I am a veteran at sealing HVAC duct systems but am new to air sealing. Approximately half of my work is in the manufactured home community. I recently started a project in Louisiana. High humidity and high heat area. I had a common issue in about half of the homes. When bringing the home to 50pa, then sealing everything our crew could find, the linoleum floor would bubble.... entire room bubbles. In most cases, the air losses through this situation would virtually kill the savings achieved on the other sealing. Obviously we are pulling air from somewhere below the home. Any suggestions or ideas for improving this?

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Make sure the belly liner has no holes, is fully in place, etc... Beyond that short of pulling up all the flooring & applying a liquid applied membrane you really can't do anything. Oh & trust me that is happening under the carpet, hardwood, etc... and good luck on pulling everything as many times the flooring is put down first & then the walls are built over it. 

Ok there is actually one other option with is the new whole house aero-sealing technique but I don 't think that would work to well for this issue as you would be pressurizing said trailer with the floor being pushed down thus sealing the leaks. In this case the floor would have to come out to seal those gaps. There are more high target areas - well at least as of 8 years ago: http://thehtrc.com/2010/weatherization-program-modular-home 

Does this really matter much?  Think of what the blower door is doing as opposed to natural wind and air flow.  During the limited heating season the pressure is at the ceiling but walls and ceiling have been air sealed so how much air infiltration will really come from the floor.  In summer the pressure is at the floor and the vinyl will be pressed against the deck but walls and ceiling are air sealed so infiltration is minimal.  Carpet can be removed and seams in the plywood sealed if absolutely necessary.  Try running the blower door to pressurize the home and see what the difference is.

This is the classic problem folks have been wrestling with forever with manufactured housing...exacerbated by the fact that the space between the floor and the belly membrane acts as both the air barrier, the vapor barrier and the thermal boundary... and often acts as a return air plenum or at least contains lots of leaky ductwork.

I'll leave it to folks with more experience the me on how to solve this problem but will use say it ain't easy and probably not much fun.

Typo corrections:

This is the classic problem folks have been wrestling with forever with manufactured housing...exacerbated by the fact that the space between the floor and the belly membrane acts as the air barrier, the vapor barrier and the thermal boundary... and often serves as a return air plenum or, at least, contains lots of leaky ductwork.

I'll leave it to folks with more experience than I on how to solve this problem but will only say it ain't easy and probably not much fun.

Many of the WAP programs have written extensively on sealing of these guys.  West Virginia in particular has been aggressive on standardizing processes.  I have been away from WAP for 10 years now, so I don't have any names for you besides Linda and Anthony (I think), but drop them a line.

Sorry if I'm preaching to the choir but careful sealing up mobiles too tightly as they are sometimes too tight for any air sealing without added mechanical ventilation. Throw 4+ people and a couple of dogs in the mix and you have a mold issue waiting to pop off.

As far as the linoleum goes too, I've seen that often enough both in mobiles and site built construction. Anytime there is a linoleum floor that isn't glued down to the subfloor. I don't know any numbers on quantifying the leakage there but I'm willing to bet it's minimal in the grand scheme of things. I don't think there is any one culprit but rather the sum of any small penetration or gaps in subfloor itself. You're going to see this in the kitchen most often correct? Bathrooms are smaller and have enough stuff there to keep the linoleum down (bath insert, toilet, sink/cabinet, duct registers). Just be sure to seal the plumbing penetrations if they're accessible. I wouldn't go around cutting the belly just to access spots to airseal as there is lower hanging fruit to be had.

I just recently did an audit for a site built with very leaky tongue and groove interior paneling and ceiling and the floor in the kitchen was still inflating. It took a while after turning the blower door off to have the floor deflate which I would think means that it took awhile for the air to find a spot to leak back out of? This place didn't have any floor or wall insulation and only an R11 or R19 tops in the cathedral pitch ceiling too.

Sorry for the longwinded reply but ultimately I don't think there is anything easy to be done to remedy this and I don't think you'll typically see large swings in your blower door number because of it. If anybody else has other experiences here please chime in.

The good news is the linoleum IS the air/vapor barrier and unless it is put under 50 Pa negative air pressure, it probably serves that purpose well. It also means this layer is significantly tighter than the outer membrane, which also is how it should be.  That being said, I would want to do some advanced pressure diagnostics (like add-a-hole) to determine how tight the lower belly board is.  It could be that it is not all that bad and the linoleum pillow is just an indication of the relative air tightness of the surfaces, not necessarily a source of concern at all...but you gotta test beyond a basic blower door depressurization test or you are just guessing and maybe prescribing major efforts that will show little benefit.

You made some very important observations.

It's really important to think about how tight you air seal a modular home.  Replacement air for combustion devices such as stoves, furnaces and hot water heaters depend on those leaks. Tighten up the envelop and you've got a problem with those devices and carbon monoxide back drafting.  The kitchen stove fan and dryer can easily cause back drafting in those cases.   AND I'VE SEEN THAT HAPPEN.

Consider also the case of a modular home that is placed onto a basement.. with the interface between the modular home and the cement -- sealed and air tight.   Modular homes don't leak air in from the roofs - you'd have water leaks.   The sidewalls are tight -- or you'd have leaks.  That incoming air is from under the home.  If it is a basement had been sealed - then use of vented appliances would indeed cause back drafting on other appliances.  Add a fireplace to the basement -- and you've got a constant depressurization of the home.

If you are tightening up a modular home - you need to include a plan for an HRV/ERV - you need fresh air coming in.

Spray foam the road barrier.

The first place to look when working on trailers / manufactured home is the "belly".  Mostly they're "covered" with a tarp like membrane that has like been penetrated by every cable installer, electrician, plumber, homeowner that has ever been under there. This must be repaired and sealed tightly for you to have any appreciable effect in air sealing the home.

Look for a copy of "Your Mobile Home Energy & Repair Guide" by John T. Krigger

In illinois WAP program we seal the belly material and lightly dense pack the cavity with loose fill fiberglass this usually stops the air leakage you are referring to. Just seal up the belly material will not stop that type of leakage because it is impossible to make it completely air tight.

ah, the Bounce House Effect

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