Sealing a new hole in existing rain screen siding
We have fiber broadband being installed in our neighborhood over the coming weeks, and I’m thinking about how to get the cable into the house and then sealing it more diligently than an underpaid contract installer is likely to do.
In a traditionally sided house a dab of sealant would probably be it, but here there isn’t really a good way to seal the penetration through the Zip behind the siding and rain screen gap that I can think of. I know in the grander scheme of things a small hole with a wire in it isn’t a huge air leak, but it does have the potential to be a bug path or method for moist air to accumulate condensation within that cavity.
Any thoughts or experiences on how to seal the hole?
Five year old house in zone 4 marine. 3/4″ Cedar board and batten over 3/8″ rain screen gap on Zip, 2×6 wall with Rockwool, 1/2″ drywall.
The house is pretty tight at 1.1 ACH and I’d like to keep it that way.
TIA for any advice.
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Replies
Andy,
For almost every penetration in a wall I like to use mounting blocks. They allow you to seal back to the sheathing and can either have a sloped top, or have head flashing installed. However for one wire over a 3/8" cavity I'd be tempted to just seal both the sheathing and cladding around the wire with caulk.
Another option is a weatherproof surface-mounted eclectic box with a hole in the cladding behind big enough to get back to the sheathing to seal the hole.
Malcolm, That's what I always do on new construction and this house has well sealed blocks for all the electrical outlets. I'm not sure if I'll have the opportunity to do this when it comes time for the install and not sure if it's going to be a fight to tell them where the cable will need to enter the house.
To put in the lines so far, they've just been rolling through the neighborhood trenching without asking and screwing the boxes to the exterior wherever they like. I just happened to be home when they were about to attach a box to my siding so I was at least able to go out there and do it myself so they wouldn't mess it up. The HOA approved this whole thing so the fiber company is just going house to house whether people want it or not.
I do broadband and fiber installations as part of my work. The best way I know to take care of those issues is to drill a 7/8" hole and insert a piece of 1/2" PVC conduit through the whole wall assembly, caulking between the building and the conduit at both ends. The remaining space is minimal (for insects) and the thermal bridging isn't terrible. After the fiber is brought in, stuff a little rock wool around the cable in the conduit, and seal that up as well. When you want to add WiFi outside your house or run Ethernet to the over-by, you can probably sneak another cable through the same conduit, saving yourself drilling another hole
Thanks! Hopefully they send someone like you to do the actual install!
From what I've seen in these installs they just plow a drill bit into the wall wherever it's convenient for them and do little or nothing to seal it.
+1 for this. I'm a contract engineer working primarily with telecom firms, and I specify wall penetrations to be done a in similar manner to this all the time
If you can't get in to caulk around the conduit in the rain screen gap, just inject canned foam around the perimeter. The canned foam will expand and seal better than caulk will if you don't have good access, and it's not going to obstruct enough of the rain screen gap to make a difference to the functioning of the rain screen itself. You can use some "duct seal", which a sticky clay-like material available in electrical supply houses and box stores, to seal around the cable in the conduit, but I prefer to just stuff some mineral wool in since it's easier to remove for service work.
Note that fiber companies are very concerned with bend radius, and usually don't want you to use LBs with conduit runs. If you need to make a 90 degree bend tight to the wall, use a 4" or 6" deep electrical box instead of an LB so that the cable has more bending space available.
Bill
Some other things to consider:
-where the wire is coming from, is the service coming in at the front and back of the house
-if overhead, where's it going to land on the house, and are you going to snake it on the exterior to where you need it to come in. Or immediate enter the house at that location.
-where do you plan on putting the modem within the house, these days the modem and router are the same device (unless you wanted to disable the router and use another) so getting it central is kind of important, depending on your house size and wall composition.
- if you're planning to snake it within the house, are you going to run it through an attic? Or basement? Would it be better to pre do a conduit to run it where you need it?
All this to say, it's a good idea to preplan this because maybe you don't need it coming through the siding.
Otherwise, you could get crafty with air sealing. The other ideas mentioned are excellent. If a minimalist look is important, you could also cut a square section of your cedar siding out, giving you access to the zip. Drill a hole through the cut section and feed the fiber wire through it, drill into the house and detail the hole with silicone, or zip sealant. And fasten the siding back.
The two cuts wouldn't be too intrusive to the aesthetic, depending on where it is, if it's eye level or up above etc.
Hope this helps,
Jamie