Quote:
Originally Posted by dankelly  I was under the impression though, that as well as sealing my inner room airtight, for maximum TL I should also be making my outer leaf as effective as possible? As an exaggerated example, if my roof were to not be there at all, I would not have a room within a room, but merely just a room. I could beef up walls and beef up the underside of the roof between the rafters but if i then have gaping holes for ventilation then it seems pretty pointless?
As everyone says on here, there is no point in putting 5 layers of drywall on the walls to then only put 2 on the ceiling as the ceiling will let the walls down. So surely by beefing up and making the best of my outer leaf, then the ventilation is going to let the whole isolation down? |
Actually adding mass is not pointless if you have ventilation holes in that layer. If you
must have vent holes, make them with sharp corners and not too much larger than about 5" diameter. The impedance difference will reflect low frequency sound by up to about 17db. The length of the path (hole or channel to the ridge vent) also attenuates sound at a calculable rate per meter/foot.
The mass of your roof (asbestos or asphalt shingles?? are heavy) is probably adequate but could be beefed up by adding drywall to the underside of the sheeting - as long as there are no protruding roofing nails to prevent you.
Quote:
Originally Posted by dankelly Am I better to :
A) Leave the outer leaf (roof) as it is (corrugated sheet on top of plywood), then double drywall my new isolated, inner ceiling and insulate the void between.
B) Beef up the outer leaf between the rafters, then do the same as (A) with the internal ceiling.
C) Drywall to the existing trusses then do the same as (A) with the internal ceiling, insulating both voids. This creates a triple leaf but there will now be a perfectly sealed room, within a perfectly sealed room, underneath a ventilated loft space. I'm trying to understand the effects of the triple leaf. I know its bad, but is it worse than not having that extra layer of isolation? |
(B) if you can. But (A) might be fine... I'm not there. Can you determine the mass of the roof?
Cheers,
John