Today was the annual Roofing Contractors Institute conference and it was another great year filled with informative speakers. My favourite thoughts of the day were:
1) Double Stud Construction is actually more dangerous than standard 2×6 construction from a condensation risk point of view. This is due to the exterior sheathing being so far removed from the interior heat source. Yes it CAN work IF the wall assembly including the WRB and the AB are perfect. Are you feeling lucky punk? Are ya? This is another example of an assembly that looks good in concept but starts to break apart when you throw building science at it.
2) ANY foam product on the exterior of a building in a thickness of 2″ or greater acts as a vapour retarder. If you are in a cold climate and therfore have to also have an internal VB, this is a very risky assembly. Yes it CAN work IF the wall assembly including the WRB and the AB are perfect. Are you feeling lucky punk? Are ya?
3) An elevated exposed concrete slab edge (just the edge, an eye brow, or a balcony) may only represent 3% of the overall wall assembly but will degrade that overall wall assemblies thermal resistance by 45% – 60%! This leads to comfort issues and can often lead to surface condensation at the wall/ceiling interface resulting in mould. See the RDH site for numerous supporting articles.
4) Michael Bousfield from Cascadia used an excellent analogy regarding the need to plug the ‘hole’. He equated thermal bridges with holes in a dam. The very common approach in buildings is to try to mitigate the hole by increasing the thermal resistance of the assemblies around the hole. But this is akin to thickening the dam all around the hole and somehow expecting the water to stop flowing out of the hole. It just is not going to work.
Cascadia has created a very useful weighted average assembly thermal resistance tool that demonstrated this fact. You can see in the following diagram that the overall effective assembly R Value is 7.41
So now lets get ridiculous with our envelope and make R1000 walls and roof.
Wow – we went up a whole R2.5. But if we address the hole and say go to a triple glazed fibreglass frame window we can improve the overall assembly by 100% without changing the walls or roof.
The moral of the storey is that holes mater and as Joseph Lstiburek states – BAH (big ass holes) matter most!