Attaching glass wool to the ceiling without drilling, possible?

Rabbithole · 31 May 2017 at 10:30 AM

45x145 I think will be good.

JensHaglof · 4 Jun 2017 at 12:18 PM

Thanks for the response! I have another question related to something entirely different.

I will also have thick glass wool in the front corners. The acoustician mentioned something about having insulation boards against an outer wall could create condensation in the wall and mold. This is because the inner wall becomes warmer than the outer one in some way. (I'm not exactly sure what he meant) He is not a carpenter and didn't know if it would be a problem in my case.

But what do you think? The wall is 4.25 m wide and will be covered with glass wool 118 cm on each side. Will this be a problem? I know that someone on another forum said that his wall turned completely black when he removed his corner absorbers. Should I be worried?

Björn Melander · 4 Jun 2017 at 12:44 PM

When building "superchunks", leave an air gap against the walls to create a ventilated structure. The sound absorption will change very marginally compared to filling the compartment completely. The same applies to the front wall, which should also be absorbed with as deep a construction as possible.

JensHaglof · 4 Jun 2017 at 1:38 PM

Björn Melander said:
When you build "superchunks," leave an air gap at the back towards the walls so it becomes a ventilated construction. The sound absorption will change very marginally versus if you fill the cavity all the way in. The same applies to the front wall, which should also be absorbed with as deep a construction as possible.

Yay, thanks for the response! I was a bit worried that it might be out of the question to have superchunks, but it's possible, right? An air gap won't be a problem, I just won't fill with wool all the way to the wall. However, the studs lie against the wall, which should create an airtight layer? If that's the case, is it enough to drill holes in the studs so that air can come in from the room into the air gap to achieve sufficient ventilation?

How wide should the air gap be, by the way, to ensure that mold cannot grow?

Björn Melander · 4 Jun 2017 at 3:04 PM

You don't need to worry about the reglarna at all. Just let them be.

A few cm of gap is enough. Set up a small ventilated joist space between the existing floor and insulation. Place a grille at the base. Do the same at the top towards the ceiling. This way, air is allowed to circulate behind the insulation.

JensHaglof · 4 Jun 2017 at 3:15 PM

Björn Melander said:
You don't need to worry about the reglarna at all. Let them be as they are.

A few cm of space is enough. Set up a small ventilated platform between the existing floor and the insulation. Place a grille at the baseboard. Do the same at the top near the ceiling. This way, the air is allowed to circulate behind the insulation.

Hi! Thanks again!
A few words there that I don't understand. Do you mean I have air between the floor and the insulation as well? And between the ceiling and insulation? And that the reglarna on the floor get a grille on them and then I lay the insulation on the grille? And create an opening in the reglarna on the floor so air can enter? Am I understanding you correctly then?

Björn Melander · 4 Jun 2017 at 3:26 PM

Studs on edge against the floor are only meant to create an air gap. The air enters through a grille at the baseboard and is vented out at the top at a suitable location. A grille is just a suggestion to make it look nice. It works just as well with hole or slot perforation. An alternative to the studs against the floor is to let the insulation rest on chicken wire or a thin reinforcement mat a bit above the floor.

JensHaglof · 4 Jun 2017 at 4:18 PM

Björn Melander said:
Studs on edge against the floor is only intended to create an air gap. The air comes in through a grille at the baseboard and is ventilated out at the top in a suitable place. Grille is just a suggestion to make it look nice. Works just as well with hole or slit perforation. An alternative to studs against the floor is to let the insulation rest on chicken wire or thin reinforcement mesh a bit up from the floor.

Still a bit unsure, do you mean that I have studs lying on edge that I then lay the insulation on? So that the studs form channels where the air passes through? Then I have a long narrow grille in front of the channels' opening?

Björn Melander · 4 Jun 2017 at 11:35 PM

Of course, the important thing is to allow air to circulate between the outer wall.

JensHaglof · 6 Jun 2017 at 5:53 PM

Okay, now I'm with you!

Just one addition. The acoustician said that moisture would arise inside the wall, as far as I remember. And something about the existing insulation being designed to prevent moisture buildup due to temperature differences between outside and inside, and that additional insulation could change this balance. Is that what you're talking about too? I don't doubt that you know what you're talking about, just got a bit uncertain.

Björn Melander · 6 Jun 2017 at 6:03 PM

Absolutely, we're talking about the same thing here (where the dew point lands in the construction). Good that your acoustician was aware of this, easy to miss.

JensHaglof · 6 Jun 2017 at 7:30 PM

What great! I was a bit unsure for a moment if you meant the same. Now I know how to shape my superchunks then!

JensHaglof · 8 Jun 2017 at 6:35 PM

Tried to calculate the weight of the rafters in the ceiling and came up to 63 kg, could that be right? I assumed 0.5 kg/dm3 and found that a 145 rafter weighs 3.26 kg per meter and a 120 rafter 2.7 kg per meter. The fiberglass alone weighs a little over 68 kg. The rafters double the weight then!

I'm thinking of mounting the ceiling on two brackets and a rafter with a total of eight plugs. Two in each bracket and four in the rafter. These plugs have a tensile strength of around 30 kg each, totaling around 240 kg. The ceiling will weigh 130-140 kg in total. Is it enough for the mount to hold double the weight of the ceiling to be safe? Or should there be more margin? I can always screw the rafter into the wall with more plugs, 6 for example. Then I would get around 300 kg of tensile strength. What would you recommend? Or rather, how would you do it if you were setting up a ceiling weighing 130-140 kg that you would sit and work under? How much safety margin would you have?

Björn Melander · 10 Jun 2017 at 10:57 AM

If the walls are made of concrete, you attach studs with regular nail plugs to the three walls. This gives you something stable to anchor the construction in. You also have the option to use the superchunks as support for the acoustic ceiling. Likewise, a vertical stud on each side against the wall, under the back edge of the acoustic ceiling if needed.

JensHaglof · 10 Jun 2017 at 11:51 AM

First of all, I must thank you for all the answers, it's wonderful that you're helping me Björn!

I'm not a carpenter, but I think it's as follows. The walls facing the outside seem to consist of plaster and then light concrete. This is because I can easily drive in a wood screw. That must mean there's plaster on the outermost layer, right? Or could it be light concrete all the way? Can you drive a wood screw into light concrete?

The inner walls, however, seem to consist solely of light concrete.

Can you use nail plugs in light concrete?

The left wall will be difficult to attach a stud to as it will sit in front of the window. Furthermore, there is ventilation above the window. However, it is possible to attach one to the right wall. Vertical studs work fine. I'll have those where I'm building the superchunks and a thicker absorber at the first reflection on the side wall. These can also rest on the ceiling.