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Hydrogap SA vs Majvest SA + Home Slicker

Jeremiah_Sommer | Posted in Green Building Techniques on

We are finalizing our WRB system details for an upcoming project and debating between two systems. 


Project Details 

CZ 6A Southwestern Ontario 

Airtightness target <1.0 ACH


Wall Assembly 

-latex paint


-2×4 insulated service cavity 


-Siga Majrex vapour control (attached to interior face of structural wall

-2×8 structural wall


-1/2” CDX ply sheathing 


-combination of standing seam and stone wall cladding 


According by to our standing seam installer, they will not install over a traditional 1×4 type rainscreen to avoid the potential for oil canning. The preferred install is directly over a self adhered WRB. This makes sense to me, however I would prefer to have some additional drainage/drying potential behind the steel cladding. Currently I am debating between using Benjamin Obdyke’s HydroGap SA system or Siga Majvest SA with Benjamin Obdyke HomeSlicker as the drainage gap. I’m comfortable with the drainage capabilities of either of these systems, especially since the masonry work will have a decent air space behind it and the steel cladding will not absorb water. My concern is with the ability for the wall assembly to dry to the outside, while both of these systems offer drainage they don’t provide much drying potential. 


Anyone use either of these methods with a double wall assembly? Suggestions & opinions please…

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  1. Expert Member
    Akos | | #1

    Sanding seam is rare wall paneling, I doubt you'll find much info on any installed over drainable wrap. My feel is that it is a bad idea as the it is easy for the screws to pull the panel in since the drain wrap is flexible.

    Not the answer you are looking for, but oil canning has nothing to do with subrate type. What matter is how flat the wall is, gauge of the metal, profile (striations/ribs) of the panels and how they are restrained with fasteners. A while back I installed standing seam siding over horizontal strapping and the only spot I ran into issues was with some wonky parapets where the strapping had to be shimmed flat. The issue there was the bow in the wall not the strapping.

    It is also unfortunately pretty easy to blame the substrate for a bad install.

    Also depending on the profile and size of striations, most will have a reasonable gap which would allow for some airflow and drying capacity. The side benefit of striations is it greatly reduces the chance of of oil canning. Using narrower panels also helps.

    P.S. Neat vented cladding with metal is a bit of a PIA, make sure you detail all the edges and how the perforated bits go together.

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