Exterior Wall Plan Feedback
Hello All,
I am building my own house in Zone 5a per the following specs listed below and would like some feedback. I’m not a builder, just a retired vet looking to build an off-grid and debt-free homestead with help from seasoned general contractors who happen to be family members. As such, these specs are from a house plan I purchased. Nonetheless, I have a few questions.
1. Will changing the OSB to Zip affect anything negatively?
2. If I change OSB to Zip will I still need an air barrier? If so, what type?
3. Will changing the insulation type from batt to blown insulation affect anything negatively.
4. I’m assuming that the vapor barrier is listed because it is needed but I’ve had a few opinionated folks tell me that vapor barrier does more harm than good. I’d like more input, though.
Thanks everyone.
Vinyl siding
1×3 furring strips
air barrier
1” rigid insulation (R5 min)
7/16 OSB
2×6 studs
Batt insulation (R-20 min)
Sealed Vapor Barrier
1×3 furring strips
1/2 gypsum board
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Replies
This needs a response from someone more knowledgeable than me. So I'm giving it a bump and also sharing to the best of my knowledge.
1. No problem with changing OSB to Zip.
2. Neither is an air barrier. But with the joints taped either can become one.
3. No problem with changing between those 2 types of insulation in that location, because both should be similar in terms of vapor permeability.
4. Vapor barrier - RED FLAG - I'm concerned, like others, that it will trap moisture in the wall and prevent drying to the interior. I believe you would be better off with a "smart" or variable-perm membrane and may need none at all.
It's not clear to me where in your wall section is the actual WRB (Water-Resistive Barrier). Is it the "air barrier"? If the air barrier is something like a Tyvek sheet, that does not make a good air barrier. Tyvek makes an acceptable WRB but is very difficult to detail as an air barrier as well. The rigid insulation could be both the air barrier and the WRB if it is properly taped. Or the ZIP could be both if properly taped. Taped OSB can be an air barrier but will not satisfy code for a WRB. So you may wish to clarify that. The option you choose has a big impact on how you detail window and door installations.
Lastly, minor detail, I don't see a purpose for the 1x3 furring strips inside and out. You may want to check on why they're needed. Most vinyl siding shapes allow air to pass freely behind.
Thanks for your feedback. I’ve begun my build with Zip. I plan to install 1 inch foam board over the Zip. I suppose it makes sense to use the 1 inch foam board as my air barrier and wrb. If I go this route, how to I detail the foam board to act as an air barrier? And how would I detail my windows and doors in this manner? Finally, I’m definitely leaning towards the Certainteed membrane at this point. Thanks!
Timothy,
Zip is designed to be used as your primary air-barrier and WRB in one. That's where you want to concentrate your taping and sealing. No need to use the foam instead.
In this scenario, I would have to install an exterior picture frame on my windows before installation of my windows and install the 1 inch foam board flush to the picture frame, correct?