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Subterranean Ductwork Issues

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Joined: Mar 24 2003

Since the forum has been re-formatted, I'm gonna repeat my old question in the hopes that maybe someone... please anyone... out there has a brilliant solution...

HELP! We live in the Balboa Highlands tract in Granada Hills, CA (Southern California). This tract features subterranean ductwork for forced air and heat (no radient heating here).

The ductwork appears to be standard metal ducts that were laid in the foundation and the concrete was poured around it. They did not actually seal the ducts in any way as I guess they assumed the concrete would seal them?

First of all, concrete is not waterproof and is a semi-permeable substance - so duh!!! And now after 40 years and a few earthquakes, we have surmised that in some instances the concrete has cracked and makes it even more susceptable to water seepage. So now water from rain seeps through the foundation and into the unsealed metal ductwork. After a heavy rain, it can get pretty wet down there...

Then of course on a cold and rainy night - you turn on the heat and voila - instant steam bath! Which of course ruins all the cool retro paper posters on our walls...

In some cases, some homes in our neighborhood have experienced where the metal has rusted and rotted away so that the ducts are exposed to the ground. Then when they finally dry out - there is the issue of mold, mildew and dust blowing through your entire heating AC system... yuck!!!

Here are some of the solutions that have been offered so far...
1) Improve drainage away from your house. Well, this is definitely a good suggestion and we would if we could... But our house is already completely surrounded by concrete patio (except for where there are small earthquake cracks) appropriately sloped in most cases with decent drainage. One insurance company suggested there could be ground water swellage actually under the concrete.
2) Jackhammer the foundation, lay in new sealed ductwork and re-pour and refloor. Uh uh - i don't think so... This would be so invasive I would be concerned about dmagaing the stability of the foundation. Plus I can't imagine how expensive that could be.
3) Pass new ductwork through the old ductwork. This is a possibility, but I would have concerns about smaller ducts having enough air flow to the farthest reaches of the system. This is already a minor issue with the current airflow.
4) Abandon the system entirely and go with ductwork on the roof. While some neighbors have done this, we are Eichler purists and don't want to radically alter the home in any way... Even with the new flat ducts, this would still mean puncturing holes where there are none now. And actually - the system does work quite well for us when it's not raining.

So this leaves us with
5) Somehow coat or line the ductwork with some kind of rubberized, plastic or ??? coating. I have heard of companies that line broken underground sewer pipes - where they are unreachable through digging down through the surface. This is what we'd like to do, but I can't locate any company anywhere that can do this process. If there was a company, there would be multiple homes in our neighborhood that would sign up fo the service.

So that's where we are. If anyone ever gets a lead on this kind of service or has another idea please help us.

Thanks a bunch!

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Joined: Mar 20 2003

Im wondering if you used a unico HVAC system if they could run their small ducts through the large ones without a loss in performance..

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Joined: Mar 20 2003

somehow option 3 seems more realistically possible than option 5, though honestly I have never heard of lining pipes. I think the unico system's piping is so small that it is designed to have more than 1 vent per room, so it might not work inside the old ducts. But perhaps there would be a slightly smaller ductwork that is accomadating. With new heating and air conditioning efficiencies out there it seems possible that even with smaller ductwork you could get good air flow.

It is commendable that you want to maintain the integrity of your Eichler home by not installing a new venting system (like the tiny Unico system that lies under your roof), but I can't believe that any purist would be against protecting one's family from health hazards. By putting that unico system in your roof, you would only have a few small holes per room ceiling.

good luck!!!

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Joined: Mar 24 2003

if we did abandon the old system - we would still need to address filling in the old system somehow?
And actually if we did run new ductwork through the old without first sealing the old - there would still be water/moisture down there - just outside the new ductwork, but with nowhere to evaporate - even worse scenario...
so back to a spray on rubberized coating sealer...

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Joined: Mar 20 2003

M-M:

Consider another option. A while ago, Mark and KC Marcinik of Greenmeadow Architects overlayed a new pipe system over a failed radiant system. It raised the floor about two inches. Removing all flooring and cleaning the slab might reduce that. Earlier posts hear explain what they did (which you can search from the home page).

Depending on your slab, it could be an option for you to check out. It's beats an "octapus" on the roof!

Good luck!

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Joined: Mar 20 2003

http://www.acecoating.com/

this company is in southern california based and provides a liquid non-toxic water-based sealer. sounds like they use this product to seal ducts on the outside...how about on the inside? maybe it is worth giving them a call; perhaps they would be interested in finding out yet another application for their product, and since they are in s.california they could visit you?

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Joined: Mar 20 2003

I know you say you've done all you can with drainage, but you don't say where your downspouts deposit rainwater. If you can get that far away, like 20 feet or more, from the slab, I think you'll have a lot less water under the house. But I know it may not completely solve the problem, just curious if you've tried this. As you say, concrete is permeable, so your patios, etc, are not preventing some water from passing right through into the underlying soil.

/te

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Joined: Mar 21 2003

Just my two cents worth. The concrete over lay idea is a good one as the products and methods are very reliable now days. This means increasing your door heights both inside and exterior. If you decide to go this route ask the contractor about plugging the old duct with water proof concrete.I think you should bite the bullit and add a drainage system around the house that takes the water out to the street.Your slab on grade floor is suspectable to heaving when the ground swells under it which may crack the new overlay. It is my experiance that the reinforcing wire which is supposed to prevent this always ends up at the bottom or under the concrete where it does the least amount of good.One last thought ,there are electrical heating systems that can be layed under ceramic tile in a thin set mortar that may be slightly thinner than the 2" over lay.Good luck.

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Joined: Mar 20 2003

I have half an idea:
It seems to me that if rather than line the inside of the ducts if there was a way to prevent water from entering the slab.

I was having a discussion with someone who repairs foundations and he was telling me that there is a process where a company can drill small holes in your foundation and inject a poly eurethane foam into the ground underneath your slab. This possiblky could line the underside of your slab and prevent the moisture from reaching your ducts.

I say half an idea because I believe that when they use this process for foundation repair it is to fill voids where water has left a cavitity causing a foundation to shift. The other thing I dont know is if this foam is fully water proof, I assume it is considering they use this same foam as insulation, to make roofs, and a heck of a lot of other applications.

Roy
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Joined: Apr 21 2003

We're in Costa Mesa and have almost exactly the same duct failure situation, but without the water into the ducting. Our's is blowing dirt throughout the house when the heating comes on.

I have researched the lining option and have talked with the firm that lines sewer and water lines. No firm answer yet, but there is some doubt that the same process would handle the heat involved. Also some question of access and the length of the runs involved.

Our best option thus far seems to be installing a hydronic system with the tubing snaked through the existing air ducts -- which would work in our situation since we're not getting water into those ducts. This tubing would connect to radiators in each room and a boiler system in place of the existing furnace.

Anyone heard of this being done in an Eichler??

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Joined: Mar 24 2003

Thanks for the tip on the company Cindy! I will definitely contact then. Keep those other tips coming, too...
We are focussing on the subterranean sealing solution as we do not want to alter the integrity of this original condition house if at all possible - i.e. through raising floors, or poking new holes in the walls and ceilings, etc. but others might be able to use those solutions?

Tom, the downspouts are actually all gone now. The previous owners took off the facia and original downspouts and put up gutters system. We have since ripped the gutters off - as we are planning on re-doing the roof back to original. But the problem existed before we did this. When there were operating gutters and downspouts they drained directly into ground drains that empy out to the street. So currently, the water just spills over the dripedge around the entire perimeter of the house. andthen flows to these ground drains out to the street.

Thanks again...

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Joined: Aug 4 2003

There is a company that lines broken sewer and drain piping with a polyester impregnated fabric sleeve that is heat cured in place. It reduces the inside diameter a small amount and completely seals the pipe. the company's name is Insituform. I don't know if they do this for rectangular ducts, or how much they would charge, or even if the equipment can be brought into your house. It just seems like an ideal solution.

Bob

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Joined: Mar 24 2003

do you have any contact info on them???

this sounds great!!!!! thanks.

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