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Ceiling insulation of built-in garage with duct running inside insulation

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Posted by: from Toronto
10/30/2015 at 10:20:53 AM

I'm redoing insulation of a bulkhead inside th built-in garage with master bedroom on top. Both return and supply ducts run inside this bulkhead.

The contractor is very determined to put Fiberglass batt on top and then vapour barrier and then close with drywall. But my home inspector insists vapour barrier on top(the warm side, bedroom floor) and then Fiberglass batt, and then drywall.

The part I don't understand is when warm meets cold on the vapour barrier, which side gets condensation water? My answer is the warm side. But when we set up the tent when we go camping, the condensation water is under the tent, which is the cold side.

In my case, if VB is at the top(warm side), there is supply duct which also gives out heat, so it seems putting VB on top doesn't make sense. But if I put it at the bottom, condensation water might form on top, at the warm side which will damage the Fiberglass batt and the wood under the bedroom.

Any idea? I'm stuck. Thank you!

REPLIES (2)
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Virgil from Complete Spray Foam Contractors in 150 Mile House
Date/Time10/30/2015 at 12:09:44 PM

Spray foam it and then never worry about it.

Virgil hoefels

Complete building

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Date/Time11/1/2015 at 7:09:02 PM

First I assume your garage is an attached garage with a living space above the garage. Secondly, your air supply is within your joist space and is supplied from your furnace. In this situation we call it a " Warm Floor", the vapour barrier is hung loosely to form a bag or balloon on the warm side. The air supply from the furnace warms the air within the balloon. You then frame down a 2 X 8 ceiling below the balloon to accommodate the batt insulation which is typically R28-23. Once the framing is finished and the batts installed you then drywall to complete the process. NOTE: Make sure you batt the sides of the warm floor.

Rick Gilley

Red Dove Developments Ltd.

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