Townhouse Wind Loading - parallel to front wall
Townhouse Wind Loading - parallel to front wall
(OP)
Wasn't sure where to post this (here or Codes).
For 4- and 3-story townhouses separated by firewalls, resulting in structurel isolation of each unit:
Does the IBC/IRC require (or do you personally consider) the lateral design of an individual townhouse unit to include wind pressures resulting from the accidental or decided removal of one or more adjacent townhouses (i.e., windward and leeward pressures on the full vertical projection of each townhouse)?
Clearly the most conservative approach is to design as a stand-alone unit, but this may result (depending on available walls at the lower levels in particuarl) in significant cost to address this unlikely condition.
Please leave seismic considerations out of this discussion. Your input is appreciated.
For 4- and 3-story townhouses separated by firewalls, resulting in structurel isolation of each unit:
Does the IBC/IRC require (or do you personally consider) the lateral design of an individual townhouse unit to include wind pressures resulting from the accidental or decided removal of one or more adjacent townhouses (i.e., windward and leeward pressures on the full vertical projection of each townhouse)?
Clearly the most conservative approach is to design as a stand-alone unit, but this may result (depending on available walls at the lower levels in particuarl) in significant cost to address this unlikely condition.
Please leave seismic considerations out of this discussion. Your input is appreciated.






RE: Townhouse Wind Loading - parallel to front wall
Chances are that the roof diaphragm will be continuous even if the floor diaphragms are not, so all the units will see the top wind load distributed over all the units. That will help with shear and overturning, but I still would design the others to resist the remainder of the wind.
Mike McCann
MMC Engineering
RE: Townhouse Wind Loading - parallel to front wall
I would inform the owner about that possibility and design accordingly.
RE: Townhouse Wind Loading - parallel to front wall
RE: Townhouse Wind Loading - parallel to front wall
I am not sure I agree with your assumption of a cost increase for stand alone design. If you have these perfectly good shear walls between each unit, and all you need are a few more connectors in terms of tie downs, then I am not sure that won't be just as economical. You made find shear load path easiest to use interior party walls.
It has been way too long since I had to deal with them, but there may be some type of requirement for redundancy or independent bearing walls or something like that in relation to progressive collapse due to fire??
RE: Townhouse Wind Loading - parallel to front wall
"Each individual townhouse shall be structurally independent."
For me, this means that each unit gets its own mwfrs.
RE: Townhouse Wind Loading - parallel to front wall
RE: Townhouse Wind Loading - parallel to front wall
kipfoot- I don't know that section. Does it explicitly state MWFRS or gravity systems? I wonder if that is not getting back to my other question about independent bearing walls for fire reasons?
RE: Townhouse Wind Loading - parallel to front wall
RE: Townhouse Wind Loading - parallel to front wall
"R302.2.4 Structural independence. Each individual townhouse shall be structurally independent.
Exceptions:
1. Foundations supporting exterior walls or common walls.
2. Structural roof and wall sheathing from each unit may fasten to the common wall framing.
3. Nonstructural wall and roof coverings.
4. Flashing at termination of roof covering over common wall.
5. Townhouses separated by a common 1-hour fire-resistance-rated wall as provided in Section R302.2."
In my opinion, each exception is an example where a lack of independence is permitted, but they are not conditions which negate the requirement for overall structural independence.
RE: Townhouse Wind Loading - parallel to front wall
As for the "side-to-side" direction (wind parallel to front wall), racookpe's thinking is in line with my own (be logical). However, if the second unit in a row is removed, the end unit now has both leeward and windward pressures. Maybe the question boils down to how long until the removed house is replaced?... is it even required to be replaced (i.e., permanently removed)? Both of which are no longer engineering questions. Nevertheless, if the condition is temporary, a wind pressure could be developed to reflect the anticipated length of time for reconstruction of the adjacent unit.
It seems unreasonable to design all units for a condition that has a very low probabilty of occurrence.
RE: Townhouse Wind Loading - parallel to front wall
The IRC commentary on this section seems to indicate that structural independence refers to the abilty of one building to be removed (fire is mentioned) while the adjacent building remains. There is no mention of design lateral loads for the remaining structure, just that it wont collpase with the failed structure. However, I am not suggesting that they aren't required to be considered. Just my take on what that section is requiring.
RE: Townhouse Wind Loading - parallel to front wall
I do not think it is the intent of this section of the code that you design each townhome unit as a stand-alone structure which can resist wind from all four directions, then take these individual units, and shove them into one big building. This would require a large and unnecessary overdesign. When a townhome, apartment, or condo is damaged from wind or fire, they get rebuilt or repaired to code. This is what insurance is for. I have done plenty of this type of work. Nobody is expecting engineers to anticipate every possible renovation, remodel, addition or subtraction to a building.
My question, since it has been a while since I designed multi-family with wood frame, is how to you use the common fire wall for bearing or shear and still maintain the one hour rating? Blocking and/or fireproofing spray foam? You have to have lateral stability in the short (front-back) direction which includes tying your floor diaphragm into a shear wall...
RE: Townhouse Wind Loading - parallel to front wall
RE: Townhouse Wind Loading - parallel to front wall
RE: Townhouse Wind Loading - parallel to front wall
RE: Townhouse Wind Loading - parallel to front wall
The issue is the wind against the end units in the transverse or long direction of the townhouse complex - the short direction of each townhouse.
The post by kipfoot should settle matters here...
Mike McCann
MMC Engineering
RE: Townhouse Wind Loading - parallel to front wall