Can you use blown cellulose overtop of fiberglass insulation?
I have a room over my garage that is unfinished (just a finished floor, no walls, you can see thru from one end of house to other). I just use if for storage as it has a stairwell entrance from inside the garage. It gets unbelieveably hot or cold, depending on the season. It currently has fiberglass insulation between the joists, Im wondering if I can increase the insulation or if that is of no use since the stairwell is open.
Blowing cellulose overtop of fiberglass insulation is no problem, but you need to be very careful about how much insulation you blow in, and make sure don’t block your ventilation openings through the soffits. Check this page first about roof ventilation –
Why roofs need to be ventilated and how to ventilate a roof properly
So that would cover the blown-in aspect of your insulation, but your design in general has me a little baffled so I’ve got no answers but a bunch of questions of my own
First of all, which climate zone are you in? I’m assuming you’re somewhat north at least.
Where are you blowing the insulation? Will you be lifting the floor boards to insulate between the joists? If so you’d need a vapor barrier at the top likely.
Is it also safe to assume the garage below won’t be heated? You can thermally separate the two spaces, and yes your stairwell may end up being the more challenging spot and still be where the most heat loss is, but there’s always a spot like that.
Happy to help but we need more info.
I live in South Carolina down near the coast. I believe the original intent of the builder was to have an extra room over the garage and sheetrock, etc would be put up to complete the room. There are certainly many electrical outlets located and full lights etc. But, previous owners never did anything, so the space is just roughed in with all the studs, etc. but not finished (with the exception of the actual floor, which is just "plywood" or similar over the joists.) Its great storage for christmas ornaments and things you use once in a great while, but otherwise uncomfortable climate-wise. The garage will not be heated.