Will Delta-Dry provide any reduction in thermal bridging?
user-1115830
| Posted in General Questions on
I like the concept of Delta Dry as a rain screen and am wondering if it will also help at all against thermal bridging, assuming that there is no additional rigid foam layer between rain screen and sheathing (only felt or building paper). My mind tells me that the presence of a positive air space between the Delta-dry and the felt/sheathing means that the sheathing suface will still experience the same temperature fluctuations and will therefore still be susceptible to thermal bridging. But I also realize that there is less conductive surface area (less surface-to-surface contact) between siding and sheathing. Any thoughts out there?
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Replies
Shane,
Your question basically boils down to, "What's the R-value of Delta-Dry and the air trapped by the dimples?" Well, since the thickness of Delta-Dry is less than 1/2 inch, I think it's safe to say that the R-value of the assembly is no more than R-1.
Thanks, Martin. While it a great design, Delta-dry becomes a very expensive rain screen for my use. Kelowna, B.C. can get quite cold at times in the winter but it is a relively dry climate compared to other parts of B.C. I'm thinking Delta-Dry is overkill for this climate, especially with no significant insulative value.
I am Product Manager with Cosella-Dorken.
DELTA-DRY has no effective R-value and is not intended to have any. Given that it is supposed to be fully ventilated, this can be reasonably deduced.
Neither is it purported to reduce thermal bridging. With no insulating value, this is also not possible.
Thermal bridging is caused by low R-value wall components such as studs that create cold or warm areas in the wall system.
If your primary goal is to address thermal bridging issues in your building enclosure and not to include a ventilated rainscreen, then DELTA-DRY is not the product to choose. Sheets of extruded polystyrene will be much more effective.
What DELTA-DRY will do is moderate the relative humidity in the space between the cladding and the sheathing by being fully ventilated. Warm moist air in the cavity rises, drawing in cooler drier air. Combined with wind pressure differentials that can draw air through the ventialtion space, drying energy is provided. The more damp the climate, the more significant the drying energy can be for the longevity of the wall.
This is well studied by the University of Waterloo and by Oaks Ridges National Laboratory. See some academic papers on the topic here:
http://www.cosella-dorken.com/bvf-ca-en/news_events/articles.php
The value will depend on the exterior cladding. The biggest benefit is seen with claddings that have a high tenedency to absorb water, like conventional stucco and manufactured stone. It will dramamticly reduce the propensity of mold to take hold in the wall due to excessive moisture levels in the building enclosure and solar -driven moisture..