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Shiplap ceiling to code

Hello- I am in zone 3A W/H - everyone is saying we need to cover up our shiplap ceiling which we were thrilled to uncover if we are to meet IBC 2013 standards for our new central heat and air installation in the attic. Is there a way to meet code but leave our shiplap exposed? There isn't much room in the attic to work with - house is older and the duct work has taken up most of the room.
Thank you,

Asked by gigimon
Posted Jul 10, 2018 8:07 PM ET
Edited Jul 11, 2018 6:17 AM ET



You may not have the working room, and I bet everyone else will say you need to rock over it to get the air barrier but why not flip it? Seal from the top down (foam?) or put down batts, acoustic sealant on the joists and put down ply? Treat it like you would a crawl space below.

Answered by Sean Cotter
Posted Jul 10, 2018 8:38 PM ET



You need an air barrier. Can you give us more detail about how the ceiling is constructed? For example, how deep are the rafters? What kind of insulation is above the shiplap? How much?

Answered by Steve Knapp CZ 3A Georgia
Posted Jul 10, 2018 9:43 PM ET


As far as I know, there is no specific requirement for an air barrier behind ceiling boards in the building codes -- but there is a general requirement to seal air leaks and to achieve a certain blower door test result. So the people who are telling you that you have to address this issue to meet code are correct.

The most common approach for new construction is to install a drywall ceiling and to put one coat of mud (compound) on the joints. This is your air barrier. Then it's possible, if desired, to install boards on the interior side of the drywall as a finish ceiling.

You are finishing your attic, evidently, and you write that you have a "shiplap ceiling." I assume that you mean that there are shiplap boards installed on the interior side of your rafters. But Sean Cotter seems to think that you are talking about the ceiling under the attic. Which is it?

As Steve Knapp suggested, we need a full description of the assembly, as well as a summary of your insulation and air sealing plan.

Answered by Martin Holladay
Posted Jul 11, 2018 6:15 AM ET


Yes Martin, I took it to mean that the the skip sheeting/shiplap is below the rafters, but the opposite could be true and it sits above and the wood is actually the attic floor.

Answered by Sean Cotter
Posted Jul 11, 2018 11:01 AM ET


I don't think these boards are attic subflooring. I assume that the boards are either the sloped attic ceiling (on the underside of the rafters) or the horizontal ceiling of the story immediately below the attic.

Answered by Martin Holladay
Posted Jul 11, 2018 11:09 AM ET
Edited Jul 11, 2018 11:21 AM ET.

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