The project I’m working on is a 2 story home with converted basement- about 80 y/o, in the PNW. The basement is now living/BR space, and there’s a lot of ambient noise transferred through the above ceiling/floor into this BR. The client had originally considered having cellulose insulation blown into the joist bay spaces, doing this at the same time that some seismic reinforcement work was being done on the building. The contractor for the seismic work received this reply from their insulating subcontractor:
“… it is strongly discouraged to use cellulose insulation as a sound barrier. In fact, it is a last resort. It can make the basement uncomfortable, because you’d be putting insulation within the thermal barrier. Ideally, we want heat to move freely within the thermal envelope. But if you put insulation in the basement ceiling, it prevents heat from being exchanged between floors. The result would be “chunks” of living spaces that would probably need to be conditioned separately. So on top of the insulation cost, you’d be looking at reconfiguring for zones and multiple thermostats, etc.”
“The better solution would be to install sound attenuating drywall. It will do as good or better of a job of sound mitigation than cellulose, without the discomfort issues. If the client is already expecting some drywall repair on top of possible insulation costs, you could suggest just layering the new drywall over the old. The total cost and timeline would probably be pretty similar. We literally just had to undo this type of situation in a house in a similar area, where we removed insulation from the basement ceiling, and now everything is more comfortable.”
Thoughts?
Replies
If you have a zoned system then insulation between zones helps keep the heat where you want it. Relying on heat transfer through walls/ceilings to equalize temps is an inferior approach to good ventilation.
The insulation contractor's advice is good. The sound-attenuating drywall will be a continuous sound barrier, not broken by joists as the cellusose would be. With joist bays full of cellulose, any future work would be messy and harder to access.
As for the heat transfer issues, it could be that he's right, although, as DanH points out, a properly designed and installed heat system would not rely on floor/ceiling heat transfer.
We did both insulation in joist spaces, and suspended drywall, but ours is a slightly different situation. Our basement is a self-contained and self-heating/cooling suite, so thermal isolation isn't an issue.
As for the drywall treatment, we didn't use the special (and VERY expensive) sound attenuating stuff. We chose instead to use rez bar (aka resilient channel), then a layer of 1/2" donna conna (that cheap fibrous board stuff), then a layer of 1/2" DW.
I think what he wrote is nuts
Ideally, we want heat to move freely within the thermal envelope.
No, you want heat to go where you want it... and that's hard to do. Hot air floats up like a helium balloon, cold air falls and pools like water. Most homes are wide open and let air rise and fall unencumbered. The typical 2 story colonial has a hot upstairs and cold downstairs - this is because the AIR moves freely, and the air and humidity carry the heat.
But if you put insulation in the basement ceiling, it prevents heat from being exchanged between floors.
Heat isn't radiated between floors, unless you actually have floor or ceiling radiators. If it is, it's probably undesirable - as in the attic radiating heat down from the ceiling. Air flow is what carries heat around, and an insulated ceiling doesn't change that.
The result would be “chunks” of living spaces that would probably need to be conditioned separately.
Chunks of a home DO need to be conditioned seperatly. If they aren't, then you need to keep the air flowing enough between the different areas to keep them all balanced. The air won't balance itself correctly in a multi story home with open stairways... it will always be hot upstairs and cold downstairs. The only way to check this is to close doors between floors, or periodicly cycle the blower to rebalance the air around the house. Modern thermostats can be programed to cycle the fan 5 minutes every hour, as a basic setting.
So on top of the insulation cost, you’d be looking at reconfiguring for zones and multiple thermostats, etc.
If they have that problem, it's because their home leaks like a seive... now it would leak in a slightly different unexpected way.
Now, after all that, I'm NOT suggesting cells is the right answer. Ted White (type in his name in the seach bar above) has made a pretty good case for using multiple layers of 5/8" drywall with Green Glue between to dampen the sound waves. Do a search on his posts, good info and back & forth there on the topic of sound mitigation.