Mini-Crawl Spaces between City Row-Home's Conditioned Stories

I have been finding more row-homes with 2' -3' sub-floors with ducts and piping running through them, that are usually opened to the outdoors (exterior walls & bypasses) and run the width & length of the home. I am wondering if anyone has ever addressed these spaces? Thanx, Bob

Tags: City, Homes, Mini-Crawl, Row, Spaces

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As a FYI, HELP is going forward with this retrofit, via dense packing all the exterior rim cavity areas between stories and will give an update when completed... (NOTE: with Cellulose of course) Thanx

Do you mean crawl spaces below the lowest floor level? or do you mean a 2-3 ft. space between floors?

What do you mean by "opened to the outdoors" and "bypasses"?

If you are talking about crawl spaces, then cellulose is not recommended at grade due to the potential for absorbing moisture.

Hi Brad, This is a space between the 1st floor ceiling and the 2nd floor floor. The area is 12' * 28' & is being used to run the duct work and water pipes to the home. Note: the HVAC is @ the rear 2nd floor. It is really deep with ~ 3' near the HVAC. I actually found another home like this shortly afterward and that is making me wonder how many of the retrofit opportunities have I missed in my 33 years? The rear sub-crawl has 3 exterior wall surrounding it and the middle has 1 long side wall to the exterior and it's opposite is buffered by a neighbor.

My thought now is to dense pack any mini sub-floor perimeter walls with Cellulose, into home about 2'. I feel by doing this I can bring the whole sub-floor back inside the home (for it is outside now due to ballooned walls and the exterior touching sills). The duct work will also come inside and though I will be bringing the ducts from a non-conditioned to a conditioned area... I am not trying to enter that data toward Total Pay-Back... 

Any other thoughts?

Also, To:
"What do you mean by "opened to the outdoors" and "bypasses"?"

This is opened to the Outdoors through open walls and the CFM's were as high as some McMansions HELP has done. Bypasses to me are Chase-ways to others.

Thanx for the Reply! Bob


 Now I am really confused. The 2nd photo shows what appears to be a typical 2x10 or 12" joist bay, with what appears to be sheetrock below and plywood subfloor above, with what appears to be mold on some of the surfaces. This is commonly called a "panned joist", which is using a joist bay to duct heated air from (or to) a furnace. This oftens results in air leakage to the exterior, where the joists meet the exterior walls.

If that is the case, then dense-packing the joist bays where they meet the exterior wall will greatly reduce air leakage and save energy. I do not see where it is feasible to do that. The exterior is all brick or mortar and would require an ~3" hole on the exterior, at every joist bay. There may be a possibility to do that from the interior by drilling through a sheetrock ceiling. The method is called "bag and blow". When done from the exterior, a bag (we use used feed or grain bags) a bag that air can flow through is pushed into the joist bay with the end of the dense-pack hose, that is lightly secured to the hose. The bag is pumped with cellulose until it is blocking the entire joist bay. The hose can then be pulled out of the bag and the space between the bag and exterior wall is then dense-packed (typ. 1-2 ft.of joist bay).

I am going to take a wild guess that the 3 ft. "chases" are boxed in areas to carry duct work or act as ducts. I cannot see how it would be feasible to dense-pack such a chase with a duct running through it.

Hi Brad sorry to confuse, but difficult to put in words, but yes going in from the inside 1st floor ceiling @ exterior wall and since the mini-crawl is 2' deeps (& may have "split layers @ 12" each?) (see pic from @ HVAC) I plan on adding 24" FG Batt as a backer about 2' from the exterior wall. I should of added some more strangeness which is the exterior walls are 10" - 14" and the home has ballooned walls and HIGH Air Leakage. The stories comfort problems are inverted too, being 2nd cold cold Winter and 1st hot hot and then it flops for Summer...

The bag idea sounds good also... Thanx and any ideas would HELP also,



This sounds like a job for AeroBarrier and AeroSealing. Both products will seal the issues from the inside out. One for the duct system and one the envelope of the building. 

I have been working with Midwest AeroBarrier and CEE out of Mn on some row house retrofits in CHI. Both products have worked exceptionally well sealing up existing homes with super high air infiltration. It has been quite surprising how well it works. 

After sealing I would look to insulate the exterior connected spaces as best as possible. Any kind of blown in cellulose of fiberglass insulation will work great and also reduce noise transfer. 

One question. Is this a single family house or is split into units per floor? Where are you locate?

First off it is called an interstitial space - a crawl space is located in only one area of a building & it isn't between floors.

For insulation: single family style, treat it like any other rim joist. Between units, you would also treat like a huge rim joist but also you would generally insulate the floor above to keep in the bottom unit heat where it is 

Ducts - pretty easy, seal them up right & fix stupidity

Balloon walls & other issues with framing - add in fireblocking & of course air seal the crap out of

Make sure all exhaust ducts are vented outside & sealed - might also be good to insulate the ducts in those areas 

Thanx for the new word Sean, being "interstitial" space!, for I didn't think mini crawl-space was correct. We proposed to try pretty do much as you noted, but instead of fire-stops we are adding Cellulose densed which is about the same thing. Access to the full perimeter access size is limited to labor and post aesthetic, for all has to be patched and painted, so dense-packing seems best?

Another problem are the side walls are ballooned out 12" and we are not trying to fill them with Cellulose, so doing next best thing and making a "poor-man sidewall retrofit" (I call it) and making them dead-air spaces to HELP insulation. I will post the results in about 3 weeks. Bob



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