Filling A Gap Between Two Buildings 2

[kxa]

I was asked to look at a five story building for damage caused by excessive moisture at the ground level interior walls. During the inspection I noticed that when the adjacent five story building was constructed, they left a two inch gap where, despite the flashing at the roof parapet, allows for water, snow and humidity to get in there. Since there is very little chance for any air flow and the sun can not reach the area to help dry it, the wetness penetrates the building. Furthermore, there have been complaints about rodents.

I am suggesting that they fill the gap to the top with concrete. Perhaps with fly ash or a mix that is less permeable. I would like to hear if anybody out there has any experience with a situation like this or any other ideas. Thanks.

 

[WillisV]

Great idea! That way, the newer building can use the older building's existing lateral force resisting system as a backup!

 

[hokie66]

Your efforts should be in keeping the water out. There is a reason that gap was left.

 

[lkjh345]

Seems like a very bad idea to me.

Unless the two building's lateral load resisting systems are tied together (wich would seem like a difficult proposition to do properly) so that the buildings moved laterally together, the buildings will want to 'bang' into each other with all kinds of ramifications.

I would definately be looking for a different solution.

 

[Ron]

Agree with keeping the water out. You may also apply waterproofing using hoses dropped into the cavity and spray as you extract. Won't be perfect but will work.

Would suggest you do both. Concrete fill can create more problems than it will solve.

 

[hokie66]

In addition to being a poor idea in general, concrete filling the cavity between two 5 storey buildings would be almost impossible to achieve. I can just see the walls collapsing due to the pressure of the fluid concrete.

 

[kxa]

Is there any type of material that will fill the gap, is water resistant and yet flexible enough to prevent lateral load transfer?=5

 

[hokie66]

Something like Uretek foam would fill the gap and is water resistant, but it is not flexible. I don't know of a material which would do all three.

 

[kslee1000]

Your original comment was right, the wall had never had chance to dry. Go to the adjacent older building, I doubt there is same type of problem exist (been exposed and dried for a while). At this moment, whatever you do is no avail.

Take to a HVAC contractor, dehumanization thru ventilation may be way to get it (the wall) ready to receive further treatment. Or the devices can be left there permanently.

 

[cvg]

dehumanization?

how about constructing weep holes and air vents to allow the water out

 

[kslee1000]

oops, dehumidify.

 

[msquared48]

I think a combination of materials would work best here. Using a foam infill with an thin exterior concrete protection, kind of a crush seal. Rodents love foam and the concrete seal will help keep them out. Minimizing the thickhess of the seal will keep it non-structural in nature.

Mike McCann
MMC Engineering

 

[kslee1000]

You also need to re-do the defective flashing and proper drain the water to keep the space dry.

 

[kxa]

How about pouring concrete for, let’s say 6’ from the ground but have it pitched so that if water gets in, it can drain out from one side and into a downspout. I can then have the rest of the wall sprayed with liquid form of waterproofing membrane. This way, the separation still exists between the two buildings except for the first 6’.

 

[apsix]

hokie said it above; keep the water out.
Even if you fill the cavity the water still needs to be kept out.
Filling the cavity will be detrimental to building movement and sound transmission.
I can't see it being possible to effectively waterproof a 2" x 5 storey cavity with a spray-on membrane.

 

[Ron]

kxa...your last proposal will work. We just did something similar where a new building abuts an old building, but because of a property boundary fight did not have accesses necessary to do repairs to the old building (messy..still in litigation).

We grouted a small part of the cavity to provide slope from center to both sides (not 6' high...just enough to get 1/4" per foot slope), then waterproofed one side of the wall cavity (they wouldn't let us waterproof both sides because of the property fight!).

We are now putting a cap on the parapet of the old building and covering the gap at the top so that as little water as possible gets in (the buildings are different heights). They finally agreed that the cap could tie to both buildings, thus we have a fairly good seal at the top, but the waterproofing/sloping is a secondary measure.

 

[csd72]

As long as the cap has adequate allowance for movement it should be good.

 

[Ron]

csd72...yes, it does. That was one of our requirements, since the "other side" was doing the cap/gutter design.

 

[RacingAZ]

Note that the gap between buildings are typically due to drift requirements which becomes more critical when the buildings are in a high seismic zone area. The amount of gap didn't just occur by accident, someone specified / designed that gap for a reason. Also, there are building jurisdictions around the country that specifically requires a certain amount of separation between buildings.

Filling the gap with concrete is asking for trouble and potential lawsuit as any movement/ shifting by each building will tend to telegraph to the other.

The normal approach to this condition is to provide a flexible cap (prefab, aftermarket one is available) at the top of the walls and fill the front and back end vertically with an expansive or elastomeric material similar to an expansion joint detail. Architects normally specify this and if you have one as a friend, he could easily give you a brand name or you can look at a Sweets catalog.

 

[hokie66]

The architect on the adjacent building bears responsibility for what has happened. These days, most of them don't know enough about waterproofing. Sure, they may pick something out of a catalogue, but that doesn't mean they know how flashing or sealants work.