Shared Crawlspace Under Row House
Hi,
I live in a historic row home in Washington DC with a very low vented crawl space (less than 1 foot in height, practically inaccessible). Build in the 1860s the crawl space appear to connected across the row of homes rather than having a full foundation wall between homes. Our home is at the one end of the row.
As we are planning to fully renovate the home (build an addition, at insulation/ air sealing etc) this will likely be the only time we can do anything significant with the crawlspace relatively easily. I see several options.
1. Do nothing about the crawlspace and leave as is.
2. Encapsulate the crawlspace (including sealing it off from attached home), closed cell spray foam on foundation wall. Possibly install dehumidifier if there is sufficient space and include the crawlspace in the ventilation system of the home (we will for sure add a ventilation system to the home).
We are currently inclined to do 2. as one of the primary issues of the home is that it is cold and draft (the floors are freezing in winter).
Any suggestions/comments would be appreciated.
Thanks! Michael
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Replies
Are you going to take up the floors on the first level? How were you planning on doing the crawlspace work? What do you have for hvac equipment and were is it? What is your heating/cooling plan?
Yes, will be taking up the floors on the first level, which is how the crawlspace would be accessed (literally the only way to get there). Will be getting a mini split heating/cooling system, so no duct work for heating/cooling will be going through the crawl space. The condenser will be on the roof.
There is the option about adding warmboard in floor heating but that's pricey (it also seems rwther inefficient if one were to not touch the crawlspace and it remained vented)
If it was me, I would investigate taking out the whole flooring system. Fill in the crawlspace and top with significant foam insulation, then a new flooring system, maybe tile. How about a radiant floor. That shallow crawlspace will be nothing but trouble, cold, rodents, moisture, etc
When dealing with these older homes, first item to fix is proper separation. Build a proper rated wall in the crawlspace to separate you from your neighbors. Once this is in, insulate and air seal. This would get you much warmer floors and reduce sound transmission. Look at photo #3 to what you want to end up with:
https://www.buildingscience.com/documents/building-science-insights-newsletters/bsi-115-crawlspaces-either-or-out
Mini split heat with no ducting means you are looking to shotgun the place with a half a dozen or so wall mounts. This is a bad idea in almost every case, lot of info on this site as to why. A good solution is one or two wall mounts for the larger living spaces and a single slim ducted unit to feed all the bedrooms.
Roof mounted outdoor unit could be problematic for sound. Mini splits are very quiet but the vibration they produce will easily travel through most light weight wood construction. If you walls are masonry, you can mount it onto that on the roof. If the walls are wood, the next best option is to ground mount in the back or front yard.
If you must put it on the roof, put it on heavy concrete blocks using spring mounts near the corner of the roof away from the bedrooms. Make sure your engineer signs off on the extra weight this will add.