Designing a House
Designing a House
(OP)
For those of you who have designed or regularly design stick-framed wood houses, what is your general approach?
I find stick-framed wood structures to be difficult to simplify. There many different angles and lengths of rafter braces and the exact locations of the braces aren't always known. Also, for complex roofs (which are usually the case with houses), the distribution of the loads down to the foundation can be very non-uniform and a pain to accurately trace, particularly with openings that don't line up from second floor to first floor.
Do you just develop a bunch of rules of thumbs through experience?
I find stick-framed wood structures to be difficult to simplify. There many different angles and lengths of rafter braces and the exact locations of the braces aren't always known. Also, for complex roofs (which are usually the case with houses), the distribution of the loads down to the foundation can be very non-uniform and a pain to accurately trace, particularly with openings that don't line up from second floor to first floor.
Do you just develop a bunch of rules of thumbs through experience?






RE: Designing a House
RE: Designing a House
RE: Designing a House
I try to avoid bearing walls which do not line up from main to second floor, but when analyzing an existing house, you must take what is there.
I have never developed any rules of thumb on such matters. I treat each job as a new challenge.
BA
RE: Designing a House
Check your local building code - the contractor is likely familiar with its requirements that prevent you from needed to detail every single connection and member. They generally have "rules of thumb" that can be followed in most cases such as required sizes of exterior stud walls, typical joist connections, etc. Be sure to reference the code in your specs.
Follow the concentrated point loads originating from the roof down to the foundation (girder truss reaction loads, etc.). This will likely require built up columns in most cases, which are very simple to call out. Sometimes engineered lumber sections will be required as lintels, etc. Check the worst case first and work your way down, you'll soon get a feel for the building's reaction loads and won't have to put much thought into it as you get deeper.
Don't over-engineer the thing. The cost savings involved with reducing sections to their absolute minimum could be voided by the time it takes you to check. Keep it simple and conservative. Use consistent details and as few of them as possible. This will also help the contractor avoid mistakes and timely repairs if every component was a different size or material.
RE: Designing a House
RE: Designing a House
That said, designing houses really is not too hard. Just do it a few times, go on a few field trips, help build one, etc., etc. and it will seem quite reasonable.
The hardest part is getting the most bang for your buck and that comes from reasonably sizing all rooms, the right amenities and pleasing the buyer.
Construction details are also important to insure a safe, dry and safe structure. A good builder can be a big help here.
AND make sure you meet all the requirements of the local codes and officials. They can make life miserable if not satisfied.
RE: Designing a House
Rules of thumb-wise, my advice is any point load over 2 kips should have multiple studs all the way to the foundation. The number of studs will be governed by your plate crushing. The IRC has most everything covered in terms of required framing methods.
RE: Designing a House
Gravity sucks...
Lateral forces tend to be pushy.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Designing a House
As the "framer" it was nice not to deal with them, but of course, the engineer in me forced me to do the right thing.
For the most part, unless the house is out-of-the-ordinary, the design is mostly empirical. And, for the most part, I believe it should be.
We would simply look over the architects pretty, usually dimension free drawings and decide what needed to be done for the home to be built properly. Most beam sizing was done by in-house engineers at the lumber suppliers. The roof trusses were of course done the same way.
RE: Designing a House
Pre-manufactured trussed roofs are the cheapest.
Stack bearing walls and columns if possible.
The most direct route of the forces to the foundation is the cheapest.
Lateral next.
Stack shear walls where possible too.
Try to avoid using transfer beams and steel moment frames.
At the top story, use only external shear walls to avoid the interior shearwall to truss detail which is messy.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Designing a House
have the basic sections:
typical footing section
bearing wall section
wall parallel to framing section
shearwall elevation
and my new favorite, the wood nailing schedule.
i basically reproduced the minimum nailing requirements schedule for wood to wood connections from the IRC table. it's kind of a CYA for any connection you don't specifically call out.
RE: Designing a House
Start at the roof. Do a sketch with you truss directions, location of girder trusses e.t.c. you can number your truss and girder truss types on this for reference. Now calculate your loads on your trusses and then the reactions on the walls.
It helps at this stage if you also number your different wall sections for reference e.g a,b e.t.c.
Work yor way down the building starting with the worst case for each member and if this looks reasonable make them all this if not then check the next one down the ladder and use 2 sizes.
RE: Designing a House
On a another note... if I understand correctly, in most states, a structural engineer's stamp is not required for design of a residential structure. I assume that builders normally size members and build the structure based on the empirical/prescriptive guidelines that are given in the IRC (of which, I am not familiar). So, if a structural engineer designs a house, does he have the liberty to use these prescriptive requirements as well?
RE: Designing a House
If you want to get a general overview of how houses may be designed (all in one book), see "Residential Design Guide - 2000 Edition", free .pdf at this link:
http://www.pathnet.org/sp.asp?id=1442
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RE: Designing a House
I've dealt with some hand-framed roofs that were literally impossible to followt the loads. If you design the hand-framing somewhat logical, then you won't have this problem. Or, worst case, you do end up with a ultra-complicated hand-framing system, then it's usually not too difficult to conservatively estimate where the loads are going, without being OVER-conservative.
RE: Designing a House
p.s. I just looked at a house this morning that had severe settlement issues. normally a geotech eng doesn't get involved with a house, but you might want to encourage the owner to hire one to come out and do at least once to do the "push the rod into the ground" test. please forgive me; i'm blanking on the proper term. what good is it to engineer the structure if it has a soft soil below it.
RE: Designing a House
I agree with vandede that a geotech should be involved in house construction more frequently than is the usual custom. Foundation movements can result in substantial claims, particularly if they were easily predictable by a cursory geotechnical examination.
BA
RE: Designing a House
Having said that, there were many occasions where I chose to stick frame a roof over trusses after seeing how messy the truss plans were going to be.
RE: Designing a House
As a sorta follow-up question: Which states require a structural engineer's involvement in house design? And how is the process usually handled, does a contractor send a set of plans which you review, make corrections, and stamp?
RE: Designing a House
Generally, any place with high wind or seismic, or when design elements don't fall in the prescriptive code portions, will require an engineering stamp. We do our own design so I can't speak to the usual process.
RE: Designing a House
I don't mind using the wood floor/roof joist tables as a quick reference.
I would NEVER EVER use the basement wall tables. You won't catch me calling out a hollow block wall.
I said it once earlier and I'll repeat it. Reproduce the IRC's minimum nailing schedule for wood to wood connections. This covers all the little stuff that you don't want clogging up your section cuts, but it's good to have in your drawings, stuff like:
ceiling joists lapped over supports
blocking to joists
collar ties to rafters
top plate splices/laps
top plates to studs
studs to sill plates
sill plates to rim joist
rim joist to joist ends
rim joist to top plates
built up box headers
built up corner studs
jack studs
etc etc etc
RE: Designing a House
very low fees.
There is never a rule of thumb. Each house is different and
have its own challenges.
RE: Designing a House
I would say to follow the loads thru to the foundations and ensure that every load path has a detail and can be built. In my experience, you don't want to leave details up to the builder because it is likely their detail will not be up to code.
Msquared,
Do you provide any connection to transfer diaphram loads into external shear walls other than nails?