Best option for extending cathedral ceiling rafters and insulating on overhang-less house?
I have a small house with an uninsulated cathedral ceiling in loft space on the second floor that I’d like to insulate to make the space usable in the winter. (Zone 6, Vermont) The place is a newer take on an old cape cod-style with essentially no overhang at the eaves, which I’d like to correct to get more siding/window protection.
My two overhang options per Fine Homebuilding (article below) and some other Web research seem to be:
1) Add 2×6 rafter extensions. Pros: allows for longer overhangs and more structural soundness. Cons: More demolition of the existing structure (siding/sheathing near the eaves) and complication of the insulation process as I’d have to work around the extensions.
2) Create dummy rafter tails. Pros: Less work and disruption of the existing roof. Cons: Limits the overhang to under a foot and less structurally sound.
The roof is 12/12 pitch with 12″ rafters. My plan is to put 1″ spacers along the top edge of the rafters. (I know, Building Science would say 2″, but I don’t have the headroom to add a lot of depth to the rafters inside the house.) Then I’d install 3″ of polyiso or similar from the local reclaimed insulation place, sealed along the edges at the rafter, followed by filling the rest of the cavity with unfaced stone wool before finishing with wallboard. I’d add a ridge vent (or more likely hire a professional to do it) and use soffit vent in my new soffits to complete the ventilation.
I’m leaning toward the dummy rafter tails since I’ll be doing most of this myself and would like to limit the amount of sheathing removal, roofing, framing, and insulation detailing necessary. The roof is so steep that I probably wouldn’t want a lot of overhang anyway since it might start looking odd. That said, I don’t want to get five years down the road and start seeing my eaves drooping like sad puppy ears off the sides of the house.
I’d appreciate any warnings/encouragements/suggestions for alternatives before I put saw to lumber. Thanks.
https://www.finehomebuilding.com/2001/05/01/adding-roof-overhangs
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
I have designed and/or built many projects with applied, "ladder-style" overhangs at the rakes and sometimes the eaves as well. The 2016 Fine Homebuilding House that I designed and Mike Guertin built had applied ladder-style overhangs. Pre-assembled with structural screws they hold up just fine. I do think it's best, and in some cases critically important, to extend the roof sheathing at the overhang up the main rafters as well; that makes the overhangs into a compression element with the sheathing in tension, making it harder for them to sag over time.
Thanks Michael. Having the roof sheathing extend up the roof to help with the support makes sense. So regardless of option, looks like I'm pulling back some sheathing and re-roofing a fair bit. I'd certainly rather do this once and never worry about it again.
Deleted
If you can get 2/3 of the rafter tails attached to the existing rafters, it's not going to sag, especially with a 12/12 pitch. I used rough sawn 2x4 rafter tails, lowered so I could put rough sawn decking on top for an exposed overhang. Many of the tails only had half of the span overlapping as my framers were too quick to slap them up. I've had no problems on 7/12.