Waterproofing detail through a joint at roof to new beam

[Ingenuity]

I was at a site meeting recently and the waterproofing consultant was discussing a proposed detail to the GC and architect where a new concrete beams interface with an existing roof slab. See sketch below.

The structural drawings detail a roughened interface across the joint with vertical post-installed dowels, at varying spacing (#5@6" and #5@12", so pretty decent size and spacing), so clearly the SER was looking for some composite/bonded action.

The waterproofing is detailed to pass through the interface. I questioned the waterproofing consultant (one of the larger multi-office consultants) and he said it was vetted through the structural engineer and it is acceptable.

The waterproofing is a cold, liquid-applied, roller-application product.

I would have lapped the WP up the vertical sides of the new beam and NOT passed it through the interface.

Anyone used or seen such a detail across an interface?

 

[MacGruber22]

That detail is asking for trouble. Why wouldn't they just cut reglets into the side of the beam and then put a flashing cap over the beam?

"It is imperative Cunth doesn't get his hands on those codes."

 

[hokie66]

Up and over, that's where the membrane should go.

 

[msquared48]

Absolutely up and over. The "expert" is nuts!

Mike McCann, PE, SE (WA)

 

[Ingenuity]

Thanks all.
The WP cannot go over the beam due to other constraints.

I was shaking my head in disbelief when it was brought up in the meeting.

After the meeting I did a brief one-on-one with the WP consultant about asked why not go up the face of the new beam and finish with a reglet etc and he stated that they did not wish to wait for 28 day cure time of the new beam, as the primer of the WP system is epoxy-based.

Seems idiotic to me to screw up the structural interface due to a curing time issue on doing it righ to begin with.

The WP consultant did state that the WP is not "really smooth" and it has some "texture". I just shook my head.

This consulting firm is well known for their forensics - I guess it may be
one to give them more work in the near future.

 

[Ron]

Agree...up and over with reinforcing scrim. Since the WP is fluid applied, use a fiberglas or polyester scrim up and over the beam. Extend scrim 6" on the horizontal surface of the roof deck, each side of beam. Asking for trouble the way it is shown.

 

[dik]

If it cannot go over, can it go up the side for 6" or so? With all those holes for dowels through the membrane, something is bound to leak...

Dik

 

[Ingenuity]

Thanks Ron and dik for your comments.

After a follow up discussion with the GC it appears that the new beams have a new slab cast integrally with the beams. New WP to the top of new slab too. Slab and beams 'formed' on syfrofoam fill.

I would still have 'turned-up' the WP to the existing slab to the vertical face of the new beam and NOT pass it through the roughened interface.

Any additional or change of thoughts considering the revised detail, as follows:

 

[hokie66]

Strange. I would wonder why the two layers of membrane are used. And how is the existing slab intended to function structurally with the new beam and slab?

 

[Ingenuity]

The EXISTING roof slab is over an interior occupied space. The NEW concrete slab will be exposed and part of a pool/rec deck.

The EXISTING top of slab will not be accessible after the NE slab is placed, so I assume the WP to this EXISTING slab will be the redundancy in the system, acting as a 'protected membrane'.

Structural drawings call for roughened and doweled interface, so IMO it is implied that they want a bonded interface.

The EXISTING slab will have to support and distribute the added loading from the NEW slab and beam, assuming that NO composite action exists, so effectively just a transfer of a bearing-type loading. The EXISTING slabs span between PT beams, as a 1-way beam and slab system.

 

[Ron]

Don't use 2 membrane layers. If (when) leaks occur in the top membrane, it will have the potential of filling the cavity before it manifests below. That will increase the load on the whole system and make it extremely difficult to pinpoint the location and cause of the leak.

 

[MacGruber22]

If the topside waterproofing is also a traffic membrane, this is not a good idea unless you have a secondary drainage system below. The traffic membrane will fail eventually.

"It is imperative Cunth doesn't get his hands on those codes."

 

[dik]

Ron: my thoughts exactly... Bad idea...

Dik

 

[Ingenuity]

Thank you for the additional comments. A bad situation all-round.

Besides the WP across the beam interface and the two separated WP layers, the "styrofoam fill" between the EXISTING and NEW slabs will prevent ANY and ALL access for the future. I hope there is a drainage system on top of the EXISTING slab after the WP is installed, and before the "styrofoam fill" is complete.