attaching insulation to inside out ceiling

[madmuso]

Hey guys,

does anyone have any ideas on how to attach insulation to an inside out ceiling? Our good friend gravity isnt helping the situation!
I was thinking to have someone hold the insulation up and I staple string across the ceiling joists but over time it may sag and press against the finishing cloth.

thanks guys

[John Sayers]

Cover the frame with 2-3mm plastic before adding the cloth panels - it will hold the insulation in plus stop dust falling on your gear.

CIMG0022.JPG

cheers
john

[madmuso]

thanks for the reply John, thats a cool pic too.

But to place that plastic over the top means you would have to physically let go of the insulation at some point causing it to fall out yeah? I can see on the pic that there are "anchors" holding up the insulation but If I was to use this method it would mean I have to pierce the plaster and I want to avoid making holes in it. The only thing I can think of is to make small light timber frames that fit within the ceiling joist spacings. So, make the frames, fill them with insulation, fasten the insulation with stapled string or cloth or plastic, then sit the finished product in the spacing between the ceiling joists and screw them into place. Time consuming and adds to costs!

My ceiling joists are 3.2 meters long at 600mm centers. The cavity depth is 145.

Out of curiosity, does covering the insulation with plastic change its acoustic properties? Or is the difference negligible?

thanks

[Soundman2020]

But to place that plastic over the top means you would have to physically let go of the insulation at some point causing it to fall out yeah?

No. The plastic is stapled to the joists as you go. If you are doing this from below after the ceiling modules are already in place, then start by stapling the plastic at one end of a joist bay and also part way up each side, insert the insulation, spread it evenly, then complete the stapling the rest of the sides plus the other end.

If your insulation is falling out as soon as you let go when doing it this way, then you have cut it too small. It should be a tight fit between the joists such that it mostly stays in place by friction alone, just sagging in the middle, then the plastic stretched across the bottom stops the sagging.

On the other hand, it is easier to build the modules completely before raising them: insert the insulation while each module is still sitting on the floor, before you put the drywall on top, with the plastic already on the frame, then raise each completed module into place.

I can see on the pic that there are "anchors" holding up the insulation

I don't think there are any "anchors" in there. Not quite sure what those wood blocks are for, but the plastic is sufficient to hold the insulation in place.

The only thing I can think of is to make small light timber frames that fit within the ceiling joist spacings. So, make the frames, fill them with insulation, fasten the insulation with stapled string or cloth or plastic, then sit the finished product in the spacing between the ceiling joists and screw them into place.

I'm not sure I understand: how would that be any different from what John is showing there? Why would you want to put a smaller module inside a a larger one? What advantage is there to that? If plastic holds 52cm of insulation width in place, why would it not also hold 56cm just as well? That method would also reduce the total surface area of insulation exposed to the room, thus reducing overall absorption. That's probably not a good idea...

Out of curiosity, does covering the insulation with plastic change its acoustic properties? Or is the difference negligible?

Yes, it does change the acoustics: it reflects part of the high frequencies back into the room while only allowing the mids and lows through for absorption. In the majority of small rooms done inside-out, that's exactly what you need to stop them room from sounding too dead: it keeps it a bit livelier. The thickness of the plastic sets the lower limit for the range of frequencies that are reflected: thicker plastic reflects down to a lower frequency, thinner plastic reflects only very high frequencies.


- Stuart -