Log Cabin vs Moisture Build-up Part II

by Cody Farmer

Air Tight Construction Colorado

Last week, we looked at rain inside a non-vented vaulted roof cavity in the Rocky Mountains. This week we’ll delve into the proper roof assembly. By following the 7 Passive House Principles we’ll see that Step 1 would have shown us that there was a dew point risk under the wood decking, a lack of insulation, a large thermal bridge with the 2x12, and an air gap between the roof decking and insulation allowing for moisture to really collect and saturate the deck.

Press on to step two we would find that the climate zone is a 7 and instead of r-38 the roof assembly would need to be R-70 without framing thermal bridges and an interior vapor barrier Intello plus taped and sealed with Tescon Vana to all penetrations. The traditional can lights were encouraged to be changed to the shallower LED look-a-likes to keep the intelligent vapor barrier, Intello consistent. An example from our supplier below.

 

Air Tight Construction Colorado

There is one last detail to mention in this perfect storm. The cabin was designed without bathroom exhaust or vented range hood. There was also a humidifier added to the HVAC system. Just like the perfect storm, the perfect solution is holistic. I’ll note that step 5 would show us that we must have ventilated spaces for good hygiene. We design for this and specify the best system called Zehnder because shower moisture and cooking moisture needs to go out especially when added humidification present.

And certainly how the wood portion of the cabin is coupled to the slab or stem wall must also be dry. If you know that your concrete pad is larger than the base of your cabin, then you already know (from our blog last week) that the size of the pad needs to be reduced to avoid water pooling near the home.

In summary, sometimes there are assemblies and situations with multiple inputs causes major issue or damage. These are costly repairs. Following Passive House principles allows a holistic view of the building's body and function. MainStream is happy to be part of the solution!

Click here to see more specifics on how we do it. And then see this page to tell us all about your home/building so that we can get to work on finding solutions for you!