Fully applied membrane substitute
mfredericks
| Posted in Green Products and Materials on
When applying exterior insulation, the PERSIST method specs a fully adhered membrane covering the sheathing to control air, moisture and water. These self adhered membranes can be costly, so I’m wondering if there is any risk in using the peel and stick membrane where it’s needed and then less expensive draining type house wrap in the field of the wall.
This might be trickier to install but right now I’m just interested in the performance of these materials – would it matter that the house is wrapped in 2 materials with very different perm ratings?
Thanks
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Replies
Mark,
Your question is addressed in this document: REMOTE: A Manual.
That document was written for Alaskan builders. It notes, "Self-adhering waterproofing membranes, i.e., Grace Bituthene, were used in early REMOTE construction due to their impermeability and ability to seal around fastener penetrations. Covering an entire house with these materials is extremely effective but typically more expensive. As an alternative, 6-mil polyethylene sheeting has been used with good results and meets Fairbanks building codes which require the use of a vapor retarder with a permeability (perm) rating of .06 or less. It is worth noting that 6 mil poly is more susceptible to physical damage during installation, and breaks down after extended exposure to sunlight. Another product that is showing promise as an exterior membrane and is particularly well suited to wet climates is Tyvek DrainWrap, a vapor-permeable air barrier."
Mixing and matching your air barriers at different locations of your building shouldn't cause any problems, as long as you pay attention to airtightness. If you expect a layer of Tyvek to be your air barrier, I would verify that it works with a blower door.