type of mineral wool should we use between the joists? A high insulation value is probably not necessary here since the rooms below and above will both be heated, right? So, which exact mineral wool would you recommend? (Please provide the precise product name)
- To reduce squeaking of the OSB panels on the joists, we would like to apply felt strips (e.g., 5 mm (0.2 inch)) or something similar in strip form by gluing or stapling them onto the joists. Which exact type of felt or product would you recommend here? Please also provide the precise name so that we can research it online in more detail.
- What type of screws should I use to fix the OSB panels to the joists? Should they be fully threaded screws or screws threaded only partially? Which type is better to prevent the OSB panels from squeaking later on?
- We are currently considering whether to use the Knauf Brio board in 18 mm (0.71 inch) or 23 mm (0.91 inch) thickness over the 10 mm (0.39 inch) wood fiberboard. How do these two boards differ in terms of load-bearing capacity? We understand that the 23 mm (0.91 inch) board is thicker and heavier, but what are the advantages of choosing the 23 mm board?
Thanks in advance for your information and your effort.
Best regards,
Markus
Hello Markus.
Regarding Question 1: It doesn’t matter! You are correct that thermal insulation is not necessary here. This is about soundproofing. And we can only achieve that by adding mass. So possibly a mineral-based filler on a protective foil layer if the crawl space floor can support the weight.
Regarding Question 2: You probably have a flooring wholesaler nearby?
Ask them for a thicker felt underlay, not too densely compressed!!
A felt underlay, for example as sheet material, with high walking comfort would be good. You can cut it into strips with a utility knife, stack it two or three layers thick, and then staple it onto the joists so that no unintended shifting occurs later during finishing and use.
Regarding Question 3:
Use only SPAX screws with full-thread!
Regarding Question 4:
If you know the total build-up height, use a 22mm OSB board; that is more than sufficient. The thinner it is, the more the system will resonate. The more mass, the better.
Humorously noted: in physics, it’s always “mass wins!”
---------------------------------
Good luck: KlaRa
Regarding Question 1: It doesn’t matter! You are correct that thermal insulation is not necessary here. This is about soundproofing. And we can only achieve that by adding mass. So possibly a mineral-based filler on a protective foil layer if the crawl space floor can support the weight.
Regarding Question 2: You probably have a flooring wholesaler nearby?
Ask them for a thicker felt underlay, not too densely compressed!!
A felt underlay, for example as sheet material, with high walking comfort would be good. You can cut it into strips with a utility knife, stack it two or three layers thick, and then staple it onto the joists so that no unintended shifting occurs later during finishing and use.
Regarding Question 3:
Use only SPAX screws with full-thread!
Regarding Question 4:
If you know the total build-up height, use a 22mm OSB board; that is more than sufficient. The thinner it is, the more the system will resonate. The more mass, the better.
Humorously noted: in physics, it’s always “mass wins!”
---------------------------------
Good luck: KlaRa
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