Coming soon to your town and plant are “two-over-two towns,” which I initially disdained, but not after I saw that they were just loaded with components. Even so, who would want to live in a two-story townhouse that was built over or under another two-story townhouse, and be packed in like sardines? Apparently, many people do since these buildings are rising in droves around the perimeter of the Washington, DC Metro area. Tough to live in, I thought, but a component plant’s dream – in which each stack of 2 units contains:
- 8 long runs of party walls with no openings.
- 3 levels of repetitive floor decks.
- Easy to handle, compact roof trusses, either flat or low pitched or both.
Then, when these two-over-twos came to my small town, I had to go to see them. [For photos, See PDF or View in Full Issue.] To get up close, I had to navigate around mountains of 84 Lumber’s wall panels. Then I spotted brave souls four stories up swinging hammers, even on Thanksgiving Day. In all I saw 8 buildings with a total of 60 units in various stages of completion. Now I looked toward their livability.
As to sound transmission between adjacent units, I observed the typical townhouse construction detail: two layers of gypsum core wall. Per Code, these area separation walls can be used in structures up to four stories or a total of 44’ in height – ideal for the two-over-two construction. Note that this barrier will completely cover the depth of the floor cavity.
To learn what would contain sound transmission between stacked units, I called on the builder, Stanley Martin Homes. They pointed out that all 60 of these units were under contract, and that they had proven the livability of these units in multiple two-over-two buildings across the Mid-Atlantic region. To minimize the transmission of sound through the ceiling of level 2 and floor of level 3, they provide:
- Two layers of sheetrock on the walls of the lower unit that are common to the stair accessing the upper unit.
- Only carpeted stair treads are allowed on the stair accessing the upper unit.
- On ceiling level 2, sheet rock is hung on metal clips and not directly attached to bottom chords of floor framing.
- On floor of level 3, a ¾” layer of gypcrete topped by sound deadening board (note extra dead load).
The lower units in the buildings are 1500 sq. ft. in size with a single car garage. Adjacent to that garage is the garage for the upper unit. The top unit is framed over the lower unit plus the two garages, yielding an extra 1000 sq. ft. of space. Because of their higher density, Stanley is able to offer these units at a considerably lower price than conventional townhouses, and this has resulted in a lengthy waiting list. And with very little change in building facades, Stanley has experienced similar success across their Mid-Atlantic region.
Perhaps these types of boxy units may eventually lend themselves to modularization, since Stanley Martin’s owner, Daiwa House Group, the largest homebuilder in Japan, specializes in prefabricated houses. Each level of the 24’ wide x 50’ deep structure could possibly be supplied as 2 – 12’ x 50’ modules and joined together onsite and stacked four high. I bet the few pop-outs and balconies, shown on these alternate elevations, could also be tacked on specific modules in the factory. As to this possibility, Stanley’s CEO Steven Alloy has observed, “They [Daiwa] have extraordinary technology and robotics. Their manufacturing plants are like walking into an automotive plant. We’ve been talking for the past few years about how we adopt off-site solutions in the U.S. and what they can help contribute through that. It’s something our team is studying now. We don’t have the answer, but we may be able to benefit from some Daiwa House synergies around manufacturing.”
For now, and I bet for long into the future, trusses and wall panels, and lots of them, are the optimal off-site solutions.