Planning for future insulation – metal shop
I am completing the construction of a metal shop, and will start with it uninsulated but want the ability to add insulation and HVAC in the future as budgets allow.
My main focus right now is the roof. The building is in Raleigh, NC and is a metal stud structure with metal 5v-type roofing on it. In the initial build the structure came with double bubble radiant barrier to install between the metal roof panels and the galvanized steel purlins (6″ tall, varies in spacing but ~21 inches on center for a running average). This should help with reducing thermal bridging.
If in the future I was to further finish the interior ceiling my thoughts were to install batts between the purlins and then sheath the inside with plywood or shiplap material to retain the insulation and create a solid interior shop surface.
Question: In the near term my question was on the double bubble; should I aim to close up the roof envelop as tight as possible, i.e. no venting allowed at the peak and a tight taping to the double bubble on the walls in between studs and wall panels? The alternative would be to allow the double bubble to be open at the peak and install peak vent instead of peak seal at the ridge cap.
If I come back later with insulation between the purlins I was wondering if its best to be venting between the double bubble and batts, or have that space be more or less air tight.
Thanks!
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Replies
What I call 5V can't be placed on purlins so it must be standard ribbed roofing. I don't think the double bubble is much of thermal break. Metal buildings around here place a thermal block, maybe 1" EPS, between the roofing and the purlin. That nay not work with screw-down roofing. Another approach is to put a thermal block on the bottom of the purlins, then fill the void of the purlins and add a very good vapor retarder, usually a scrimmed vinyl or similar. Attention to detail is important. Gaps in the vinyl cause air infiltration. I've seen condensation fill the insulation between the purlins like a full diaper. Very important transition from walls to roof also.
Since steel conducts heat so well, I would install all the insulation on the outside.