Waterproofing approaches for inset balcony
Hi all. Building a garage with a one bedroom unit above in Nova Scotia.
Looking ahead to sealing the 6’x8′ inset corner balcony. I have sloped the joists and the dropped them so these will be a few inches gap between finished decking and door threshold. Once the membrane(s) are down, will add PT sleepers and decking.
My initial plan was to apply a shingled layer of ice and water membrane, overlapping the wall WRB off the edges, and extending up the walls on the inside (WRB lapping over). I’ll have to pay special attention to the inside corner, post intersection, and door RO. Afterwards, the plan was to attach metal flashing with a drip edge that extends a few inches down the finished siding, with a strip of peel and stick at the top.
Is one layer of ice and water sufficient long-term protection for this application?
Are there any other approaches / materials that you’d recommend?
Appreciate your thoughts and input.
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Replies
Ry_buc,
Balconies over conditioned spaces are risky assemblies in the best of circumstances, because they are hard to do properly, and when they leak - and at some point they invariably do - the consequences are often structural damage. They are one of the few things I refuse to design into a project.
So if you are building one, you want to get it right. There are a number of acceptable methods and membranes ( I&WS isn't one of them), none of which I would advise you to DIY. This is something you should sub out.
Fair enough. I naively thought a covered balcony was not as risky as you describe. But, I suppose it is essentially a flat roof over a conditioned space. Thanks for the feedback.
Ry_buc,
I didn't realize it would be covered. That does reduce the risk a lot - but I still wouldn't DIY the waterproofing layer. The critical detail to get right is the edge of the membrane where it will terminate over the exterior walls. You want to make sure it doesn't just drain onto the siding below, so any small overhang you can provide will be beneficial.
The added overhang protection is a good detail. Thanks, Malcolm.
I think I would use EPDM, fully adhered, wrapped up the sides under the siding as far as you can. Use standard EPDM drip edge, but you have to figure out what to do with the posts for the deck railing. I guess mount the posts first and run the rubber up. Use .060 thick. They make walking pads for EPDM that bond to the surface. I would put them wherever your floating roof touches the membrane. Consider how to keep the mice out from underneath the deck surface
I&W will not last, it is not meant to have any exposure, the sun will eat it. Seen it happen, twice, when someone wouldn't listen.....
Appreciate the advice, Gusfhb. I hadn't considered doing floating decking but that would eliminate the penetrations through the EPDM.
Ry_Buc,
Definitely plan to float whatever your finished surface is. You have all sorts of options, including wood or concrete pavers on pedestals.
sub out a liquid applied roof. suggest a PMMA or PUMA system. drop the joists so that you can use a cement-based cover-board. detail with vertical upturns at 8" above the deck and install reglet flashing. if you do want to do a peel and stick then you double the layers and have a drainage mat over top. polyguard, CCW/Henry have 20 year systems. the peel and stick won't be uv stable though.
plan on some robust sheet metal flashings all the way around. balconies over occupied space are pretty run-of-the-mill in commercial construction but require experienced installers and very good detailing, especially at the railings/parapet.
stamant,
" balconies over occupied space are pretty run-of-the-mill in commercial construction"
The big difference is those are almost always steel or concrete buildings, which don't experience the damage wood ones do when something goes wrong.
I did two exposed roof decks over living space about 25 years ago, with an EPDM membrane. Over the membrane we put one of those heavy dimple mats (sorry, can't remember the name) and then tiled over that.
25 years later and there's never been a leak.
JGSG,
My experience is they don't fail or leak catastrophically, and it isn't usually spotted. The space water gets into is enclosed with no good drying path, and the damage is gradual. By the time you find it, the remediation usually requires replacing structural elements.
I haven't found the decision not to use them much of a design impediment. Same with low-slope roofs.
I'm entirely confident in this installation, which is in perfect condition after 25 years. It would be evident in the room underneath if there were a problem.
I'm confident in this particular installation because the roof deck finish surface is a tile installation which slopes to drain very well, freely. It's easy to maintain and the it would be noticed if water were resting on the deck or the scuppers were blocked. The deck is used regularly, so it's not getting a build up of leaves and debris. All this means that very little water ever actually makes it to the EPDM membrane below. And then that membrane is 100% protected from UV, as well as the worst of the weather. These are ideal conditions for preservation of the membrane.
I have absolutely no problem with designs that have no roof decks or low slope roofs. I just don't see a reason to take those options off the design palette if they can be done properly. I understand about reducing risk. But it's always a balance of factors.
I have designed and/or built a lot of decks and balconies over living spaces in wood-framed single family homes without any failures that I'm aware of, also going back 25 years. EPDM's lifespan is about 20-26 years so some of those are due for replacement. It's never my preference, for various reasons, but it's not particularly hard to do well.
I have only used adhered EPDM with floating sleepers. In fact one is being built now, in the mountains of western Maine. The challenge is how to handle posts and other penetrations. There are various approaches, depending on the situation.
Insulating the floor can only be done safely using closed-cell spray foam.
“ Insulating the floor can only be done safely using closed-cell spray foam.”
Or exterior insulation
Freyr, good point, though I generally design roofs for R-49 or R-60, which is a lot of exterior insulation. In my climate, zone 6, half of that could be fluffy insulation on the interior but that's still a thick layer of exterior insulation and in most cases the desire is to keep the floor/roof system thin, for various reasons. But technically you are absolutely correct.
Yes, and you generally have to worry about coverboard also, but in milder climates it often makes sense as you can create ideal drainage with tapered insulation.
I frequently see mention of the supposed short lifespan of EPDM
We put the 060 membrane on the back of my house in 2009, and the inked on lettering is still visible.
I guess I will see in 5-11 years if that prediction comes through. There are no doubt many reasons for flat roof failures, but it is hard to believe that the material fails in that short time.
In the case for this poster, with no need for seams or internal protrusions, and protection from the sun of whatever surface is chosen, I would think that moderate care to prevent punctures it should last a very long time
I've done posts two ways that seem to work well.
One is to use an adjustable post base upside down (essentially using at as plate with the screw welded to it) and put another post base on the threaded end for the actual post. This way the only thing poking through your roof membrane is a 3/4" galvanized screw which is easy to waterproof properly.
The other option is to treat the post as a wall. Run the membrane up the post, wrap the post in a WRB, flash around the base with metal and clad the post (metal, PT, wood all work). The bonus of this setup is the cladding protects the post so it should last much longer.
The one you don't want is simply brining the roofing up a bare post. There is no way to prevent water making its way into this joint and will eventually rot.
The other thing you have to watch is your railing attachments (if these are not part of a floating deck over the roof). These should only be attached to the side of the deck and not go through the membrane. What you want is to be able to replace the roofing without having to redo the railings. There are also a lot of structural issues to watch with this as it needs to hold up to a lot of force, usually you need something like a Simpson dd2z for proper support.
https://roofingmagazine.com/epdm-service-life/
A trade rag certainly, but seems fairly sciencey....
That article notes that the extended lifespan is for fully balasted systems, which aren't exposed to UV degradation. Adding decks over EPDM roofing limits UV exposure but depending on the design, it often doesn't eliminate it, especially around the edges.
from the link:
Five roofs, four ballasted and one fully adhered, with in situ service lives approaching or over 30 years were identified and samples were taken. All roofs were fully performing without moisture intrusion.
I missed that sentence, thank you.
The EPDM failures I have seen (not on my jobs) are not in the field anyway; they are at seams, or in a couple of cases at roof/sidewall intersections that had bituminous membrane and made the EPDM brittle. There are now different systems and materials for sealing the perimeter flashing and sheet overlaps than the ones I used 15-25 years ago but I don't know how they compare in terms of longevity. I'm not sure how thick those roofs were but I only used and spec 0.060" material.
It would certainly be great news if EPDM roofs could reliably be considered to last longer than 20-25 years.
I had a feeling this was the case. I don't care for the flashing tape compared to the membrane itself.
At my last house there was a small section of flat roof where the addition I built connected to the original house. Where do you suppose the roofers put a seam? Right at the junction where the old house ended and the flat roof began. Fer chrissakes. Leaked after 5 years. I added a sheet on top tucked under the shingles and comically glued down, as I had never dealt with it before. Stopped the leak anyway.
Install quality and how any perforations are handled, I think, are the drivers of lifespan.