How much is R-value reduced by screws/nails and other fasteners?
AlanB4
| Posted in Energy Efficiency and Durability on
Plywood/OSB is installed with nails/screws, the same with foam board, siding, studs and many other components, has anyone done the math to figure out how much they reduce the insulating value (since they are usually metal).
I’d like to hope its almost zero, but data/calculations may show an appreciable effect?
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Replies
Alan,
This topic has been discussed several times on the Q&A pages of GBA. Perhaps the most useful discussion occurred in this thread: Do screws through exterior insulation reduce the wall R-value?
Here are some quotes to give you the gist:
Martin Holladay: "This question has been discussed on GBA several times. When building scientist John Straube was asked to respond to a report that fasteners through rigid foam could reduce the thermal performance of the rigid foam by 45%, here's how he responded: 'The effect [that fasteners have on the thermal performance of rigid foam sheathing] is on the order of 1 to 2 percent. Variations of this have been modeled repeatedly. 45 per cent [reduction in thermal effectiveness is] technically preposterous.' "
Bill Dietze: "This may be the report referenced by John Straube: Thermal Impact of Fasteners in High-Performance Wood-Framed Walls. That answer (thinner insulation, but higher R-value, more fasteners, each with smaller diameter) is about 4.5% whole-wall degradation of R-value. This paper models ALL the fasteners in the wall - drywall side as well."
Thanks for those links Martin, its always good to see modeling :)