HOW TO INSTALL A VAPOR BARRIER AND INSULATION IN A METAL ROOF

brian lynch
3/24/2010
I RECENTLY HAD BUILT A 16' X 20' HUNTING LODGE WITH A 16'-15' LOFT IN AMBY NEW YORK. THE AREA SEES PLENTY OF SNOW DURING THE LATE FALL, WINTER AND SPRING TIME. THE BUILDER INSTALLED A METAL ROOF OVER THE WOOD ROOF RAFTERS AND WOOD CROSS BRACING. THE METAL ROOF IS EXPOSED INSIDE THE CABIN WITH NO PLYWOOD OR SHEATHING UNDER IT AS MOST ROOFS ARE CONSTRUCTED. I WAS TOLD TO INSTALL A VAPOR BARRIER PRIOR TO INSERTING R-30 INSULATION AND CLOSING IT ALL IN WITH KNOTTY PINE WOOD. CAN SOMEONE EXPLAIN WHAT A VAPOR BARRIER IS, HOW ITS INSTALLED AND WHAT WILL KEEP MOISTURE FROM ACCUMMULATING AND DRIP ONTO THE INSULATION AND THE KNOTTY PINE CEILING COVER??? THANK YOU
Eric Novotny
An informed customer is the Best Customer!
3/24/2010
A vapor retarder is typically a plastic layer of a low enough perm rating to keep the warm moist air in the living space from migrating to the cold attic and roofing material. It needs to be installed on the warm side (living space) prior to the installation of the ceiling cover. Special care need to be taken that you do not perforate the vapor retarder layer when you install the ceiling cover or you will have lessened its effectiveness. I would also blow in R-49 for insulation as a minimum and use cellulose as it actually works compared to the less effective fiberglass.
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