Want a Velux Skylight in my Living Room
… but don’t want to cut thru the cathedral ceiling’s drywall (‘popcorn’ finish) until I’ve framed in a properly sized rough opening.
Easiest way is to remove sufficient roof sheathing (3/8″ OSB I suspect) to permit cutting out one rafter, adding doubled headers top & bottom to pick up the cut rafter ends, then single rafter ‘scabs’ at either side to complete the r/o?
Then remove the drywall from inside, maybe even once the skylight’s installed.
I don’t want to mess up the popcorn ceiling finish by building temporary interior support to keep the cut rafter from sagging so expect I’d just support it topside with construction-screwed-down 2×6’s spanning two or three rafter bays either side of the two I’m opening up… BEFORE making the necessary cuts.
Question I have: is notching the tops of the rafters on either side before replacing the roof sheathing sufficient to preserve adequate airflow above the fiberglass insulation up there? Soffits have continuous ventilation strips in them & there’s a ridge vent that appears to be properly installed & working. Don’t want to create potential problems doing anything that’d cause restricted airflow under the sheathing.
Roof pitch is kinda shallow @ 3.33:12 but above the 3:12 minimum recommended by Velux for the product my wife’s picked out….
Replies
May need to rethink your "properly" sized R.O.
Doubling headers top and bottom is not necessarily the answer to your main structural hurdle. If your adjacent rafters to new skylight are being asked to carrying additonal load by cutting one rafter and introducing eccentric concentrated loads at header points, then (IMO) you need to check existing single rafters for structrual capacity with new skylight R.O.'s. Usually this means adjacent rafters need to be doubled full length (not scabbed); not your top and bottom headers. Also, I suggest using hangers for the clipped rafters and headers.
Thanks Deadnuts...
... you're right, that's a factor I'd overlooked.
When I remodeled a house we used to live in to include a skylight in a 2nd floor room and another over the main entryway I doubled the rafters on either side of the R/O's the better to take the increased load. Both roofs framed w/ 2x10's 16" o/c.
Doing full-length sistering'd be a major undertaking, what with the cathedral ceiling design in the new place's living room. Not an impossible task but certainly more work than originally envisioned.
Guess I need to get out the rafter tables, see just what kind of loads the existing structure's limited by. And yes I agree on the hangers for the new connections.