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Community and Q&A

How to fill the smallest of cracks with foam or silicone

Boro | Posted in Energy Efficiency and Durability on

I’m trying to fill some small spaces in between 2 x 6 roof decking that sits on top of finished timber frame rafters at the point above the exterior wall. The deck boards for the finished ceiling inside are the same ones that continue to the outside where they become the finished soffit boards.
These boards are not tongue and groove and were freshly milled when installed. They have since shrunk and left gaps of 1/16 of an inch to a 1/4 inch allowing for outside air to pass through the gaps and into the interior loft space.
I’m looking for a tool and/ or product that could fill these long narrow voids. Ideally the tip of the tool could reach into the full depth of the wall (18 inches with a 6″ wide rafter on either side), and fill the entirely space.
Does anyone know of a tool or an attachment for a spray foam gun or an attachment for a tube of silicone that would work, or should I just try and fabricate something and cross my fingers?
Hope my description is clear and thanks for any input.

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  1. GBA Editor
    Martin Holladay | | #1

    Most hardware stores sell clear flexible plastic tubing (I think it is polyethylene) that is sold by the foot in a variety of diameters. Buy 2 feet of plastic tubing and slip it over the nozzle of your tube of caulk.

  2. Boro | | #2

    Yes, I was thinking something similar except I don't think I could find a tube narrow enough outside diameter to penetrate into some, if not most of the voids. Maybe a metal syringe like the ones used in furniture repair...only longer.

  3. gusfhb | | #3

    When I reroofed my house with a similar roof structure I drilled a 1/4 inch hole at every board intersection and injected canned spray foam into the hole. The idea is that it would expand to fill the entire gap, not just the bevel at the bottom. I imagine that you could do it from below if you masked off the wall but it would be more time consuming.

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