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Replacing siding, should I seal my OSB seams?

old_ | Posted in General Questions on

I have a 1988 built ranch house in climate zone 5a. I am replacing the siding with a mix of LP smart side vertical board/batten and hardie shakes. I will be replacing the WRB with Tamlyn drain wrap. Some sections of the house were sheathed with osb and some with fiberboard. I plan on putting 7/16 osb on top of the existing sections of fiberboard so I have a solid surface for the hardie shakes. (I figure it can’t hurt to have the fiberboard under the osb, it will give a slight thermal break). 

The house is 2×6 framed with a poly vapor barrier behind the drywall. The poly was not sealed to the studs and there was no sealing around electrical boxes, wiring, plumbing, etc. 

I don’t plan on adding any exterior insulation or rain screen beyond the Tamlyn drainable wrap. To add the extra depth will be difficult to detail in several areas of the house and there just isn’t a payoff for me. I do not plan on living here more than 2-3 more years. I am trying to do some basic improvements but I do not want to go overboard.

My question is should I air seal sheathing joints? I was planning on using 3M 8067 tape to air seal the joints but am concerned this will create a double vapor barrier and cause moisture problems down the road. I just don’t know enough to know what I should do in this situation. Any advice would be greatly appreciated.

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  1. Expert Member
    Michael Maines | | #1

    Patrick, you should tape the sheathing joints to reduce air infiltration and exfiltration. OSB is not a vapor barrier; it is somewhat vapor permeable, as is the LP Smartside, so during heating season the wall can dry to the exterior. Drying potential will be limited; a safer assembly would include a thicker rain screen, but a drainable housewrap is better than nothing. Reducing air flow means you will have less potential moisture accumulation, not more. If you want an added level of resilience you could use a vapor-permeable tape instead of the 3M 8067, but it's probably not necessary.

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