what should I do? it's a cold roof now, but it's ventilated, and I need to remove that ventilation to get isolation. the ceiling currently has pink insulation up against the inner sheeting, soffits on the underside of the roof outside the wall. I was thinking the easiest way to seal it would be to add sheeting going straight up from the wall and add my extra mass there, leaving some open triangular cross sections on the outside of the wall. If the soffits are left open, would that keep it from creating a resonating chamber/third leaf? (material to add indicated in red) so there's a catch 22 between isolation and ventilation for the space within the trusses how do I get around that?Are you going to have a hot roof or cold roof?
New Home Rehearsal/Recording Studio build. advice?
Originally posted at johnlsayers.com, topic 22349.
Actually, you can maintain isolation and ventilation at the same time if you do it correctly. Here's a diagram I drew to show you how to do that: You need a continuous free air air flow from your soffits all the way up to your ridge vent. There needs to be a 50mm gap (2") between your roof deck and your drywall. So, install some 50mm battens to the rafters and then install the drywall on the bottom of those battens. This Is your outerleaf, so you would install however many layers you need here and seal it air tight. You connect those layers to your walls, which seals the ventilation cavity as well as sealing your outerleaf. Make sure your rafters (and I'm assuming ridge beam?) are strong enough to take the load, check with an engineer. Below that you would build your inner leaf assembly. So, you will have a double leaf assembly with a ventilated roof on top. If your roof already has a ridge vent and soffit vents then double check with the Owens Corning calculator here to make sure you have enough inlet and outlet ventilation (please do not overlook this, it's extremely important that you have the correct amount otherwise you're going to be tearing everything down again to fix it!) https://www.owenscorning.com/roofing/co ... calculator I know in the UK if the building is less than 10m wide with a pitch of less than 35 degrees then you can get away with just 70mm soffit vents installed every 160mm, but it may be different in the USA. You might be thinking, "isn't this a triple leaf assembly" No, not really. The roof "leaf" is not really a leaf since it is incredibly leaky, you have continuous holes in the soffits and ridge, so do not view it as a third leaf it is simply a rain screen to protect your double leaf assembly. The alternative to this would be to convert your roof to a warm roof (or I think you call it a "hot" roof in the states). This type of roof completely does away with the need for any ventilation, and is how a lot of new houses are being built to save energy. This would be where you take off your tiles (or shingles, whatever you have as your waterproof layer) install a vapour control layer completely sealed with no gaps, then cover that with thick rigid foam insulation and then your final roof layer over that. Having just gone through a nightmare condensation problem in my own studio I highly recommend you sort this out ASAP, it does not take long to completely destroy your whole roof and ceiling. I am worried about the pink fluffy you have up tight against the roof deck... make sure you have the correct roof ventilation in there otherwise you'll be in for a nasty surprise. Paul EDIT: I just noticed from your pics that you have what looks to be OSB already on the bottom of your rafters? and the ventilated roof deck is above that OSB correct? That's cool, you can leave it like that and just beef up that ceiling. It will save you having to install battens and cut in drywall between your rafters. All it means is you will not be able to use the depth of your rafters as part of your double leaf cavity, but you can just make your inner leaf ceiling lower to achieve the required gap that you need for your MAM assembly. Hope that makes sense? Still double check that your current rafters and Ridge beam can take the extra weight if you do need to beef that OSB up.what should I do? it's a cold roof now, but it's ventilated, and I need to remove that ventilation to get isolation. the ceiling currently has pink insulation up against the inner sheeting, soffits on the underside of the roof outside the wall. I was thinking the easiest way to seal it would be to add sheeting going straight up from the wall and add my extra mass there, leaving some open triangular cross sections on the outside of the wall. If the soffits are left open, would that keep it from creating a resonating chamber/third leaf? (material to add indicated in red) so there's a catch 22 between isolation and ventilation for the space within the trusses how do I get around that?Are you going to have a hot roof or cold roof?
I do have OSB on the inside of the rafters/trusses. if you go back to my original post, there are a couple photos of the new trusses before the roof covering went on. A contractor did that part for me, up to where it had to pass a building inspection so there is vapour barrier behind the OSB, so if I'm making another inner wall, I'll have to take off the OSB to remove the vapour barrier, put the OSB back up, and put my vapour barrier on the inner leaf.
I made another diagram just now, which now that I look at it next to yours again, looks like it is a simplified version of yours. brown is wood, red is "leaf":
that look like it's going to work?
Yep, exactly, that’ll work just fine. The only thing you might need to add in order to stick to code is a fire stop at the top between the two walls, so check that out. If you do need to add it then see if you can just use rockwool instead of a solid connection, I’m not really clued up on Canadian regulations.
Paul
Progress report
more RIP AND TEAR (I've also been playing the new Doom game)
before adding mass to the outer layer, I suppose I'll have to snip off all those nail ends poking through that hold the siding on.
on the side that goes into my garage, I suppose I will have to seal up the peak there, where it goes higher than the other wall, making my outer leaf on the inside of that wall, much the same as I would be doing with the ceiling itself, so that should be fine.
now, since it will work to keep the ceiling with the same construction and add to it, can I save myself some work by leaving the vapour barrier in place? and if so, how do I account for it when finishing the rest of the vapour barrier? I have some options in mind:
next steps... (if I can skip taking down vapour barrier):
- have electrician pull the wires,
- filling in the framing where the garage doors used to be (well, where one still is, gotta take it down still) and put in all the outer-leaf doors.
- caulking everything and self-levelling-concrete-ing the floor.
stop me if I'm going to mess something up!
:)
Yes, board up that gap in the peak, if you can't do it from the other side then from the inside is fine provided it is completely sealed to the rest of the leaf with no gaps anywhere.
Regarding your vapour barrier - definitely do not put 2 vapour barriers in a single assembly, that is asking for trouble.
Ideally it would go on the warm side of the cavity insulation...
Do you also have insulation behind that OSB on the ceiling inside the vented cavity? If you do, then I would be tempted to remove that anyway to guarantee there is free air flow behind your roof deck.
Paul
yes, there's insulation right behind the OSB, with air space above that before you hit the roof covering:
so need to take the extra step of taking the OSB off to take the Poly off. dang.
on to increasing the outer mass soon, do my cleats have to be a certain size? can I get away with just chopping up 1x2s for that since it's just the walls that will be cleated, ceiling will have to be screwed.
Anything any size will work. As long as it holds up your beef up sheathing. Gregon to increasing the outer mass soon, do my cleats have to be a certain size? can I get away with just chopping up 1x2s for that since it's just the walls that will be cleated, ceiling will have to be screwed.