Setting a pass-through block for the hot water system

Well, I didn’t exactly cure cancer today (you’d have to start working before 1 PM to do that) but I did discover a few new tricks for cutting penetration blocks into a rain screen siding detail.

What I’m working on today is setting a pass-through block for the copper pipes that will connect the solar hot water panel outside the house to the reservoir inside.

The first step is to drill a pilot hole through from the inside and then use a small nail to align that with a hole in a small scrap of plywood the same size as the block I’ll be adding. Then I trace that with a pencil to mark where I need to cut into the siding.

The cool thing about a rain screen detail where there is air space behind the siding is that if you cut carefully you can remove a small piece of siding without disturbing the weather barrier. There is still the risk of cutting too deeply though so I drilled a hole in the blade of my oscillating tool and pushed a small machine screw through into a nyloc nut. This worked like a charm to keep the tool from cutting too deeply. (of course in typical Brian fashion I later dented the siding trying to make it cut deeper and forgetting about the screw.) I also employed a small piece of sheet metal to slide behind the flush mounted cor-a-vent so I could cut that out of the way as well without cutting through the Tyvek. I cut the top and bottom at a 15 degree angle to ensure that water would drain out and away.

The next step is to make a corresponding cedar block and coat the front and sides with a quick coat of Timber Pro and then goop the back with Vulkem before pressing it into place.

After that I re-drill my pilot holes from the inside also at a downward angle to both prevent rainwater from following the pipes into the building but also because all of the pipes in a passive hot water system like this need to slope upwards towards the reservoir.

The end result is a nearly flush block with the male end of two 1/2 inch copper unions just barely peeking out of the building. I like to keep things nice and tight on the sides of the trailer especially considering that our driveway is mere inches wider than the house!


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