Re-siding with Hardiplank over felt paper and board sheathing. Where’s the air barrier?
Hello All,
I’m in Sacramento, CA. 1940s house with 2′ roof overhangs.
I’m re-siding a small portion of my house (two walls, 10’x9′ each) that was never finished to the interior and was sided on the exterior with various types of mismatched siding. I’ve stripped off all the old siding back to the board sheathing, which is 10″ to 12″ wide redwood spaced 1″ apart, and is in excellent condition. I would like to add siding now, and at the same time prepare the wall to eventually be finished on the interior and brought into the envelope of the house (it’s now sort of an addition the the garage).
My plan was to add felt as a wrb and then the Hardiplank directly over that. Then eventually finish the interior as described in the article below by creating an air gap on the interior of the sheathing with spacers, an air barrier with rigid foam, and then filling the cavity with air permeable insulation and finishing with drywall. But I’m wondering if that’s the wrong approach since I have the siding off now.
https://www.finehomebuilding.com/project-guides/insulation/insulating-walls-no-sheathing
Am I overthinking it? Should I just try and create an air barrier on the outside? I would prefer to not to have to re sheathe the whole thing in plywood. Can I detail the felt so that it will work as a good air barrier? Should I add a layer of rigid foam outside the felt and air seal that?
I don’t need a lot of insulation – my energy costs are very low as is even with the rest of the house lacking any insulation in the walls. But it is very effectively air-sealed and I feel like that makes the house comfortable. I just want a wall that will be safe and sound moisture wise and won’t leak crazy amounts of air.
Any thought you all might have on this would help me out.
Thanks
John
Replies
The article you linked to is specifically about a house with siding directly attached to studs, with no sheathing. That’s why they created the WRB inside. Your situation is different, you have sheathing, so no gap with WRB barrier needed inside. Asphalt felt paper is fine on the outside of your sheathing (or a house wrap type), then Hardi-plank over that. I highly recommend a rain screen, but that may not be possible in your project. Do your air sealing inside (smart membrane vapor barrier, caulking around dry wall, or other options).
Thanks for the reply.
So you don't think I need to worry too much about the fact that the sheathing has 1" gaps between the boards? Just put a wrb up, and a rain screen and then the siding and concentrate on air sealing the drywall on the interior. Thanks for the advice.
Actually, the only thing I'd worry about with the spacing is that HardiPlank has a very narrow range of where to nail it, and is marked for where to do it. So you may wind up needing to nail it where one (or more) of those 1" gaps are located, and since you will have already covered it with the WRB you won't be able to tell until it's too late. Your options, unless you carefully measure where the clapboards will be nailed (a story pole could help you there), are to sheath completely over the redwood or fill the 1" gaps with the same thickness boards. Or only fill the gaps where your measurements/story-pole show a nail wants to be at a particular gap.
I'd examine the redwood very carefully. Old growth rw is almost priceless. You might want to reclaim it and use plywood sheathing.
I fully appreciate the sentiment. I make furniture for a living and I habitually grab redwood that people are discarding and pile it in my yard for future use. If I didn't already have a pile I would consider trying to use this for a higher purpose - but in this case I'll probably just leave it on and try to get a good application of housewrap or felt over it, seal the seams as best I can, and put up some furring strips and then the hardiplanks. My wife is sick of me delaying every project because of my love of old wood.