keeping a converted garage dry

[DougL]

OK here's a tricky planning problem. I have a converted garage where the outside wooden wall drops down to contact the driveway. The driveway slopes down toward the wall so, in a hard rain, water tends to puddle up against the wall and it leaks through into the interior. Yes, the driveway under the wall is mildly depressed, so the water SHOULD run off, but if the rain is hard it doesn't quite run off fast enough. Exacavating a drain in the concrete is not feasible, because there isn't much of a drop-off at the edge of the driveway. (Drain contractors have confirmed this. They recommend against that.) So the question is, how do I keep the lower edge of the wooden wall dry when there is a shallow puddle up against it? We're talking just an inch or so. The bottom of the wall is more than an inch below the top of the slab on the side.

Now, I could always just put in a a line of brick or concrete at the base of the wood, but mortar and concrete are somewhat permeable, and really wouldn't be very effective in keeping all the water out. But maybe a WIDE concrete barrier in front of the wall? Or else tile glued onto the wall with some kind of thick sealer at the base? Maybe a waterproof caulk? Is there some variety of concrete that is NOT permeable to water?

See photo below of the left side of the wall.

 

[Sparky617]

I would find a way to get the wood off of the concrete. That is never a good idea. I would cut off the bottom 5.5" of the T1-11 and install a piece of PVC trim between the bottom of the shortened T1-11 and the concrete with a good silicone caulk sealing the gap between the PVC and the concrete. Don't use that between the PVC and the T1-11 as it doesn't take paint. Also, too late now, but for T1-11 I prefer Hardi-panel T1-11 over the wood stuff. It is easier to paint and isn't subject to rot like wood.

This is the product I'd use between the T1-11 and the concrete.

https://www.lowes.com/pd/Royal-Building-Products-0-75-in-x-5-5-in-x-8-ft-PVC-Trim-Board/5002041393

 

[DougL]

Thank you. That's a very sensible solution. Should I affix the trim board to the siding with screws, or just epoxy it on? Probably no need to slice off the siding. Doesn't matter much what happens to the bottom it where it contacts the concrete and ideally it will stay mostly dry anyway. You're saying the PVC doesn't take paint? Not a big deal. Why should I not use caulk between the PVC and the trim boards? If I'm going to use it where the PVC contacts the concrete, I might as well use some higher up.

 

[Sparky617]

Thank you. That's a very sensible solution. Should I affix the trim board to the siding with screws, or just epoxy it on? Probably no need to slice off the siding. Doesn't matter much what happens to the bottom it where it contacts the concrete and ideally it will stay mostly dry anyway. You're saying the PVC doesn't take paint? Not a big deal. Why should I not use caulk between the PVC and the trim boards? If I'm going to use it where the PVC contacts the concrete, I might as well use some higher up.

The PVC will take paint, but it doesn't need to be painted. I used that for trim on my attic dormers and painted it to match the trim on my house. I paints well and can be installed with the wood grain exposed or the smooth back side exposed. Pure silicone caulk won't take paint, but is a better solution than painters caulk for sealing the bottom to the concrete. Between the T1-11 and the PVC paintable caulk would be better. I lean towards cutting the bottom off because you'll have gaps at the grooves of the T1-11 and the PVC if you just apply it to the top. Plus I'd want to get the wood off of the concrete.

Any job worth doing is worth a new tool. If you don't already have a multi-tool/oscillating saw, this would be the project to justify it. you can use a circular saw for the longest part of the cut with it adjusted just to the depth of the T1-11, and finish the ends off with the multi-tool.

 

[DougL]

Ah, it's the caulk that doesn't take paint? No sweat. I can have a bead at the bottom with a different color. Now, I have to assume that the underlying studs behind the trim are contacting the concrete as well, and I'm sure not going to saw them off. So I guess I have to wonder why I should worry about sawing off the trim. The purpose of the PVC and caulk is to protect everything behind it. Can I assume that silicone caulk will take weathering, and have a significant lifetime? I'd rather not have to recaulk every few years.

I should also ask ... what's the best way to slice off a strip of the PVC trim board? Do a get a neat cut if I just use a circular saw?

Well, I take that back, a 5" wide trim board doesn't need any slicing! I like the 0.75" thickness of this stuff. You can get a wide bead underneath it!

 

[slownsteady]

Another concern, besides the puddling of water, is the moisture that is being absorbed into the wall. Hopefully the base plate of the wall is pressure treated. and sitting on a sill seal.
Another possible solution is flashing. You would still need to cut back the T1-11. Then install flashing six inches up the wall and turning out away from the wall - essentially like step flashing on a roof. You would need to seal the flashing down to the concrete. Then I would cement over the flashing feathered out to create a slight slope away from the wall.

I'm writing this on the fly, so I'm sure there's more details to consider in this method.

 

[DougL]

Well, that's what Sparky617 is proposing. Essentially installing PVC flashing, and sealing it to the concrete with caulk. Still not sure why I need to cut back the T1-11. If it's behind the flashing it's not going to be exposed to any liquid water. Though yes, to the extent the concrete can get damp by just wicking up moisture the T1-11 would not like to be sitting on it. But it's been sitting on it for 40 years and looks fine.

 

[Sparky617]

Well, that's what Sparky617 is proposing. Essentially installing PVC flashing, and sealing it to the concrete with caulk. Still not sure why I need to cut back the T1-11. If it's behind the flashing it's not going to be exposed to any liquid water. Though yes, to the extent the concrete can get damp by just wicking up moisture the T1-11 would not like to be sitting on it. But it's been sitting on it for 40 years and looks fine.

You could just apply the PVC to the T1-11 but at every groove you'll have a gap to fill. Alternatively, you could cut into the T1-11 and slide a piece of Z-channel flashing behind it and have it come over the top of the PVC trim. I like to try to direct water away and not count on caulk to keep things sealed. Flashing would help do that. There are any number of ways to address your issue, I'm looking at ways to do it with the least work. I don't like to see untreated wood in direct contact with concrete.

 

[DougL]

Not sure why I have to fill grooves in the T1-11. The T1-11 is going to be firmly behind the PVC, and as long as the water doesn't get any higher than 5 inches, it won't drip into the grooves. There is substantial fascia overhead, so no rain is coming down on the wall itself. As I said, if you want to worry about the T1-11 getting wet, you have to worry abut the underlying studs as well. They sure aren't PT. Z-channel flashing is an interesting idea, but the PVC is already 0.75" thick. You'd still have to rely on caulk under that flashing. I don't see how the Z-panel flashing would avoid that. That water is sliding down the concrete, and it will slide right under the flashing if not for caulk.

 

[havasu]

I would find a way to get the wood off of the concrete. That is never a good idea. I would cut off the bottom 5.5" of the T1-11 and install a piece of PVC trim between the bottom of the shortened T1-11 and the concrete with a good silicone caulk sealing the gap between the PVC and the concrete. Don't use that between the PVC and the T1-11 as it doesn't take paint. Also, too late now, but for T1-11 I prefer Hardi-panel T1-11 over the wood stuff. It is easier to paint and isn't subject to rot like wood.

This is the product I'd use between the T1-11 and the concrete.

https://www.lowes.com/pd/Royal-Building-Products-0-75-in-x-5-5-in-x-8-ft-PVC-Trim-Board/5002041393

Before even reading the responses, this was exactly my thoughts. Wood touching concrete in any fashion is a "no-no", and PVC makes a great bridge between products.

 

[DougL]

I agree but, like I say, the siding has been touching the concrete for at least 40 years, and the siding is in fine shape. The water only gets up to less than half an inch below the siding once every few years, and the flooding itself happens maybe once a decade, so the concrete under the siding is staying pretty dry already. We're talking about a simple fix to an engineering/architectural error, that's for sure.

I was just out there with my stud sensor, and I can find the studs, so anchoring the PVC trim board to the studs ought to be straightforward. (The nails for the trim were painted over, so I can't find them!)

 

[Sparky617]

Not sure why I have to fill grooves in the T1-11. The T1-11 is going to be firmly behind the PVC, and as long as the water doesn't get any higher than 5 inches, it won't drip into the grooves. There is substantial fascia overhead, so no rain is coming down on the wall itself. As I said, if you want to worry about the T1-11 getting wet, you have to worry abut the underlying studs as well. They sure aren't PT. Z-channel flashing is an interesting idea, but the PVC is already 0.75" thick. You'd still have to rely on caulk under that flashing. I don't see how the Z-panel flashing would avoid that. That water is sliding down the concrete, and it will slide right under the flashing if not for caulk.

Water coming down the face of the T1-11 would flow into the gap between the PVC and the T1-11. That is why I'd cut it off and not depend on caulk to seal that joint. I've done enough rot and insect damage repairs over the years to try to eliminate the paths for it as much as possible. The Z-channel would direct it out away from the junction between the T1-11 and PVC trim. Flashing anywhere on a house doesn't count on mastic or caulk to work. It works using gravity not fighting it. YMMV.

 

[DougL]

Well, as I said, there is 18" wide fascia keeping the rainfall off of the T1-11 siding, so there is no water coming down face of it. Ever. The siding is ALWAYS dry. So unless the flood gets deeper than the PVC trim is high (5 inches), no water will ever get in the T1-11 siding gaps. Just no way for it to get in there. Just gotta keep my lawn sprinkler away from that wall! I need the caulk specifically to seal the gap between the concrete and the PVC trim.

Just a thought. Instead of using PVC trim, would it be stupid to just use PT 2x6 with caulk underneath? Slightly cheaper.

 

[Sparky617]

Well, as I said, there is 18" wide fascia keeping the rainfall off of the T1-11 siding, so there is no water coming down face of it. Ever. The siding is ALWAYS dry. So unless the flood gets deeper than the PVC trim is high (5 inches), no water will ever get in the T1-11 siding gaps. Just no way for it to get in there. Just gotta keep my lawn sprinkler away from that wall! I need the caulk specifically to seal the gap between the concrete and the PVC trim.

Just a thought. Instead of using PVC trim, would it be stupid to just use PT 2x6 with caulk underneath? Slightly cheaper.

Doug,
Water has a way of finding its way into things. Your 18" overhang isn't going to protect this in a driving rain. Or if you pressure wash the siding in preparation for painting, or your sprinkler misfires. At a minimum I'd seal those grooves from above , but like I said earlier, you don't want to count on caulk beating gravity. Gravity isn't just a good idea, it's the law. Caulk fails and water will take the path of least resistance. Adding the PVC to the bottom and not having a fool proof way to keep water out of the gap between it and the siding is a sure way to trap water there, that will have no way out. I've seen water find its way into too many places causing havoc. But you do you.

 

[DougL]

I've never seen the wall get wet, even in a hard rain, BUT, the point about pressure washing is a very good one. If water does get into the gaps and gets trapped there, it'll take a long time to evaporate and would probably dribble through the wall. So how do you suggest I fill the gaps? I could just plug them with caulk at the top edge of the PVC trim. That would be pretty easy, as long as I'm laying down a lot of caulk at the bottom. The Z channel would keep water out of the gap, but I'm just reluctant to go cutting into the T1-11 if I don't have to.

But let me ask again about using PT lumber instead of PVC trim. Is that a stupid idea? It doesn't care about getting wet, but the seal with the caulk might not be as clean.

 

[Sparky617]

Personally, I'd use the PVC. It won't soak up water, split, crack, or warp. PT wood will do all of those things. PT wood is a poor choice for finish lumber. If you don't want to do what I've recommended with cutting out the bottom 5.5" of wood, I'd use silicone caulk (non-paintable) to fill the gaps in the grooves completely. Then after it dries I'd apply a bead of paintable caulk across the top between the T1-11 and the PVC. IMO it would not be the best solution, flashing would be the best solution but that will require cutting into the T1-11.

 

[DougL]

The gaps in the T1-11 are 1.5" wide and 3/8" deep, on 9" centers. A few tubes of caulk should fill them pretty well. In principle, I can do some of that caulking witht the non-paintable caulk just before mounting the PVC trim, so I can just press the PVC trim onto that caulk in the T1-11 gaps. I can then fill in the tops of the gaps when the trim is affixed with the paintable caulk along with a line across the top between the PVC trim and the T1-11 siding.

OK, this is excellent. I think I have a plan. Many thanks for your insights and consideration.