I have an exterior mezzanine that will have an occupied space below. This mezzanine needs to be completely watertight. The problem is that metal deck below the concrete and waterproofing above the concrete traps all the moisture of the slab inside. Has anyone ever had to waterproof an elevated concrete slab on metal decking?
Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations MintJulep on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
waterproofing concrete on metal decking 4
- Thread starter sponcyv
- Start date
With occupied space below, I'd go with a topping and membrane system. You can get deck with pre punched weep holes.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
sponcyv....in your area, your code requires that any topping on concrete over occupied space serve as a roof as well, so you have an added issue of having "traffic" on a roof membrane system. This can be handled in several ways. First you can put a proper roof system such as a modified bitumen roof on the concrete deck, and then cover the roof membrane with pavers for protection.
A second option is to provide a fluid applied, reinforced membrane on the concrete deck in multiple layers with the final layer having coarse sand broadcast onto the membrane before it dries. If you use this option, make sure the manufacturer approves its membrane for roofing application and that your local code jurisdiction will also approve it as a roofing membrane. Option 1 will not require this step as it is already an approved roofing system.
A second option is to provide a fluid applied, reinforced membrane on the concrete deck in multiple layers with the final layer having coarse sand broadcast onto the membrane before it dries. If you use this option, make sure the manufacturer approves its membrane for roofing application and that your local code jurisdiction will also approve it as a roofing membrane. Option 1 will not require this step as it is already an approved roofing system.
- Thread starter
- #4
Kootk - thanks for the info about pre-punched holes. I didn't know that.
Ron - there isn't an architect involved on this one and the code issue that you brought up is a good one. I recommended a roofing membrane to the client (contractor) and they told me that the owner is ok with some leaking (going to be a bathroom below). I'm going to call out a waterproofing system on my drawings to cover my rear and they can do what they want.
Ron - there isn't an architect involved on this one and the code issue that you brought up is a good one. I recommended a roofing membrane to the client (contractor) and they told me that the owner is ok with some leaking (going to be a bathroom below). I'm going to call out a waterproofing system on my drawings to cover my rear and they can do what they want.
With that approach, I'd CYA even further and design the slab with some rebar so that the deck can be considered sacrificial if need be.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
Owner is OK with some leaking but how about his tenants? Did a flood test on a floor once and the slab "leaked" just like the tenants had been complaining about. The daycare had actually moved one of those kiddy sandboxes under one of the "leaks." It was overflowing in less than 15 minutes. Owner found a way to pay for an upgraded waterproofing system. What about health issues related to "leaking?" Maybe there's a code issue you can use. Having a leaky floor will look bad for everyone involved and, in the long run, will be bad for your shortsighted client.
- Thread starter
- #7
Kootk - for sure - definitely don't want to count on the deck.
Teguci - I'm strongly urging for them to properly waterproof the slab. I don't think they realize how much water can get through a small crack.
This is a patio at a restaurant and they will have bathrooms below it. May not be end of world if water gets through, but would be stupid if they didn't try to protect their investment.
Teguci - I'm strongly urging for them to properly waterproof the slab. I don't think they realize how much water can get through a small crack.
This is a patio at a restaurant and they will have bathrooms below it. May not be end of world if water gets through, but would be stupid if they didn't try to protect their investment.
sponcyv....in this age of design/construction defect litigation, you have an obligation to design at least to the code minimums and YOUR standard of care, not the owner's or the contractor's. I just spent 3 days testifying in direct examination and 1 day in cross examination in a large construction defect trial.....so maybe I'm a little jaded on the subject, but please be careful for your liability sake.
If the code expects a roof, then design a roof (See Chapter 15, IBC). No more, no less. If they want to "value engineer" (btw...I hate that term!)your design away and you're not involved in construction/contract administration, then so be it...you won't know. If you are involved in C/CA, then you will have an obligation to write a letter recommending against their actions, but you still won't likely be able to do anything about it....the difference is that you will have met your standard of care in two respects...the design and the obligation to warn against code violations.
One thing to keep in mind....if they get a permit to construct based on your proper design and they fundamentally change it, there might be a violation of the code from that action alone, without regard to what they change it to. The administrative portion of the code (Chapter 1) requires resubmittal to the AHJ (Authority Having Jurisdiction) of design changes.
Good luck.
If the code expects a roof, then design a roof (See Chapter 15, IBC). No more, no less. If they want to "value engineer" (btw...I hate that term!)your design away and you're not involved in construction/contract administration, then so be it...you won't know. If you are involved in C/CA, then you will have an obligation to write a letter recommending against their actions, but you still won't likely be able to do anything about it....the difference is that you will have met your standard of care in two respects...the design and the obligation to warn against code violations.
One thing to keep in mind....if they get a permit to construct based on your proper design and they fundamentally change it, there might be a violation of the code from that action alone, without regard to what they change it to. The administrative portion of the code (Chapter 1) requires resubmittal to the AHJ (Authority Having Jurisdiction) of design changes.
Good luck.
I've never meet an owner who approved of leaking after said leaking has occurred (unexpectedly of course).
This seems like once you have seen it, the it cannot be unseen and must be addressed by all involved. If ignored you are potentially opening yourself up to a world of pain later on.
This seems like once you have seen it, the it cannot be unseen and must be addressed by all involved. If ignored you are potentially opening yourself up to a world of pain later on.
- Thread starter
- #11
I honestly don't want to get involved in the waterproofing period. It is not my specialty. That would be a building envelope consultant and I am planning on putting the following note on my drawings:
"It is the understanding of the structural engineer that the elevated floor shown on this plan will cover an occupied space. Waterproofing is outside of the scope of the structural engineer, but it is strongly recommended to provide either a waterproofing membrane system rated for pedestrian use or a waterproofing coating such as sikalastic mt primer with sikalastic 710/715/735/ AL traffic system. If waterproofing is installed, metal decking should be vented. Manufacturer will pre-punch holes. It is highly recommended that a building envelope consultant be retained to fully detail the waterproofing system.
Furthermore, I intend to add a note similar to this: "Structural drawings provided by ......INC cover only items related to structural portion of project. ......LNC takes no responsibility for architectural, mechanical, civil, building envelope, or any other disciplines as these are outside of the services provided by ......LNC. ......LNC recommends that these disciplines be consulted to ensure the constructed deck meet all code requirements as this deck is considered a roof assembly."
I don't have any legal experience and am sure that you could shoot holes through this. If you have any advice regarding this, I'm all ears.
"It is the understanding of the structural engineer that the elevated floor shown on this plan will cover an occupied space. Waterproofing is outside of the scope of the structural engineer, but it is strongly recommended to provide either a waterproofing membrane system rated for pedestrian use or a waterproofing coating such as sikalastic mt primer with sikalastic 710/715/735/ AL traffic system. If waterproofing is installed, metal decking should be vented. Manufacturer will pre-punch holes. It is highly recommended that a building envelope consultant be retained to fully detail the waterproofing system.
Furthermore, I intend to add a note similar to this: "Structural drawings provided by ......INC cover only items related to structural portion of project. ......LNC takes no responsibility for architectural, mechanical, civil, building envelope, or any other disciplines as these are outside of the services provided by ......LNC. ......LNC recommends that these disciplines be consulted to ensure the constructed deck meet all code requirements as this deck is considered a roof assembly."
I don't have any legal experience and am sure that you could shoot holes through this. If you have any advice regarding this, I'm all ears.
I think that you want the vented deck when the waterproofing system is absent.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
- Thread starter
- #13
It was my understanding that the venting is to allow moisture to dissipate out of the bottom because the top is completely sealed. If the top is not sealed and water gets through cracks, then it would just go right through the deck, so it doesn't seem like venting would be good to me. I think it all boils down to they absolutely have to waterproof or else they will have issues down the road.
No!No!No!.....if you are going to distance yourself from the waterproofing, don't then specify the waterproofing or even recommend it!!
I would edit to the following:
"It is the understanding of the structural engineer that the elevated floor shown on this plan will cover an occupied space. Waterproofing is outside of the scope of the structural engineer. It is highly recommended that a building envelope consultant be retained to fully detail the waterproofing system."
Leave it at that!
sponcyv said:
I would edit to the following:
"It is the understanding of the structural engineer that the elevated floor shown on this plan will cover an occupied space. Waterproofing is outside of the scope of the structural engineer. It is highly recommended that a building envelope consultant be retained to fully detail the waterproofing system."
Leave it at that!
I see it differently:
1) If the top is completely waterproof then you're inside the building envelope like any normal composite deck and there should be no water. No vents required.
2) If the top is not waterproof then water will seep down through the concrete and get trapped at the deck causing rampant corrosion. Vents required.
Building envelope is not my strong suit however.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
1) If the top is completely waterproof then you're inside the building envelope like any normal composite deck and there should be no water. No vents required.
2) If the top is not waterproof then water will seep down through the concrete and get trapped at the deck causing rampant corrosion. Vents required.
Building envelope is not my strong suit however.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
- Thread starter
- #16
Ron - I was kind of thinking that myself. Thank you and I think that is a great recommendation.
Kootk - I could see that if they didn't water proof and I called out for vented deck and they got cracking in the slab and water poured through the deck that I would get fingers pointed at me. If the deck is not vented, the deck will rust out over time, but I would make sure the reinforced concrete cans pan without the deck.
Kootk - I could see that if they didn't water proof and I called out for vented deck and they got cracking in the slab and water poured through the deck that I would get fingers pointed at me. If the deck is not vented, the deck will rust out over time, but I would make sure the reinforced concrete cans pan without the deck.
sponcyv said:
So you want the deck to serve as poor man's waterproofing and rust out? Keep in mind that, if water is getting to the deck and corroding it, the rebar may not be far behind. You know, unless you're planning on galvanized/stainless rebar.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
If there was an architect involved, this wouldn't even be a question, there would be waterproofing. Architects are even more risk adverse than engineers!
(I agree with Ron, just reference to others for waterproofing. If there are no others, the client should seek advice from others. You can guide them in the right direction but if you aren't comfortable with specifying something then don't be forced into it)
(I agree with Ron, just reference to others for waterproofing. If there are no others, the client should seek advice from others. You can guide them in the right direction but if you aren't comfortable with specifying something then don't be forced into it)
- Thread starter
- #19
Kootk - guess I'm damned if I do, damned if I don't. I do see your point. My primary responsibility is to design the structure so that it remains intact. That means that if I anticipate water intrusion into the deck that I should probably vent the decking. This way if water gets through, it won't be trapped. If water gets down into the occupied space below, this will be a waterproofing problem, but the structure will not be effected as badly.
Agent666 - yes, I agree - architect should be involved.
Agent666 - yes, I agree - architect should be involved.
It's a tough spot to be in. If you treat the deck as sacrificial and/or spec vented deck, then you're creating the impression that you expect there to be inadequate waterproofing. Kinda flies in the face of plausible deniability.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
- Status
Similar threads
- Question
- Question
