Why is all this exterior trim rotting and how do I fix it?

Question

We realized there was some rot on the exterior of the house when we bought it two years ago, and I knew obviously I would want to deal with it eventually.

As I've been looking more around the outside of the house, getting ready for new projects (planning on painting the exterior soon) I'm noticing just how much and how bad this rot actually is.

Before I go ripping this wood off the side of the house and trying to replace it, I want to know what the actual cause may have been so I can prevent this from happening to this extent in the future. The house was only built in the early 1990s, so I feel like it's not nearly old enough for this extent of damage to happen naturally, but I really don't know.

I'd also like to point out that all that foam/silicon/paint trying to fix or hide the issue has been there from the outset; I have not touched this at all yet.

Any ideas or suggestions are greatly appreciated, thanks all.

https://i.sstatic.net/tCTpr.jpg

Answer 1

The cause is simply nature. You've got wood that's outside. It gets wet, the wet stays in the wood, the wood rots. This happens when wood is left outside in an area where water can get stuck and the wood wasn't properly installed (no caulk) and isn't properly maintained (not regularly painted/caulked).

Much of the rot seems to start near places where wood was penetrated (nails, etc) which would make sense as an initial entry point for water.

The fact that it's on a corner near a downspout is probably a contributing factor. You should watch this area of the house during heavy rain to see if the gutters/spout are leaking.

To repair - replace the wood, replace it with new wood, seal the seams between wood pieces with paintable exterior caulk. Properly prime and paint the wood with exterior paint. Apply new paint regularly as per manufacturer (the paint that is) guidelines. Also check caulk regularly for potential need to replace.

Answer 2

1. Because that's what wood does, especially when exposed to regular and/or prolonged moisture. The lack of gable overhangs on the home are a factor. Even cedar and other rot-resistant species have their lifespans, and apparently 25 years is it in your climate.

2. You'll need to replace the boards (or the portions that are decaying) with properly treated or sealed boards. The good news is that this is fairly basic (and dare I say, fun) carpentry.

Answer 3

It's hard to say for sure without pulling it apart but your pictures suggest to me that you have water getting behind the wood at that corner. The reason I think this might be the case is that you basically have no visible problem except at the bottom of the board where it intersects with a horizontal piece.

What I mean to say here is that this looks to me in picture 1 that the rotted section is where the water is exiting, not entering. Contrary to popular opinion, wood is not likely to just rot from water splashing on it. It takes a while for water to penetrate wood. Whenever I've had serious rotting issues like I see here, it's when water is trapped at some choke-point within the structure. The neighboring sections look perfect and it doesn't look like there's any significant reason less rain hits those areas.

Anytime you have a water issue, you need to make sure the roof, fascia, drip-edge, and gutters (if you have them) are all super tight.

UPDATE: Because you live in a cold area with snow, I suggest you watch the roof closely during the winter, especially in that area. An otherwise perfect roof can leak if you have an ice dam. In a nutshell, you can end up with a pool of water standing on your roof. In your area, I would expect that the roof would have some protection against this (e.g. ice and water shield) but this is typically only installed a few feet up the roof. The pitch on your roof appears to be pretty gradual which means any pooling will extend farther back and it will not shed snow as readily as a more steeply pitched roof. If you get major 'killer' icicles, it's a sign you might have an issue. Ice dams are really hard to get rid of once they form and it's freezing out so the key is to remove the snow before they form using a roof rake or roof razor.

You need to pull down the wood around that corner and make sure there is no rot in the structure. You really don't want the corner of the building sagging. If find any rot in the structure, you need to remove it and replace it with new wood. Open it up. It's scary at first but you really need to do it.

I would also recommend not painting exterior wood and use a solid stain (or at least use a 'breathable' paint) instead. Paint can end up contributing to water being trapped within wood. In theory, it should keep it out but it's never completely sealed on all edges. This means moisture in the wood can be blocked from exiting.

Answer 4

We require “back priming”. That means pre-paint all surfaces before the trim is installed...especially cut ends. End grain on trim sucks up moisture more than side grain.

Answer 5

The wood rots because water gets under the paint, but can't evaporate. The wood on the facade allows that. You can use breathable paint on linseed oil base or something similar. That will protect the wood and let it breathe. It has to be renewed regularly. That was done on my house.

On the other hand, you can use a water-resistant material to protect the structure. In that case you have to take care that there is space in the adjacent areas where the wood is furthermore allowed to breathe.

Answer 6

Softwood rots quite quickly, when water gets into it. Which it inevitably will unless you live in a desert.

One option is to replace it all with a non-rotting material such as PVC.

If you do replace with more wood, use timber that has been pressure-impregnated with preservative ("Tanalised" in the UK). Then, most importantly, after cutting to length, treat the cut ends (because the preservative doesn't go all the way through the timber). The best way to do this is to leave the timbers standing, cut end down, in a tin of the appropriate preservative for the recommended time, which is likely to be at least 24 hours. Merely painting on preservative will be much less effective.

Cutting along the grain, or planing more than a few millimetres, makes the whole exercise pointless.

In my experience, painting and sealing softwood joints does not work. Wood expands and contracts with heat and humidity. The joints soon crack and water gets in. If it gets past the preservative, the timber will rot. If not, the bare timber will last and paint is merely cosmetic. A garden shed that's manufactured as a set of panels which are then pressure-treated in their entirety will last for decades.