Finish for Deck Surface
I’m looking for some ideas for deck finish options for our new house. The house will have a raised deck that is just below the living area, to avoid steps between the two areas. The deck will be supported by 2x framing, resting on concrete stemwalls similar to a crawlspace. The surrounding grade will be brought up to within 6″ of the deck surface to reduce steps between the deck and the yard.
Our architect is showing wood boards for the deck, but I would like to avoid wood or composite boards. I’d love to have some kind of a continuous deck surface, such as concrete or lightweight pavers (I realize that this would require more deck support).
Can anyone suggest some type of a continuous surface finish for this type of deck?
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> The house will have a raised deck that is just below the living area, to avoid steps between the two areas.
Kind of a funny detail to have a stem wall like that for a deck. Where are you located? I ask because if you have snow, no step down can be problematic for snow build up against the bottom of the door, which can become a water issue.
> The surrounding grade will be brought up to within 6″ of the deck surface to reduce steps between the deck and the yard.
What about the grade at the bottom of the "crawlspace"? I worry about this taking on water, particularly if it's lower than surrounding grade.
leon_g,
I share your dislike of wood surface decks and have done this several times. You have essentially two options: You can strap the top of the deck with 2"x4"s and simply use any of the common patio stones, or use one of the propriety systems designed to support a range of solid pavers. In both cases you will need to beef up the framing to take the extra dead load of the pavers.
If you go the first route, apply gaskets to the top of the strapping to stop the stones from rocking.
There are all sorts of proprietary systems. Here is one example: https://www.decksgo.com/paver-deck.html
Make a raised paver patio instead.
Replace the poured concrete footings and stem walls with segmental retaining walls, remove ledger, add a srw there with an air gap from the structure. Include drain tiles. Fill with compacted, open graded crushed 3/4" stone. Top with 1" bedding layer of 3/8" rock chips. Lay pavers.
There are more details that go into it but thats the general idea. I find that for 2' or less of elevation it is usually about the same cost or less as a well built composite deck.
Taller than that you can pour a concrete deck on piers and beams and lay pavers on that. No wood.
> Replace the poured concrete footings and stem walls with segmental retaining walls, remove ledger, add a srw there with an air gap from the structure. Include drain tiles.
Can I assume the retaining wall against the foundation gets you around worrying about additional unbalanced fill against the house foundation walls?
Having a true "air gap" there seems like it would invite debris and critter build up. How do you tend to detail it?
(I've been planning for a < 30" above grade deck immediately out my back door and now you have my mental gears turning...)
>Can I assume the retaining wall against the foundation gets you around worrying about additional unbalanced fill against the house foundation walls?
Yes, and also to keep everything away from the wood rim joist area. I've only done this with 8" poured foundation walls, open graded stone and pavers aren't going to add any more pressure than potentially saturated soil in a full basement situation.
<Having a true "air gap" there seems like it would invite debris and critter build up. How do you tend to detail it?
Run the srw's perpendicular to the house closer to the house, and close up with a combination of flashing, backer rod, and sealant.
I let my border pavers cantilever over the wall block and be nearly tight to the sheathing. Install the pavers, which requires sealant in the joints that hang over the srw so you don't lose all your paver sand into the air gap. Then depending on the cladding, put a piece of aluminum flashing over top, sealing to the pavers.
Currently working on a ICF house with brick veneer, I will just seal the joint between the pavers and masonry.
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May be worth looking into Porcelain pavers. They are almost designed for situations like this.
Thanks for the suggestions, gives me a lot to think about. It looks like there are two possible options - porcelain pavers over the raised framing, or bring the grade up higher and avoid that deck "crawlspace".
Our house is a bit unusual because it is a modular home, so it is built in the builder's factory then brought on site and dropped (hopefully not literally) onto the foundation. That's why the floor joists have to be on top of the foundation. So to meet code requirements of 6" between wood and grade, the finish floor ends up being about 15" above grade, as shown in the sketch I attached earlier. So the architect specified that "crawlspace" type deck system to avoid steps, but still meet code.
@Patrick_OSullivan - the project is in Portland, so not much snow. Also, most of the deck will be covered by a roof overhang. There will be at least 5' of overhang beyond the exterior door openings.
@MALCOLM TAYLOR and @Andy2022 - thanks for the suggestions about porcelain pavers, they look like a good choice for use with a system like Silca Grate. I wonder about the relative cost of using the Silca/porcelain system compared to composite deck boards? I can estimate the materials easily, but labor is a wildcard. What can I expect the installed cost to be for the two systems (assuming hidden fasteners for the composite boards) - similar, 2X, 3X?
@JustusM - I would really like to do what you are suggesting (i.e. avoid the whole raised deck structure, and just make it a patio rather than deck). Can you expand a little more about the construction details of what you are proposing? What is srw? Any chance you could post a sketch of the system?
I'm not completely sure about code requirements, but I'm wondering if something like the attached sketch would be possible - essentially bring that outer stemwall to the foundation wall, and then simply build a patio on the grade (either a concrete slab or some paver system). Does this violate some code requirements?
Leon,
Here is a sketch and a picture. SRW is segmental retaining wall, dry laid block on a stone footing. In my area at least significantly cheaper and more attractive than a poured wall. Instead of pouring another stem wall and footing you could also have a brick ledge incorporated into the house foundation, or reduce the foundation wall to 4" and drop in your floor system, eliminating the wood rim joist and sheathing in this area that would be below grade. Then you wouldn't need an additional wall against the house period. I would also fill the foundation hole overdig area up completely with open graded stone from the footing drain up in the area you want a patio. If you don't you really need to compact the overdig fill. Keep in mind I live in rural Iowa, with good stable soils and no code enforcement so your mileage may vary.
JustusM,
The times I've used pavers suspended on woof framing have all been retrofit situations, which were really only geared to getting rid of the wood decking.
On new construction close to grade, I agree it makes more sense to go with an elevated patio, and also to use a less permanent foundation that poured stem-walls. It makes even more sense to do as you suggest and deal with the elevation problem at the house by dropping the floor structure. That opens up all sorts of options, and makes for a seamless transition out into the yard.
Thanks JustusM, I really appreciate this detail. I think that would have been a good way to go. Unfortunately we're already in the permit review phase, and I think that changing the foundation type, along with the rim joist framing etc, will be too much of an undertaking.
But I would like to build on the idea of losing that deck crawlspace, and instead building a patio right on grade (with whatever base would be needed).
As I understand things, it's OK to have wood below grade level as long as there is no direct contact, e.g, if the concrete foundation extends above the grade.
So what if I did something like in this attachment - basically pour a second concrete barrier, along the foundation wall, to create that pocket that you were referring to. They would run the WRB down the outside of the barrier wall, just like they were going to do with the foundation wall.
Then we could bring up the grade to whatever level we needed and install a concrete patio, pavers, etc - no wood! Also we wouldn't need that second stemwall at the perimeter of the deck.
Does this look reasonable? Or would this violate some code requirement?
In this diagram, is "VB-2" a vapor barrier? If so, this is a recipe for disaster. You have wood below grade exposed to a moisture source on one side, with a vapor barrier on the other side that would prevent it from drying.
Good question! VB-2 is actually a Vapor Retarder, not a Vapor Barrier. I think that it will allow any moisture in the wood to escape, right?
The image provided describes VB-2 as "6-mil vapor retarder sheet product". That sounds a lot like 6 mil poly, which is a vapor barrier.
As an example, Here's the data sheet for "STEGOCRAWL® WRAP 6-MIL VAPOR RETARDER": https://www.stegoindustries.com/hubfs/Data-Sheets/StegoCrawl-Wrap-Vapor-Retarder-6C-Data-Sheet.pdf
It has a perm rating 0.04, which would be considered a vapor barrier.
I would not install such an assembly.
I have done a few decks like this. I used porcelain pavers. The last 2 I did were from Mbrico. https://www.mbricotiledecks.com/
It prices out close to what an Ipe deck would cost. Install is much faster than Ipe. You can do this right on top of wood framing with their clip/rail system. On a project I just finished I had the tiles over a living space so this was on a roof deck. For that one I used Bison pedestals.
gawdzira,
Nice! It looks great, and I bet is pretty maintenance-free.
That looks like a really nice system too. And a pretty quick install, which is nice. Thank you for that lead.
Sometimes, it's best to embrace the constraints instead of working around them. The options look expensive and/or they have some major downsides (such as becoming a place to collect water and critters, future maintenance requirements, extreme challenges with respect to any problems you may need to address at the rim joist in the future, etc.)
I'd give very serious consideration to having two or three steps down to a patio. It's a more robust design with a lower risk of water or snow against the bottom of the door. It allows you to keep water away from your foundation. It doesn't introduce hard-to-predict and hard-t0-model risks associated with potential rot of your rim board. You don't need to deal with a ledger board and all of the flashing and risks associated with deck to house connections. It's easier to hose off without getting water in your door. If done right, the patio won't need any major maintenance for decades. It will never rot. You can place hot tubs, etc. on the patio with no concern for moisture or weight capacity issues. It will be more fire resistant. It will give you an extra 16" of ceiling height in the patio area (consider adding some lights and maybe a fan.) Doing it this way will also provide you with better sight lines out of your house, especially when you throw in a few patio chairs and a table - drop those 16" lower and they no longer block your view when you are sitting in a chair inside your house.
And on top of all of that - it will probably be cheaper!
If I were you, I might even think about how I could go a little lower than 16".
I appreciate the thoughtful response and suggestion. Stepping down onto the patio certainly has its advantages. But we really would prefer to avoid steps - we're both retired and are not getting any younger, so less steps = less tripping/fall hazards.
I really would like to do something similar to this - https://www.greenbuildingadvisor.com/question/concrete-patio-floor-at-same-elevation-as-interior-finish-floor.
I realize that we have the added complexity of the floor joists sitting on top of the foundation, but I'm hoping to come up with a barrier/drain system that would allow us to bring the patio level up higher. I don't want it to be level with interior floor, just a couple of inches lower would be perfect.
I would combine these into one.
Wait to backfill the foundation until after the house is installed. Run self adhered water proofing up the foundation all the way to above the rim joist. Dimple matt over that. Backfill and retaining wall for the patio but I would still include a trench drain by the door.
Akos, could you clarify what you would combine into one?
Also, would the self adhered water proofing and dimple mat sufficiently isolate the wood rim joist from the backfill? That has been the architect's constant pushback about doing a patio.
Your sketch in #8, Justus in #10 and the Malcolm's suggestion in the link.
This would be (from the inside):
-peel and stick up to the wall
-dimple matt down to the footings to the weeping tile drain to daylight.
-SRW up to height, trench drain on top along the house.
-backfill for patio area
This way most of the bulk water is handled by the trench drain. The trench drain can also be cleaned so less chance of it getting clogged like the dimple matt would if it had to handle a lot of water/debris. The backfill is also resting against the SRW instead of directly on the dimple mat.
In that case, the plan you posted in your original drawing may be a great option. That way, you can use all of the traditional and proven flashing and decking methods to attach to the house.
With respect to the deck surface:
- As others have pointed out, there are systems that will allow you to use pavers or tiles on top.
- Here is one system you may want to look at: https://paverdeck.com/
- These folks have an alternative to deck boards made of some type of stone or porcelain: https://www.tanzite.com/appalachian-collection
- You might also consider a high quality composite board. If a lot of it is covered by the ceiling and you get a high-end product, it may be appropriate for your application.
My main concern with a deck in this application is that you want the framing to breathe so that it can dry out after it rains. What are the dimensions of the deck? If you leave the two sides open (don't install stem walls on those two sides or bring those two sides to grade) then air will be able to flow through.
The deck is large, about 1000 sq ft. I also don't want this dead space for moisture and pests, that can't properly air out.
I just need to find a robust way to bring the finished surface up higher, while still isolating the wood form the backfill.
You need more than that though. In your current assembly, your vapor barrier is on the inside. With your proposal, you will have a vapor barrier on the outside (to isolate the rim board from the backfill). So you would need the inside to be breathable but that may be a more significant change to your overall envelope design. Do you know what climate zone you are in?
Patrick, looks like I can't reply to your post about the vapor barrier.
You said: > You have wood below grade exposed to a moisture source on one side, with a vapor barrier on the other side that would prevent it from drying.
I'm not sure how the wood in the structure is exposed to moisture on one side - it's covered by the waterproofing membrane on one side, and the vapor retarder on the other. Am I missing something?
> I'm not sure how the wood in the structure is exposed to moisture on one side - it's covered by the waterproofing membrane on one side, and the vapor retarder on the other. Am I missing something?
I can't quite see the waterproofing detail on the exterior side, but regardless, it's wood below grade that has no clear drying path if it gets wet. It would concern me.
Leon-G,
Leaving aside Patrick's concerns of having the rim-joist area sandwiched between two impermeable surfaces, even if there was no exterior membrane (as there will not be in areas of the house where there is no deck), the rim-joist detail is risky because it has a wrong side vapour-barrier with permeable insulation on the inside.
The usual detail there is to use either spray or rigid foam to insulate the rim-joist, as permeable insulation allows interior moisture to move through it and condense on the lumber. https://www.greenbuildingadvisor.com/article/insulating-rim-joists
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Please stop changing the titles of existing threads!
Oh my word...
Word! I don't know why they keep poing that, I can't find my own threads.
My guess is a misguided attempt at search engine optimization.
@Akos >
This would be (from the inside):
-peel and stick up to the wall
-dimple matt down to the footings to the weeping tile drain to daylight.
-SRW up to height, trench drain on top along the house.
-backfill for patio area
This way most of the bulk water is handled by the trench drain. The trench drain can also be cleaned so less chance of it getting clogged like the dimple matt would if it had to handle a lot of water/debris. The backfill is also resting against the SRW instead of directly on the dimple mat.
Thank you, that makes sense!
Thanks for the points about the poorly insulated rim joist, and the rim joist sandwiched between two impermeable membranes. I read the rim joist insulation article that Malcolm posted, it's very helpful.
So should I ask the architect to specify spray foam insulation at the rim joist, and then have no vapor barrier at all on the inside? Or should we look for some type of a permeable barrier (smart vapor retarder)?
We have a conditioned crawlspace, so I think the architect wanted some type of encapsulation, but I want to make sure it's detailed correctly.
Really appreciate all the suggestions here.
Malcolm, in your comment "the rim-joist detail is risky because it has a wrong side vapour-barrier with permeable insulation on the inside. ", did you mean to say "impermeable"?
Leon_G,
No it's the permeable insulation that is the problem, and why they recommend spray foam or foam board instead in the link I posted.
With the detail shown on your section, moist interior air will move through the batts and condense on the cold vapour-retarder. That problem is independent of whether there is a deck outside or not.
Malcolm,
Gotcha - you are referring to the permeable batt insulation. I was confusing that with the vapor barrier, which is impremeable.
Doesn't the fact that vapor barrier extends all the way to the top of the rim joist prevent moist air from contacting the rim joist though?
Leon_G,
Problems in walls caused by interior moisture moving through them occur on what they call "The first condensing surface". That is the first surface cold enough to cause the moisture to either wet the material faster than it can dry though diffusion, or have water bead on its face. So yes, in your assembly that first condensing surface is the poly rather than the rim-joist, but that just transfers the possible damage from the rim-joists to the sill-plate and ends of the floor joists.
I've been reading about crawlspace encapsulation, and every article I read says that a Class I barrier must be used (i.e. impermeable). In fact, the code seems to say the same thing:
" R408.3.1 Unvented crawl space
Ventilation openings in under-floor spaces specified in Sections R408.1 and R408.2 shall not be required where the following items are provided:
Exposed earth is covered with a continuous Class I vapor retarder. Joints of the vapor retarder shall overlap by 6 inches (152 mm) and shall be sealed or taped. The edges of the vapor retarders shall extend not less than 6 inches (152 mm) up the stem wall and shall be attached and sealed to the stem wall or insulation."
So how should we comply with this without trapping moisture in the rim joist? It seems like an over-constrained problem. Or are we saying stop the barrier below the sill plate?
Leon_G,
"So how should we comply with this without trapping moisture in the rim joist? It seems like an over-constrained problem. Or are we saying stop the barrier below the sill plate?"
It is kept safe by allowing drying to occur to the outside. That's one of the dominant themes of this thread. The rim-joist has to be insulated sufficiently to stop condensation, and the material you use to insulate it has to be an air and vapour-barrier. That basically leaves you foam board or spray foam.
The problem you face is ensuring the the walls can dry to the outside with the deck assembly you are proposing.
Malcolm,
So does this mean that there is no way to have the detail I want, a patio that is close to the level of the interior floor?
It seems like all the solutions offered (which made sense to me) use a waterproof barrier on the outside of the rim joist (to keep outside moisture out). But if there is no way to have a robust vapor permeable barrier inside, then the rim joist becomes trapped and can't dry out.
So I'm out of luck?
It just seems hard to believe that there is no workable solution for this. Maybe I can compromise in some area to make it work?
BTW, I'm attaching the relevant sections of the permit set to show how the wall sections are specified, and how the WRB and VB are routed. It's interesting to note the statement on the drawing that "All framed walls, floors, and roofs/ceilings that are elements of the building envelope shall have a Class II vapor retarder installed on the warm-in-winter side of the insulation per ORCS R318.1". So it looks like a Class II VB is required everywhere on the inside.
I should probably start a new thread on this, and just focus on air and vapor barriers, since we've gone off the topic of deck surface finishes.
Vapor retarder is not the same as a vapor barrier, which should allow your rim joist some drying to the inside. Condensation on rim joists is mostly a cold climate problem. Usually the bigger issue with rim joist rot is water leaks or capillary wicking up through the foundation.
Important detail there is the crawlspace needs to be conditioned, lower humidity in there will also help with drying.
Also your drawings show fluffy in the floor joists. If you are already insulating the stem walls in the crawlspace, this is not needed, if anything it can create issues.
Thanks Akos - so as I understand your reply, you're saying to retain the vapor retarder on the inside as shown in the drawings, because condensation is not as much of a concern in my climate (4C)? And then just go with the waterproofing on the outside where the patio will be, as you described earlier? I do like this approach because any change at this point is going to be a bit of a struggle with our architect and builder.
Would you also recommend spray foam at the rim joist - or would that prevent drying to the inside?
And that's a great point about the fluffy insulation above the conditioned crawlspace, seems redundant to some extent. Maybe that's because the rigid they are specifying for crawlspace walls and floor is only R15-R20, and they need R30 for the underfloor by code? But they are showing R38 for the underfloor. Can we not take credit for the crawlspace floor rigid?
What issues do you see with the fluffy in this situation?
Leon_G,
All my comments have been how to safely insulate the rim-joist area. Let's put that issue to bed.
Moving to the outside: In the areas where there is no deck, the rim-joists can dry to the exterior, because you have a permeable WRB. Isn't your whole problem that rather than use the same mechanism where there is a deck ledger, that you want to cover the whole area in an impermeable membrane, which stops the drying to the outside?
Why not treat the whole wall the same way, with the same drying paths, install a properly flashed ledger and be done?
Malcolm, I just wanted to clarify this point:
" Isn't your whole problem that rather than use the same mechanism where there is a deck ledger, that you want to cover the whole area in an impermeable membrane, which stops the drying to the outside?
Why not treat the whole wall the same way, with the same drying paths, install a properly flashed ledger and be done?"
So you are suggesting that we NOT put any waterproofing membrane on the outside of the rim joist where the patio will be, and let it dry out to the outside? By having an air gap and free draining stone next to the exterior, like JustusM is suggesting?
Leon_G,
Sorry I hadn't followed that you had decided to go with a raised patio and not a deck. That actually makes things much easier. Insulate the rim-joist area with foam board on the exterior and all the moisture problems disappear. You can protect the area with membrane, as it can dry to the interior.
> You can protect the area with membrane, as it can dry to the interior.
But as drawn, there is a vapor barrier on the interior. So, to be clear, if you put rigid foam at the rim joist exterior, I think Malcolm would agree with the idea that you'd have to remove the discrete vapor barrier and any impermeable insulation inside.
Patrick,
Yes, good point. It's an either/or choice as to where the foam should be located - and the interior discrete vapour-barrier should go.
He could just flip it at the patio, or locate it at the exterior of the rim-joist everywhere.
In either location it should conform to the minimum R-values and ratio of permeable to impermeable insulation for that climate zone.
If you have an air gap between and free draining stone and tile below, why does the rim joist area need to be treated any differently than the rest of the wall assembly?
Or how is this assembly any different than a raised stoop poured against the wall?
Very common here to include a stoop foundation with the house foundation, fill that area with soil and or stone, cover sheathing with wrb and or some flashing and pour a concrete cap on it. Not saying that doesn't have some potential issues, but I have seen it done for 20 years and can't recall seeing or hearing about that causing a problem. Deck ledgers on the other hand. . . .
>".. how is this assembly any different than a raised stoop poured against the wall?
Very common here to include a stoop foundation with the house foundation, fill that area with soil and or stone, cover sheathing with wrb and or some flashing and pour a concrete cap on it."
That's what I keep pondering - it's fairly common to have a concrete stoop against the house, level with the interior floor (or a couple of inches below), and against the rim joist.
Maybe this is not ideal in the perfect world, but we have to make compromises sometimes, and I think that having a non-step-down patio is important enough to me that I'm willing to take some risk of slightly reduced longevity of the structure. I obviously don't want to have something built that will make the home uncomfortable or defective from the outset, but if I get 30 years out of some parts of it instead of 50, I would be OK with that.
JustusM & Leon_G,
"Not saying that doesn't have some potential issues, but I have seen it done for 20 years and can't recall seeing or hearing about that causing a problem."
"but if I get 30 years out of some parts of it instead of 50, I would be OK with that."
Those brings up couple of issues:
- There are all sorts of local practices that are risky that builders justify by saying they have been using them for decades and haven't noticed a problem. On its own, I don't think that's a useful endorsement.
- There are some parts of a building - like the roofing - we expect to replace periodically. The load-bearing structure isn't one of them. Building a house where that structure has a good chance of needing remediation in 30 years may work for the initial owner, but the chances are in 30 years they will have left the problem for the future occupants. That's both sort-sighted and unfair.
Malcolm,
Fair point, I certainly don't want to have a substandard house built. I'm balancing between a perfect house that may never be built (because our architect and builder may not want to do things that way) vs a house that is not perfect but still meets all code and good design practices (even if maybe not best). I'm just saying that I am OK with the latter.
I need to get back to you and Patrick on the other posts you made, I'm having a hard time seeing how exterior rigid would work with our detail, since the rim joist extends to the level of where the patio top will be, so I'm not sure how we would use rigid on the outside, and still have the drain channel. I'll post a picture.
It seems to me that the better way to go is what you suggested as the other option - waterproof the outside, and allow the rim joist to dry to the inside, by stopping the VB at the top of the stemwall. I'll post that picture too.
Leon_G,
I would suggest something along these lines:
- Since you only need the exterior foam at the rim-Joist, inset the foam so it doesn't interfere with the exterior patio.
- Cover the exterior of the sheathing with an impermeable membrane, from the floor down onto the foundation. Provide protection for this - flashing or a similar material that will last - as the area becomes inaccessible once the patio is built.
Her is a rough sketch to give you some idea of what I'm trying to describe.
Malcolm,
Thanks for the sketch, I see what you mean. I think that at this point of the design and permit process, this would be too big a change for us to try to undertake.
What if I tried the approach of drying to the inside? Then we can install the waterproofing membrane on the outside, along with the trench drain, maybe the SRW, etc, that were suggested earlier.
Can we do that by stopping the VB at the top of the stemwall, and using open cell spray foam all along the rim joist and sill plate, like in the picture below?
Leon_G,
I'm not sure how helpful I'm being. Your questions might benefit from a fresh perspective. Hopefully some other posters will chime in.
How about one more option.
Go with regular infill, bring the grade up to code max bellow the joists.
On top of that, set retaining blocks about 3" to 4" away from the wall up patio level, infill, lay larger patio pavers cantilevering to the house a bit while still keeping say a 1" gap.
This keeps the rim joist clear, the patio pavers can always be lifted for access and there is no soil resting against the house.
Instead of a gap, a trench drain by the house would still be a good idea though. Some critter proofing would also be needed but not as big an area as a whole deck.
Malcolm
"I'm not sure the mandate of GBA is to give advice on what we can get away with that might work over the short term."
I agree and that is not what I intended to convey. The potential issues was alluding to were more along the lines of improperly flashing or drainage allowing bulk water to get to the rim joist area. Just as deck ledgers and windows have potential issues.
I have a question as to why the rim joist in this section can't be treated the same as the rest of the wall, assuming bulk water isn't getting behind the flashing and wrb, it is going to be very difficult for water to jump the air gap and get to the sheathing/rim joist. Assuming those things why can't a permeable wrb be used to allow it to dry into the air gap? Similar to a brick veneer wall would be.
>"Assuming those things why can't a permeable wrb be used to allow it to dry into the air gap? "
JustusM, I'd like to know that too, because it seems that this would allow me to have the pation I want.
Also, any chance you could post a higher resolution picture of your approach, I can't quite make out the words in the labels. Or email me a copy?
Leon,
Hopefully this works, highest resolution I can fit in file size.
JustusM,
You are quite right. That was an unnecessarily harsh interpretation of what you were suggesting - caused in large part to my posting after day spent in a rat infested 18" crawlspace where I managed to cover my head with cuts and bruises. I have edited my post, and let me start again.
I think relying on the air-gap is problematic for a couple of reasons, although maybe it could be detailed to mitigate the worry.
When I have worked on old houses, my experience is that if there is moisture damage, that's where I will find it. The gap relies on being kept open to allow the drying. When I have worked on them I invariably found they have accumulated debris over time, which stays wet in the largely enclosed space.
The other problem is that the area is inaccessible both for routine maintenance, or eventual replacement of the cladding. It's akin to the situation you often see on spaced ledgers on decks. You can't paint or replace the cladding behind - and there is where it is most vulnerable.
If you can come up with a detail that allows the area both to dry into a gap that will be maintained over time, and uses robust enough materials not to need maintenance or replacement, then yes think it would work.
Stepping back a bit: I guess my larger point is that these are the complex fixes, which include both some risk and compromise, that you expect to see on renovations, not built into new construction. You don't see new houses relying on air-gaps or membranes to protect wood frame construction below grade, because better alternatives exist.
Malcolm, I always appreciate your advice, you're very helpful! I think the topic has drifted from decking materials into insulation/vapor barriers, so perhaps starting a new thread is a good idea.
Akos, thanks for the suggestion! That sounds a lot like JustusM's approach earlier, right? Would it be something like this sketch? (I also added spray foam at the inside of the rim joist).
I appreciate everyone's inputs. I think at this point I have some ideas on how to build the patio, but I do have remaining questions about what insulation and vapor barrier are needed for my specific situation, which is a mild climate and a conditioned crawlspace. I think (hope) that many of the concerns with moisture would be alleviated by those two facts.
I'll start a new thread to get some thoughts on that.
I would limit the height of the green infill to code min distance bellow the rim joist. This way there is no soil resting against the wood construction and you can always lift up the trench to check on things (ie termite strip).
Make sure the trench drain or any flashing for it is not blocking the weep holes on your sliding doors.
Makes sense to me, I like that. So something like this?
So this would create a nice air gap all along the rim joist - can this then be built with a vapor permeable (instead of waterproofing) membrane on the outside? That way we have rim joist drying to the outside, which seemed to be the big concern in this thread.
Looks good to me. Since the rim joist is now exposed you can use regular vapor open membrane.
Y0u can also skip the spray foam as long as you have a plan for air barrier continuity from framing to foundation. Lot of times it is easier to spray foam just to air seal properly.
Thanks Akos!
A couple of follow ups:
- As an alternative, if I wanted to go with a concrete patio instead of pavers, can I do something like this?
- Also, in this setup, the drain trench is not resting on anything, like most of the trench systems I see are designed to do. Do I need the actual trench, or can I use some kind of a grate for decorative purposes, with the assumption that all bulk water will go through the grate and then into the stone and foundation drain below, just like around the rest of the house?